2017 Symposium Summary The Tennessee Valley Interstellar Workshop, in partnership with Starship Century and Tau Zero Foundation, proudly put on a wonderful symposium at the Embassy Suites in Huntsville, AL on October 4th – 6th, 2017. Attendees from around the world represented their universities, military branches, government organizations, and scientific companies during the three-day sessions. What follows is a summary from Paul Gilster of Centauri Dreams, and we are extremely indebted to him for such a fantastic window into the conference. I want to thank Les Johnson and the conference organizers at TVIW, Tau Zero and Starship Century for the opportunity to make this presentation, and for the huge outlay in time and energy they devoted to the event. That includes our workshop leaders and participants who carried the original workshop notion forward. What I now hope to do is give an overview of what we have done here and what it signifies. Somewhere around the 6th Century BCE, a man named Lao Tzu, an almost legendary philosopher and writer, purportedly produced the book known as the Tao Te Ching, a fundamental text of Taoism and Chinese Buddhism. This year’s Tennessee Valley Interstellar Workshop arrived made to order for Taoist thought, with its theme “Step by Step: Building a Ladder to the Stars.” Because for years I’ve used as the line on my digital signature the Tao Te Ching’s aphorism: “You accomplish the great task by a series of small acts.” Confucius, who may have known Lao Tzu, would echo the same philosophy. As anyone paying attention to this year’s sessions learned at the beginning, many of the acts we are trying to accomplish are anything but small. A 100 GW laser array is not small either in concept or in physical dimension. A sail five meters to the side is small by many earlier standards, but what we discuss doing with it, a mission to the nearest star, is not small, nor is the exploration of the outer Solar System — with precursors fueled by fusion or driven by plasma sail — a small accomplishment. But conceptualizing each of these things, one at a time, that is a series of small steps, and we need many such steps. The emergence of Breakthrough Starshot clearly changes the game for everyone in the interstellar community. We have a congressional subcommittee report that ‘encourages NASA to study the feasibility and develop propulsion concepts that could enable an interstellar scientific probe with the capability of achieving a cruise velocity of 10 percent of the speed of light.” I doubt seriously that that phrasing would have emerged without the powerful incentive of the funding provided by Breakthrough, nor would the Tau Zero Foundation’s recent grant. We’re on new terrain that is a long way from where we once were, in the days when there were few interstellar meetings as such and most discussions among those of an interstellar bent happened at occasional get-togethers in meetings on largely different subjects. Today we have a community and, if it is one with a pointing problem in terms of how often it meets and how well it stays focused, it is at least one with high energy levels and a steep drive to succeed. TVIW 2017 gave us a range of focused sessions which I have chosen to group, trying to avoid being too arbitrary, into loose themes. Pete Klupar gave us the Breakthrough overview, which includes the welcome and related work of both Breakthrough Watch and Listen, a reminder that we must gain more information about the target of our mission, and indeed decide whether there may not be an even more attractive target near Centauri A or B. The welcome news that the RFP process has begun with work on the project’s laser array shows us a community with an actual interstellar project seriously defining the parameters of a mission. Here we are in the larger realm of vision, as Andrew Siemion reminds us when he tells us that we search for ourselves as we venture to the stars. We also, whether or not we send Starshot sails on their journeys in 40 or 50 years, define the limits of our present technology and infuse the entire enterprise with an unprecedented prospect of well funded trade studies. The interstellar enterprise advances whether or not Starshot’s sails launch to Centauri, and who can say what spinoffs we won’t gain from the effort in the interplanetary arena with its tools. On the matter of overview, let me mention Marc Millis’ discussion of the Tau Zero grant from NASA, which as I mentioned derived from the impetus of the Starshot initiative. Comparing propulsion approaches to take us through what Millis calls the era of precursors, the era of infrastructure and the non-extrapolatable future helps us identify the critical issues that need study, just as Starshot itself helps us locate, one by one, the major problems we need to solve for a specific mission concept. What we do need to be wary of is premature lock-in when competing methods for doing interstellar missions remain very much on the table. In the realm of hard decisions and trade studies that illuminate them, Kevin Parkin showed us a system model that allows Starshot to study not only a Centauri mission at 20 percent of c, but also a precursor mission to a closer objective