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Space development on the Moon, Mars and beyond featured in 2023 NIAC Phase I Grants

Conceptual illustration of an oxygen pipeline located at the lunar south pole. Credits: Peter Curreri

This year’s list of NASA Innovative Advanced Concepts (NIAC) Phase I selections include a few awards that look promising for space development. For wildcatters (or their robotic avatars) drilling for water ice in the permanently shadowed craters at the lunar south pole and cracking it into hydrogen and oxygen, Peter Curreri of Houston, Texas based Lunar Resources, Inc. describes a concept for a pipeline to transport oxygen to where it is needed. Clearly oxygen will be a valuable resource to settlers for breathable air and oxidizer for rocket fuel if it can be sourced on the Moon. The company, whos objective is to develop and commercialize space manufacturing and resources extraction technologies to catalyze the space economy, believes that a lunar oxygen pipeline will “…revolutionize lunar surface operations for the Artemis program and reduce cost and risk!”.

Out at Mars, Congrui Jin from the University of Nebraska, Lincoln wants to augment inflatable habitats with building materials sourced in situ utilizing synthetic biology. Cyanobacteria and fungi will be used as building agents “…to produce abundant biominerals (calcium carbonate) and biopolymers, which will glue Martian regolith into consolidated building blocks. These self-growing building blocks can later be assembled into various structures, such as floors, walls, partitions, and furniture.” Building materials fabricated on site would significantly reduce costs by not having to transport them from Earth.

A couple of innovations are highlighted in this NIAC grant. First, Jin has studied the use of filamentous fungi as a producer of calcium carbonate instead of bacteria, finding that they are superior because they can precipitate large amounts of minerals quickly. Second, the process will be self-growing creating a synthetic lichen system that has the potential to be fully automated.

In addition to building habitats on Mars, Jin envisions duel use of the concept on Earth. In military logistics or post-disaster scenarios where construction is needed in remote, high-risk areas, the “… self-growing technology can be used to bond local waste materials to build shelters.” The process has the added benefit of sequestration of carbon, removing CO2 from the atmosphere helping to mitigate climate change as part of the process of producing biopolymers.

Graphical depiction of biomineralization-enabled self-growing building blocks for habitats on Mars. Credits: Congrui Jin

To reduce transit times to Mars a novel combination of Nuclear Thermal Propulsion (NTP) with Nuclear Electric Propulsion (NEP) is explored by Ryan Gosse of the University of Florida, Gainesville.

Conceptual illustration of a bimodal NTP/NEP rocket with a wave rotor enhancement. Credits: Ryan Gosse

NTP technology is relatively mature as developed under the NERVA program over 50 years ago and covered by SSP previously. NTP, typically used to heat hydrogen fuel as propellant, can deliver higher specific impulse then chemical rockets with attractive thrust levels. NEP can produce even higher specific impulse but has lower thrust. If the two propulsion types could be combined in a bimodal system, high thrust and specific impulse could improve efficiency and transit times. Gosse’s innovation couples the NTP with a wave rotor, a kind of nuclear supercharger that would use the reactor’s heat to compress the reaction mass further, boosting performance. When paired with NEP the efficiency is further enhanced resulting in travel times to Mars on the order of 45 days helping to mitigate the deleterious effects of radiation and microgravity on humans making the trip. This technology could make an attractive follow-on to the NTP rocket partnership just announced between NASA and DARPA.

Finally, an innovative propulsion technology for hurling heavy payloads rapidly to the outer solar system and even into interstellar space is proposed by Artur Davoyan at the University of California, Los Angeles. He will be developing a concept that accelerates a beam of microscopic hypervelocity pellets to 120 kilometers/s with a laser ablation system. The study will investigate a mission architecture that could propel 1 ton payloads to 500 AU in less than 20 years.

