TVIW 2019 Abstracts

State of Research in a Pulsed Hybrid Nuclear Propulsion Engine

Author: Rob Adams / Propulsion Research Engineer / NASA

Background: There is great potential in nuclear reactions as a source of energy for driving an in space propulsion system. Many studies, models, and experiments have been conducted over the preceding decades and while much has been learned, significant obstacles remain to be resolved to realize a nuclear propulsion system. Proposed fusion systems are particularly attractive due to their high specific power and efficiency but have been hampered by instabilities and the high energy density barrier for breakeven energy production. It may be possible to use a coupling effect between fission and fusion reactions to lower the energy barrier to breakeven for a hybrid nuclear reaction. It may also be possible to generate this type of reaction in a pulsed power z-pinch system capable of being flown on a deep space exploration vehicle.

Objectives: The objective of this author’s work is to explore the physics of fuel implosion and identify a potential parameters space in which breakeven hybrid nuclear reactions can be achieved at minimal peak driving current. This ties into the larger effort of the associated research team of demonstrating the key technologies for a pulsed fission fusion engine.

Methods: The author makes use of multi-physics modeling software to simulate the physical processes of the implosion of candidate fuel configurations. This is coupled to theoretical analysis and anchored to empirical data from literature.

Results: The author presents current progress in fuel configuration design, parameter space assessment, analysis, and model anchoring to literature. The author also presents progress of the greater pulsed fission fusion engine team.

Conclusions: While there is still work to be done to refine various aspects of a pulsed fission fusion engine, the concept shows promise. The potential is for a specific power on the order of 10-20 KW/kg and a specific impulse of a few 10,000’s of seconds. This could be a tremendous step forward in capability and would open up many exciting new possibilities for the exploration of deep space.

Human-Machine Ethics: Experiments in Moral Responsibility

Author: David Burke, MS, Principal Scientist, Galois, Inc.

Abstract Background: The success of any human-crewed interstellar mission depends on the existence of effective human-machine relationships. We anticipate that machines during such a mission won’t simply play the part of a supporting, background role, like an autopilot. Instead, navigating the demands of such a mission means that machines need to be equal ethical partners with humans, making decisions under conditions of irreducible uncertainty, in scenarios with potentially grave consequences.

Abstract Objectives: The objective of our work is to identify the salient factors that would either encourage or discourage effective partnerships between humans and machines in mission-critical scenarios. Our hypothesis is that there needs to be ethical congruence between human and machine: specifically, machines must not only understand the concept of moral responsibility; they must be able to convey to humans that they will make decisions accordingly.

Abstract Methods: Using participants obtained through Amazon Mechanical Turk program, we conducted experiments to tease out salient differences between trust granting to humans and to machines by adapting the well-known trolley problem. In this scenario, a trusted advisor (either human or machine) gives ethical guidance for a situation that turns out catastrophically. We looked for differences in how blame (moral responsibility) was apportioned.

Abstract Results: The empirical differences were unambiguous and striking: in scenarios with a trusted human advisor, blame was most often shared between humans, but when the advisor was a trusted, intelligent robot, the advisor was not assigned accountability. These results demonstrate that as things stand today, people are not willing to grant moral responsibility to intelligent machines, even when the actual behavior in question is identical to that of a human.

Abstract Conclusions: Our experiments demonstrate that intelligent behavior, by itself, is not sufficient for demonstrating the ethical congruence necessary for humans to grant moral agency to machines. Our future research focuses on devising conceptual approaches to enable machines to demonstrate that they understand the stakes involved for humans when confronted by an ethical dilemma/violation. Only then will machines be considered equal decision-making partners.

Calculation and Analysis of the Curvature Invariants for Traversable Lorentzian Wormholes and for Warp Metrics

Author: Gerald Cleaver, Ph.D. Early Universe Cosmology & String Theory, Professor and Graduate Program Director, Dept. of Physics & Center for Astrophysics, Baylor University

Abstract Background: In their classic papers, Morris and Thorne and Morris, Thorne, and Yurtsever were the first to analyze traversability of a classical wormhole. They studied the question of what the properties of a classical wormhole would have to be in order for the wormhole to be traversable by a human without fatal effects on the traveler.

Abstract Objectives: We present a process for applying the full set of spacetime curvature invariants as a new means to evaluate the traversability of Lorentzian wormholes and also of warped spacetime manifolds. This approach was formulated by Henry, Overduin, and Wilcomb for black holes.

Abstract Methods: Curvature invariants are independent of coordinate basis, so the process is free of coordinate mapping distortions and the same regardless of your chosen coordinates. The thirteen independent G’eh’eniau and Debever (GD) invariants are calculated for a given metric and the non-zero, independent curvature invariant functions are plotted and displayed. Four example traversable wormhole metrics are investigated: (i) thin shell at-face, (ii) spherically symmetric Morris and Thorne, (iii) thin-shell Schwarzschild, and (iv) Levi-Civita. We similarly calculate and display the curvature invariants for Alcubierre and Natario Warp Drive metrics. Both the constant velocity and accelerating Alcubierre and Natario metrics are presented.

Abstract Results: The wormholes are shown not to contain within physical bounds any internal divergences. The invariants plots demonstrate very non-trivial and non-intuitive time evolution dynamics of the warp bubbles.

Abstract Conclusions: The wormholes investigated are (at least theoretically) traversable.

Damage to Relativistic Interstellar Spacecraft by ISM Impact Gas Accumulation

Author: Alexander Cohen, BS, Jr. Specialist, University of California, Santa Barbara

Abstract Background: As part of the NASA Starlight collaboration we look at the implications of directed energy driven spacecraft capable of achieving relativistic flight impacting the interstellar medium (ISM) along their journey. These same considerations apply to the Breakthrough Starshot effort. Relativistic spacecraft will experience the ISM as a wide, MeV-range beam composed primarily of hydrogen and helium at constant velocity. A straightforward calculation of the sputtering yield for impacts at these energies shows that it is negligible. However, sputtering is not the only damaging process caused by particle irradiation. Bubble formation, blistering, and exfoliation are meso-scale processes driven by the accumulation of implanted insoluble gas atoms in solids, resulting in macroscopic changes to material properties and, in the cases of blistering and exfoliation, material erosion via blister rupture and delamination.

Abstract Objectives: In this work, we present a model of the local gas concentration threshold for material blistering from exposure to the ISM at relativistic speeds. Expected effects on the spacecraft and mitigation strategies are also discussed.

Abstract Methods: Contemporary understanding of these phenomena comes from a combination of theoretical, empirical, and computer models. Careful application of these models is necessary to understand the cumulative effects of ion bombardment. To perform this analysis, we find implantation profiles of ISM gas atoms at relativistic speeds using a BCA code, calculate critical concentrations for blistering onset for hydrogen and helium individually assuming a worst-case scenario of negligible diffusion, and show the effect of non-negligible diffusion on local gas concentrations.

Abstract Results: For a 20-year journey without an adequate shielding system, hydrogen bubble formation and subsequent bursting may induce damage to the spacecrafts leading edge which, as the damage continues to make its way into the spacecraft body, will eventually damage components and electronics essential to the spacecrafts performance. Moreover, secondary particle production and heavy species impacts have the potential to induce damage at a greater rate, depth, and severity than the common proton impact.

Abstract Conclusions: Various shielding schemes are proposed as mitigation strategies. Since the spacecraft is designed to fly edge-on into the ISM, a circumferential shield is proposed to protect the ISM-facing edge.

Light sails for interstellar travel

Author: A.R. Davoyan, Assistant Professor of Mechanical and Aerospace Engineering, University of California, Los Angeles

Background: So far only two probes have left the boundaries of our solar system. It took Voyager 1 – the fastest spacecraft ever built – 40 year of flight to reach the interstellar medium. Further exploration of deep space, interstellar medium and travel to neighboring stars requires new ways of spacecraft design and propulsion. Conventional chemical and electric propulsion systems are impractical for such far-reach missions. Photon propulsion, in contrast, is not bounded by the rocket equation and provides practical means for fast deep-space exploration.

Objective: In this talk we discuss of light sail design needed for future breakthrough photon propulsion missions. Specifically, we discuss two scenarios: beamed energy propulsion with high power ground based lasers and extreme solar sails making use of small perihelion approach. We consider material challenges and photonic designs that can enable such extreme light sails for future photon propulsion.

Methods: In our analysis we make a comprehensive analysis of materials properties, their thermal stability an optical responses, particularly absorbance and deduce that a certain set of ceramic and high index semiconductor materials is particularly suited for high radiation power. We then discuss different photonic structures that can help minimizing the mass of the sail.

Results: Our analysis suggests that ultrathin film materials for solar and laser beam sailing may designed. Specifically we show that solar sails capable of >30Au/year may be designed, as well as laser sails that can be propelled to relativistic speed.

TRL: Our technology is at TRL 2.

Development Roadmap: We further identify next steps needed to extend the TRL, specifically we will discuss the use of machine learning, optimization, and experimental testing. The long term goal is flight demonstration and in-space technology testing.

Near-term technical milestones and performance metrics: Near term goals include laboratory stauied of materials and demonstration of their performance in extreme radiation environment.

Conclusions: Our analysis shows a great promise for the design of novel photon propulsion systems for a scalable and fast space exploration and deep space travel.