and a 70 km/sec ground vacuum tunnel test facility. It is heartening to realize that Parkin’s system has been used to conduct trade studies since March of 2016. Meanwhile, the inputs from the broader community continue. Al Jackson showed us an analysis of trajectories for a Starshot probe, and we’re reminded by Benjamin Diedrich, who has been working with the NEA Scout mission, that we can learn much from a mission with a much different objective, and one with the ability to apply guidance and control forces that our Centauri-bound sail will be unable to muster. Congratulations to Diedrich and particularly Les Johnson for the recent successful deployment tests of the NEA Scout sail. I want to also mention in the realm of trade studies and laboratory work the importance of the kind of measurements George Hathaway discussed for any work of this kind. Looking at problems in testing high voltages in high vacuum at cryogenic temperatures, Hathaway showed the measurement pitfalls that can ensnare experimenters, hard lessons to be kept in mind at all times by those who are evaluating propulsion technologies both understood and exotic. Starshot’s mission components were a major factor in our deliberations. That 100 gigawatt laser array that Robert Fugate described can put something on the order of 30,000 g’s on the sail if we can get it to operate, despite the major issues of laser phase noise, optical path length differences, atmospheric fluctuation and pointing accuracy. We are considering a sail that goes from Earth orbit to 10 times the distance of the Moon in a matter of hundreds of seconds. Can we make this happen? Starshot fails if it does not, and it fails if Jim Benford and those working with him cannot come up with a sail that can withstand the huge forces to be slammed into it. Here I want to pause to mention the rich sail background on display at the conference. The Benford brothers did the first work on sails in the laboratory — and as far as I know — the first actual tests of beamed sails, some 16 years ago. In the audience, we had Gregory Matloff, a distinguished figure in sail history who has been examining their prospects for decades. Geoffrey Landis has published key papers on sail materials, and although his role in this TVIW was to discuss the Solar Gravity Lens, his contributions help us as we look toward possible sail materials and shapes within the Starshot envelope. The welcome presence of Giancarlo Genta reminds us of the tremendous contribution of the Italian sail effort through Project Aurora and other work in the 1990s. The need for the kind of sail test facility Jim Benford so carefully described is obvious and one hopes it will be the target of quick action, especially with the new wave of RFPs starting to translate the concept into reality. Phil Lubin’s analysis of directed energy as the enabler for interstellar missions, beginning with a NIAC Phase 1 study under the name Starlight, led to Pete Worden’s making the connection with sails as a possible driver for a Centauri mission with a wafer scale payload. I was sorry that Mason Peck wasn’t here to participate in the discussion given his role in ‘spacecraft on a chip’ through his work at Cornell, but Lubin reminded us that an infrastructure like this can do much more than drive chip spacecraft. It can become a huge factor in planetary defense, in power beaming to Earth, in space debris removal and beamed transport within the Solar System. Giancarlo Genta presented a preliminary analysis of inflated spherical sails of the kind recently proposed by Avi Loeb and Zac Manchester for Breakthrough Starshot. Working at far lower power levels for beam intensity, Genta found that an inflated sail essentially holds its shape under beam power, using a one meter diameter sail at 30 g’s acceleration. Further testing at increased power levels approximating Starshot are ahead. Key questions include whether hitting a sail with 30,000 g’s will not both deform and spin the sail, although as Genta pointed out, the sail can be abandoned for the duration of cruise if it can be brought safely up to speed. I heard several people in the audience calling communications back to Earth the biggest challenge for Starshot, and although Dr. Fugate might disagree, I have to say that David Messerschmidt’s talk on data return was sobering. We have to make up 7 orders of magnitude of signal power when compared to our outer Solar System missions, perhaps a doable proposition if we allow decades for data return. We also deal with formidable issues of background radiation, pointing accuracy, atmospheric turbulence and scattering, and optical losses. All these factors push an increase in aperture area to 565 meters. Our communications and imaging discussion, though, also takes in Slava Turyshev’s work on imaging an exo-Earth with the Solar Gravitational Lens. Clearly, getting a good idea of our target from a technology that could allow images of 1000 x 1000 pixels would be an outstanding precursor in its own right, and one that could be used at distances up to 30 parsecs if we can make it work. Geoff Landis’ reservations about the Gravity Lens don’t question its potential but do make us ask how likely we are to make it work