Artist depiction of pellet-beam propulsion for fast transit missions to the outer solar system and beyond. Credits: Artur Davoyan

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A brief history of starship pioneering

The photon rocket on an interstellar voyage exploring exoplanets. Credit: © David A. Hardy / www.astroart.org

Eventually we will get to the stars. It may not happen in our lifetime but its going to happen some day. Adam Crowl has provided a nice historical review of the interstellar pioneers from the last century that worked out the physics of the starships that will take us there. He does this in a chapter he wrote for James and Gregory Benford’s ground-breaking anthology Starship Century which was based on the findings of the 100‐Year Starship Symposium seeded by a DARPA solicitation and executed by NASA back in 2011.

Crowl begins the story with the early days of rocketry pioneered by Tsiolkovsky determining the rocket equation and Goddard and others experimenting with liquid fueled rockets. Tsiolkovsky was the first to come up with the idea of a generation starship (sometimes referred to as a worldship) when he realized that existing chemical propellants would be insufficient to fuel a space ship for interstellar travel.

Artist depiction of an interstellar worldship. Credits: Michel Lamontagne / Principium, Issue 32, February 2021

More practical interstellar craft don’t come on the scene until after WWII when advanced propulsion concepts really take off. The possibility of harnessing light to “push” a rocket, feasible because photons carry momentum, first appeared in science fiction. As it turned out, physicists realized that to generate the needed thrust with light pressure would require enormous amounts of energy, the waste heat of which would vaporized the vessel. Nevertheless, the photon rocket was still being discussed as late as 1972 when I first saw the rendering at the top of this post by David Hardy in the book he coauthored with Patrick Moore called Challenge of the Stars. Fast forward to today, Dr. Young K. Bae’s Photonic Laser Thruster shows great promise if it can be scaled up for interstellar travel.

Diagram depicting the layout of the Photonic Laser Thruster. Credits: Young K. Bae, Ph.D.

In the latter half of the last century, as the physics of nuclear energy and laser technology progressed, we see a proliferation of many concepts for star travel, including various forms of fusion rockets, laser sails, antimatter propulsion and my personal favorite, the Bussard ramjet. Conceived by the physicist Robert Bussard in 1960, the ship eliminates the need to carry fuel by collecting hydrogen from the interstellar medium using a magnetic field as a ram scoop and compresses the gas to fusion temperatures to create thrust. Crowl summarizes some of the physical limitations of the original concept and discusses several physicist’s alternative designs to address them.

One concept that didn’t make it into Crowl’s piece was developed recently by Leif Holmlid and Sindre Zeiner-Gundersen. Called the laser induced annihilation drive, it uses a pulsed laser to initiate “antimatter-like” annihilation reactions in hydrogen fuel producing high velocity K meson elementary particles at relativistic speeds to generate thrust.

Diagram of a laser-induced annihilation generator for space propulsion. Credit: Leif Holmlid and Sindre Zeiner-Gundersen, Acta Astronautica 23 May 2020

When I asked Crowl if he had any updates to some of the starship propulsion concepts he sent me an article penned by an unknown author for Medium that came up with another alternative to address the limitations of the original Bussard Ramjet. The author, who goes by the pseudonym “deepfuturetech”, reminds us like Crowl discussed in his piece, that the cross section ( i.e. the probability that a given atomic nucleus or subatomic particle will undergo a nuclear reaction in relation to the species of the incident particle) of the Bussard ramjet proton-proton fusion reaction is too low to be useful. Deepfuturetech proposes a different fusion mechanism via (p,n) reactions which involve a nucleus capturing a proton and subsequently emitting a neutron. These type of reactions have higher cross sections and could be tested in reactors in the near future. Further analysis is needed to confirm whether these reactions could produce neutrons at sufficiently low energy cost to enable profitable hydrogen fusion.

Artist depiction of a Bussard ramjet. Credits: NASA

Incidentally, Crowl talked about many of these starship concepts at a subsequent Starship Century Symposium held in 2013 by the Arthur C. Clarke Center for Human Imagination in collaboration with the Benford brothers who shared the highlights from their Starship Century anthology summarizing scientific results from the 100‐Year Starship project. You can also get a “Deeper Future View” of his independent research on interesting items not typically covered by the mainstream science media at his blog Crowlspace.

