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Orbital Sustainment and SML

Illustrations © James Vaughan, and used by permission. More of his work can be found here:

By Alexander Jehle and Dr. George Sowers


Water is the “oil” of space. Water, H2O – two parts hydrogen and one part oxygen, can be used as a steam or plasma propellant for spacecraft and space tugs and be split into hydrogen and oxygen as a chemical rocket propellant. Water is ubiquitous in the inner solar system and exists as ice on the Moon. Recent research indicates lunar water can be economically mined, processed, and exported into cislunar space. Refueling space vehicles using space-sourced propellant breaks the tyranny of the rocket equation, lowering the cost of missions beyond low Earth orbit. This paper describes cislunar propellant distribution architecture anchored by a logistics node at the first Earth-Moon Lagrange point. This node receives and stores propellant sourced from space and distributes it using tanker vehicles. Three cases are described. The first is refueling launch vehicle upper stages carrying payloads en route to locations beyond low Earth orbit. The second is supporting space exploration activities on the Moon and missions to Mars. The third is refueling and servicing spacecraft in geostationary orbit. The fuel storage node occupies strategic real estate in cislunar space, providing space domain awareness and access to any point on the Moon, Earth orbit, and beyond.


…A peaceful, gain-loving nation is not far-sighted, and far-sightedness is needed for adequate military preparation, especially in these days.[3]


One of the great planetary science discoveries of recent decades is that water is ubiquitous in the inner solar system. Water exists at the poles of Mercury[4] and is chemically bound in hydrated minerals within C-type asteroids and near-Earth objects (NEOs).[5] Water is abundant on Mars,[6] but most importantly, water exists in permanently shadowed regions (PSRs) near the poles of the Moon.[7] The existence of water on Earth’s nearest celestial neighbor is of paramount importance for space exploration, space commerce, and defense. Water is the foundation of a space logistics chain enabling long term space sustainment and unprecedented space mobility. The core competencies of the United States Space Force (USSF) could all benefit from expanded space mobility.[8]

Logistics capabilities are operational capability multipliers in that they are the systems that deliver sustainment. Effective sustainment is critical to enabling operations to go farther, do more, and stay longer. Sustainment exists in all phases of an operation—from preparation through operations to returning to a state of readiness for the next mission. Joint Publication 4-0, Logistics defines sustainment for the Joint force, now including the USSF, as:

Sustainment—one of the seven joint functions—is the provision of logistics and personnel services to maintain operations until mission accomplishment and redeployment of the force. Effective sustainment provides the joint force commander (JFC) the means to enable freedom of action and endurance and to extend operational reach. The relative combat power that military forces can generate against a threat is constrained by their capability to plan for, gain access to, and deliver forces and materiel to points of application.[9]

The USSF’s capstone document defines Space Mobility and Logistics (SML)—a core competency of the USSF—as movement in, from, and to space.[10] They further define in-space logistics as orbital sustainment:

Orbital sustainment and recovery is another important application of SML. Already demonstrated in the commercial sector, orbital sustainment will allow military space forces to replenish consumables and expendables on spacecraft that cannot be recovered back to Earth. Orbital sustainment will also enable spacecraft inspection, anomaly resolution, hardware maintenance, and technology upgrades.[11]

The USSF clearly envisions that orbital sustainment will expand to replenishing consumables and expendables, conducting spacecraft inspection, and technology upgrades. Looking farther into the future, building a logistics architecture in cislunar space to distribute water and propellant from the Moon and elsewhere will greatly enhance sustainability and mobility of assets in geostationary orbit (GEO) and across the space domain.

Figure 1. The Army’s Principles of Sustainment.

As the USSF’s logistics doctrine evolves, it must be integrated with its entire operational concept. A valuable source of thought in this arena is found in the U.S. Army’s principles of sustainment, depicted in figure 1, and underlying logistics culture, partially defined in the Army Doctrine Publication 4-0.[12] This paper suggests that a particular technology—lunar-sourced, on-orbit-stored propellant—could be a key enabler of the USSF’s cornerstone responsibilities.