An Interstellar University in the Ad Astra State

Author: Steve Durst, MA, Publisher, Editor, Co-founder, Space Age Publishing Company, and Ad Astra Kansas news and Foundation

Abstract Background: The rise of the Interstellar community, and even the unfolding of an Interstellar age, is a remarkable phenomenon of this new millennium / 21st Century — particularly its second decade. Centauri Dreams, as early as May 2013, inventoried the expanding list of interstellar organizations and initiatives: Tau Zero Foundation, Tennessee Valley Interstellar Workshop, 100-Year Starship, Icarus Interstellar, Starship Congress, Initiative for Interstellar Studies (i4is), Breakthrough Starshot, Breakthrough Initiatives, among other enterprises.

Abstract Objectives: An Interstellar University in the State of Kansas, with official motto ‘Ad Astra Per Aspera’, is well suited to help host, support, inspire, and direct this Interstellar phenomenon. An Interstellar University (IU) is a timely 2019 initiative of high relevance and value to a wide range of Interstellar activities, such as those in Wichita in November, and to inaugurate and characterize the dawning 2020 Decade.

Abstract Methods: For the Interstellar community, an IU provisional curriculum of high relevance and value can be found in the ‘Interstellar Research and Development” bi-annual feature of the Ad Astra Kansas Foundation newsletter, Ad Astra Kansas News, published consistently on schedule since 2001 / 2002. The 35 IR&D features provide a faithful chronicling during the first two decades of the new millennium of interstellar “Observation”, “Communication” and “Transportation” contemporary news events, developments and theories, which provide a template to evaluate the mission, direction and character of the IU in the 20s decade ahead.

Abstract Results: It is highly desirable that, pursuing an Interstellar University goal with IR&D information and networking from the Ad Astra Kansas News and Foundation, an Interstellar University could be founded in the State of Kansas by January 29, 2021 — 160 years after the admission of the State of Kansas into the Union.

Abstract Conclusions: Similar to the highly successful, influential International Space University in France, for Europe and the world, an Interstellar University and its graduates may generate science, technology, economy and broad education benefits and advances for the Ad Astra State, for America, and for other worlds, well into the 22nd century, if not centuries beyond.

Will Self-Replication Technology Precede Interstellar Propulsion Technology? The Prospects for Interstellar Self-Replicating Probe & a Human Type III Civilisation

Author: Alex Ellery, BSc (Hons), MSc, PhD, P.Eng, C.Eng, C.Phys, C.Math, Professor, Carleton University

Abstract Background: Most effort in researching interstellar flight has, not unnaturally, focussed on propulsion technology. There are other salient technologies in particular, self-replication technology acts as an exponential amplifier of both productive value and cost amortisation. A single (or small number of) interstellar spacecraft equipped with an appropriate payload could colonise the entire Galaxy within only 23 generations.

Abstract Objectives: We have been developing fundamental capabilities in self-replication technology by exploiting advances in extraterrestrial in-situ resource utilisation and 3D printing.

Abstract Methods: Specifically, we shall be describing our experiments in: (i) closed loop extraterrestrial (lunar and asteroidal) resource-based industrial ecosystems from which to construct any kinematic machine; (ii) 3D printing as a universal construction mechanism including 3D printing electric motors; (iii) 3D printing analogue neural network computers as a direct instantiation of the universal Turing machine. We contend that this work tackles the key critical capabilities necessary to realise self-replicating machines. Their sheer utility renders them inevitable – a single self-replicating facility as a payload to a starship opens the prospects for a fully self-replicating probe.

Abstract Results: One application of our technology that we are exploring as a transitory concept to our self-replicating spacecraft is a fully 3D printed cubesat including not just structure but also 3D printed motorised reaction wheels and multifunctional structure-embedded 3D neural network circuitry. A miniaturised 2D flat-pack version may be embedded onto a solar sail that might be suitable for a StarChip concept of the Breakthrough Starshot project.

Abstract Conclusions: Our embryonic self-replicating probe may offer strategies on searching for physical evidence of prior visitation by postulated extraterrestrial intelligence in our own asteroid belt. Given that self-replication technology is under development with prospects for near-term demonstration, I submit that the first starships that we send will be self-replicating probes. If so, it may be that the transition from an emerging Kardashev Type I civilisation through Type II to Type III civilisation is rapid and transitional. An intriguing corollary is that, given advances in 3D printing biological organs, the self-replicating probes could 3D print entire humans at destination without the necessity for physical transport – the worldship concept may be rendered obsolete.

Analysis of Light Sail Geometries and Stability for Directed Energy Interstellar Propulsion

Author: Jacob Erlikhman, N/A, Researcher/Student, University of California, Santa Barbara

Abstract Background: A 1 m2-class light sail has been proposed as a method of achieving speeds of appreciable fractions of the speed of light using a ground-based, kilometer-scale, GW to multi-GW phased laser array. Such a sail could accelerate a light (~10 g) spacecraft to 0.2 c over several minutes of continuous acceleration, enabling travel at the relativistic speeds necessary for interstellar missions.

Abstract Objectives: Due to the enormous loads incident on the sail, rapid acceleration, and the inherent mass constraints of the spacecraft, the sail must be designed to passively remain trapped in the laser beam, which may be Gaussian or shaped with a central null.

Abstract Methods: We have conducted fully analytic, as well as numerical simulation analyses in COMSOL, over different sail geometries, spacecraft mass distributions, and beam shapes.

Abstract Results: A number of stable designs have been found in the regimes of a central-null beam and Gaussian beams profile; a parabolic and conic sail; and orientations of the sail towards and away from the direction of travel.

TRL Assessment: Currently TRL 1, progress towards TRL 2.

Abstract Development: Future simulations will include structural and environmental effects, including sail tearing, deformations, vaporization due to absorption, and impacts of interplanetary medium (IPM) particles, advancing the technology towards a TRL 3 prototype.

Abstract Near-Term Technical Milestones: Sail system requirements will be derived from the analysis, including maximum absorption, minimum reflectivity, material strength and rigidity. This data will be used to drive sail structural design and identify materials for the construction of a prototype.

Abstract Conclusions: Passive-spacecraft stability in the acceleration phase of directed energy interstellar propulsion is possible with the co-design of the space and ground segments. Sail geometry and spacecraft center of gravity are primary stability parameters.

A Reaction Drive Powered by External Dynamic Pressure as Second Stage for Interstellar Flight

Author: Jeffrey Greason, B.S., Chairman, Tau Zero Foundation

Abstract Background: The Plasma Magnet work sponsored by NIAC in 2004-2005 developed a means of producing drag against the interplanetary solar wind or interstellar medium with high drag-to-mass ratio. By itself that would be sufficient for interstellar precursor missions as summarized in a talk at TVIW 2017, but that potential has not been realized, in part because of a lack of methods for braking after such fast transits for planetary missions.

Abstract Objectives: A new class of reaction drive is discussed, in which reaction mass is expelled from a vehicle using power extracted from the relative motion of the vehicle and the surrounding medium, such as the solar wind or interstellar plasma.

Abstract Methods: The physics of this type of drive are reviewed analytically and shown to permit high velocity changes with modest mass ratio while conserving energy and momentum according to well-established physical principles.

Abstract Results: For interplanetary missions, use of the plasma-magnet device as based on past NIAC research updated with modern superconductors offers acceleration ~0.05 m/s^2. For acceleration, the mass ratio needed is the square of the ratio of final to initial velocity. Departure velocities of ~7500-15000 km/s (advanced fusion rocket) then give 0.1-0.2c at mass ratio 16 for the second stage.

TRL Assessment: The plasma magnet itself has been demonstrated in a realistic environment for TRL5. The new reaction principle for braking in the solar system and interstellar acceleration has now had the physical principles and governing equations worked out and submitted for publication, with some paths for implementation at conceptual design level, making it TRL2.

Abstract Near-Term Technical Milestones: Next step is to extend the equations to include losses and inefficiencies and lateral thrust, to explore fast flight to Mars near conjunction. Then take design of the interstellar implementation to a preliminary stage, and test a subscale version in a laboratory.Next step is to extend the equations to include losses and inefficiencies and lateral thrust, to explore fast flight to Mars near conjunction. Then take design of the interstellar implementation to a preliminary stage, and test a subscale version in a laboratory.

Abstract Conclusions: For interplanetary missions, combination of this principle with plasma magnet permits fast interplanetary transits (one year to accelerate, coast, and brake to a Neptune orbit). If used as a second stage for a fusion or other advanced rocket, 0.1-0.2c velocities appear achievable.

Assessing Crewmember Musculoskeletal Health with Long-Duration Spaceflight

Author: Katelyn Greene, BS, Graduate Student, Virginia Tech, Wake Forest University Center for Injury Biomechanics

Abstract Background: Astronauts on long-duration spaceflight missions (6-months or longer) are susceptible to musculoskeletal alterations that persist even after return to Earth-normal gravity. Vertebral bone deterioration accompanied by muscle atrophy may elevate injury risk. As we step towards deep space exploratory missions, it is crucial that we better understand the impact of extended microgravity on human health, both during mission and upon return to normal gravity.

Abstract Objectives: This team investigates skeletal degradation and muscle morphology changes from pre-flight to post-flight using quantitative computed tomography (qCT) and magnetic resonance imaging (MRI) of crewmembers on International Space Station missions. The measurements are integrated into computational models, which simulate extreme conditions such as spacecraft landing to quantify vertebral strength and injury risk.