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Update on the Photonic Laser Thruster and the interplanetary Photonic Railway

Diagram depicting the layout of the Photonic Laser Thruster (PLT). Credits: Young K. Bae, Ph.D.

SSP reported last year on the promise of an exciting new Photonic Laser Thruster (PLT) that could significantly reduce travel times between the planets and enable a Phonic Railway opening up the solar system to rapid exploration and eventual settlement. The inventor of the PTL, Dr. Young K. Bae has just published a paper in the Journal of Propulsion and Power (behind a paywall) that refines the mathematical underpinnings of the PLT physics and illuminates some exciting new results. Dr. Bae shared an advance copy of the paper with SSP and we exchanged emails in an effort to boil down the conclusions and clarify the roadmap for commercialization.

Illustration of a Photonic Railway using PLT infrastructure for in-space propulsion established at (from right to left, not to scale) Earth, Mars, Jupiter, Pluto and beyond. Credits: Young K. Bae.

In the new paper, Dr. Bae refines his rigorous analysis of the physics behind the PLT confirming previous projections and discovering some exciting new findings.

As outlined in the previous SSP post linked above, the PLT utilizes a “recycled” laser beam that is reflected between mirrors located at the power source and on the target spacecraft. Some critical researchers have argued that upon each reflection of the beam off the moving target mirror, there is a Doppler shift causing the photons in the laser light to quickly lose energy which could prevent the PLT from achieving high spacecraft velocities. The new paper conclusively proves such arguments false and confirming the basic physics of the PLT.

There were two unexpected findings revealed by the paper. First, the maximum spacecraft velocity achievable with the PLT is 2000 km/sec which is greater than 10 times the original estimate. Second, the efficiency of converting the laser energy to the spacecraft kinetic energy was found to approach 50% at velocities greater than 100 km/s. This is surprisingly higher than originally thought and is on a par with conventional thrusters – but the PLT does not require propellent. These results show conclusively that once the system is validated in space, the PLT has the potential to be the next generation propulsion system.

I asked Dr. Bae if anything has fundamentally changed recently in photonic technology that will bring the PLT closer to realization. He said that the interplanetary PLT can tolerate high cavity laser energy loss factors in the range of 0.1-0.01 % that will permit the use of emerging high power laser mirrors with metamaterials, which are much more resistant to laser induced damage and are readily scalable in fabricating very large PLT mirrors.

With respect to conventional thrusters, he said the PLT can be potentially competitive even at low velocities on the order of 10 km/s, especially for small payloads. This is because system does not use propellant which is very expensive in space and because the PLT launch frequency can be orders of magnitude higher than that of conventional thrusters. Dr. Bae is currently investigating this aspect of the system in terms of space economics in depth.

The paper acknowledges that one of the most critical challenges in scaling-up the PLT would be manufacturing the large-scale high-reflectance mirrors with diameters of 10–1000m, which will likely require large-scale in-space manufacturing. Fortunately, these technologies are currently being studied through DARPA’s NOM4D program which SSP covered previously and Dr. Bae agreed that they could be leveraged for the Photonic Railway.

Artist’s concept of projects, including large high-reflectance mirrors, which could benefit from DARPA’s (NOM4D) plan for robust manufacturing in space. Credits: DARPA

I asked Dr. Bae about his timeline and TRL for a space based demo of his Sheppard Satellite with PLT-C and PLT-P propellantless in-space propulsion and orbit changing technology. He responded that such a mission could be launched in five years assuming there were no issues with treaties on space-based high power lasers. There is The Treaty on the Prevention of the Placement of Weapons in Outer Space but I pointed out that the U.S. has not signed on to this treaty. Article IV of the Outer Space Treaty states that “…any objects carrying nuclear weapons or any other kinds of weapons of mass destruction…” can not be placed in orbit around the Earth or in outer space. Dr. Bae said “We can argue that the [Outer Space] treaty regulation does not apply to PLT, because its energy is confined within the optical cavity so that it cannot destroy any objects.  Or we can design the PLT such that its transformation into a laser weapon can be prevented.”