The Water Resources on the Moon

Water has many uses in the context of space exploration and development. It is essential for human life and agriculture. Oxygen, one of its constituents, is a necessary component of breathing air. It is one of the most effective substances for radiation shielding on a per mass basis.[13] But perhaps its most valuable use is to support space mobility as rocket propellant. It can be used directly in the form of steam or plasma for low to medium thrust applications. When split into hydrogen and oxygen and liquefied, it produces LO2 (often called “LOX”) and LH2, the most efficient chemical propellant combination known. Water is truly the oil of space. And like oil on Earth, water will be the foundation of the space economy, underpinning all activities including those of the USSF.

Figure 2. Ice exposures at the North Pole and South Pole of the Moon.

There is overwhelming evidence that water exists near the poles of the Moon, trapped in PSRs. Most of this evidence comes from remote sensing observations[14] although ejecta from the impact of a Centaur upper stage was observed by the LCROSS spacecraft indicating 5.6±1.9wt% water ice.[15] Figure 2 shows the extensive availability of lunar surface ice.[16]

To be viable as an economic resource, the water on the Moon must be extracted and processed into propellant. One promising technique under development at the Colorado School of Mines (CSM) is called Thermal Mining. Thermal Mining applies heat in-situ to the water bearing lunar material. This avoids the cost, mass, and complexity of the more traditional excavation methods. A recent study indicates a 65% mass savings for in-situ Thermal Mining compared to excavation. The effectiveness of direct heat in sublimating ice from within icy regolith samples has been demonstrated in the laboratory at CSM.[17] Figure 3 shows heat in the form of simulated sunlight being applied to an icy regolith simulant sample under cryogenic vacuum conditions—the same conditions at the lunar poles.[18]

In addition to proving the physical concepts underlying Thermal Mining, CSM has also developed an architecture for exploiting this technique in the lunar PSRs. CSM has developed a functional and physical architecture for a LO2/LH2 propellant production system anchored by a Thermal Mining based ice extraction system. Figure 4 is CSM’s ice extraction concept described in the NASA Innovative Advanced Concepts (NIAC) phase I report.[19]

Figure 3. Heat applied to an icy regolith simulant sample under cryogenic vacuum conditions.

Based on this architecture, a business model suggests that it can be profitable for a commercial mining and propellant production company to sell into a cislunar propellant logistics stream.[20]

Figure 4. Ice extraction concept, from Sowers et al., 2020.

Benefits of Refueling and Propellant Sources in Space

The cost of most space activities is dominated by transportation cost. The energy to escape Earth’s gravity well is enormous and the distances between interesting or valuable destinations in space is vast. For the sixty years since the first human mission into space, all space missions have originated on Earth with all propellants brought from there. This situation gives rise to what is known as the tyranny of the rocket equation. The rocket equation is simply written:


where is the velocity added to the rocket, is the exit velocity of the rocket engine, is the initial mass of the rocket including propellant, and is the final mass after all propellant has been expended. The difference between the initial mass and the final mass is essentially the mass of the propellant.[21]

The equation is exponential if it is solved for propellant mass in terms of . In other words, the “farther” one wants to go in space (generally requiring more ), the required propellant increases at an ever-increasing rate. This is the reason rockets leaving Earth consist mostly of fuel, and that a rocket going to the Moon and back must be the size of the Saturn V used in Apollo or the Space Launch System currently in development by NASA.

However, if a spacecraft can be refueled en route, reusing the propulsion system through multiple refuelings, the tryanny of the rocket equation is broken. The exponential increase of propellant with becomes linear. Figure 5 shows the the enormous benefit of one, two, or three refuelings in reducing required propellant for a given , while maintaining a stage mass fraction of 0.92 (The Saturn V’s stage mass fraction was roughly 0.94, and the Space Launch System Block 1 has a stage mass fraction of .91).[22] Furthermore, reduced requirements for propellant to do a given mission entails a reduction in the size of the rocket or the number of rockets required. Either of these situations results in a significant reduction in the cost of the mission. Table 1 shows the results of calculations based on the model of Sowers, 2021. The estimated costs saving benefits in table 1 are based on propellant prices in figure 7.[23]

Figure 5. Benefits of refueling with space sourced LO2/LH2 propellant. A round trip from LEO to GEO costs nearly 9000m/s, while a round trip from LEO to low lunar orbit costs nearly 12,000 m/s: this results in a propellant mass savings of 75% for a round trip from LEO to GEO, and significantly more for LEO to LLO. Modified from Sowers, 2021.