Abstract Methods: The study will ultimately include 31 pre- and post-flight crewmember biomedical images on previous and upcoming 4+ month missions and are obtained from the National Aeronautics and Space Administration. Our image processing software and custom algorithms collect vertebral geometry and musculoskeletal health metrics including muscle volume, muscle cross-sectional area, bone cortical thickness, and bone mineral density. These measurements are used to adjust the geometry and material properties of computational human body models to match crewmember anatomy. The models are evaluated under various loading conditions to quantify injury risk.

Abstract Results: This study is ongoing; therefore, results are currently limited to muscle size data from previous missions. In the lumbar spine, we found statistically significant decreases in the total muscle volume (mean: 5.1 ±4.2%), quadratus lumborum (9.5 ±2.0%), and paraspinal muscles (5.3 ±1.0%). Surprisingly, in the cervical spine, we found significant increases in the cross-sectional areas of the trapezius (25.1 ±9.9%), semispinalis capitis (11.5 ±4.4%), sternocleidomastoid (9.0 ±2.3%), and rhomboid minor (23.1 ±11.7%). Once the entire imaging dataset is available, we will collect additional musculoskeletal measures and integrate them into the computational models.

Abstract Conclusions: This research better characterizes how prolonged microgravity influences musculoskeletal degradation around the vertebral column. With this insight, we can assess injury risk for crewmembers after return to Earth-normal gravity. It is crucial that we understand these physiological changes to improve the efficacy of in-flight countermeasures and mitigate injury on upcoming missions to Mars and beyond to interstellar space. Acknowledgments: NASA-NNX16AP89G

Strategies for Mitigation of Dust and Charged Ion Impact on Laser-Driven Lightsails

Author: Andrew Higgins, PhD, Aeronautics and Astronautics, Professor, McGill University

Abstract Background: The impact of interplanetary and interstellar dust grains on lightsails is a significant concern for laser-driven interstellar flight. Over a light year of travel, the mean spacing between impact sites on forward-facing surfaces is estimated to be on the order of 100 microns. The fundamental particles of the interstellar medium (ISM: protons, alpha particles, etc.) are also of concern. A particular source of apprehension are impacts on the sail in near-earth space (estimated mean spacing of impact sites ~ 1 mm) which could degrade the low absorptivity/high reflectivity requirements of the sail. In the worst case, laser energy deposition could couple to the sail material, resulting in near-instantaneous destruction of the sail, similar to the well- known phenomena of “fiber fuze” and “laser-supported detonation”.

Abstract Objectives: This study will critically examine a number of strategies to minimize or eliminate the threat to the sail presented by the dust grain and ion impact problems: (1) Use of the drive laser as a means to displace or vaporize interplanetary dust in advance of the sail during the acceleration phase. (2) Design of a “fault-tolerant” sail that can withstand local catastrophic failure of the sail due to laser-coupling, but does not propagate to adjacent regions of the sail. (3) For the interstellar cruise phase (when the sail flies edge-on to the ISM), the use of graded materials (bilayers) on the leading edge to act as channels to direct ions outward from the main sail.

Abstract Methods: Given the embryonic nature of the techniques considered here, the modelling is done via first-order analytic models, including accepted models for laser ablation, laser-supported detonation propagation, and charge particle penetration.

Abstract Results: Dust removal or vaporization in the volume the light sail will traverse during the acceleration phase does not appear feasible due to the large volume that would need to be cleared. Displacement of dust via the laser light transmitted through the sail, as would be the case with thin dielectric sails, may be feasible. A fault-tolerant sail that prevents laser-supported destruction from propagating across the sail appears possible but may necessitate large gaps in the sail, resulting in wasting much of the laser illumination. Charged particle re-direction via graded materials is an established technology that has been demonstrated experimentally in the particle accelerator community.

TRL Assessment: The present level of the technologies considered in this study are Level 1. Completion of the analyses presented will contribute to elevating the TRL to 2-3.

Abstract Development: The talk will conclude with a proposed roadmap of a progressive hierarchy of models and laboratory validation to evolve the more promising of the proposed approaches to TRL 4.

Abstract Near-Term Technical Milestones: Bench-top demonstration of CW-laser-driven ablation of dust should be feasible with 1 W lasers. Demonstration of the ability to prevent propagation of laser-supported sail destruction would necessitate use of 1kW-class lasers. Charged particle re-direct

Abstract Conclusions: The first-order analysis proposed here suggests that the concepts have sufficient potential to warrant additional analysis. It is hoped that this preliminary analysis will stimulate further thinking about nonconventional solutions to the dust grain impact problem.

Antimatter-Based Interstellar Propulsion

Author: Gerald Jackson, Ph.D. Physics, Co-Founder and President, Hbar Technologies, LLC

Abstract Background: While antimatter-based propulsion concepts have been proposed for several decades, the limited production of antimatter and its storage difficulties have retarded their development. Dr. Steven Howe identified an antimatter niche for the acceleration of small unmanned interstellar probes, a concept funded by NIAC starting in 2002, wherein the antimatter was used to initiate fission events whose daughters provided thrust.

Abstract Objectives: The purpose of this research is to improve the Howe concept by focusing all fission daughters into a coherent exhaust stream, thereby reducing the amount of antimatter needed and enabling spacecraft velocities as high as 0.1c.

Abstract Methods: The first step was to critically evaluate antimatter-based propulsion in light of the rocket equation, which pointed to the induction of fission as the most efficient use of antimatter. The second step was to identify a particle accelerator architecture coupled with a focusing system that mixed antimatter with depleted uranium while simultaneously allowing both fission daughters to escape into the focused exhaust stream. The third step was to generate an unmanned scientific Proxima Centauri mission profile that decelerates and orbits Proxima b, returning data for decades. The fourth step was to generate a plan to synthesis antimatter at the rate needed to enable such a mission.

Abstract Results: Given that the maximum exhaust velocity of fission daughters is only 0.046c, a spacecraft velocity of 0.1c requires 33g of antimatter for every kilogram of spacecraft dry mass. If the spacecraft velocity were reduced to 0.05c the amount of needed antimatter drops to 8g. A plan for producing antimatter at a rate of 10g/year with accompanying cost estimate has been developed.

TRL Assessment: The propulsion concept is based on experimentally validated accelerator and particle physics experience: TRL 3. Enhanced antimatter production consistent with a Proxima Centauri mission is a large extrapolation of experimental work performed at several laboratories: TRL 4.

Abstract Development: The critical path is demonstrating enhanced antimatter production rates. An experimental program has been developed.

Abstract Near-Term Technical Milestones: Generate a technical design report for the first enhanced antimatter production experiment validating technology and production costs.

Abstract Conclusions: Interstellar antimatter-based propulsion at 0.1c and kilogram-scale is feasible and experimentally validated. Demonstration of economic feasibility is required.

Inflatable Technologies for Interstellar Missions: Bounce House to the Stars

Author: Jamey Jacob, PhD, Professor, Oklahoma State University

Abstract Background: While inflatable designs have been developed and tested since the earliest days of manned space flight, only recently have they come into their own with the deployment of man-rated modules in space. The advantages are obvious, with both potential weight and volume savings allowing optimization for either volume or mass limited launch vehicles.

Abstract Objectives: This work covers aspects of where the technology lies right now and extrapolates to potential future missions focused on human interstellar flight. Inflatable technologies have the potential for many elements of an interstellar spacecraft, including habitats, airlocks, elemental structures such as booms and trusses, and other components for generational spaceflight support, such as gardens and reservoirs, as well as heat shields and debris deflectors.

Abstract Methods: Material requirements include both yield strength and longevity, particularly in the harsh interstellar environment. In addition to traditional inflatable designs, we will examine novel design possibilities. One such approach is to use airbeam technology that explore different methods of joining inflatable beams to form a continuous cellular structure that creates arched arrangements or a series of connected rings to form cylinders, allowing a wide array of designs to be explored and developed.

Abstract Results: Key advantages of this approach lie in the separation of structural support and internal habitable conditions. The structure can maintain strength and stiffness independent of pressure in the habitable volume. Thus, the structure does not rely on maintaining internal pressure and can be used for other applications, such as temporary shelters for shielding from solar storms, micrometeorites or for equipment storage not requiring atmospheric conditions. Any potential leaks can be isolated in the affected elements of the structure without compromising habitat pressure or structural integrity. Additional advantages exist in the ability to fill the beams fully or partially with various materials for improved strength or radiation protection. For example, water or other radiation absorbing material can be used to fill beams, and a rigid structure can be created with relative ease by filling the beams with rigidizing material.

Abstract Conclusions: The authors will present prospects for use in future missions and concepts for ships using inflatable systems, both as components and integral elements.

The Physics of Negative Mass: applications for propulsion and interstellar travel

Author: Geoffrey Landis, Ph.D., physicist, NASA John Glenn Research Center

Abstract Background: As first analyzed by Hermann Bondi in 1957, matter with negative mass is consistent with the structure of Einstein’s general theory of Relativity. Although initially the concept was considered just a theoretical curiosity, negative mass, or “exotic matter,” is now incorporated into the body of mainstream physics in a number of forms. Negative mass has a number of rather non-intuitive properties, which, as first noted by Bondi, and then later commented on by Forward (1990), Landis (1991), and others, results in possible applications for propulsion requiring little, or possibly no, expenditure of fuel.