He then went on to say: “For space demonstration of PLT spacecraft manipulation including stationkeeping, I think using the International Space Station platform would be one of the best ways … I roughly estimate it would take $6M total for 3 years for the demonstration using the ISS power and cubesats. The Tipping Point [Announcement for Partnership Proposals] would be a good [funding mechanism] …to do this.”

Once the technology of the Photonic Railway matures and is validated in the solar system Dr. Bae envisions its use applied to interstellar missions to explore exoplanets in the next century as described in a 2012 paper in Physics Procedia.

Conceptual illustration of the Photonic Railway applied to a roundtrip interstellar voyage to explore exoplanets around Epsilon Eridani. This application requires four PLTs: two for acceleration and two for deceleration. Credits: Young K. Bae

Be sure to listen live and call in to ask Dr. Bae your questions about the PLT in person when he returns to The Space Show on March 29th.

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Wind Rider propellentless space drive for rapid transit across the solar system

Conceptual illustration of the Wind Rider plasma magnet drive: Credits: Brent Freeze

When humanity eventually moves out into the galaxy to settle new worlds, we will need to take stock of potentially habitable planets capable of sustaining life as we know it to identify potential new homes. The James Webb Space Telescope will have the capability to search for exoplanets in the habitable zones of stars in our local neighborhood by using spectroscopy to reveal biosignatures in the planet’s atmosphere as starlight filters through it when transiting across the disk of the host star. But to discern more detail on the surfaces of these distant new Earths, much more powerful methods for imaging will be needed.

One such method could be to utilize a solar gravitational lens (SGL), a property arising from the Theory of Relativity where large gravitating masses bend light resulting in the possibility of a natural telescope capable of very powerful magnification and significant angular resolution. This would require placing a detector beyond 550 astronomical units from the sun. Such an instrument could potentially resolve the size and shape of continents adjacent to oceans on exoplanets orbiting TRAPPIST-1 or other nearby stars. Located 40 light years away, this star is an ultra-cool red dwarf with seven rocky planets, three of which are in the habitable zone where liquid water can exist.

But getting out to this distance with conventional rockets would take over a hundred years. Voyager 1 is currently over 150 AU from the sun and was launched back in 1977. Enter the Wind Rider plasma magnet drive. A pathfinder mission using this concept to demonstrate the technology of a mission out to the SGL to image planets in the TRAPPIST-1 system will be presented by Brent Feeze, an AIAA mechanical engineer, in a poster session at the American Geophysical Union meeting this month. Calculations show that a spacecraft using this drive could sprint to the SGL focal plane in about eight years. The Wind Rider was also described recently by Alex Tolley on Centauri Dreams.

Originally conceived by John Slough at the University of Washington under a NASA NIAC grant from 2004 – 2005, the system is a propellentless drive that works by creating a rotating magnetic field that traps the charged particles in the solar wind to create a large circular electric current, inducing a large scale magnetosphere. Thrust is imparted to the craft via magnetic fields, analogous to the coupling induced in an electric motor. Unlike a solar sail, the trajectory of the craft is a straight line out from the sun toward its destination, with no gravity assists from other planets and a rapid acceleration to a velocity approaching that of the solar wing (400 km/s).

Jeff Greason, Board Chairman of the Tau Zero Foundation covered the technology during a presentation at the Tennessee Valley Interstellar Workshop back in 2017. He called it a “Ridiculously high thrust to weight magnetic sail” that by chemical propulsion standards is “blindingly fast”. Greason was looking into how Tau Zero could help support a small technology demonstrator on a ride share launch but it would have to be on payloads headed out toward cislunar space to be free of the Earth’s magnetosphere which deflects the solar wind.

