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The prospects for mining precious metals and structural materials from asteroids

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.

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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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DARPA announces Novel Orbital and Moon Manufacturing, Materials and Mass-efficient Design (NOM4D) program

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.