and deliver genuinely useful information. We got into these matters at the Sagan session on the 550 AU mission that Claudio Maccone has called FOCAL, where Landis, Turyshev, Greg Matloff and Pontus Brandt debated the issue. It should be kept in mind that some of Maccone’s recent work on the lens has shown the potential for communication, a feature that, if it could be realized, would suddenly turn many of the issues David Messerschmidt examined on their head. Thus, if it could be determined a lensing option is workable, an early Starshot mission to explore this region is a possibility. Let me also mention the Sagan session on detecting life through biosignatures in planetary atmospheres in which I spoke along with Greg Benford and Angelle Tanner. This is by way of looking at what we can learn about nearby stars, the fact being that nearby red dwarfs are going to be under intense scrutiny by the James Webb Space Telescope, and we have the possibility of detecting gases like oxygen and methane which, if found together, offer us a strong indicator of some kind of metabolism. Tanner’s analysis of planet finding techniques in a later session took us through the range of methods available, ranging from radial velocity to direct imaging and transits, particularly in terms of distinguishing stellar noise from terrestrial mass planets. We moved into the realm of other interstellar precursor missions with Pontus Brandt’s discussion of probe missions to 200 AU up to 1000 AU. This gets us into virgin territory, for going to this distance puts us into the relatively pristine interstellar medium. Quaoar lines up as an interesting target along the way because of what it may tell us about the KBO population, but we also would learn a great deal about dust distribution within the system, seeing the heliosphere from outside as we see similar astrospheres around other stars. Brandt’s comments on how we manage long-term missions ring true in the era of decadal data return from a Starshot mission and destinations that may require more than a single lifetime. Gary Pajer’s take on precursors would use the Princeton Field Reversed Configuration machine to reach out to that magical 550 AU target, where the lens effects begin, with a mission time of 13 years, or 18 if we choose to stop. Using this technology, an Alpha Centauri flyby becomes feasible within 550 years, with both power and propulsion generated by a single engine. Could we do this with a solar sail mission? Olga Starinova asked that question, noting a close solar flyby based on recent studies by Greg Matloff, Les Johnson, Claudio Maccone and Roman Kezerashvili to reach the inner Oort Cloud within 30 years. And Stacy Weinstein-Weiss discussed a key interstellar question: Why is science return from an interstellar mission better than local studies from Earth? Here, we learned about the unique science measurements that would be performed en route to the exoplanet, including the outer regions of our solar system, the Oort Cloud, the local interstellar medium, and the astrospheric environment around the host star. Perhaps trumping all of these is the search for life with in situ measurements. Richard London and James Early helped us understand the dust impact hazard, which they believe will not threaten a sail, but of course our concern is likewise with the payload, which must be protected at all costs. London and Early used the HYDRA code for inertial confinement fusion in this work to study how we might reduce risks using optimal materials on a fast-moving craft’s leading side, with leading thin foil to atomize dust grains. Robert Freeland pointed out to me that one of Jeff Greason’s plasma magnet sails, discussed in a moment, could also serve as a useful shield. On useful precursor technologies, Sandy Montgomery provided a way to avoid growth in the boom diameter and mass of sails as we move toward larger-scale missions by using what he calls a ‘space tow architecture,’ a train of gossamer sails integrated with a tension truss column. The advantages: We get much larger sails without growth in boom diameter and mass, using lightweight longeron filaments to connect a stack of smaller sails, much like a tandem kite. I had mentioned to Pete Worden in a recent online exchange that I had seen several small sail analyses springing up and asked if they had any connection with Starshot. His answer was that they didn’t, but as he put it, the more the merrier given the magnitude of the problem. Thus it’s tremendously heartening to see the outgrowth of sail ideas that may eventually influence Starshot or, more likely, feed into designs outside of immediate interstellar goals that could play into our move toward the space-based infrastructure we need here in our system. Thus Grover Swartzlander’s analysis of diffractive meta-sailcraft, which proposes that we look more carefully at diffractive sails, which absorb little light — a key issue for beamed sails — and have none of the re-radiation problems of reflective materials. Moreover, we might recycle photons to multiple sail layers if we can develop the right broadband space-qualified diffractive films. TVIW 2017 was marked by its focus on sail technologies, due to all the factors I’ve