Alex Tolley: “If it works as advertised, it would open up the solar system to exploration by fast, cheap robotic probes and eventually crewed ships.”

To be able to image a potentially new world for interstellar settlement is an exciting technology. The hardware required is not expensive and the scientific payoff of such a mission would be valuable from an astrophysical perspective. However, what we already know about the TRAPPIST-1 system is that life as we know it would have a tough time getting started and persisting because these worlds are bathed in intense ultraviolet radiation as they orbit within a range of about 3 – 6 million kilometers from TRAPPIST-1. That said, a pathfinder mission of a Wave Rider to send imaging equipment to the SGL could help prove the technology for rapid transit to the outer solar system as well as validating imaging techniques which could be used on more promising exoplanet candidates for eventual settlement. And expanding our knowledge of planetary systems in the galaxy would be icing on the cake.

TRAPPIST-1e – JPL Travel Poster. Beautiful but life is unlikely due to intense radiation from stellar winds: Credits: Jet Propulsion Laboratory

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Astrosettlement Development Strategy for human expansion into the solar system and beyond

Conceptual illustration of a Habitat Autonomous Locomotive Expandable (HALE) mobile self sustaining habitat under propulsion near a planetary destination. Credits: unknown artist via Thomas Matula

Dr. Thomas Matula, Professor at Sul Ross State University Uvalde, Texas, has developed an economically based strategy for space settlement. His plan addresses the deficiencies in many proposed visions of human expansion beyond earth, namely the missing economic and legal aspects needed for sustainable settlement of the solar system. Matula discussed his approach with David Livingston on The Space Show September 14 and in a paper entitled An Economic Based Strategy for Human Expansion into the Solar System attached to the show blog.

Astrosettlement Development Strategy (ADS) can be boiled down into a four step economically based roadmap for space settlement which could be started with minimal private funding. Each step would achieve economic success before moving on to the next level. The four levels are Earth based research, industrialization of the Moon, developing and settling the solar system and interstellar migration.

In the first step of Earth based research, Matula suggests developing a subscription based online role playing computer game with the purpose of creating a virtual simulation of a space settlement to model the social and economic aspects of communities beyond Earth. SSP has been following similar efforts already underway by Moonwards. Further research in this phase would look into space agriculture to understand the types of plants and dietary needs of space settlers and improving the efficiency of crop growth paving the way for self sustaining habitats. Matula has penned a different paper along these lines called The Role of Space Habitat Research in Providing Solutions to the Multiple Environmental Crises on Earth, also attached to the Space Show Blog, which could have duel use applications in addressing environmental problems on our home planet. There are already efforts underway in this arena with Controlled Environment Agriculture (CEA) utilizing greenhouse automation through the Internet of Things leading to reduction of water needs and an increase in crop yields.

“Developing the technology
to green the Solar System will also green the Earth for future generations”

Next on the roadmap is lunar industrialization. The focus of this step is to use robotics and in situ resource utilization to minimize the mass of materials lifted from Earth and to create lunar manufacturing capability in a cislunar economy that can be leveraged to build space based habitats for expansion into deep space.

Developing the solar system comes next. Once an economic foundation of industrialization of the Moon has been established, large mobile habitats can be built at the Earth-Moon Lagrange points L1 and L2. Called HALE, for Habitat Autonomous Locomotive Expandable, these are 1km wide self sustaining habitats with 1G artificial gravity capable of low energy transit throughout the solar system including out to the Kuiper Belt, where they can use the resources there to add to their size or build copies of themselves.

The final phase combines mobile free space settlement with advanced propulsion to develop the capability of expansion into the Oort cloud and on to the stars.

“…propulsion technology could advance to a point that would allow mobile space habitats designed for the Oort Cloud to be transformed into the first generational starships.”

