IRG 2021 Abstracts

Here are abstracts of the papers that have been accepted for presentation at the 7th Interstellar Symposium. As more papers are accepted, they will be added here. Check often for additions!

Is ET Lurking in Our Cosmic Backyard?

Author: James Benford

Description: I argue that a strategy of exploring for alien artifacts near Earth is a credible alternate approach relative to the existing listening-to-stars SETI strategyStars come very close to our solar system frequently. About two stars per million years come within a light year. An extraterrestrial civilization that passes nearby can see there is an ecosystem here, due to the out-of-equilibrium atmosphere. They could send interstellar probes to investigate. I estimate how many probes could have come here from passing stars. And where could we find them now? The Moon and the Earth Trojans have the greatest probability of success. Close inspection of bodies in these regions, which may hold primordial remnants of our early solar system, yields concrete astronomical research. I suggest additional resources devoted to imaging of our Moon’s surface, the Earth Trojans and Earth co-orbitals, and for probe missions to the latter two. The Search for Extraterrestrial Artifacts (SETA) concept can be falsified: if we investigate these near-Earth objects and don’t find artifacts, the concept is disproven for this nearby region. I construct a ratio of a Drake Equation for alien artifacts to the conventional Drake Equation, so that most terms cancel out. This ratio is a good way to debate the efficacy of SETI vs. SETA. The ratio is the product of two terms: One is the ratio of the time Lurkers could be present in the solar system to the length of time extraterrestrial (ET) civilizations transmit electromagnetic signals. The second term is the ratio of the respective ‘origin volumes’: the volume from which Lurkers can come (which is affected by the long-term passage of stars nearby) to the volume of transmitting civilizations. This Drake Equation logic argues for emphasis on artifact searches, a strategy of ET archaeology.

Orbital Architectures of Nearby Planetary Systems

Author: Jeremy Dietrich

Background: Exoplanet systems display a large variety in their architectures, from single planets to tightly packed compact multiple systems, from sub-Earth-sized planets to planets larger than Jupiter. Our knowledge of how to form these variations in planetary frameworks is still improving, but we are able to now infer general properties at a population level.

Objective: Here, we will review the orbital architectures of the planetary systems within 15 parsecs. Methods: We will provide statistical interpretations of their parameters and discuss the most likely and most unlikely system characteristics. We can then perform an analysis of the system to predict the likelihood of additional “hidden” planets in these systems

Results:  We will further fill out our interpretation of exoplanet systems in the solar neighborhood, narrowing down orbital configurations and planet parameters.

Conclusions: In the future, this could enable us to determine the most likely system to contain an Earth-like planet when the known architecture seems to be incomplete. Our knowledge of orbital architectures can help provide targets for interstellar probe missions and potential human interstellar travel.

Visiting an Exoplanet

Author: Louis Friedman, Executive Director of The Planetary Society, Emeritus

Description: There are two ways to visit an exoplanet — real and virtual.  Real involves going there — something not possible now nor, except with extreme limitations, in the foreseeable future.  Those limitations are with trips times of eons or with a one gram (or so) spacecraft to only the nearest star  powered by a cost and politically prohibitive laser array.   To visit a potentially inhabited exoplanet with extraterrestrial life will require searching over a large number of candidates probably within a distance of 10-50 times the distance to the nearest star, and a spacecraft 2-3 orders of magnitude larger.  The spacecraft will also have to be capable of observing the exoplanet continuously for a while, rather than flying by it at an interstellar speed of (say) 1.5 AU/hour. But, fortunately, nature comes to the rescue – enabling virtual visits to exoplanets by remote observation using the solar gravity lens and positioning a spacecraft and its telescope along its focal line, beginning at 547 AU from the Sun.  That is still a very tall order — but it can be done with today’s technology with a smallsat-solar sail combination and a trip time of 20-30 years.   Such a mission has been under study for several years and is now the subject of a NASA Innovative Advanced Concepts Phase III study including the development of a technology demonstration mission to prove the smallsat-sail concept for high-speed exit of the solar system.  The mission requires technology development — including lightweight electric micro-thrusters with a small RTG or nuclear battery, and multiple small spacecraft to enable a 1-2 meter optical telescope to operate in the solar gravity lens focal region.  The resulting kilometer scale high-resolution of the exoplanet will enable seeing continents, large features, and even (should such exist) large scale evidence of life, as well as incredibly detailed spectral and compositional analysis of the atmosphere.  No other scheme exists for such high-resolution observations, and it is possible even many tens of light-years from our Sun.  It may be the only way to see life on another world.