As pointed out by Morris and Thorne (1988) and others, negative mass (or, more strictly, a violation of the null energy condition) is also a requirement for any proposed faster than light travel. This paper presents the basic theory of negative mass, the ways by which it can manifest in contemporary physical theory, and the counterintiutive properties that result, including possible uses for interstellar propulsion. to advanced propulsion.

Abstract Objectives: The objective of this work is to summarize the physics of negative mass and the relevance and applications

Abstract Methods: The work uses fundamental concepts of physics to analyze negative mass and its consequences for propulsion.

Abstract Results: Although negative mass has moved from a theoretical curiosity to a concept fundamental to the contemporary understanding of physics, it is still not clear whether bulk negative mass can be manufactured, or if it is limited to only appearing at the cosmological scale (e.g., “dark energy:) or in the quantum (e.g., Casimir vacuum) limit. If it can be manufactured, the propulsion applications would be significant.

TRL Assessment: TRL 1

Abstract Development: Still theoretical

Abstract Near-Term Technical Milestones: Technolgical milestone: continue study in the context of theoretical physics and quantum mechanics.

Abstract Conclusions: Although negative mass has moved from a theoretical curiosity to a concept fundamental to the contemporary understanding of physics, it remains a theoretical concept, not an engineering reality. If it can be manufactured, the propulsion applications would be significant.

Power System for Miniature Interstellar Flyby Probe

Author: Geoffrey Landis, PhD, Researcher, NASA John Glenn Research Center

Abstract Background: In the last few years,the concept that an ultra-lightweight probe could be sent to one of the nearby stars pushed by a laser beam reflecting from a lightweight sail has moved from science fiction into conceptual design. The Breakthrough Starshot project envisions a two- to three-gram “starchip” micro probe, flying past a planet of Proxima Centauri after a 20 year voyage.

With the probe moving at 60,000 km/sec, the flyby encounter at the target planet lasts at most a few hours. With current technology, no power system exists that can produce the required power with a mass of less than one gram.

Abstract Objectives: Baseline requirements for the power system are:

Weight: 1 gram or less

Lifetime: 25 year cruise, followed by encounter phase.

The operational lifetime during the encounter phase can be a trade-off against the power level. The baseline requirement is 1 watt peak, 10 mW continuous, with higher power levels desirable.

Abstract Methods: Several power systems were analyzed.

Abstract Results: Radioisotope Power

Analysis shows that radioisotope thermal power system scale poorly to small sizes, and would be four to five orders of magnitude too heavy for such a microprobe.

An alternative proposal would be to use direct energy conversion, rather than thermal conversion. Betavoltaic decives scale well to low power levels. Betavoltaic cells have future specific power anticipated at 1 W/kg. The half life of tritium, 12.3 years, results in decay to about 25% of baseline power during the cruise.

An alternative uses the energy of alpha particles from spontaneous fission. Isotopes include plutonium-238 or curium 244. Semiconductor alphavoltaic converters, however, are subject to alpha-induced degradation, and may not make the lifetimes required.

Advanced Technology: The proposed flyby spacecraft has a kinetic energy of 10 million megajoules per gram. We can use the energy of the spacecraft’s motion through the interplanetary medium by using the ambient plasma and magnetic environments. The anticipated density of solar-wind generated plasma is ~6E12 protons per cm2 at an energy of ~5 MeV. Thiscould be turned into power with an electrostatic grid. Alternatively, for a target magnetic field of 1 nT, we can create an electric field by the spacecraft’s motion of about 60 volts per meter to generate power.

Abstract Conclusions: The power system for a small (Starshot-sized) interstellar probe is a major component that has, to date, not been well analyzed. The low mass requirement makes the problem very difficult. Several approaches to this power system are possible.

Fundamental Challenges of Self-Guided Beamed Propulsion and Prospects for Near-Term Experiments

Author: Chris Limbach, PhD, Assistant Professor, Texas A&M University

Abstract Background: Beamed propulsion concepts based on laser or particle beams are affected by finite beam divergence due to diffraction or thermal spreading of the beam particles, respectively. These effects, in addition to the low thrust provided by photons, often result in large-scale transmitter systems and very light payloads.

Abstract Objectives: A combination of laser and particle beams, exploiting optical dipole forces and refraction, has recently been proposed to mitigate beam spreading and provide increased thrust from the particle beam. This study examines the conditions for self- guiding and applicable scaling laws for future laboratory experiments.

Abstract Methods: Determination of self-propagating modes and simulation of guided propagation have been performed by numerically solving the paraxial wave equation and gas-kinetic equation (Boltzmann equation), with and without optical coupling. Stationary solutions for self-guiding are obtained from an iterative method for the paraxial Helmholtz equation and the method of characteristics solution of the 2D, axisymmetric, collisionless Boltzmann equation.

Abstract Results: Self-guiding solutions for the laser intensity and particle density profiles have been found to exist over a range of parameterizations of the phase-space distribution function and the waveguide V-parameter. Application of fundamental scaling laws show these modes can be observed in the laboratory. The effect of collisions and light scattering are also considered in the context of planned experiments.

TRL Assessment: The present study continues the TRL advancement of self-guided beamed propulsion from TRL 2 to towards TRL 3.

Abstract Development: Challenges and potential solutions to larger-scale ground testing are described, with the goal of defining a roadmap to TRL 5.Challenges and potential solutions to larger-scale ground testing are described, with the goal of defining a roadmap to TRL 5.

Abstract Near-Term Technical Milestones: Observation and study of self-guiding should be feasible over the next several years, necessitating only commercially available lasers and cold atomic beams produced through conventional laser-cooling techniques. Development of predictive computational models will be helpful to design such experimental demonstrations and understand optimal operating conditions.

Observation and study of self-guiding should be feasible over the next several years, necessitating only commercially available lasers and cold atomic beams produced through conventional laser-cooling techniques. Development of predictive computational models will be helpful to design such experimental demonstrations and understand optimal operating conditions.

Abstract Conclusions: Analysis of the governing equations suggests that direct observation of self-guiding and validation of numerical simulations could be achievable in near-term lab-scale experiments. Indeed, laser and atomic beam propagation over several tens of meters may be used, by virtue of scaling laws, to simulate and study self-guided propagation of high energy atomic beams over thousands of kilometers.

Securing the Stars: The Security Implications of Human Culture for Crewed Interstellar Flight

Author: Michael Massa, NA, Program Manager, Omitted – representing self, not employer

Abstract Background: Manned interstellar vehicles will operate in an unforgiving medium for extended periods and will not share the advantages of the more resilient terrestrial craft. Important differences in shipboard culture may be required in order to maximize the chances of success.

Abstract Objectives: The design of crewed vehicles represents a long lead item which must be addressed before human interstellar travel. Identifying the cultural shifts needed in order to create the most resilient ship/crew system can be supported during the ship design and crew selection phase advances the goal of manned interstellar travel.

Abstract Methods: This abstract draws upon my education and practical experience as former Naval Special Warfare (SEAL) Officer responsible for assessing target vulnerabilities, a Global Managing Director for Risk and Resilience at Deutsche Bank AG and my current role as a Program Manager for the Software Engineering Institute at Carnegie Mellon University specializing in the Department of Defense Risk Management Framework.

I use informal comparative analysis to characterize and prioritize the culturally relevant risk factors that existing and historical modes of human travel have in common with interstellar flight. Specifically, I contrast transoceanic sail-powered ship travel, Antarctic research and nuclear deterrence submarine patrols with the conditions that we can expect during space travel. The phase of interstellar travel, from fitting-out and in-home-system testing, to deep-space transit and arrival and assay phase, may also be distinct in terms of cultural risk.

Abstract Results: The relatively low resilience of interstellar craft to traditional categories of human-originated risk will drive the requirement to modify, for a long period, the culture of the crew and passengers. Examples of these cultural topics include but are not limited to religion, recreational sex, privacy, politics, personal hygiene etc.

Abstract Conclusions: Voyage designers must take deeply personal elements of culture into account. Constraints and modifications to sensitive cultural touch points must be accepted by the crew and passengers of a successful interstellar flight. I suggest the application and modification of existing risk management frameworks.

The Spacecoach : A scalable and upgradable platform for long duration crewed flights based on electric propulsion using water rich propellant

Author: Brian McConnell, BSci, Founder, Open SETI Data Archive

Abstract Background: The spacecoach, first described by authors Brian McConnell and Alex Tolley in JBIS in 2010, uses water and waste gases as propellant in a solar electric propulsion system. This radically improves the mass budget for long duration crewed missions by transforming consumables that would otherwise be dead weight into propellant mass. A good overview with additional references can be found here.

Recent modeling shows that the same approach can be used with a fusion powerplant to drive an electric propulsion system to achieve 0.1c transit speeds while providing a large mass budget for water and other consumables that would be needed for a long duration flight.

Abstract Objectives: While the spacecoach was originally conceived as a platform for exploration within the solar system, it can be upgraded as new power and propulsion technologies become available. First generation ships, starting with scaled down robotic systems, can be flown with present day solar electric propulsion technology, while providing an evolutionary pathway to inter-planetary and eventually interstellar flight as lightweight nuclear electric power plants become available.

Abstract Methods: The authors developed a detailed parametric model for platforms designed for missions within the solar system, and demonstrated that order of magnitude improvements in payload mass budgets are enabled by using consumables as propellant. In this workshop, we will model the performance of a spacecoach that is outfitted with a nuclear electric propulsion system.