Table 1. Benefits of lunar-sourced propellants.[24]

Space Activity Lunar-Sourced Propellant Benefit
Transportation from Earth to Geostationary orbit. 10-20% lower cost.
Transportation from Earth to the lunar gateway. 2 times lower cost.
Transportation from Earth to lunar surface. 3 times lower cost.
Transportation from the lunar surface to the lunar gateway and back. 70 times lower cost.
Cost of a human mission to Mars. 2-3 times reduction.
In-space transportation. Essentially the cost of lunar-sourced propellant.

Cislunar Propellant Economics

The Moon is uniquly situation to enable space activities in cislunar space and beyond due to its viable sources of water and thus LO2/LH2 propellant. The Moon is the closest source of resources to the Earth. Escaping the Moon’s gravity well is far easier than Earth’s. As shown in Figure 6, the from the surface of the Moon to the first Earth-Moon Lagrangian point (EML1) is a factor of five less than from Earth—inclusive of Earth to orbit (ETO) plus LEO to EML1—and launch from the Moon does not require flying through an atmosphere.[25]

Of course, a source of fuel is not valuable unless there is a refuelable space transportation architecture able to take advantage of it. Fortunately, there are several commercial companies working on refuelable upper stages and landers including SpaceX, Dynetics, Blue Origin, and United Launch Alliance (ULA). For example, ULA made a public offer[26] to buy propellant in space to support its future upper stage, currently being designed to be refuelable. The rates ULA would be willing to pay at locations within cislunar space, depicted in Figure 7, reflect both the physics and the corresponding economics of propellant in cislunar space.[27] The blue bars represent the cost of propellant (or any mass) launched from Earth. The green bars were set by the criterion that the price of lunar propellant in low Earth orbit (LEO) be less than the price of propellant launched from Earth at the same location. The LEO price chosen was $3000/kg, lower than the $4000/kg to launch from Earth. If this condition is met, then ULA would be able to lower the cost to launch a payload from Earth to GEO, a critical piece of ULA’s current market.[28]

The price of propellant on the lunar surface required to ensure meeting $3000/kg in LEO is estimated to be $500/kg. This depends on several assumptions regarding transporting the propellant from the Moon to LEO. First, the tranportation uses a vehicle that can store cryogenic propellants for long periods, such as ULA’s Advanced Cryogenic Evolved Stage (ACES) upper stage and Experimental Enhanced Upper Stage (XEUS) lunar lander. Second, all maneuvers are propulsive. This assumption is very conservative, given that aerobraking using Earth’s atmosphere to decelerate to LEO could reduce the cost by a factor of two. The other key location for pricing is EML1. This location is a good proxy for any location in high Earth or Lunar orbit, such as the orbit of NASA’s proposed Lunar Gateway station. For EML1 propellant sourced from the Earth, the price is $10,000/kg. Sourced from the Moon, the price estimate is $1000/kg, a factor of ten reduction.

Finally, the orange bars in Figure 7 represent the price to move mass from Earth to EML1 or the lunar surface, with a single refueling using propellant from the Moon. The use of lunar propellant will reduce the cost to move mass from Earth to the lunar Gateway by a factor of two and reduce the cost to move mass from Earth to the lunar surface by a factor of three. These two facts make a compelling argument to move forward with lunar propellant production as a top priority. Every space mission beyond LEO could benefit from the use of refueling with lunar propellant.

Figure 7. Propellant prices in cislunar space.

Cislunar Propellant Logistics Architecture

Beyond supporting civil and commercial activities in cislunar space, a logistics architecture based on lunar water and propellant would enable long term sustainment of our critical space infrastructure in Earth orbit. It would provide key logistics support to enable unprecedented space mobility through the supply of propellant, both as water and as LO2/LH2. We envision a logistics architecture that consists of three basic elements, shown in Figure 8.

