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Solar system rapid transit with the Direct Fusion Drive

Artist rendering of a Direct Fusion Drive nuclear rocket. Credits: Princeton Satellite Systems

A small New Jersey company called Princeton Fusion Systems (PFS) is close to developing a nuclear rocket using an innovative reactor that could also have applications that are down to Earth. Called the Princeton Field Reversed Configuration (PFRC) reactor, the system is based on over 15 years of research at the Princeton Plasma Physics Laboratory (PPPL), with funding primarily by the U.S. DOE and NASA. PFS, a subsidiary of Princeton Satellite Systems, could have a space based system by the end of this decade which could significantly reduces trip times to the outer solar system and increase payload capability while ensuring a robust power source at the designation. The second iteration of the research reactor, PFRC-2, is currently undergoing testing at PPPL.

Second generation Princeton Field Reversed Configuration (PFRC-2) undergoing testing at Princeton Plasma Physics Laboratory. Credits: Princeton Plasma Physics Laboratory

The PFRC reactor is simple, small and produces very little radiation through the fusion of deuterium and helium-3. This makes it uniquely suited for space-based applications. The field-reversed configuration is a magnetic-field geometry in which a toroidal electric current is induced in a cylindrical plasma by radio frequency (RF) heating. The plasma is confined in a “magnetic bottle” composed of a linear array of coaxial magnets. The design is compact (about the size of a minivan) as compared to some of the more complex fusion devices currently under development such as the ITER donut shaped tokamak. A Princeton Satellite Systems video explains how the PFRC reactor is used in a DFD for space applications by exhausting fusion byproducts out one end of the device through a rocket nozzle:

In May of 2019, Stephanie Thomas, a VP at Princeton Satellite Systems made a presentation at the Future In-Space Operations working group on the DFD technology. Of particular note was the slide on the product development roadmap on technology readiness for flight hardware. If all goes according to plan, fusion could be achieved in the fourth generation research reactor PFRC-4 within 5 years and a flight ready payload could be launched before this decade is out.

DFD notional roadmap to flight. Credits: Stephanie Thomas, Princeton Satellite Systems

Travel time for a 1-2 MW fusion engine and 10,000 Kg payload would be 1 year to Jupiter, 2 years to Saturn and 5 years to Pluto, a significant reduction over chemical rockets using gravity assists. Many other missions to the outer solar system and beyond have been scoped by Princeton Satellite Systems using this technology. In his thesis for a Master Degree in Aerospace Marco Gajeri used the DFD architecture to design a trajectory for a mission to Titan. This blog covered a trip to Saturn using the DFD back in 2019. An interstellar mission to Alpha Centuari has also been considered.

The PFRC reactor has a multitude of clean energy applications on Earth as well:

Update March 10, 2023: An engineering analysis of the feasibility of of the Direct Fusion Drive has just been published by Yuvraj Jain and Priyanka Desai Kakade in Acta Astronautica

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Why space matters

Credits: Space Matters

A new YouTube channel has just been launched called Space Matters. Hosted by Rhonda Stevenson, President/CEO of the Tau Zero Foundation, the show is a weekly digest covering a wide array of current space activities, challenges and accomplishments which aims to show how our success in space will improve life on Earth. This could become an influential forum for discussion among industry leaders on how to steer humanities course toward becoming a spacefaring civilization. The first episode, a panel discussion with pillars of the space industry, aired on March 20th and featured Jeff Greason of Tau Zero and Electric Sky, Justin Kugler of Redwire Space, Grant Anderson of Paragon Space Development Corporation, Andy Aldrin of the ISU Center for Space Entrepreneurship, at FIT and Rod Pyle, editor of Ad Astra and author of Space 2.0. The group had a lively discussion on each of their contributions to space development as well as current trends in the New Space economy. Subscribe to get an update every week on why Space Matters.

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A novel ablative arc mining process for ISRU

Illustration of Ablative Arc Mining Process. Credits: Amelia Greig

A NASA NIAC Phase 1 grant has been awarded to Amelia Greig of the University of Texas, El Paso to study an innovative mining technique called ablative arc mining. The process works by using a pair of electrodes to zap surface regolith with an electrical arc thereby ionizing it into its component constituents. The ablated ions are then sorted and collected by subjecting them to an electromagnetic field which separates the material groups by their respective mass. Such a system, when mounted on a mobile rover, could extract both water and metal ions in the same system.

