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ISRU technology gap assessment

Diagram depicting the three main areas of in-situ resource utilization and their connections to surface systems. Credits: ISECG

The International Space Exploration Coordination Group (ISECG), a forum of 14 space agencies which aims to implement a global space exploration strategy through coordination of their mutual efforts, established a Gap Assessment Team (GAT) in 2019 to examine the technology readiness of in-situ resource utilization (ISRU). The purpose of the ISRU GAT effort was to evaluate and identify technology needs and inform the ISECG on gaps that must be closed to realize future missions. The assessment was intended to initiate an international dialogue among experts and drive policy decisions on investment in exploration technologies, while identifying potential areas for stakeholder collaboration. A report has just been released summarizing these efforts.

ISRU systems that can collect and utilize resources available at the site of exploration, instead of transporting them from Earth with considerable expense, cover three broad areas depicted in the diagram above; In-Situ Propellant & Consumable Production, In-Situ Construction, and In-Space Manufacturing with ISRU-Derived Feedstock.

To help understand how each function interacts and influences other areas of ISRU and how they integrate with life support systems, a functional flow diagram shown below was created to help visualize the flow of resources step by step to final product realization.

Integrated ISRU functional flow diagram (Including ties to life support). Credits: ISECG

The GAT reached consensus on key findings and recommendations (listed below) to stakeholders and decision-makers for implementing ISRU capabilities deemed essential for future human space exploration and settlement activities.

Key Findings
* ISRU is a disruptive capability and requires an architecture-level integrated system design approach from the start.
* The most significant impact ISRU has on missions and architectures is the ability to reduce launch mass, thereby reducing the size and/or number of the launch vehicles needed, or use the mass savings to allow other science and exploration hardware to be flown on the same launch vehicle. The next significant impact is the ability to extend the life of assets or reuse assets multiple times.
* The highest impact ISRU products that can be used early in human lunar operations are mission consumables including propellants, fuel cell reactants, life support commodities (such as water, oxygen, and buffer gases) from polar resources (highland regolith and water/volatiles in PSRs).
* While not in the original scope, evaluation of human Mars architecture studies suggest that there is synergy between Moon and Mars ISRU with respect to water and mineral resources of interest, products and usage, and phasing into mission architectures.
* A significant amount of work is underway or planned for ISRU development across all the countries/agencies involved in the study, particularly in the areas of resource assessment, robotics/mobility, and oxygen extraction from regolith.
* While it appears each country/space agency has access to research and component/subsystem size facilities that can accommodate regolith/dust and lunar vacuum/temperatures, there are a limited number of large system-level facilities that exist or are planned.
* The assessment performed on the type and availability of lunar and Mars simulants for development and flight testing shows that 1) while simulants are available for development and testing, greater quantities and higher fidelity simulants will be needed soon, especially for polar/highland-type regolith, and 2) selection and use of proper simulants is critical for minimizing risks in development and flight operations.
* Examination of resource assessment development and activities identified new efforts in refocusing technologies and instrumentation for lunar and Mars operations, and several missions to begin surface and deep assessment of resources are in development, especially to obtain maps of minerals on the lunar surface, surface topography, and terrain features, or to understand the depth profile of water and volatiles.
* While there is significant interest in terrestrial additive manufacturing/construction development, development for space applications has been limited and primarily under Earth-ambient conditions.
* Further research, analysis, and engagement are required to identify synergies between terrestrial mining and in-situ resource utilization (ISRU). Throughout the mining cycle and ISRU architecture, key areas for investigation include; dependence on remote, autonomous, and robotic operations; position, navigation, and timing systems; and energy technologies (e.g., small modular reactors and hydrogen technology).
* Stakeholder engagement is required between the terrestrial mining and space sectors to drive collaboration to identify and benefit from lessons learned from terrestrial innovations for harsh or remote operations.
* Long-term (months/years) radiation exposure limits for crew currently do not exist to properly evaluate radiation shielding requirements. These are needed to properly evaluate Earth-based and ISRU-based shielding options.