Wind-Pellet Shear Sailing

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

Background: Gaining the kinetic energy required for interstellar flight affordably is difficult and tapping existing natural sources of energy such as the solar wind is attractive for reducing costs.  However, a gap exists in the published concepts, in that solar wind speeds are limited to ~700 km/s, while even with concepts such as the wind-powered reaction drive (‘q’-drive), speeds of ~5% of c must be reached before they can take over.  A cost effective way to fill that gap has been lacking. Objective – Demonstrate a method by which inert pellets, accelerated by the solar wind, can be used to accelerate a spacecraft from solar wind speeds up to ~5% of c.

Methods: Classical physics computations to support the basic physics and feasibility of the approach.

Results: When two matter streams are in proximity but with different velocities, or when they move through the same space but with different velocities and distinguishable properties, the difference in velocities, or velocity shear, can be used to gain propulsive energy.   A stream of pellets moving through the interstellar medium is an example of such a case.   Propulsion by pellets is an idea explored in the prior art that requires high speed pellets; the extraction of useful work from the difference in speed between the pellets and the interstellar medium allows a ship running over the pellets and also drawing energy from the passage through the interstellar medium to gain propulsive energy even when faster than the pellets and even when the pellets are composed of inert reaction mass.  We will discuss the basic physics of this and the performance equations and discuss this in the context of using relatively slow pellets (accelerated by solar wind), to send a spacecraft to a substantial multiple over the solar wind velocity.   Another case where small macroparticles and a plasma wind are at different speeds is the inner solar system in the plane of the ecliptic, where the solar wind and zodiacal dust have different velocity distributions; this may offer further applications of the same principle.

Dynamic Soaring as a Means to Exceed the Solar Wind Speed

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

Background: A number of concepts exist for exploiting the solar wind as a means of propulsion: the MagSail, the e-sail, and the plasma magnet. All of these concepts work predominately as drag devices and thus are limited to velocities equal to the solar wind (~700 km/s), with only limited ability to generate force transverse to the local direction of the solar wind (i.e., lift). An interesting possibility to be explored is dynamic soaring: Exploiting the difference in wind speed in two different regions of space. Albatrosses and sailplanes are known to use this technique, circling in and out of regions of wind shear. Birch (JBIS, 1989) suggested such a technique could be used via a “MHD Wing” for interstellar travel applications, but did not explore the concept further.

Objective: The potential for dynamic soaring to enable a spacecraft using the dynamic pressure of the solar wind in order to greatly exceed the wind speed will be explored. Analysis of the concepts will be organized around passive (meaning simple wing- or sail-like structures) and active (wherein there is a power and thrust interaction with the solar wind) approaches.

Methods: For passive methods, charged particle interaction with static electromagnetic fields will be directly numerically simulated and the lift and drag values derived. Techniques of generating electromagnetic fields capable of providing ideally (specular) reflection of particles will be assessed. For active methods, the ability to extract power from the wind and accelerate a transverse flow—thus generating lift—will be analyzed. Simple analytic models of the fast/slow solar wind and the termination shock will be adopted to explore the required trajectories for soaring.  3-degree-of-freedom simulations of spacecraft trajectories will be performed to assess the potential gains that might be realized by the dynamic soaring maneuver.

Results: While passive methods appear capable of generating high lift-to-drag ratio, the requisite structural mass limits them to very low accelerations and thus not directly applicable to interstellar flight. Active concepts wherein plasma structures have a power and momentum transfer interaction with the solar wind are more promising, but have greater uncertainty associated with their principles of operation.