Abstract Results: We modeled a spacecoach with a mass ratio of 100:1, where most (> 90%) of the propellant mass is water or water equivalent material, and the remainder fusion reactant. A fusion powerplant drives an electric propulsion system that accelerates this material to 0.01-0.1c. We show that the system can reach transit speeds of 0.1c or greater while providing a large mass budget for water and consumables.

Abstract Conclusions: The spacecoach architecture, by allowing for generous consumable budgets, is a promising approach for long duration crewed flight, and can be validated in near earth missions and upgraded as new power and propulsion technologies become available.

Overview of the Lockheed Martin Compact Fusion Reactor (CFR) Project

Author: Thomas McGuire, Principal Investigator of the Compact Fusion Reactor Project and LM Fellow, Lockheed Martin Aeronautics Company

Background: The Lockheed Martin Compact Fusion Reactor (CFR) Program endeavors to quickly develop a compact fusion power plant with favorable commercial economics and military utility.

Objectives: The goal of the experiments is to demonstrate a suitable plasma target for heating experiments, to characterize the behavior of plasma sources in the CFR configuration and to then heat the plasma with neutral beams, with the plasma transitioning into the high Beta confinement regime.

Methods: The CFR uses a diamagnetic, high beta, magnetically encapsulated, linear ring cusp plasma confinement scheme.

Results: Major project activities will be reviewed, including the T4B and T5 plasma heating experiments. The design and preliminary results of the experiments will be presented, including discussion of predicted behavior, plasma sources, heating mechanisms, diagnostics suite and relevant numerical modeling.

Metamaterial-Enhanced Graphene as a Beamed Energy Sail for Interstellar Probes

Author: Joseph Meany, Ph.D., Principal, Ionic Flask Materials Group

The primary goal of solar sail research is to identify materials whereby the structure has as low a mass as possible while maximizing its reflectivity. Selecting pure substances for their intrinsic bulk reflectivity is limiting. Bulk masses are defined by the atomic or formula mass of the material used. To date, effort has focused on developing multilayer thin-film approaches in order to increase the reflectivity. The best modern reflectors involving uninterrupted thin film substrates unfortunately suffer from high areal density due to their thickness. It is absolutely key to reduce this mass in order to produce a sail capable of high acceleration and high speed.

While metal films on a polymer substrate are the current state-of-the-art in solar sail design, excitement has grown over the last decade on using graphene as a replacement substrate both for its durability and its low areal density. Graphene by itself, however, is almost entirely transparent. Therefore it is necessary to deposit some inherently reflective material onto the Earth-ward surface of the graphene monolayer. Optical metamaterials have recently achieved near-perfect reflectivity in the NIR region of the electromagnetic spectrum using nano-patterned Si cubes. Here, the determination of basic parameters concerning the metamaterial-on-graphene solar sail is presented, alongside some promising areas of further research.

Some Challenges in Low-Mass Interstellar Probe Communication Downlinks

Author: David G Messerschmitt, Roger Strauch Professor Emeritus, Electrical Engineering and Computer Sciences, University of California at Berkeley

Abstract Background: We have done a preliminary paper design of a downlink from a swarm or armada of low-mass interstellar probes for returning scientific data from the vicinity of Proxima Centari. The primary goal is to identify major challenges or showstoppers if such a downlink were to be constructed using currently available off-the-shelf technology, and thereby provide direction and motivation to future research on the constituent design challenges and technologies. In this talk we summarize our findings, which conclude that there are no fundamental physical constraints, but currently available technologies fall significantly short in several areas and there are other major design challenges with uncertain solutions. The greatest identified challenges are in mass constraints, multiplexing communication from multiple probes, attitude control and pointing accuracy, and Doppler shifts due to uncertainty in probe velocity. The greatest technology challenges are electrical power, high power and wavelength-agile optical sources, very selective and wavelength-agile banks of optical bandpass filters, and single-photon detectors with extremely low dark-count rates. In each of these cases we describe the nature of the difficulties we encounter and their origins in the overall design.

Abstract Background: In a recent paper* we have done a preliminary paper design of a downlink from a swarm or armada of low-mass interstellar probes for returning scientific data from the vicinity of Proxima Centari.

*P. Lubin, D Messerschmitt, and I. Morrison, Interstellar Mission Communications Low Background Regime, soon to be replaced by Challenges in Scientific Data Communication from Low-Mass Interstellar Probes.

Abstract Objectives: The primary goal of this talk is to identify major challenges or showstoppers if such a downlink were to be constructed using currently available off-the-shelf technology, and thereby provide direction and motivation to future research on the constituent design challenges and technologies.

Abstract Methods: We utilize the methodologies of communication engineering. The physical layer (sources, apertures, detectors) are modeled statistically, and results from the information theory are utilized to determine the theoretical limits on reliable communication of scientific data. To understand the implications of physical device technologies, model parameters are varied.

Abstract Results: While we conclude that there are no fundamental physical constraints, currently available technologies fall significantly short in several areas and there are other major design challenges with uncertain solutions. In each of these cases we describe the nature of the difficulties we encounter and their origins in the overall design.

Abstract Conclusions: The greatest identified challenges are in mass constraints, multiplexing communication from multiple probes, attitude control and pointing accuracy, and Doppler shifts due to uncertainty in probe velocity. The greatest technology challenges are electrical power, high power and wavelength-agile optical sources, very selective and wavelength-agile banks of optical bandpass filters, and single-photon detectors with extremely low dark-count rates.

Breakthrough Propulsion Study: Assessing Interstellar Flight Challenges and Prospects

Author: Marc Millis, MS, Propulsion Physicist, NASA, retired

Abstract Background: An assessment of interstellar propulsion concepts is proceeding in 3 stages: (1) assessment methods tailored to interstellar ambitions [Done, HQ-E-DAA-TN60290], (2) relevant information on proposed solutions collected, and (3) comparisons run. Assessment challenges:

• Prior concepts proposed using different missions and assumptions.
• Divergent propulsion measures cannot be directly compared (e.g. specific impulse versus beam divergence).
• Most performance predictions not yet experimentally verified.
• Readiness levels vary significantly.
• Required infrastructure is unplanned.
• Development times are comparable to historic technological revolutions.
• The next decisions are about choosing research, instead of selecting a mission and its technology.
• There are differing motives and priorities from which to infer relative merit.

Abstract Objectives: Identify which propulsion concepts might be the most advantageous and under what circumstances. Identify which research paths have the greatest leverage for increasing NASA’s ability to travel farther, faster, and with more capability.

Abstract Methods: Assess concepts using common mission scenarios and calculate performance in common terms. Develop defensible figures of merit. Use analyses consistent with predictions uncertainty. Use historic patterns to model technological progress.

Abstract Results: To begin stage 2, creating a database of comparison-enabling information, the following will be presented:

• Work breakdown structure for organizing information.
• Basic analysis flow diagram and analysis methods.
• Top 10 list of technology challenges.
• Baseline mission scenarios.
• Methods to distill performance measures to energy, time, and mass.
• Infrastructure modeled as proportional to spacecraft mass and propulsive energy.
• Technology progression modeled using successive S-curves.
• Figures of merit: mission value, energy required, time required, and efficiency.

Abstract Conclusions: This study is not about picking the next interstellar mission and its technology, but rather to identify the most impactive suite of research to get to that point. Information needed for stage 2:

• Concepts performance tailored to analysis questions.
• Scaling information to apply concepts to differing missions.
• Consistent specs for ancillary technologies (e.g. radiators, magnets, power storage).
• Research plans to validate and advance concepts (next research task, plus conceptual plans thereafter).
• History of performance gains and readiness levels.
• Upper physics limits of concepts performance.

QUELLER drive: Q Uranium Enhanced Linear Long Endurance and Range Drive

Author: Theodore Mouratidis, PhD candidate, Massachusetts Institute of Technology

What does it take to colonize Mars? In the same MIT graduate course which spawned the ARC high field fusion reactor design, students use and develop modern design tools to attack integrated design issues of a spacecraft which could carry out such a mission, in the Fall 2018 edition of the course. We focus on applying recent technological advances and scientific discoveries to this project, including high temperature superconductors (HTS), the discovery of substantial water and thorium on Mars, and improved performance of stabilized magnetic mirrors (Novosibirsk, Russia). A fusion-fission hybrid spacecraft is designed to be able to handle the requirements of transporting a very large payload to Mars for human colonization, while minimizing the travel time. The fusion plasma core is in the form of a linear mirror design, with a surrounding subcritical fission blanket with high multiplication to produce an overall system thermal power of . An MHD (Magnetohydrodynamic) generator is selected and optimized with an efficiency of to replace the standard turbine in a Brayton cycle for electricity generation on board. In order to reject the waste heat a carbon fiber radiator with a radius of is implemented. In addition to the magnetic mirror and the MHD generator, the toroidal rotating habitat also utilizes HTS to generate a magnetic field which will reduce radiation exposure to colonists to levels which will not cause long term genetic damage. After optimizing for payload and speed, we choose a design point with , favorable for the VASIMR propulsion system. This fusion-fission system is able to transport of payload from Low Earth orbit (LEO) to Low Mars Orbit (LMO) in days. With some inspiration from Space 1999, we name our spacecraft the QUELLER drive: Q Uranium Enhanced Linear Long Endurance and Range Drive. And so begins the colonization of Mars.