The goal of the this grant is to identify a feasible ablative arc mining scheme for ISRU on upcoming lunar exploration sorties. The study will define the design of an ablative arc and electromagnetic transport system for extraction and collection of water, silicon, and nickel. The architecture should have an output of 10,000 kg/yr of water for use by lunar outposts or other operations. Finally, a trade study will be performed comparing the efficiency of the proposed concept against other ISRU processes such as microwave or direct solar heating which are designed to only collect a single constituent.

We’ll need ISRU methodologies to enable long-term space settlement on the Moon, Mars, in the Asteroid Belt or to support free space habitats. The ablative arc mining architecture may be an efficient alternative for extraction and collection of multiple volatile constituents in a single system when compared to methods that collect only one material at a time.

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Cyanobacterium-Based Life-Support Systems on Mars

Diagram of a Mars based life-support system using cyanobacteria fed from in situ resources to decrease dependence on Earth-imported materials. Credits: Cyprien Verseux et al.* via Frontiers in Microbiology

A Team* of researchers at the University of Bremen, Germany has just published results of an experiment to grow cyanobacteria fed from regolith and atmospheric gases available on Mars. The study, published in the February 16 2021 issue of Frontiers in Microbiology, showed that an analog of Martian regolith consumed as a nutrient source by cyanobacteria which could then potentially be used to feed secondary heterotopic consumers downstream in a life support system producing food, oxygen, energy and recycling functions.

The results of the study indicate that a low pressure mixture of gases extracted from the Martian atmosphere would be suitable for a photobioreactor of cyanobacterium-based life-support system. More work is needed to optimize the design of such systems on Mars, such as investigating the effects of different concentrations of N2 on cyanobacteria, variation in the composition of regolith mixtures, and the transfer of nutrients from cyanobacteria to organisms downstream in the life support system.

In an email to Dr. Cyprien Verseux, the lead author on the paper, I asked about using E. Coli as a secondary consumer in the study. He responded: “We used E. coli as a model here, but it does not mean that we suggest using this bacterium specifically. The point was to show that heterotrophic organisms could be fed using cyanobacteria, which themselves could be fed using resources available on Mars. It is on purpose that we remained vague on the downstream processes: what we’re trying to develop is not a BLSS [bioregenerative life-support systems] per se, but rather a way of connecting [a] BLSS, some of which are being developed by others (see, e.g., the MELiSSA project), to resources available on Mars.”

When asked about planetary protection concerns about introducing cyanobacteria into the Martian environment even though appropriate precautions would likely be taken to completely contain the organisms within the BLSS, Dr. Verseux, said “Certainly, we need to bring the risk of outward contamination as close to zero as reasonably possible. A low pressure inner pressure is a first step: it reduces the risks related to leakage. Other potential measures include the use of several levels of confinement, and the installation of the setup far from areas of astrobiological interest.”

Dr. Verseux has more information about using green bacteria on the Red Planet on is blog Walking on Red Dust.

Artist’s rendering of a cyanobacterium-based life-support system on Mars (CyBLiSS). Credits: Sean McMahon (artistic work) and Cyprien Verseux (source)

* Authors: Cyprien Verseux, Christiane Heinicke, Tiago P. Ramalho, Jonathan Determann, Malte Duckhorn, Michael Smagin and Marc Avila – Center of Applied Space Technology and Microgravity (ZARM), University of Bremen, Bremen, Germany

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Stability and limitations of environmental control and life support systems for space habitats

Image of Biosphere 2, a research facility to support the development of computer models that simulate the biological, physical and chemical processes to predict ecosystem response to environmental change. Credits: Biosphere 2 / University of Arizona

Once cheap access to space is realized, probably the most important technological challenge for permanent space settlements behind radiation protection and artificial gravity is a robust environmental control and life support system (ECLSS). Such a system needs to be reliably stable over long duration space missions, and eventually will need to demonstrate closure for permanent outposts on the Moon, Mars or in free space. In his thesis for a Master of Science Degree in Space Studies, Curt Holmer defines the stability of the complex web of interactions between biological, physical and chemical processes in an ECLSS and examines the early warning signs of critical transitions between systems so that appropriate mitigations can be taken before catastrophic failure occurs.

Holmer mathematically modeled the stability of an ECLSS as it is linked to the degree of closure and the complexity of the ecosystem and then validated it against actual results as demonstrated by NASA’s Lunar-Mars Life Support Test Project (LMLSTP), the first autonomous ECLSS chamber study designed by NASA to evaluate regenerative life support systems with human crews. The research concluded that current computer simulations are now capable of modeling real world experiments while duplicating actual results, but refinement of the models is key for continuous iteration and innovation of designs of ECLSS toward safe and permanent space habitats.