The first part of the architecture is the sources of supply. We discussed the lunar supply above. Other sources of supply include NEOs and the Earth itself. Once a robust water/propellant economy is established in space, water and LO2/LH2 propellant will become commodities and prices will be set by the market. Water and propellant prices will decrease due to competition between Earth, Moon and asteroid sources of supply. The second component is the transportation system that moves propellant from the supply source to the point of demand. This will include tankers to carry either water or LO2/LH2 propellant, vehicles that can land and take off from the Moon, tankers to refuel launch vehicle upper stages and servicing vehicles that can refuel (and potentially repair) satellites in GEO. The third part is logistics hubs (or depots) that will include water and propellant storage and transfer, water to propellant processing, and transportation element servicing capability.

Consider an initial architecture with a single logistics hub located in the vicinity of EML1. This is a critical location in cislunar space for a number of reasons. First, EML1 is easily accessible from any point on the lunar surface with about the same . Second, EML1 is always in line of sight to the Earth, facilitating continuous communications. Third, tankers dispatched from EML1 are able to access almost every Earth orbit, enabling optimum refueling of launch vehicle upper stages en route to destinations beyond LEO. Finally, the from EML1 to GEO is modest, enabling efficient servicing of that critical domain. Since EML1 is an unstable equilibrium point, the logistics hub would consume a small amount of the propellant stored there to remain on station.

There are a number of practical delivery routes for both water and propellant. Water and propellant can both be delivered from the lunar surface to the logistics hub in EML1. Eventually, water may also come from NEO mining operations to EML1. From EML1, tankers can be dispatched into Earth orbit to meet and refuel upper stages delivering payloads to beyond LEO destinations. Satellite servicing vehicles will transit from EML1 to GEO carrying water to refuel GEO belt satellites.

Figure 8. Water and LO2/LH2 propellant logistics architecture in cislunar space.

The EML1 Propellant Depot

A conceptual design for an EML1 logistics hub is shown in Figure 9. It has a number of critical functions It stores both water and LO2/LH2 propellant. Once NEO mining begins, it will process water into propellant. It transfers both water and propellant from delivery tankers to storage and from storage to delivery tankers. It must maintain its attitude to keep the sunshade pointing toward the sun. It must harvest solar energy to power its operations and store enough energy to cope with periodic solar eclipses. Energy storage could be in the form of batteries and/or fuel cells. With a ready supply of water, hydrogen, and oxygen as well as electrolysis capability, generating energy through fuel cells is an attractive option.

The propellant storage tanks are placed into a transverse spin to facilitate transfer operations and to reduce boil-off of the cryogenic propellants. Preliminary estimates indicate cryogenic boiloff rates can be reduced to 10% per year through purely passive measures.[29] These include the sunshield, multi-layer insulation, and vapor cooling using hydrogen boil-off.

Figure 9. Preliminary system concept for an EML1 logistics hub.

Cislunar Propellant Use Cases

Three primary use cases can be supported by the logistics network: refueling upper stages en route from Earth to destinations beyond LEO; supporting space exploration missions around the Moon, to Mars, and beyond; and providing orbit sustainment support to the GEO belt. As logistics operations become mature, costs will decrease opening up other activities such as permanent human presence on the Moon, asteroid mining, and in-space manufacturing. These activities and more will be enabled by the wide availability of propellants sourced in space.

The concept of operations for the first use case, upper stage refueling, is straight forward. A tanker vehicle loaded with LO2/LH2 propellant is dispatched from the logistics hub to a predetermined rendezvous orbit around the Earth. This orbit is optimized based on the launch vehicle design and final destination of the payload. The rendezvous orbit will typically be an elliptical orbit similar to a geostationary transfer orbit. The tanker arrives in the rendezvous orbit before the payload is launched from Earth. Upon completion of the booster phase of flight, the upper stage and payload will reach the same orbit and rendezvous with the tanker. Propellant is transferred from the tanker to the upper stage and the upper stage proceeds to deliver the payload to its final destination. The tanker then returns to the EML1 logistics hub. This process is depicted in figure 10. As calculations listed in Table 1 indicate, refueling can reduce the cost of these missions anywhere from 10% to 70% depending on the final destination.

Figure 10. Preliminary system concept of operation for upper stage refueling. Work by authors.

The exploration use case has a number of scenarios. Missions leaving the surface of the Moon can be refueled directly on the lunar surface, saving a factor of 70 compared to bringing fuel from Earth. A single Mars mission can save $12B through the use of lunar propellant compared to launching everything from Earth.[30] For a Mars mission, propellant will be shipped directly to the mission aggregation point (EML2 is a possibility). Mars mission hardware will be refueled en route to the aggregation point.

