Company images of a Neumann Drive at upper left with it’s plasma discharge produced in the lab at upper right overlayed above the Earth from space. Credits: Neumann Space / NASA
Neumann Space has announced completion of initial on-orbit tests of its innovative electric propulsion system, the first of its kind utilizing solid metal as propellent to fuel a cathodic arc discharge to generate thrust via plasma exhaust. The commissioning campaign for the system confirmed that the electronics worked properly and that the thruster fired. Next up: following last December’s launch of the company’s second experiment in space, an engineering demonstration later this year will test that the propulsion system can change the orbit of a satellite.
Neumann Space has already lined up both a customer and a potential space-based source of fuel through a partnership with CisLunar Industries. In this symbiotic relationship, CisLunar will utilize Neumann’s thruster to propel their servicing vehicle that hunts down chunks of metallic space debris which will be captured and delivered to a salvage platform to be recycled into metal propellent via CisLunar’s Modular Space Foundry (previously called Micro Space Foundry). The servicing vehicle can then refuel itself to proceed to its next target. SSP reported previously on this propulsion ecosystem which could literally turn trash into treasure while cleaning up orbital debris.
Conceptional illustration of propulsion ecosystem based on CisLunar Industries Modular Space Foundry process for recycling orbital debris. Credits: CisLunar Industries
The orbital debris issue not only poses a serious threat to human spaceflight in Earth orbit, unless policies and standard practices are implemented to mitigate the issue, remote sensing, climate monitoring, weather forecasting and all commercial activities in space could be at risk, not to mention long term sustainable space settlement. The on-orbit recycling partnership between Neumann Space and CisLunar Industries will help implement the remediation pillar of the National Orbital Debris Mitigation Plan promulgated in 2022 by the White House Office of Science and Technology Policy.
In other news, CisLunar Industries was one of fourteen other companies selected by DARPA for its LunA-10 program, a lunar architecture study that will define commercial activities in an integrated infrastructure for lunar development over the next 10 years. CisLunar will collaborate with industry partners to develop what they call METAL, a framework for Material Extraction, Treatment, Assembly & Logistics in a lunar economy based on in situ resource utilization.
Artist impression of an asteroid smelting operation. Credits: Bryan Versteeg / spacehabs.com
When humanity migrates out into the solar system we’ll need a variety of elements on the periodic table to build settlements and the infrastructure needed to support them such as solar power satellites. But before that future becomes a reality, there may be a near term market on Earth for precious metals sourced in space as transportation costs come down. There is also the added benefit of moving the mining industry off planet to preserve the environment. Could the asteroid belt provide these materials? Kevin Cannon, assistant professor at the Space Resources Program at the Colorado School of Mines describes the prospects for mining precious metals and building materials for space infrastructure asteroids in a recent paper in Planetary and Space Science. Coauthors on the paper Matt Gialich and Jose Acain, are CEO and CTO, respectively, at the asteroid mining company AstroForge which just came out of stealth mode last year.
The asteroids have accessible mining volume that exceeds that available on the Moon or Mars. This is because only the thin outer crust of these bodies is reachable by excavation, whereas the asteroids are small enough to be totally consumed resulting in higher accessible mining volume.
To-scale accessible mining volume of terrestrial bodies, calculated as the total volume for the asteroids (main belt mass of 2.39 x 1023 kg, mean bulk density of 2000 kg/m3), and as the volume for an outer shell 1.2 km in thickness for the Moon, Mercury, and Mars, equivalent to the deepest open pit mine on Earth. Note the combined volume of the near-Earth asteroids (~5 x 1012 m3) is too small to be visible at this scale. Figure 1 in paper. Credits K.M. Cannon et al.
The authors take a fresh look at available data from meteorite fragments of asteroids. Their analysis found that for Platinum Group Metals (PGMs), the accessible concentrations are higher in asteroids than ores here on Earth making them potentially profitable to transport back for use in commodity markets.
“Asteroids are a promising source of metals in space, and this promise will mostly be unlocked in the main belt where the Accessible Mining Volume of bodies greatly exceeds that of the terrestrial planets and moons”
PGMs are indispensable in a wide range of industrial, medical, and electronic applications. Some examples of end-use applications include catalysts for the petroleum and auto industries (palladium and platinum), in pacemakers and other medical implants (iridium and platinum), as a stain for fingerprints and DNA (osmium), in the production of nitric acid (rhodium), and in chemicals, such as cleaning liquids, adhesives, and paints (ruthenium).
It has been pointed out by some analysts that flooding markets here on Earth with abundant supplies of PGMs from space will cause prices to plummet, but the advantage of reducing carbon emissions and environmental damage associated with mining activities may make it worth it. The authors also point out that there are probably various uses where PGMs offer advantages in material properties over other metals but are not being used because they are currently too expensive.
Asteroids are rich in other materials such as silicon and aluminum which would be economically more useful for in-space applications. As the authors point out, some companies are already planning for use of metals and manufacturing in space such as Redwire Corporation with their On-Orbit Servicing, Assembly and Manufacturing (OSAM) and Archinaut One, which will attempt to build structural beams in LEO. Another example mentioned in the paper has been covered by SSP: the DARPA NOM4D program with aspirations to develop technologies for manufacturing megawatt-class solar arrays and radio frequency antennas using space materials. Finally, another potential market for aluminum sourced in space is fuel for Neumann Thrusters (although spent upper stage orbital debris may provide nearer term supplies). And of course, silicon will be needed to fabricate photovoltaic cell arrays for space-based solar power.
AstroForge will test their asteroid mining technology on two missions this year. Brokkr-1, a 6U CubeSat just launched on the SpaceX Transporter 7 mission last April, will validate the company’s refinery technology for extracting metals by vaporizing simulated asteroid materials and separating out the constituent components. Brokkr-2 will launch a second spacecraft on a rideshare mission chartered by Intuitive Machines attempting their second Moon landing later this year. Brokkr-2 will hitch a ride and then fly on to a target asteroid located over 35 million km from Earth. The journey is expected to take about 11 months and will fly by the body and continue testing for two years to simulate a roundtrip mission.
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
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.
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.
Artist’s concept of projects which could benefit from DARPA’s (NOM4D) plan for robust manufacturing in space. Credits: DARPA
Pronounced “NOMAD” the Defense Advanced Research Projects Agency plan aims to develop technologies for adaptive, off-earth manufacturing to fabricate large structures in space and on the Moon.
Bill Carter, program manager in DARPA’s Defense Sciences Office explains in an announcement of the program, “We will explore the unique advantages afforded by on-orbit manufacturing using advanced materials ferried from Earth. As an example, once we eliminate the need to survive launch, large structures such as antennas and solar panels can be substantially more weight efficient, and potentially much more precise. We will also explore the unique features of in-situ resources obtained from the moon’s surface as they apply to future defense missions. Manufacturing off-earth maximizes mass efficiency and at the same time could serve to enhance stability, agility, and adaptability for a variety of space systems.”
The program will be split into three 18 month phases driven by metrics associated with progressively challenging exemplars such as respectively, a 1-megawatt solar array, a 100m diameter RF reflector, and finally IR reflective structures suitable for use in a segmented long-wave infrared telescope.
Lessons learned from the program could be applied to on-orbit manufacturing operations by commercial space companies as launch costs come down and access to cislunar space becomes more routine for both government and commercial entities.