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Progress on warp drives and wormholes

Artist’s concept of an Alcubierre warp drive starship. Credits: NASA via Phys.org

New research is bringing us closer to understanding the physics of two modes of interstellar travel popularized in science fiction. The first is a paper by Alexey Bobrick and Gianni Martire at the Advanced Propulsion Laboratory at Applied Physics in New York on physical warp drives. Readers may remember the initial excitement of the Alcubierre warp drive and then subsequent disappointment when the devil came out of the details, namely that “negative energy” (what ever that is) and lots of it were needed to make the concept work. Even Dr. Miguel Alcubierre had doubts about the feasibility of this “unphysical” approach and moved on to different areas of research in theoretical physics such as gravitational waves and black holes, as he explained at the Starship Congress 2017 and later on The Space Show.

In this new paper the authors show that it is theoretically possible to construct a class of subluminal warp drives based on physical principles known today. Even Sabine Hossnefelder, a theoretical physicist at the Frankfurt Institute for Advanced Studies, was impressed by this paper and gives a good overview in this short video.

A second line of investigation involves wormholes as shortcut conduits through spacetime. In a paper in Physical Review D, researchers Juan Maldacena and Alexey Milekhin show that with accelerations less than 20 g, a human-traversable wormhole is theoretically possible making a journey across the galaxy in less than a second! Of course the practical engineering details, not to mention discovery of an actual worm hole, remains to be realized.

Artist impression of a human traversable worm hole. Credits: Tomáš Müller via Quanta Magazine

Understanding the physics of interstellar space travel is the first step toward practical engineering solutions for the methods of transportation humanity will use in our spacefaring future. Skeptics may need reminding that there were doubters that considered the possibility of space ships carrying humans to the Moon a fantasy over 100 years ago when Tsiolkovsky and others first worked out the physics of the rocket equation.

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Worldships for interstellar space settlement

Image of an interstellar Worldship. Credits: Michel Lamontagne / Principium, Issue 32, February 2021

The feasibility of Worldships has been covered previously on SSP by The Initiative and Institute for Interstellar Studies via Principium. A new article by Michel Lamontagne on page 29 of the most recent issue examines the concept from a perspective of an interplanetary society which has harnessed fusion energy and life support systems for space settlements, while reducing costs through self replicating factories.

Such a starship is envisioned to use a deutrium/He3 fusion drive to accelerate to 1% of the speed of light completing a journey to Alpha Centauri in about 430 years. The author envisions a fleet of 3 or 4 (or more) Worldships housing about 1000 passengers each in rotating torus habitats 1,200m in diameter with artificial gravity.

Image of the interior of a worldship habitat. Credits: Michel Lamontagne / Principium, Issue 32, February 2021

Self replication is the key to this architecture. Lamontage explains: “If fully self replicating systems exist at the departure of the mission, Sprinter starships carrying self replicating machines can be sent at the same time as the Worldship flotilla departs. The Sprinters will arrive centuries before the Worldships, and the self replicating machines will have ample time to create multiple habitats, and perhaps begin to seed them with simple life forms.”

Lamontage cautions that the needed AI technology and practical self replicating machines may be more difficult to develop than predicted. The Worldship habitat ecosystems may encounter instabilities over centuries-long journeys leading to eventual breakdown of life support systems. Finally, rapid technological advances may lead to advanced propulsion schemes or other opportunities that would make a Worldship obsolete before getting started.

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Directed energy propulsion technology for rapid travel to the outer solar system (and the stars)

Artist’s depiction of propulsion concept using Directed Energy. At left, Directed Energy Launch Technology Array (DELTA) beams power to laser powered electrical propulsion (LEP) spacecraft for rapid travel to the outer solar system or for laser sailing to the stars. At right, a sub-module from a close packed array of laser emitters within DELTA. Credits: Todd F. Sheerin / International Astronautical Federation

A concept for fast transit to the outer solar system and beyond has just been published by Todd F. Sheerin et al.* in Acta Astronautica. Since the article is behind a paywall, SSP has obtained permission by one of the coauthors, Professor Philip Lubin at the University of California, Santa Barbara to link to an earlier version of the paper presented at the 70th International Astronautical Congress held in Washington D.C. back in October 2019. Professor Lubin is Director of the Experimental Cosmology Laboratory at UCSB where he oversees research on several interesting directed energy projects.