Terraforming Venus, and Similar Planets, using a Pneumatically Supported Shell

Author: Kenneth Roy, P.E,, Retired, TVIW

Abstract Background: Venus is a terrestrial planet having a hot, thick atmosphere of mainly CO2. Various ideas have been proposed to terraform the planet into an Earth-like world but the scale of the effort is immense and the results are generally considered to be unsatisfying. The main difficulties involve removing or modifying the thick atmosphere, cooling the planet, adjusting the spin of the planet, protecting the planet from solar flares and solar radiation, and dealing with the long-term effect of a thick crust devoid of plate tectonics. These efforts, baring some magical technologies, will require time frames measured in tens or even hundreds of millenniums. A new, previously unpublished approach (to the best knowledge of the author) toterraforming Venus that avoids most of these issues is discussed in this paper.

This is relevant to interstellar colonization because Trappist-1 has several planets that seem to be terrestrial with thick hot atmospheres, indicating that such planets may be very common around K and M class stars. If it is possible to terraform Venus using this approach with a time frame of one or two millennium then this approach should be workable for many other similar planets allowing for human expansion into the Galaxy.

Abstract Objectives: This paper examines the possibility of constructing a material shell in the Venusian atmosphere at an altitude of approximately 40 kilometers above the surface using Venusian materials. The building blocks of this shell are brought to altitude using buoyancy of a large vessel containing oxygen and nitrogen gases similar to Earth’s atmosphere. Their shape and design are based on Geodesic Sphere theory. These building blocks can then be used as floating cities until enough of them have been positioned to create a solid Geodesic spherical shell. These building blocks are then lowered a few kilometers and a solid continuous shell is established as the building blocks are welded together.

At that point gas processing begins where the atmosphere above the shell is separated into its components and oxygen and nitrogen (Venus has a lot of nitrogen) are released above the shell and most CO2 is compressed and released below the shell. Over time (estimated at about a millennium) the atmosphere above the shell is adjusted to Earth-normal composition with nitrogen, oxygen, and argon and Earth-normal pressures. The technology needed for the processing of atmospheric gases can be used to extract nitrogen and helium from the Venusian atmosphere. Nitrogen is useful for other terraforming operations throughout the solar system and helium production suggests He-3 availability on a fairly large scale.

The pressure below the shell supports the shell and as been demonstrated in previous works, is stable. The shell is entirely supported by the Venusian atmosphere and not connected to the planet’s surface in any way. The original Venusian atmosphere is mostly unmodified and available for future use. The shell itself can rotate independently of the planet and can be spun up to duplicate Earth’s axial tilt and the 24-hour day night cycle.

A device located at the Sun-Venus L1 point is discussed that can reduce the solar constant at the planet to Earth levels, or even lower, and can also supply energy to the planet using beamed energy. This device can also support magnetic fields to deflect solar particles away from the planet.

Abstract Methods: A Spreadsheet is used to validate the approach and to quantify significant values.

Abstract Results: A spreadsheet examines a number of the parameters necessary for this approach and concludes that materials and technologies available in the near term make this terraforming idea viable. However, a vibrant interplanetary society is required to provide the resources for this project.

The resulting habitat will have near Earth gravity, a good view of the stars, a shirt sleeve environment for humans and plants. Oceans cannot be accommodated with this approach but, small shallow seas, lakes, rivers, and canals are possible. It also has an area in excess of three times the land area of Earth. And it has the planet Venus just a few kilometers away to support industrial and mining operations.

There are open questions relating to the contained atmosphere under the shell and how it might react to lack of solar input. The heat transfer issue at and within the shell is considered but not evaluated in detail assuming that insulation and active cooling systems will be required.

Abstract Conclusions: A significant effort will be required but Venus can be terraformed into a very Earth-like environment on the shell above the planet’s surface using near-term technologies and materials. This could serve as a template for later interstellar terraforming efforts.

Near-Earth Resources: Short-Term Limitations with Interstellar Consequences

Author: James Schwartz, Ph.D., Fairmount Lecturer, Wichita State University

Abstract Background: There is a tendency of space mining advocates to focus on, e.g., total near-Earth asteroid (NEA) resource inventories, suggesting a picture that the resources of near-Earth space are (nearly) limitless, and that we needn’t worry about how (or how much or often) these resources are exploited and used.

Abstract Objectives: I will present evidence undermining the “limitless” perspective on NEAs and lunar resources. Focusing on water in particular, I will show that when important practical limitations are taken into consideration (e.g., delta-V requirements; asteroid distributions; launch windows; etc.), the easily accessible near-Earth resource pool appears quite small. Since these resources are (for all practical purposes) non-renewable, the ways in which they are used over the short term will affect our ability to satisfy longer-term goals, including our ability to provision interstellar missions.

Abstract Methods: Data is gathered from the planetary science literature describing NEA and lunar resource availability, focusing on publications discussing resources as energetically accessible as the Moon. This data will be used to provide a practical perspective on the (surprisingly limited) quantity of easily accessible space resources, and what this means for interstellar travel.

Abstract Results: There are multiple ways to filter the NEA population for accessibility, and several are discussed. One estimate, which looks at water-rich NEAs with a return delta-V equal to lunar escape velocity, suggests there is perhaps 8×10^11 kg water among this population. An estimate of water ice deposits in the bases of lunar polar craters comes to 3×10^12 kg. Altogether this water would form a sphere of about 2 km in diameter, which is hardly a limitless quantity of water to use for drinking, hydroponics, propellant, etc. It must also be kept in mind that only small quantities of this total will be available at any given time, given the orbital dynamics of the NEA population.

Abstract Conclusions: Unless some portion of our early spoils is reserved for the expansion of spaceflight capabilities, more energetically distance resources pools will remain out of reach, significantly impairing our ability to provision interstellar missions. Thus, the fate of interstellar exploration depends on the way that space mining conducted and regulated.

Direct Drive Fusion Propulsion with Centrifugal Plasma Confinement

Author: Ray Sedwick, Keystone Professor, Aerospace Engineering, University of Maryland

Abstract: The proposed direct-drive fusion concept merges several technologies: Gas Dynamic Mirror (GDM); Centrifugal Confinement; Advanced Magnetic Nozzle Flows, HTS Magnets and Power Management.  The GDM has been researched for many years as a direct-drive fusion device, leveraging the unavoidable plasma loss as a mechanism to produce thrust.  However, plasma stability issues dictate that the aspect ratio of a simple mirror device must be prohibitively large for practical purposes.   A novel modification of the GDM that addresses both confinement and stability is Centrifugal Confinement.  Starting from a low aspect ratio GDM, an electrode is inserted along the axis and biased with respect to the platform.  This drives an azimuthal ExB rotation of the plasma.  The centrifugal acceleration of the rotation forces ion guiding centers along the B-field toward the mid-plane.  When the rotation is sufficiently supersonic, the centrifugal acceleration can contain the pressure and the ions are completely confined, even under collisions.  In addition, the usual MHD interchange instability is stabilized by the supersonic velocity shearing rate.  The electrons are electrostatically held in due to deeply confined ions.  While electron heat loss can occur along the field, it can be shown that at Mach 6 the Lawson Criterion for net fusion energy under electron heat loss can be achieved, as a result of the well-known Pastukhov factor that arises from the deeply confined ions.  The escaping plasma is necessary for direct-drive propulsion, but is generally too energetic for optimal performance.  To address this, we introduce a bypass flow to be entrained within the highly energetic fusion plasma flow, reducing the specific impulse and increasing the thrust at (ideally) constant power.  This method, proposed in early fusion propulsion concepts, has not been fully investigated and must be incorporated into exhaust flow simulations.  This provides the possibility of using a more prevalent propellant – like water – with other advantages, such as a high storage density, safe handling, and natural neutron moderation.  An overview of the concept and preliminary performance estimates will be presented.

Fusion space propulsion system based on the sheared flow stabilized Z pinch

Author: Uri Shumlak, Professor, Aerospace and Energetics Research Program, University of Washington

Abstract Background: Thermonuclear fusion provides a large energy release per reactant mass and offers a solution for rapid deep space propulsion if a configuration can be developed with a small system mass. Many magnetic confinement configurations require large magnetic field coils to stabilize the plasma at the expense of lower plasma beta and higher system mass. The Z pinch has no magnetic field coils and unity beta; however, it generally suffers from MHD instabilities. The sheared flow stabilized (SFS) Z pinch uses axial flows to provide stability, has demonstrated an ability to confine plasmas to fusion conditions without magnetic field coils, and promises a compact fusion device with Q>1. Recent experimental results will be presented that demonstrate high performance plasmas and sustained fusion reactions from the FuZE (Fusion Z-pinch Experiment) SFS Z-pinch device at the University of Washington. High-fidelity numerical simulations indicate that sheared flow stabilization of the Z pinch continues to be effective at reactor-grade plasma conditions. Building on the ZaP, ZaP-HD, and FuZE projects, scaling studies will be presented of an SFS Z pinch as a fusion space thruster, which generates high exhaust velocities and high thrust with low system mass, as will be shown through calculations that account for input power, repetition rate, and duty cycle.