already mentioned, but of course we have other options to consider. Jason Cassibry talked about the problems of solid state nozzles when dealing with pulsed fusion and fission/fusion hybrids for rapid precursor missions, the primary issues being erosion and wall heating. He showed us a 3D plasma simulation of a pulsed magnetic nozzle crafted for z-pinch propulsion. Pauli Laine examined fission fragment possibilities, given the fact that uranium fission releases 81 percent of its energy in the form of kinetic energy. The escape of fission fragments rises when particle size decreases, so low density fissile material like americium or curium comes into play, with the escaping fission fragments being used as rocket propulsion. As Laine noted, fission fragment advocates also have to contend with fuel production — how to produce enough of the needed materials — as well as daunting issues of using such rockets safely. Antimatter appeared in two sessions this year, with Gerald Jackson describing crowdfunded ongoing experimentation into antimatter production. Jackson would like to see antimatter emerge at a rate of at least 1 gram per year, a startling figure given that I can remember when NASA gave a figure of $62.5 trillion per gram of antihydrogen. Measure this against a Fermilab production rate of 2 nanograms per year. If we can do this in a way that is economically feasible we have the option of missions like the antimatter sail that Jackson and Steve Howe, also at Hbar, has developed through NIAC work. Jackson also examined antimatter storage possibilities through diamagnetic levitation. Antimatter storage was the key of Marc Weber’s talk, which looks at the problem of controlling space charge, the repulsive force of all those stored charges in the fuel we would like to use. Weber is experimenting with storing electrons in a massively parallel micro-array of tubes in a 7-tesla magnetic field, seeking to discover the possible configurations in trap arrays. Everyone in the interstellar community from Les Shepherd and Robert Forward on has pondered the energetics of antimatter rockets, which still face the daunting storage and production issues Weber and Jackson have explored. A bit less exotic but with exciting potential of its own is the plasma magnet sail described by Jeff Greason. Here we can imagine deploying magsails for braking against the interstellar medium as an interstellar probe enters a destination system, achieving orbit around the target star using the stellar wind. But Greason pointed out that such technologies are likewise ideal for precursor missions to 1000 AU, for example, and conceivably, using local beamers, within braking systems for a fast mission infrastructure inside the Solar System including cycling systems to Mars. Greason considered using particle beams and even fusion pellet delivery to the sail. I should mention that a Sagan session also explored flyby vs. deceleration with the help of Jackson, Stacy Weinstein-Weiss and Gerald Jackson, along with David Messerschmidt. The deceleration problem looms large. If we do get Starshot probes to Proxima Centauri, the imagery we receive may well make clear the need for a sustained presence in that interesting system. The payoff, as Weinstein-Weiss made clear, would be in the search for extraterrestrial life, where we may need all the resources we can muster to verify a detection. Talking about interstellar mission concepts reminds me inescapably of a loss we suffered this year in science fiction writer Jerry Pournelle. Familiar, I think, to most of us here, Jerry explored numerous interstellar schemes including beamed sails (early on), and in Footfall used Orion technology to save the species. Because Larry Niven wrote Footfall with Pournelle, I want to mention how pleased I was to be able to shake his hand at long last. Larry brought a whole new dimension to my science fiction reading back in the early 1970s with short stories and the novel Ringworld. What a compliment to TVIW to have Larry along with writers Geoff Landis, James Cambias, Greg Benford and Alan Steele here for tonight’s writers’ panel, not to mention our host Les Johnson himself. About Steele, I want to say that I’ve read Arkwrighttwice, and if you don’t know the novel, you need to acquire a copy immediately, as it addresses the issues a small community of devoted advocates face when trying to do something as outlandish as build vehicles that can move between stars. The valedictory theme continues: Let me also mention that this year we lost Jordin Kare, an innovative physicist who came up with ideas like SailBeam, a stream of micro-sails delivered to a receding starship as a form of propulsion, and the Bussard Buzz Bomb, as he called it, a starship that came up to speed through collision fusion with a string of pellets that had been laid out along a predetermined track. I never met Jordin, but he spent a lot of time on the phone with me when I wrote my Centauri Dreams book, and I think the field is diminished by his passing. The infrastructure theme emerged several times at this year’s sessions, with Tracie Prater looking at NASA’s In-Space Manufacturing Project, under the theme Make It, Don’t Take it. And it only makes sense