This research will be critical for establishing space settlements especially with respect to how much consumables are needed as “buffers” in a closed, or semi-closed life support system, when the model’s metrics indicate they are needed to mitigate instabilities. Such instabilities were encountered during the first test runs of Biosphere 2 in the early 1990s.

As SpaceX races to build a colony on Mars, they will need this type of tool to help plan the life support system. Holmer believes that completely closed life support systems for relatively large long term settlements are at least 15 to 20 years away. That means that SpaceX will need to resupply materials and consumables due to losses in their initial outpost who’s life support system in all probability will not be completely closed during the early phases of the project over the next decade. Even SpaceX cannot reduce launch costs low enough to make long term resupply economically viable. They will eventually want to drive toward a fully self sustaining ECLSS. That said, depending on how the company funds its initiatives and sets up it’s supply chains, they may not need a completely closed system for quite some time.

Of course there are sources of many of the consumables on Mars that could support a colony but not all the elements critical for ecosystems, such as nitrogen, are abundant there. There are sources of some consumables outside the Earth’s gravity well which could lower transportation costs and extend the timeline needed for complete closure. SSP covered the SHEPHERD asteroid retrieval concept in which icy planetesimals, some containing nitrogen and other volatiles needed for life support, could be harvested from the asteroid belt and transported to Mars as a supply of consumables for surface operations. TransAstra Corporation is already working on their Asteroid Provided In-situ Supplies family of flight systems that could help build the infrastructure needed for this element of the ecosystem. It may be a race between development of the competing technologies of a self-sustaining ECLSS vs. practical asteroid mining. The bigger question is if humans can thrive long term on the surface of Mars under .38G gravity. In the next century, O’Neill type colonies, perhaps near a rich source of nitrogen such as Ceres, may be the answer to where safe, long term space settlements with robust ECLSS habitats under 1G will be located.

Curt Holmer appeared recently on the The Space Show discussing his research. I called the show and asked if he had used his modeling to analyze the stability of ecosystems sized for an O’Neill-type colony. He said he had only studied habitats up to the size of the International Space Station, but that it was theoretically possible to analyze this larger ecosystem. He said he would like to pursue further studies of this nature in the future.

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Simpler methane production on Mars

Artist’s depiction of activities at an early Mars base which could include methane production. Credits: NASA

A team of physicists at the University of California, Irvine has found a short cut for efficient propellant production on Mars. The UCI researchers have discovered a way to streamline the conventional two step Sabatier process which first electrolyzes water into hydrogen before reacting with carbon dioxide in the Martian atmosphere to create methane. Both SpaceX and Blue Origin use methane in their rocket engine designs. The novel approach simplifies fuel production by leveraging zinc as a “synthetic enzyme,” which catalyzes carbon dioxide to synthesize methane directly. The improved process will reduce the amount of ISRU equipment (and therefore weight and launch costs) needed for transport to the surface of Mars to facilitate propellent production required for the trip home. The research has only demonstrated proof of concept so follow-on studies are required to improve the TRL for flight-ready hardware.

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ArmorHab mission architecture for Mars Colonization

ArmorHab transport habitat configured for artificial gravity. Credits: Dark Sea Industries LLC / University of New Mexico / The Mars Society

The innovative ArmorHab mission architecture was presented at the Mars Society Conference in 2016. This novel approach should be considered as part of a strategy for settlement of the Red Planet. The concept integrates several engineering solutions for habitat design to address radiation protection, life support, and transportation while leveraging in situ resource utilization to enhance crew health, safety and reduce costs.

The basic building block of the architecture is a cylindrical Mylar shell wrapped in superconductive tape providing radiation protection through emulation of a magnetosphere. This structure is encased in a protective aerogel for strength and insulation including layers of water ice to further protect the crew from micrometeorites and algae bioreactors for scrubbing carbon dioxide for life support.

ArmorHab wall structure with superconducting tape for radiation protection and algae bioreactors for life support. Credits: Dark Sea Industries LLC / University of New Mexico / The Mars Society

Leveraging Buzz Aldrin’s Mars Cycler invention, the plan starts by building out infrastructure in cislunar space including automated factories on the Moon, then expanding out to Mars with space stations, cycling habitats and connecting “trucks” to provide transport to and from the surface of each destination.