The third use case is the sustainment of satellites in GEO. This will consist primarily of refueling, but satellite maintenance and repair will also be enabled as these capabilities are developed. A critical prerequisite for enabling sustainment via the space logistics architecture is to transition satellites to a water-based propulsion architecture. This technology is well along in development by a number of companies including Bradford Industries (which acquired Deep Space Industries), Tethers Unlimited, and the Aerospace Corporation. In this case, a satellite servicing vehicle given a full load of water at the EML1 logistics hub transits to GEO. Since water is storable, the satellite servicing vehicle can linger in GEO or near GEO providing refueling services when needed. Once its supply is depleted, it returns to the logistics hub for another load.

Historically, satellites in GEO have been inserted by a launch provider into a geostationary transfer orbit. They then used their own apogee kick motor to raise their perigee from an altitude of 300 kilometers to GEO’s 36,000 km altitude. This required on average 1.7 km/s of ∆V and, if using a chemical propellant, consumed roughly 2,000 kg. They then had a residual station keeping ability of ~500 m/s for the remainder of the life of the satellite (~55m/s per year). They either remain in the original orbital slot or consume a portion of their ∆V budget to move to another GEO belt slot. Additionally, a fraction of propellant must be preserved to dispose of the satellite at the end of its design life. However, if the satellite is refueled after reaching GEO, it will have roughly 5 times its previous ∆V budget and have the ability to maneuver as well as station keep. The GEO satellite now can reposition itself without regret.

Refueling or providing ∆V assistance—”final leg” delivery to upper stages or satellites destined for GEO, EML1 or beyond—has a similar economic incentive. Instead of paying to launch propellant from Earth, buy it in space. A typical satellite bound for GEO usually pays the launch provider to launch their payload mass (2,000 kg), plus the mass of their apogee kick motor and propellant combined (also just over 2000 kg). Instead, the satellite service provider could launch two 2000 kg satellites and purchase final leg services from a company like Momentus Space, who could purchase water from EML1. This would reduce the launch cost per satellite in half, netting a 30% saving to the satellite operator after paying for the “final leg” services.

Legal Considerations

The legal environment surrounding extracting and utilizing space resources is moving towards increased clarity, promoting investor confidence. The international community and individual nations, including the United States, are collectively and independently working on legislation to define in space resource utilization ownership, property rights, and responsible activity, while upholding international agreements.[31] Under the Outer Space Treaty of 1967, all nations have agreed to disavow claiming sovereignty over celestial bodies or territories on those bodies. They still retain quasi-territorial jurisdiction and responsibility over their activities and objects launched into space, and personal jurisdiction and responsibility over their astronauts, citizens, and juridical persons, including non-governmental organization’s activities launched into space.[32] The Hague International Space Resources Governance Working Group’s recently released Building Blocks for the Development of an International Framework on Space Resource Activities are the first step to establish prospecting rights and property rights in space.[33] Jurisdiction, therefore, is going to extend to the activities involved in extracting the claimed resources and to the final products, vehicles, and facilities manufactured from these space resources. Sovereignty in space, as opposed to on celestial bodies, does not need to be claimed. By defining, occupying, and establishing logistical nodes American is projecting quasi-territorial jurisdiction and responsibility into space—establishing outposts of the law-abiding world with its Artemis Accords partner nations.

America and its allies can extend their reach, peacefully, or at least non-aggressively, into the cislunar system. This effort can and should be led by NASA, civilian providers of space capabilities, and the space resources industry; however, it will create operational capabilities that the USSF will leverage. The USSF should intently follow the progress of the space resources industry and be prepared to enable and protect its development, much as the U.S. Army served to secure, explore, and expand the economy of America into the western frontier.

