Here are abstracts of the papers that have been accepted for presentation at the 6th Interstellar Symposium and Advanced Interstellar Propulsion Workshop. As more papers are accepted, they will be added here. Check often for additions!

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.


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.


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.


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.


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).


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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

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.