Recommendations
* To help advance ISRU development and use in future human exploration, it is recommended that countries/agencies focus on the defined Strategic Knowledge Gaps (SKGs) that have been identified as high priority for each of the 3 human lunar exploration phases described. Early emphasis should be placed on geotechnical properties and resource prospecting for regolith near and inside permanently shadowed regions.
* Since the access and use of in-situ resources is a major objective for human lunar and Mars exploration and the commercialization of space, locating, characterizing, and mapping potential resources are critical to achieving this objective. While work on resource assessment physical, mineral, and water/volatile measurement instruments are underway, and new orbital and lunar surface missions are in development or planned, a focused and coordinated lunar resource assessment effort is needed. It is recommended that Science, ISRU, Human Exploration, and Commercial Space coordinate and work closely on Geodetic Grid and Navigation, Surface Trafficability, and Dust and Blast Ejecta to ensure surface activities and data collection are performed efficiently and safely.
* While short-duration lunar surface crewed missions can be completed with acceptable radiation exposure risk, it is recommended that long-term exposure limits be established and radiation shielding options (Earth and ISRU-based) be analyzed as soon as possible to mitigate risks for sustained operations by the end of the decade.
* Long-term sustained operations will require a continuous flow of missions to the same location. While distance and placing of landers can be initially used to mitigate damage to already delivered equipment and infrastructure, an approach for sustained landing/ascent (in particular for reusable vehicles and hoppers) is needed. Dedicated plume-surface interaction analysis and mitigation technique development are recommended. It is also recommended that development of capabilities and establishment of landing/ascent pads be incorporated into human lunar architectures early to support sustained operations
* Experience from Apollo missions indicates that wear, sealing, and thermal issues associated with lunar regolith/dust may be a significant risk to long-term surface operations. Coordination and collaboration on dust properties/fundamentals, and mitigation techniques and lessons learned are highly recommended. This effort should also involve coordination and collaboration on the development, characterization, and use of
appropriate lunar regolith simulants and thermal-vacuum facility test capabilities and operations for ground development and flight certification.
* To maximize the use of limited financial resources, it is recommended that the ISECG space agencies leverage the information presented in the report, in particular, the content of the “Technology Capture by WBS and Country/Space Agency portfolio” as a starting basis for further discussions on collaborations and partnerships related to resource assessment and ISRU development/operations.
* Collaboration and public-private partnerships with terrestrial industry, especially mining, resource processing, and robotics/autonomy are recommended to reduce the cost/risk of ISRU development and use.
* This includes establishment of an international regulatory framework for resource assessment, extraction, and operations, which are necessary to promote private capital investment and commercial space activities.
* The sustainable development aspects of the ISRU activity are recommended to be taken into account from the start of activity planning for the surface exploration of Moon and Mars.
* Aspects of reusing and recycling hardware are recommended to be taken into account from the design and architecture phase of mission planning. This will contribute to minimizing the exploration footprint (e.g. abandoned hardware) and therefore is key towards sustainability.
* To accelerate the development of key technologies, close knowledge gaps, and expedite testing/readiness, it has been seen that the use of unconventional models, such as government-sponsored prize challenges can be effective innovation catalysts operationalizing the above recommendations, and ultimately, bringing ISRU to the Moon and onwards to Mars.

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Artificial gravity space settlement ground-analog

Cross sectional diagram of hypergravity vehicle with tilted cabin on track in max G orientation. Credits: Gregory Dorais / American Institute of Aeronautics and Astronautics

Gregory Dorais, a research scientist at NASA Ames Research Center, has combined several existing technologies including centrifuges, tilted trains and roller coasters to devise a novel hypergravity space settlement ground-analog that could be used to study the effects of artificial gravity on humans, animals and plants for extended periods. He introduced the concept in a paper presented at the American Institute of Aeronautics and Astronautics Space 2016 Conference in Long Beach, California. Experimental results using such a facility could inform designs for orbital rotating habitats providing up to 1G of artificial gravity or even surface-based outposts on the Moon, Mars or anywhere. The facility could also study higher levels of gravity (thus the name “hypergravity”) which could be beneficial in mitigating deleterious effects of microgravity on human physiology.