Pulsed Plasma Rocket- Developing a Dynamic Fission Process for High Specific Impulse and High Thrust Propulsion

Author: Troy Howe, PhD, CEO, Howe Industries

Background: To realistically establish a human presence on Mars or to enable faster transit on any deep-space mission, high specific impulse and high thrust are key. Having each of these would allow for efficient propulsion and fast transit, eliminating restrictive launch windows and risks of long-term radiation exposure to crewed missions. The Pulsed Plasma Rocket (PPR) aims to meet these needs via a fissioning propulsion system that produces rapid plasma bursts. Previous efforts have examined pulsed propulsion methods, including the use of plasma as propellant, but the PPR achieves these plasma bursts via a fission-based system, wherein a highly moderated fuel projectile is propelled through a uranium barrel to reach supercriticality. The barrel and projectile material architecture results in much higher energy deposition in the projectile than in the barrel. After experiencing significant fission events, the projectile changes from a solid to a plasma over a period of a few microseconds, and is expelled through a magnetic nozzle. 

Methods: Performed for a Phase I NASA NIAC study to determine feasibility and performance.  Computational modeling has been performed using MCNP, MOOSE, and SERPENT neutronics programs. Thermal systems analyzed using COMSOL Multiphysics. Plasma interactions modeled with SPFMax. 

Results: Neutronics modeling has determined the projectile constituents to include a high-assay low enriched uranium water-ice mix encased in a thin iron shell. Control drums generate a pulse of extreme supercriticality by rotating at different rates to create a Fourier series delta function which flashes the projectile into an ionized plasma at the end of the barrel. With the combined use of a coilgun as the initial propellant injector and a magnetic coil and nozzle for exhaust, the projectile is able to produce a thrust of roughly 100 kN with an Isp of 5,000s. 

Conclusions: The necessary criticality to reach plasma-generating temperatures can be achieved in the projectile, while maintaining overall system integrity. The ship is capable of a 2-month transit to Mars, consumes no highly enriched uranium material, and can power itself by recuperating energy from the propulsion system.

Deceleration of Interstellar Spacecraft Utilizing Antimatter

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

Description: This paper summarizes the results from a recently completed NASA Innovative Advanced Concepts (“NIAC”) Phase I grant. The grant explored a mission architecture wherein a 10kg-scale unmanned spacecraft decelerates and inserts itself into orbit around an exoplanet.  In this research the antimatter-initiated fission of depleted uranium produces electrical power, thrust, or both to accomplish these maneuvers and enable robust scientific discovery and two-way communications with Earth.  A mission to the nearby habitable-zone exoplanet Proxima b is explored as a concrete example, wherein the acceleration stage of the spacecraft is separated after its 10-year burn and deflected to perform a fly-by through the Alpha Centauri AB binary system.  Similar to the Voyager 2 mission, wherein a grand tour of the outer planets justified the spacecraft investment that is still yielding scientific results decades later beyond the heliopause, a program of prompt science results regarding interstellar clouds, Oort cloud population distributions, interstellar magnetic fields, and radiation spectra in the interstellar void are envisioned.  As one example, an exciting conclusion is that the detection of 10km-scale Oort cloud objects by a small semi-relativistic spacecraft is indeed feasible.  During this grant, several potential methods of deceleration were investigated, starting with the emission of electrostatically-focused  fission daughters as reaction mass, each having an average exhaust velocity of 4.6% of the speed of light.  The other methods involve dissipating the large kinetic energy of the spacecraft into the interstellar medium, using a variety of possible coupling mechanisms.  A significant impediment to progress along these lines is the lack of data concerning plasma composition and density of the interstellar medium and the directions and intensities of the interstellar magnetic field.  The allure of these other methods is the possibility that their consumption of scarce antimatter, in this case used to generate onboard electrical power, might be smaller than the primary reaction mass method.  This paper will also briefly summarize other results in the areas of antimatter production and storage, spacecraft instrumentation, and other mission objectives.

Mass and propulsion implications for interstellar scientific observation by flyby