as we contemplate long-term manned missions that we look at manufacturing and recycling parts on demand, using the ISS while we can, before its 2024 deorbit, as a testbed. We learned about NASA’s plans for a multi-process fabrication laboratory called FabLab, with current experiments on the ISS pointing to a robust future for assembly of materials in space with 3-D printing technology. Jon Barr told us about the United Launch Alliance’s robust work with ACES (Advanced Cryogenic Evolved Stage) and XEUS, a vertical-landing, vertical-takeoff lunar lander demonstrator. Can we use these refuelable, reusable technologies in company with the Vulcan booster to establish what will become trade routes to Cislunar space? The idea here is connecting Low Earth and Geostationary Orbits with Earth Moon L1 and the lunar surface. The goal: A robust Solar System economy, which will eventually translate our early interstellar precursors like Starshot into a longer-term framework of exploration and perhaps colonization. Our leadership panel included Rep. John Culberson, whose language we’ve already discussed regarding a NASA inquiry into interstellar prospects to coincide with the anniversary of the Moon landing in 2069. Also Congressman Brooks of Alabama, Lt. General Kwast and Paul McConnaughey, who directs Marshall Space Flight Center. It was rousing to hear the energy in Rep. Culberson’s voice as he described missions like Europa Clipper and the possibilities of the Space Launch System. A takeaway was his belief that the discovery of life, either in our system at Europa or Enceladus, or in biosignatures in an exoplanet atmosphere, will be a civilization-changing discovery that ignites public support for future exploration. But it was also sobering to consider the budgetary dilemmas of ever-rising deficits and accumulating national debt. Lt. Gen. Kwast emphasized that expansion into space demands we take our values with us even as we plan missions to ever more distant targets. The panelists’ responses to Pete Klupar’s concerns over installations like the Starshot 100 GW laser show that we still have many policy questions to answer as private initiatives like these go forward. Can we get beyond bureaucracy and current cultural fatigue to expand the realm of values responsibly? Brent Ziarnick reminded us that interstellar technology presents us with the most daunting energies human beings have ever thought to develop. The analogy with nuclear energy is clear, and fortunately supported by deep scholarship. Our preoccupation with nuclear gloom, part of Sheldon Ungar’s ‘dynamic oscillation’, as Ziarnick described, ended Project Orion and threatens our development of nuclear power options as a positive tool for exploration. Is METI likewise an ethical issue? Kelly Smith asks whether scientists are up to the challenge of dealing with broadcasting to the stars, given that this is a matter that potentially involves the entire species. METI may be low risk, but the risk is not zero, and that risk involves the survival of the entire species. Or what about the ethics of sending humans to the stars? For we may discover that exoplanets are not empty, but filled with life. And given the fact that we use but 21 specific amino acids to build our proteins — and that there are some 300 naturally occurring amino acids — we cannot know what life may choose to use. Perhaps, as Ken Roy reminds us, we might look for lifeless worlds on purpose, seeking places we can terraform. We’re now looking at issues of humans among the stars, a future that could involve vast worldships taking human populations to distant systems. Ore Koren discussed the vital question of how we reduce conflict in a closed environment in which causes of violence are numerous. Koren used large datasets to look at historical examples of violence, along with strategies by which we might reduce problems like lack of external ideas and migration. The result: Our worldship emerges as multicultural and semi-centralized, a hybrid of Sweden and Singapore. James Schwartz worked similar turf but examined the ethics of worldship travel itself. Are colonists on dubious ground imposing a worldship future on their children? Perhaps not, but the real question becomes, should we put parents on worldships in the first place? Schwartz reminded us of the need for sufficiently large crews, and the fact that we will use extraterrestrial settlements much closer to home to learn valuable lessons before embarking starward. And there we are, TVIW 2017. Thank you all for the opportunity to listen to and learn from your deliberations. If there is one thing that the interstellar community has taught me, it is that scientists working at the top of their form are willing to listen to questions and explain their work to writers like me, and to put breathtaking concepts out to a receptive and growing audience like those who gathered here. This is a mission that all of you make possible, and while it may seem less dazzling than a Starshot, it is vital in making our interstellar effort a planet-wide affair. I close by returning to Lao Tzu: “To avoid disappointment,” says the Tao Te Ching, “know what is sufficient. To avoid trouble, know when to stop.” I’m done.