Dorais’ Extended-Stay HyperGravity Facility (ESHGF) would merge technologies of centrifuges and trains, creating a 150 meter circular track with a series of connected tilting cars. The tracks could use tubular rails similar to today’s rollercoasters or eventually use magnetic levitation. An optional transfer vehicle placed on an outer concentric track is proposed where people and cargo can be moved between a depot and the hypergravity vehicles while they are in motion so that a constant velocity can be maintained without disruptive force changes during operations.

ESHGF system depicted in a complete ring configuration (not to scale). Credits: Gregory Dorais / American Institute of Aeronautics and Astronautics
Hypergravity vehicle single cabin side and perspective views. Credits: Gregory Dorais / American Institute of Aeronautics and Astronautics

The interior of each car could be customized to meet the needs of its inhabitants, but would likely include all the expected functions of a thriving space colony including living quarters, agricultural facilities, marketplaces, recreational centers and much more.

The system is modular and extendable allowing the facility to start small and then expand into a variety of configurations to investigate multiple gravity level environments as sanctioned by budgets. Dorais says that the facility “… will permit research on the long-term health and behavioral effects of various artificial-gravity levels and rotation rates on humans and other life, among other things, to establish the design requirements for long-term space settlements.”

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Sustainable space commerce and settlement

Artist impression of a sustainable settlement on the Moon. Credits: ESA – CC BY-SA IGO 3.0

Dylan Taylor of Voyager Space Holdings recently wrote an article in The Space Review on sustainable space manufacturing. He makes a convincing case that long-duration space missions and eventual human expansion throughout the solar system will require radical changes in the way we design, manufacture, repair and maintain space assets to ensure longevity. In addition, the cost of lifting materials out of Earth’s deep gravity well will drive sustainable technologies such as additive manufacturing in space and in situ resource utilization to reduce the mass of materials needed to be launched off our planet to support space infrastructure. In-space recycling and reuse technologies will also be needed along with robotic manufacturing, self-reparability and eventually, self-replicating machines.

But there is more to the philosophy of sustainability and its impact on the future of space activities. According to the Secure World Foundation (SWF), sustainability is essential for “Ensuring that all humanity can continue to use outer space for peaceful purposes and socioeconomic benefit now and in the long term. This will require international cooperation, discussion, and agreements designed to ensure that outer space is safe, secure and peaceful.” Much of the discussion centers around the problem of orbital debris, radio frequency interference, and accidental or irresponsible actions by space actors. SWF is active in facilitating dialog among stakeholders and international cooperation.

The National Science and Technology Council released a report in January called the National Orbital Debris Research and Development Plan. To address the issue, there are several companies about to start operations in LEO to deal with the orbital debris or in-orbit servicing. Japan based Astroscale just launched a demonstration mission of their End-of-Life Services by Astroscale (ELSA) platform to prove the technology of capturing and deorbiting satellites that have reached their end of life or other inert orbital debris.

Image of the Astroscales ELSA-d mission showing the larger servicer spacecraft releasing and preparing to dock with a “client” in a series of technical demonstrations, proving the capability to find and dock with defunct satellites and other debris. Credits Astroscale.

Even financial services and investment houses like Morgan Stanley are pushing for sustainability to reduce the risks to potential benefits emerging from the Newspace economy such as remote sensing to support food security, greenhouse gas monitoring, and renewable energy not to mention internet access for billions of people.

Sustainable operations on the Moon are being studied by several groups as the impact of exploration and development of Earth’s natural satellite is considered. Lunar dust when kicked up by rocket exhaust plumes could create hazards to space actor’s assets as well as Apollo heritage sites. SWF, along with For All Moonkind, the Open Lunar Foundation, the MIT Space Exploration Initiative and Arizona State University have teamed up on a project called the Moon Dialogs to advance interdisciplinary lunar policy directions on the mitigation of the lunar dust problem and to shape governance and coordination mechanisms among stakeholders on the lunar surface. SSP’s take on lunar dust mitigation was covered last July.

These few examples just scratch the surface. NASA, ESA and the UN Office for Outer Space Affairs have initiatives to foster sustainability in space. Humanity will need a collaborative approach where public and private stakeholders work together to ensure that the infrastructure to support near term commercial activities in space and eventual space settlement is both durable and self-sustaining.

The long-term sustainability of space. Credits: ESA / UNOOSA
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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