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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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Planetoid Mines completes development of ISRU Tech

Planetoid Mines Corporation’s ISRU off-world extractor. Credits: Planetoid Mines Corporation

A New Mexico based startup called Planetoid Mines Corporation has just completed development of an autonomous robotic platform for mining the moon or other extraterrestrial worlds via in situ resource utilization. The system features a multi-head icy regolith extractor that feeds directly into an ore beneficiation tool, the output of which is channeled to an onboard oven that extrudes 3D printed structures via a robotic arm.

Through a post on his LinkedIn profile, CEO Kevin DuPriest says “Our self-contained system provides end-to-end continuous mining operations with multiple excavator heads, mineral concentration through beneficiation, a pyrometallurgy oven and thermal printing head. Using lunar surface minerals the system can print landing pads, extrude fused quartz rods, large antenna arrays, etc. ISRU platform designed to fit most lunar landers.”

The company’s website highlights a solid oxide hydrogen fuel cell and steam electrolysis stack that can split lunar water into hydrogen and oxygen for rocket fuel while generating heat and power on-demand. There is even potential dual use benefits of the ISRU architecture for mining on Earth. The website intimates the possibility of a mission to the Moon by 2022, but provides no further details on suppliers of launch or lander services.

In a recent Tweet DuPriest announced the company is considering going public through a Special Purpose Acquisition Corporation (SPAC) and looking for partners to assist with cislunar infrastructure and logistics for mission operations.

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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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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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Seeding asteroids with fungi for space habitat soil

Illustration of a process for making soil for space habitats by seeding asteroids with fungi. Credits: Jane Shevtsov

The asteroid belt will be a treasure trove of raw material for space settlers to use to build their habitats, especially the O’Neill-type rotating cylinder variety. To support plentiful green spaces and robust agricultural systems envisioned for these large scale settlements, an abundant source of fertile soil will be needed. But how could the enormous cost of bringing soil from Earth be avoided? An innovative in situ method under development by Jane Shevtsov of Trans Astronautica Corporation may provide the answer. In a just awarded NASA NIAC Phase 1 grant proposal, she explains that the envisaged soil-making process would be a “…natural fit for asteroid mining operations targeting volatiles, as they use carbonaceous asteroids and leave behind leftover regolith that should make a suitable parent material for soil production.”

The Phase 1 research will be broken down into two tasks. In Task 1 the leading fungal species will be identified for experimentation on asteroid material simulant followed by determination of soil production rates of the fungi along with the effects of environmental factors such as temperature, humidity and oxygen concentration. Task 2 will explore various methods of breaking down asteroid regolith by the chosen fungi in the space environment optimizing for productivity and costs, with the ultimate goal of determining the size of a payload to support a reference mission habitat within a feasible timeframe.

In the above diagram, there are hints that the concept may use an inflatable enclosure around the asteroid to retain volatiles, reminiscent of some of the applications of the SHEPHERD asteroid capture architecture previously covered by SSP, in which a gas atmosphere within the enclosure can keep water in a liquid phase so that the asteroid provides a substrate for introduced biological agents for the generation of foodstuffs and other consumables.

Trans Astronautica has been working on their own asteroid capture method which may come in handy when used in combination with the output of Ms. Shevtsov’s project.

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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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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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Power towers at the Peaks of Eternal Light

Peaks of Eternal Light at the lunar south pole annotated with crater labels. Mosaic of 40 images taken by the ESA SMART-1 spacecraft 2005/2006. Area covers 500 x 150 km. Credits: ESA/SMART-1/AMIE camera team; M. Ellouzi/B. Foing, CC BY-SA 3.0 IGO

As most space settlement enthusiasts know, the Peaks of Eternal Light on the rims of craters in the lunar polar regions hold much promise as the ideal location to place collectors for solar energy to power ice mining operations. At the south pole in particular, these peaks lie within just a few kilometers of large frozen water deposits in the permanently dark shallows. But how much solar power is available? Companies such as Trans Astronautica Corporation will want to know so they can inform plans for their Sun Flower™ collector invention as part of a Lunar Polar Mining Outpost.

In a paper posted this month on the pre-print server arXiv.org, a team of researchers at Harvard University and Technische Universität Berlin present the results of a study to answer this question. Using data from high resolution maps of solar illumination on the ridges of Shackleton crater and others, they determined the total available power from collector towers of various heights if they were placed at these locations.

The study found that the power available depends heavily on the height of the panels above the local surface but could be substantial, from a few megawatts for towers of heights less than 100m up to the gigawatt range for towers of 500m or more. This is sufficient power for mining several thousand tons of water per year from Shackleton crater.

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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.