The concept makes use of an Earth-based Directed Energy Launch Technology Array (DELTA) to beam laser energy to photovoltaic cells on an electric propulsion vehicle for travel within the solar system, or for photon reflection via a laser sail on gram-scale spacecraft accelerated to relativistic speeds for interstellar missions. In the former case, this method leverages existing solar electric propulsion technology which converts optical energy to propulsive jet power like what was used on NASA’s Dawn mission. An existing NASA Innovative Advanced Concepts (NIAC) program at UCSB has demonstrated proof of concept for elements of the array.

The DELTA architecture development can be terraced in progressive stages starting with small one meter arrays building up to large 10 km systems. The concept could support a range of missions, from swarms of gram-scale robots all the way up to human-rated spacecraft greater than 100 tons.

The authors believe this approach “… enables a scalable, cost effective roadmap to rapid solar system transportation for robotic and human missions alike, including robotic and human Mars-in-a-Month missions, with transit times of 30 days, as well as the first robotic relativistic interstellar flight within our lifetime.”

* Authors: Todd F. Sheerin, Elaine Petro, Kelley Winters, Paulo Lozano, Philip Lubin

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The Space Show fund raising drive

Credits: The Space Show

The Space Show – the nation’s first talk radio show focusing on increasing space commerce, advancing space science and economic development, facilitating our move to a space-faring economy which will benefit everyone on Earth – needs your help. The Space Show is hosted by Dr. David Livingston, who completed his doctoral dissertation in 2001 on the commercialization and expansion of space development. Take a moment to visit The Space Show website and read Dr. Livingston’s end of year message. Please give generously to ensure this valuable resource continues to promote, encourage, and support future global economic opportunities, scientific discoveries, and medical advances for all humankind through peaceful and cooperative ventures in outer space.

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The feasability of interstellar worldships

Artist’s impression of a fleet of worldships on an interstellar voyage. Credits: Michel LaMontage / Initiative for Interstellar Studies

In the August 2020 Issue of Principium, Richard Soilleux summarizes current research on the feasibility of interstellar voyages via multi-generation worldships. The starting point is assumed to be free flying orbital settlements as envisioned by Gerard K. O’Neill that will eventually be tooling around the solar system way before a trip to the stars would be possible. The baseline for the analysis was an orbital space settlement called Avalon, the result of a complex study by the British Interplanetary Society called the BIS Space Project which took a fresh look at O’Neill’s smallest habitat Island 1, a settlement that would house 10,000 inhabitants.

Artist’s impression of the Avalon orbital settlement. Credits: Mark Hempsell / Initiative for Interstellar Studies

Much of the technology needed for an interplanetary ship like Avalon could be leveraged for an interstellar craft, but there are several challenges for permanent occupation over many generations as would be needed for a trip to the stars. For example, the ships would obviously have to be much more robust and reliable. Design lifetimes of 1000 years, as what is estimated to be needed, would require rigorous maintenance and repair schedules. Major periodic replacement of damaged or worn components and obsolete parts would also be required.

Soilleux’s analysis breaks down the key features of the settlement in terms of technology readiness and extrapolates to the interstellar case. One key element of the design is the environmental control and life support system (ECLSS). Avalon’s ECLSS does not need to be fully closed when voyages are limited to within the solar system as there are plenty of resources to replace nutrients and materials that cannot be recycled. Interstellar voyages are another matter all together and the study found that the recycling rate needs to be better than 90% for at least 36% of a material to remain useable after 100 years. This ratio would have to be significantly higher for an interstellar journey, the duration of which could be an order of magnitude longer. Soilleux concludes that “Recycling must therefore be managed carefully, and a detailed inventory maintained of all materials and nutrients wherever they are in the system.”

ECLSS technology is clearly one of the gating items for space settlement in the solar system and for journeys beyond. More information and research can be found in the Life Support Section.