Strategic Benefits

America has long realized that the nation does not need to have sovereignty over territory or colonial subjects to project force on the sea but that effective refueling and resupply stations become the dominant consideration in achieving control.[34] When A.T. Mahan wrote The Influence of Sea Power upon History in the 1880s, he pointed out that America had no need of a Navy, as America had no threats to its naval commerce, and that its commercial ships could go to foreign ports—generally without fear—for refuge from storms, to repair, and to resupply. This is not always the case. When peace does not prevail, Mahan continued, the merchant seaman:

…intuitively sought at the far end of his trade route one or more stations, to be given to him by force or favor, where he could fix himself or his agents in reasonable security, where his ships could lie in safety, and where the merchantable products of the land could be continually collecting, awaiting the arrival of the home fleet, which should carry them to the mother-country.[35]

In space, the need to establish logistics hubs and the need to conduct space mission logistics is the same need that ships of the 1800s had for coaling stations, fresh produce, and safe harbors. Currently though, there are no friendly foreign ports—there are no in-space ports in which to refuel at all. There is a need to refuel our space vehicles, provide our astronauts with fresh food, and protect critical systems and humans from radiation and solar storms. The means of securing safe harbor in cislunar space are technically feasible, as discussed above. They are also legal under international law.

The cislunar logistics hub could eventually serve as a robotic space station,[36] expanding over time to host more and more capability, eventually becoming an in space fabrication laboratory to responsively manufacture and distribute repair parts, fabricate structures, subsystems, and components for tech refresh.[37] This concept is similar to the DoD’s interest in pushing logistics as far forward as possible, as responsive as possible. Naval Additive Manufacturing, in the office of the Deputy Assistant Secretary of the Navy (Research, Development, Test and Evaluation), has a goal of establishing permanent additive manufacturing installations on multiple ship classes, with a 24-hour response time to additive manufacturing requests.[38] Coupled with an independent source of raw materials, establishing factories in space that can deliver components, and eventually satellites to Earth orbits would be a significant capability. The EML1 hub would serve as a foundational element for a future, incrementally evolving, industrial capability in space.

Operational Benefits

Beyond the direct benefits discussed above, the establishment of a propellant logistics architecture anchored by the EML1 logistics hub delivers other operational benefits. For example, the logistics hub at EML1 and at other future locations allows for resupply of maneuvering spacecraft without waiting for an Earth-based launch. A logistics hub coupled with a robotic servicing vehicle, space tug, or refueling spacecraft at a “High-GEO” orbit would increase the flexibility of mission planners. USSF spacecraft could be refueled at regularly scheduled intervals and be available for on demand or “emergency” resupply. Those spacecraft would then be at peak readiness.

The EML1 logistics hub also allows for the emplacement of other capabilities. The hub could host additional payload sensors to conduct passive space domain awareness activities, or with adequate power, conduct active space domain awareness activities including space object identification, cislunar orbital element set (ELSET) generation, and traffic management. Future versions of USSF spacecraft could be deployed directly from the hub for applications throughout cislunar space. This would inform the military with precise position and velocity information and could also publish ELSETs for the international community, without charge, similar to the way currently functions.

In addition, by refueling communication satellites, the satellites gain the ability to reposition on orbit, either rapidly by a few degrees within a theater of operation, or between theaters as needed. Future USSF spacecraft could have the ability to reposition itself anywhere within the GEO belt within hours with high-∆V transfers. Again, because of assured resupply, planners would be willing to conduct such transfers and increase the number of propulsive missions, including forced motion navigation inspections for cooperative and non-cooperative space domain awareness.

A space-sourced logistics supply line adds redundancy to the sustainment of our space infrastructure by establishing a new celestial line of communication (CLOC) from the Moon. A CLOC is a route used for the “movement of trade, materiel, supplies, personnel, spacecraft, electromagnetic transmissions, and some military effects.”[39] Currently, we have only one CLOC: we must sustain all spacecraft and constellations via Earth launch, which is well understood, preplanned, and interdictable. The Missile Defense Agency’s 2019 Ballistic Missile Defense Review includes endorsement of a space sensor layer to detect ballistic and hypersonic missiles during the launch and flight phases and pass on targeting information to ground, air, or sea-based weapons to defeat the missiles over the launching nation’s territory.[40] This capability could be expanded to prevent space launches. America’s position on militarization of space does not appear to extend to conducting or endorsing space blockades in either the Defense Space Strategy[41] or in the Space Capstone Publication. The Space Capstone Publication takes a nuanced approach to achieving space superiority and supremacy:

Space superiority is a relative degree of control in space of one force over another that would permit the conduct of its operations without prohibitive interference from the adversary while simultaneously denying their opponent freedom of action in the domain at a given time. Space supremacy implies that one side could conduct operations with relative impunity while denying space domain freedom of action to an adversary. Space supremacy is not always desirable, or attainable against a peer adversary, and should not be the unconditional goal of military spacepower. [42]

A space blockade would be one way to achieve space supremacy, however freedom of use of space is protected by the Outer Space Treaty (OST). [43] America’s and the OST’s stance on allowing space to be used for peaceful purposes explicitly includes using space for non-aggressive purposes, including missile warning.[44] America would be unable or unwilling to prevent an adversary from developing similar capabilities that could deny or disrupt its launch capabilities. Having a second celestial line of communication for propellant, and eventually in-space manufactured consumables and repair parts, would mitigate against the threat of an adversary targeting Earth-launch.

Finally, developing a strategic reserve of in-space propellant enables and enhances the maneuverability and extends the reach of all satellites and space vehicles. The water at EML1 could also serve as shielding for other prepositioned equipment, repair parts, and feedstock for advanced in-space manufacturing capabilities, or as radiation shielding for humans. Products and feedstock can be delivered to these nodes (whether launched from Earth or sourced from space) to test out capabilities and start building logistical staying power.

Tactical Benefits

The tactical benefits of a cislunar logistics system accrue to both commercial and military users. Rapid repositioning of a GEO satellite (as opposed to passively drifting near the GEO belt) enables commercial satellites to respond as the market or customer’s needs change. Active station keeping can increase the number of satellites within the geostationary belt—if satellites maintained a smaller station keeping box, they could potentially reduce the space between satellites, although other factors may limit this.

Repositioning a satellite has multiple national benefits across the diplomatic, informational, military and economic, “DIME,” spectrum. Maneuvering satellites can serve as an indication that the military is planning to conduct an exercise or an actual operation. It could also be purely for diplomatic signaling. It could also serve to potentially break or disrupt an adversary’s plan by disrupting their find, fix, track, target, engage, and assess processes—eventually even giving the satellite operator the “power of giving or refusing battle at will.”[45]

The Geostationary Space Situational Awareness Program (GSSAP) Satellite has a unique mission that requires it to frequently reposition itself in the GEO belt to inspect other satellites, typically without their cooperation. The GSSAP system is highly classified except for its existence. Some conjectures are possible, however, and some estimates may be made simply based on open source literature. Beyond mere station keeping, GSSAP must accomplish safe rendezvous and proximity operations (RPO), to include staging points, standoff, and mission abort capability, perhaps including forced motion circumnavigation and other propulsive events to ensure safe encounters. If the GSSAP launches with its lifetime supply of propellant, then mission planners are constrained in how they consume propellant, putting a high price on each kg of propellant. With an estimated program cost of $700 million,[46] the six satellites each cost roughly $115 million. With an estimated total mass of 700kg and ∆V budget of 1000 m/s a GSSAP with a chemical propulsion system perhaps has 140kg of propellant. Each kg of propellant is then worth $800,000 if the satellite cannot be refueled. However, if we can refuel GSSAP for $2,000/kg (the green bar above “GSO” in Figure 7) or $300,000 total, we could save >99% percent of the cost of launching a replacement GSSAP. A propellant provider could charge up to $400,000/kg and still result in the USSF achieving 50% savings on replacement capabilities.

A more active GSSAP provides more intelligence, faster. With on demand refueling, GSSAP can maneuver across the GEO belt as needed. This can dramatically reduce the cost of intelligence while at the same providing increased operational flexibility. Further, maneuvering geostationary satellites defensively becomes a feasible, affordable option.


Establishment of a water and propellant logistics architecture has enormous benefits to the nation across the civil, commercial, and military space sectors. Refueling with space sourced propellants dramatically lowers the cost of every space mission beyond LEO. It is enabling for developing a sustained presence on the Moon and eventual exploration of Mars. It is also enabling for the establishment of commercial space mining, processing and manufacturing businesses. Mining and processing lunar water ice for propellant and other uses is likely to be the first economically viable use of a space resource.