Farmer in the Sky

Author: Catherine Smith, M.S. Entomology, Molecular Biologist, Cambridge Technologies

Abstract Background: The International Space Station has a history of unexpected microbial hitchhikers. Additionally, astrobiological experiments with the EXPOSE-R platform have illustrated the survivability of various extremophiles in what were once considered unsurvivable conditions. The documented tendency of microgravity to induce biofilm production in prokaryotes, with its increased resistance to chemical sterilization is also of concern. Given the goal of increased human presence in enclosed microgravity environments, what are the approaches to control hitchhikers currently in use, and what other options are available?

Abstract Objectives: With the limitations on chemical usage in a microgravity habitat, how do we develop an effective integrated biological management program for that system?

Abstract Methods: This talk will consider approaching the issue of terrestrial hitchhikers in microgravity from an integrated pest management angle rather than an exclusively quarantine angle. Using methodologies developed in agricultural production systems, it is possible that a multi-prong approach that accepts that it cannot eliminate hitchhiking organisms but instead tries to manage them would be a better long-term solution.

Abstract Results: Current efforts to control the microbial populations on the ISS are considered, along with current practices in terrestrial integrated pest management and how those could potentially be translated for future applications in microgravity.

Abstract Conclusions: It is concluded that current practices are exploring more options, but that we need to expand our efforts if we want to have healthy long term microgravity environments.

Can a Complex Universe Provide “Religious” Inspiration Without Religion?

Author: Kelly Smith, M.S., Ph.D., Professor and Chair, Department of Philosophy & Religion, Clemson University

Abstract Background: It is undeniable that religion provides a sense of purpose, ethical direction, and social belonging that most human beings for most of recorded history have found to be profoundly important. But it is equally undeniable that its supernatural metaphysics and dogmatic conservatism have retarded society’s progress in many ways and caused untold human suffering. An obvious question is thus: Is it possible to preserve the beneficial aspects of religion while excising the problematic ones?

Immanuel Kant fathered the postmodern age with his devastating critique of the possibility of human knowledge of the Ultimate. However, Kant himself was far from skeptical about the possibility of objective human knowledge – as long as its claims were carefully qualified. The key to understanding this seeming contradiction is his (often misunderstood) transcendental method. The method may offer a way to have our postmodern skepticism concerning traditional religious supernaturalism and still eat our metaphysical cake, as it were. Combining a transcendental approach with new scientific findings about the nature of the universe may allow us transcend the stalemate between scientific rationalism and faith, constructing a belief system which blends positive elements of each perspective.

Scientists in a number of disciplines are beginning to hypothesize that the universe naturally creates complexity. On the one hand, this undercuts the most common justification for belief in the supernatural, since there is no need for divine intervention to explain things which occur naturally. On the other hand, it invites those so inclined to view themselves as part of a universal telos involving the creation of complexity. Such a move requires only the smallest step of faith to adopt and may provide believers with the sense of purpose, ethical foundation, and social support they long for while sidestepping any conflict with the essential claims or methods of science.

Abstract Objectives: To outline how a spontaneously complexifying universe might provide a sense of purpose similar to religious faith, but without the problematic supernaturalism.

Abstract Methods: This research should be of interest to anyone who is skeptical of traditional religious approaches, yet wishes to make claims about universal principles and goals – whether we are talking about objective ethics or a human manifest destiny in space.

Abstract Conclusions: If the complexification hypothesis holds water, it should be possible to construct a sense of purpose and meaning that is especially relevant to space exploration, since it is in space that humankind will realize its long term future.

Directed energy photon propulsion via free-space coherent beam combination

Author: Jonathan Suen, Ph.D. Researcher, University of California Santa Barbara

Abstract: Directed energy photon propulsion via free-space coherent beam combination avoids the inherent scaling limits of ultra-high-power lasers and telescopes. By using thousands, millions, or even billions of apertures, flux at each aperture is reduced to reasonable levels, while an incredibly directive CW beam of up to 100 gigawatts can be formed. For such a beam to be synthesized efficiently, a feedback system must actively compensate for atmospheric turbulence, mechanical disturbances, as well as phase noise in interconnecting fibers and amplifiers.

We will discuss techniques, models, and results covering the scalable coherent phasing of large arrays. Due to the sheer number of elements, it is necessary that modules be able to compensate for phase noise in parallel, autonomous, and inexpensive manner. We find that with the use of a beacon-feedback architecture, this technology is largely available today.

Beyond Pluto: Status of Direct Fusion Drive

Author: Dr. Charles Swanson, senior scientist at Princeton Satellite Systems.

Background: The Direct Fusion Drive (DFD), based on Princeton Plasma Physics Laboratory’s (PPPL’s) Princeton Field-Reversed Configuration (PFRC) experiment and reactor concept, is a concept for a steady-state magnetic confinement fusion reactor designed from the ground up to be compact and portable, particularly as an in-space rocket engine. Princeton Satellite Systems (PSS) has had three NASA grants supporting research into DFD: a NASA NIAC which concluded in May, 2019; a Phase I STTR on the RF heating system; and an ongoing Phase II STTR on superconducting magnets.  We have leveraged these grants into a new ARPA-E effort under their 2018 OPEN solicitation, as part of a new ARPA-E focus on fusion. The DFD is well-suited to be the propulsion system of interstellar precursor and interstellar missions.

Objectives: Our experimental objectives are to demonstrate the plasma physics required to confine and heat plasma to fusion-relevant conditions. Our engineering design objectives are to produce high-fidelity models of the various subsystems required for a DFD-based interstellar spacecraft, including neutron shielding, heat recovery, RF amplifiers, superconducting magnets, optical communications, and in-space startup. Our mission architecture objectives are to determine the trajectories and payloads appropriate for interstellar precursor and interstellar missions.

Methods: To accomplish our experimental objectives, we are performing electron and ion heating experiments on the PPPL PFRC experiment, supported by an ARPA-E grant. We are also applying appropriate plasma physics models to the outstanding physics questions. To accomplish our design objectives, we are performing studies on each of the subsystems to determine suitable near-term technology. To accomplish our mission architecture objectives we are consulting with planetary scientists to determine the required and desired scientific payloads, and performing trajectory analyses of interstellar precursor and interstellar missions.

Results: We will present the current status of DFD design, our ARPA-E electron and ion heating milestones, and the plan and status for our superconducting magnet experiments. We will also present the relevance of DFD to interstellar missions including interstellar precursor, the solar gravitational lens, and a rendezvous mission to Alpha Centauri. A DFD mission to Alpha Centauri would take longer than a beamed mission but enable orbit insertion around an exoplanet and provide substantial power – hundreds of kW – for returning data.

TRL Assessment: We evaluate the TRL of the DFD to be 2.

Near-term milestones:

• Next-level design of the interstellar DFD spacecraft
• Demonstrate ion heating in the PFRC-2 experiment
• Design the PFRC-3 experiment

Development:

• Build a balance-of-plant testbed to demonstrate all subsystems of the DFD, without fusion
• Build a plasma physics testbed to demonstrate reactor-relevant plasma physics and fusion yield, without thrust production or energy capture
• Build a terrestrial prototype power plant to provide dispatchable, portable, high-value remote power

Conclusions: The DFD is a near-term steady-state magnetic confinement fusion propulsion technology for interstellar precursor and interstellar missions, which would require a much longer mission time than a beamed-power approach, but enable an orbital insertion at the target system and provide substantial power for interstellar communication.

Diffractive Lightsails

Author: Grover Swartzlander

Abstract: Beamed energy propulsion of a diffractive lightsail will be discussed. Experiments and predications of a stable beam diffractive beam rider will be described along with theoretical opto-mechanical calculations.Unlike metallized reflective sails, diffractive sails provides opportunities to achieve a low loss, high efficiency, high damage threshold optical surface.  What is more, a space variant diffractive film allows opto-mechanical control to be decoupled from the sail attitude.

Interstellar Material within the Solar System

Author: Timothy Swindle, PhD, Professor, Lunar and Planetary Laboratory, University of Arizona

Abstract Background: One of the primary goals of interstellar missions is to directly observe what conditions apply in stellar systems other than our own. However, it is worth asking whether there are interstellar materials within our own system that can add to our understanding of other systems, and whether they can be of use in developing interstellar missions.

Abstract Objectives: I evaluate three types of interstellar material that have been observed within the Solar System and discuss their potential utility for the goals of interstellar missions.

Abstract Methods: Review of recent scientific literature.

Abstract Results: The best-studied type of interstellar material available is presolar grains within meteorites, grains grains that survived the formation of the Solar System intact and were incorporated into rocks 4.5 billion years ago. Unfortunately, they typically formed as condensates in outflows of dying stars, so they do not reflect current conditions.

In recent decades, interstellar dust grains have been discovered to be streaming through the Solar System. The most detailed analyses come from the dust collector on the Cassini spacecraft, but give only minimal chemical information. The Stardust comet coma sample return mission probably succeeded in returning samples of interstellar dust, but they are so small (<1 micrometer) that they are difficult to find, and difficult to separate from the collector material in analyses.

The most promising avenue is probably the study of larger objects like 1I/2017 U1 ‘Oumuamua (100 m in longest dimension), which was discovered by an asteroid survey in 2017. Several ideas for missions to future interstellar visitors of this type have been suggested. Because they are likely to spend no more than a few weeks in the inner Solar System, even a flyby mission would likely require a spacecraft already launched and waiting. Because the encounter velocities are so high (‘Oumuamua had a geocentric velocity of >60 km/sec), there are significant propulsion issues for a rendezvous mission.