Illustration of cycler model showing six TransportHabs, three space stations and a Mars Truck. Credits: Dark Sea Industries LLC / University of New Mexico / The Mars Society
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SAM: Space Analog for the Moon and Mars

Exterior view of SAM. Credits: samb2.space
Interior view of greenhouse controlled environment with depiction of SIMOC temperature, humidity, and carbon dioxide level control panel. Credits: samb2.space

Located at the iconic Biosphere 2 facility in Arizona, SAM is a hi-fidelity, hermetically sealed science center about to begin cutting edge research into environmental control and life support systems (ECLSS). The facility will host researchers to perform experiments on plant physiology, regolith chemistry, food cultivation and a host of other studies in the context of a space habitat analog.

Utilizing the original Test Module which completed three closed cycles to test water and human waste recycling prior to the main Biosphere 2 facility construction, SAM will be fitted with an airlock and pressurized enclosure including quarters for research crews to stay up to two weeks at a time.

Of particular interest, SAM in partnership with National Geographic, will help validate SIMOC, an interactive closed-loop life support system simulator based on authentic NASA data. Feedback from SAM will refine the SIMOC mathematical model that balances food, air, water, agriculture and solar energy to support humans in a closed ECLSS.

SIMOC was developed though a grant by Arizona State University’s Interplanetary Initiative. Unveiled at the Mars Society 23 Annual International Convention last October (see page 87 of the Conference Abstract) the software is licensed and hosted by the National Geographic Society for integration into classrooms globally where curricula is provided for teachers to get students involved as citizen scientists to design habitats to sustain human life on the Moon and Mars.

Screen shot of SIMOC habitat interactive simulation software. Credits: Kai Staats / National Geographic Society

As stated on the SAM at B2 website:

“There is no single-run experiment that results in the ideal solution for providing breathable air, recycled water, food and waste reprocessing. Rather, we will see an unfolding of experiments, findings, and prototypes for decades to come. Much as farming evolved from the art of crop rotation to the science of genetically modified organisms, living on the Moon, Mars, and in free space will demand constant improvements in our systems as more humans move to off-world homes.”

Kai Staats, Director at SAM, was a recent guest on The Space Show where he provided a history of the creation of the facility and his role in developing SIMOC.

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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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NASA investing in nuclear propulsion for Mars missions

Illustration of a nuclear thermal rocket in low earth orbit. Credits: NASA

Two U.S. companies are partnering with NASA to develop new fuel sources and reactor designs for future nuclear-fueled crewed space missions. Nuclear thermal and fusion powered rockets could significantly reduce the travel time to the Red Planet, lowering the risk of radiation exposure and the cost of life support consumables.

In an article in IEEE Spectrum, freelance journalist Prachi Patel describes the challenges of designing space nuclear reactors that are safe and lightweight, which will be needed to propel exploratory missions to Mars. These type of space reactors have the added benefit of being able to switch from propulsion to a power source at their destination.

Seattle based Ultra Safe Nuclear Corporation has a reactor design that uses a grade of nuclear fuel enriched to less then 20% uranium classifying it below the limit of highly enriched uranium, thus reducing proliferation risks by nefarious actors. The company coats its microscopic uranium fuel pellets with ceramics in a zirconium carbide matrix. This design approach ensures that the fuel can withstand the extremely high temperatures and volatile conditions inside a nuclear thermal reactor.

BWX Technologies Corporation located in Lynchburg, Virginia has extensive space nuclear reactor experience and has been working under contract to NASA since 2017 to explore designs also using a temperature resistant ceramic composite fuel with low enriched (< 20%) uranium.

Both companies may benefit from the recent Trump Administration Space Policy Directive-6 released December 16 which aims to limit the use of highly enriched uranium in space nuclear reactors unless absolutely necessary. The Memorandum on the National Strategy for Space Nuclear Power and Propulsion specifies that “The use of highly enriched uranium (HEU) in SNPP [space nuclear power and propulsion] systems should be limited to applications for which the mission would not be viable with other nuclear fuels or non‑nuclear power sources.” Although Space Policy Directives can be negated or modified by new administrations this particular directive should have bipartisan appeal.

The article also mentions the Princeton Plasma Physics Laboratory’s Direct Fusion Drive that SSP covered last year. Fusion rockets, although further behind in technology readiness levels, hold promise to outperform fission-based propulsion as fusion reactions release up to four times as much energy.