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

Description: In view of the vast distances to an interstellar target, the highest technologically achievable spacecraft speed is often assumed, thus minimizing the mass of the scientific payload and communication gear. This is generally a compelling assumption for human spaceflight,  where many considerations favor short time to target. These include biological constraints such as the lifetime of astronauts, life support and physiological needs, and even psychological well being and onboard culture. However, for the coming century interstellar missions are expected to be robotic and employ flyby observation (as opposed to landing) to avoid deceleration. We address missions in which a space probe performs a target flyby during scientific observations, with data conveyed back to earth by electromagnetic radiation. In this scenario the scientifically relevant metrics are the observation time, the total volume of data returned, the number or frequency of probe flybys, and the total data latency (time elapsed from probe launch until completion of data return). The four components of data latency are travel time to target, observation time at target, the subsequent data transmission time, and the signal propagation delay. The mission design should be optimized with respect to objective functions like maximizing data volume for a given latency or, when a swarm of probes is launched, launch cost per unit of data volume. While  reducing probe speed (increasing payload mass) does increase the travel time to target, for directed-energy propulsion with a fixed launch infrastructure the dependence is a weak quarter-power penalty. Offsetting this is an expected mass-squared increase in data rate, a longer scientific observation time, a moderation of the distance-squared decrease in data rate, and a smaller signal propagation delay at the end of transmission. Several examples of design optimization under appropriate criteria illustrate the benefits of substantially increased probe mass with a resultant lower speed. The scaling law governing the relationship of probe mass and transmission data rate is observed to be a significant issue in interstellar probe design.

SAM: Construction of a hi-fidelity, hermetically sealed Mars habitat analog at Biosphere 2.

Author: Kai Staats, project lead, SAM at Biosphere 2

Description:Space Analog for the Moon and Mars (SAM) is a hi-fidelity, hermetically sealed analog and research center composed of a living quarters for four inhabitants, airlock and hub, and greenhouse with temperature, humidity, and carbon dioxide level controls. When complete, SAM will include a half-acre Mars yard for pressure suit, tool use, and rover tests; a constructed lava tube and gravity-assist rig for reduced gravity simulations.

In 1987 Taber MacCallum and William Dempster designed and build the now iconic Test Module, a sealed greenhouse prototype used to test the fundamental functions of the structure and lung used to build the massive Biosphere 2. Now, project lead Kai Staats, Trent Tresch, John Adams and a compliment of volunteers are constructing SAM with intent to welcome the first research teams in the fall of 2021.

SAM design and development is guided by experts at NASA Johnson Space Center, Grant Anderson, CEO of Paragon SDC; Dr. Murat Kacira and Dr. Gene Giacomelli at the Controlled Environment Agriculture Center at the University of Arizona, and original Biospherian Taber MacCallum.

In this presentation Trent will engage the audience in the construction process, lessons learned, and the long-term goals of this unique research facility as it relates to sealed habitats of any volume or duration, and how SAM will inform the computer model SIMOC with a long-term goal of management of on-board life support systems.

Objective: To build a habitat analog and research station that welcomes research teams from around the world, to help prepare our species to become interplanetary.

Methods: Grinder, sander, scraper, primer and paint; electrical wiring, lighting, HVAC. CO2 scrubber, pressure seals, monitors and regulators, pressure suits and EVAs.

Results and Conclusions: To be determined!

An Overview and Plan for an Interstellar Mission Study with the novel Helicity Drive fusion propulsion concept

Author: Alan Stern, Ph.D., Astrophysics and Planetary Science, Univ. Colorado-Boulder

Background: Helicity Space is a startup based in California developing an in-space fusion propulsion drive.

Objective: In this presentation we will summarize the company’s objectives, team, technology, progress, and plans. We will also outline our planned 2021 NASA Innovative Advanced Concepts (NIAC) proposal to study an interstellar probe traveling to 1000 Astronomical Units (AU) using the Helicity Drive fusion propulsion system.

Methods: The Helicity Drive is a new magneto-inertial fusion concept based on decades of experimental and theoretical fusion plasma research. The concept exploits magnetic reconnection and a new magnetic confinement configuration (plectonemes) to enable scalable propulsion characteristics and simplify fusion engineering.

Results: Our calculations show that the engine concept can operate from small 100 kW engines to 10 Giga-watt engines by increasing the number of plasma sources, similar to the way a car engine increases power with more cylinders. With variable high specific impulses inherent to fusion, our Helicity Drive engines could thus take, for example, a 5-ton probe to 1000 Astronomical Units in about 11 years using medium-sized 37 Megawatt-thrust engines or as little as 3 years using large 5 GW-thrust engines.

Conclusion: The Helicity Drive fusion propulsion system presents a significantly new capability for an interstellar mission concept. The interstellar mission could use larger scientific instruments and be completed substantially earlier and faster, eliminating the need for difficult and expensive design and qualification issues associated with conventional propulsion approaches.