Abstract Conclusions: As asteroid surveys improve and new programs come online, more macroscopic interstellar objects will be discovered passing through the Solar System, but studying them poses significant challenges.

Staged Z-pinch: a target for fusion and a possible source for interstellar propulsion

Author: Dr. Hafiz Ur Rahman, President & Chief Scientist, Magneto-Inertial Fusion Technology Inc.

Abstract: The gas-puff Staged Z-pinch (SZP) is a magneto-inertial fusion concept in which an annular liner of a high-Z material, such as Ar or Kr, implodes onto a column of target plasma of D or DT fuel. The success of the concept necessarily requires mitigation of the magneto-Rayleigh-Taylor instability, which develops on the surface of the imploding liner and can feed through to the target and disrupt the pinch. One well-known method of MRTI mitigation is by axial pre-magnetization. As the liner implodes, a modest initial magnetic field Bz0 is amplified significantly due to flux conservation inside the liner plasma, and the resulting magnetic field line tension acts against MRTI growth. Recent experiments on a 1-MA, 100-ns driver at the Nevada Terawatt Facility at the University of Nevada, Reno, demonstrated that Bz0 = 0.1-0.2 T can significantly mitigate MRT growth of a SZP with initial liner radius of about 1.3 cm. DD neutron yields of 109-1010/shot were measured and appear to be isotropic and of thermonuclear origin. MACH2 MHD simulations show reasonable agreement with measured neutron yields at the 1-MA level, and also show favorable yield scaling to 10-MA and 20-MA machines, providing a path towards scientific breakeven and beyond. As the footprint and wall-plug efficiency of such a high-current machine is important to consider, the use of linear transformer driver (LTD) technology to improve driver/load energy coupling, and compact switch assembly (CSA) technology to decrease driver size, are also discussed as part of a conceptual design for future experiments and a possible future interstellar propulsion system.

Fusion and Antimatter: A Hybrid Approach to Reaching 0.1c

Author: Ryan Weed, PhD, Founder, Positron Dynamics Inc

Abstract Background: The incredible energy density of antimatter is the key to exploration beyond our solar system. When antimatter annihilates with matter, it releases an amount of energy equal to the rest mass of both particles. This results in a specific energy of 90MJ/ug, the highest known specific energy of any process. Since the prediction and discovery of antimatter in the 1920’s and 1930’s, its’ use as an energy source for rocket propulsion has been considered in many forms but has yet to be demonstrated. The key difficulties have been:

1. Trapping large amounts of antimatter
2. Directing the annihilation energy to produce thrust.

To solve these problems, our research has focused on radioisotope sources of positrons, utilizing the annihilation energy to catalyze fusion reactions. This hybrid antimatter/fusion approach avoids the problems associated with trapping antimatter through the use of a radioisotope antimatter source, while maintaining the ability to guide the fusion reaction products to produce thrust at very high specific impulse (>100,000 s).

Abstract Objectives: Key technical questions that this research addresses to determine feasibility:

1. Is fusion fuel ignition achievable using radioisotope based pulsed positron source?
2. Can the required positron source, accumulator and charged particle pulsing ion optics be integrated into Size, Weight and Power envelope of a spacecraft, while maintaining reasonable propulsion performance metrics?
3. Will the propulsion system benefit a proposed mission supplication (Interstellar transit)?

Abstract Methods: The research team utilized a custom 0-D Energy balance model and 2-D PIC code to determine annihilation catalyzed microfusion ignition requirements. In addition, Monte-Carlo neutron propagation (MCNP), PENELOPE, and SIMION codes were used to model the fuel cycle, positron fuel implantation, and beam optics to determine propulsion system properties.

Abstract Results: Ignition modeling results indicate that fast ignition can be achieved using a realistic number of pulsed positrons with standard temporal and spatial compression techniques. Neutron propagation simulations show that fusion neutrons can be thermalized and efficiently captured to produce positron emitting radioisotope (Kr-79). Mass properties of the required subsystem lead to a minimum spacecraft mass of approximately 1,000kg at 100km/s delta-V, with prospects for scaling to much larger mass and delta-V capability.

TRL Assessment: Currently, antimatter annihilation catalyzed fusion propulsion is a concept that has been formulated and analyzed inliterature. In addition, the feasibility of the propulsion system was recently documented in a Phase I NIAC Report. Thus, we assign the current TRL as (3).

Abstract Development:
2020-2022: Use existing neutron generators and pulsed positron facilities to demonstrate 79Kr enrichment and microfusion ignition, respectively.
2022-2025: Combined fuel cycle ground demonstration
>2025: Vacuum thrust measurement

Abstract Near-Term Technical Milestones:

1. Predictable and reproducible dense Deuterium production on fuel substrate.
2. Use PIC microfusion modeling to optimize target design for mission application (Isp/Thrust)
3. Develop ignition test bed for fusion yield demonstration at existing positron facility
4. Demonstrate Kr radioisotope enrichment and positron beam production using existing DD neutron generator and natural Kr isotopes.
5. Use PIC microfusion modeling to optimize target design for mission application (Isp/Thrust)
6. Develop ignition test bed for fusion yield demonstration at existing positron facility
7. Demonstrate Kr radioisotope enrichment and positron beam production using existing DD neutron generator and natural Kr isotopes.

Abstract Conclusions: In conclusion, initial feasibility of performance capability has been demonstrated using the realistic physics based modeling and constraints. We also present a path forward towards the first vacuum thrust measurement of an antimatter/fusion hybrid propulsion system. Such a propulsion system would have broad applicability beyond interstellar transit missions (e.g. planetary defense, asteroid capture, constellation servicing).

Inevitability, Adaptablity, Destiny: Religious and Non-Religious Arguments for a Human Future in Outer Space

Author: Deana Weibel, Ph.D., Professor of Anthropology and Religious Studies, Grand Valley State University

Abstract Background: As an anthropologist of religion I have been studying sacred places and religious travel for more than two decades. Recent work has explored the religious aspects of space exploration. Here I consider space exploration as having religious elements for some, but not all, individuals doing “space work”. My research combines elements of the anthropology of pilgrimage with the anthropology of space exploration.

Abstract Objectives: My objective is to understand the place of religion as humans move forward in their understanding and exploration of space. My premise is that religion is a universal in nearly all studied societies, and that the ubiquity of religion means that religion will likely be a part of humanity’s future in space. Therefore, it is important to understand how religious and scientific ideas about “the heavens” impact each other in individuals. Understanding how humanity’s “destiny” is conceived, both religiously and non-religiously, among contemporary “space workers” will clarify how the concept of destiny may motivate future space travelers.

Abstract Methods: As a cultural anthropologist, my methods are qualitative and ethnographic, based on participant-observation (essentially “embedding” myself) and conducting interviews with people whose work is connected to space, such as astronomers, engineers, astronauts, practitioners of space medicine, etc. Ethnographic research sites include NASA workshops, space centers, public presentations, laboratories, universities, the Mojave Space Port and the Vatican Observatory.

Abstract Results: Preliminary results indicate that people involved in space exploration often draw on ideas of an inescapable “destiny” when discussing the future of humans in space. Many of these ideas draw from religious scripture (including the Bible, the Qur’an and the Vedas), but even in the non-religious, a sense of an “inevitable” human destiny in space prevails. A high level of scientific knowledge seems to make participants more confident in humanity’s ability to adapt to life in space.

Abstract Conclusions: I conclude that a belief that humans are destined to have a future living in outer space is a powerful motivator for both the religious and non-religious alike. This belief encourages problem-solving in many fields, giving “space workers” confidence that any difficulties will be overcome, a belief that may be of great benefit in human space exploration.

The ALPHA Plasma Liner Experiment (PLX) – First Steps towards a Plasma Jet Driven Magneto-Inertial Fusion Reactor

Author: F. Douglas Witherspoon, President, CEO & Chief Scientist of HyperJet Fusion Corporation (presented by Jason Cassibry)

Background: Plasma Jet Driven Magneto-Inertial Fusion (PJMIF) is a pulsed fusion approach, generating a continuous power output by repetitively imploding magnetized fuel target plasmas by a spherically collapsing dense plasma liner. PJMIF is the only embodiment of magneto-inertial fusion that has the unique combination of standoff and high implosion velocity (50-150 km/s).

Objectives: The primary near-term objective of the Plasma Liner Experiment (PLX) at Los Alamos National Laboratory is to demonstrate the formation of spherically imploding plasma liners by merging dozens of supersonic dense plasma jets, and to demonstrate their viability and scalability toward reactor-relevant energies and scales.

Methods: PLX uses a spherically symmetric array of discrete high momentum flux inward firing plasma jets to form a spherical liner after merging. The nine foot diameter PLX vacuum chamber can support up to 60 plasma guns in a roughly symmetric configuration. The present ALPHA experiment uses 36 guns. Testing with 6 guns forming a small section of a liner have been completed at LANL. Mounting and testing of the first 18 gun hemispherical array is currently underway. An additional 18 guns currently being fabricated will be installed soon, completing the first 36 gun fully spherical array. A suite of diagnostics, including laser interferometry and fast imaging, are used to study the merging of the plasma jets and the liner. These results are compared with numerical simulations.

Results: We will provide an overview of the PJMIF concept, followed by a description of the design and operating characteristics of the supersonic plasma jets. This will be followed by a description of the past and ongoing experiments on PLX, ending with a brief discussion of the next steps and applicability to fusion propulsion.