Perhaps most importantly in the near term, space sourced propellant logistics provides unprecedented sustainment and mobility capabilities for our national security infrastructure in GEO. A satellite that runs out of fuel will no longer be a “mobility kill.” It will no longer be necessary to decide between preserving propellant or preventing intelligence loss. The Space Force’s Core Competency of Space Mobility and Logistics is inclusive of movement from, to, and in space. USSF plans on taking advantage of recent advancements in on-orbit servicing; they should not overlook the benefit of sourcing propellants from space resources.

Major Alexander Jehle is a space operations officers in the U.S. Army’s Advanced Civil Scholar Program, and he is currently a doctoral candidate in the Space Resource Program at the Colorado School of Mines. Dr. George Sowers is a Professor of Practice in the Space Resources Program at the Colorado School of Mines. This paper represents solely the authors’ views and do not necessarily represent the official policy or position of any Department or Agency of the U.S. Government.


  1. PhD Candidate, Colorado School of Mines Space Resources Program, and Major, LG (FA40), U.S. Army.
  2. Professor of Practice, Colorado School of Mines Space Resources Program.
  3. Alfred Thayer Mahan, The Influence of Sea Power Upon History 1660-1783, 5th ed. (New York: Dover, 1987), 26.
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  5. Angel Abbud-Madrid, “Chapter 15 Space and Planetary Resources,” in Planetary Geology, ed. Angelo Pio Rossi, Stephan van Gasselt (Cham, Switzerland: Springer International Publishing, 2018), 378.
  6. Abbud-Madrid, “Planetary Resources” 375
  7. Paul D. Spudis, et al., “Evidence of water ice on the Moon: Results from anomalous polar craters from the LRO Mini-RF imaging radar” JGR:Planets 118 no. 10 (October 2013); Paul O. Hayne, et al., “Evidence for exposed water ice in the Moon’s south polar regions from Lunar Reconnaissance Orbiter ultraviolet albedo and temperature measurements,” Icarus, 255, (15 July 2015) 58–69,; Elizabeth S. Fisher, et al., “Evidence for surface water ice in the Lunar polar regions using reflectance measurements from the Lunar Orbiter Laser Altimeter and temperature measurements from the Diviner Lunar Radiometer Experiment,” Icarus 292 (August 2017), 74-85; A.B. Sanin, et al., “Hydrogen distribution in the lunar polar regions,” Icarus, 283 (February 2017), 20-30.; Shuai Li, et al., “Direct evidence of surface exposed water ice in the lunar polar regions,” PNAS (20 August 2018),
  8. U.S. Space Force, Space Capstone Publication Spacepower Doctrine for Space Forces (Washington, DC: U.S. Space Force, 2020), 33-40.
  9. Joint Chiefs of Staff, Joint Publication 4-0, Joint Logistics (Washington, DC: Joint Chiefs of Staff, 2019), ix.
  10. U.S. Space Force, Spacepower, 34.
  11. U.S. Space Force, Spacepower, 37.
  12. U.S. Army, Army Doctrine Publication 4-0 Sustainment (Washington, DC: Headquarters, Department of the Army, 2019), 1-3.
  13. Siqi Xu, Mohamed Bourham, and Afsaneh Rabiei. “A Novel Ultra-Light Structure for Radiation Shielding.” Materials & Design: Design of Nanomaterials and Nanostructures, 31, no. 4 (April 2010): 2140–46.; T. Sato, et al., “Evaluation of Dose Rate Reduction in a Spacecraft Compartment Due to Additional Water Shield,” Cosmic Research 49, (August 2011): 319–24.; M. Vuolo, et al., “Exploring Innovative Radiation Shielding Approaches in Space: A Material and Design Study for a Wearable Radiation Protection Spacesuit.” Life Sciences in Space Research 15 (November 2017): 69–78.; S. Kodaira, et al., “Verification of Shielding Effect by the Water-Filled Materials for Space Radiation in the International Space Station Using Passive Dosimeters.” Advances in Space Research 53, no. 1 (January 2014): 1–7.
  14. Spudis et al., “Ice on the Moon,” (2013); Hayne et al., “Exposed water ice,” (2015); Fisher et al., “Surface water ice,” (2017); Li et al., “Direct evidence,” (2018).
  15. Anthony Colaprete, et al., “Detection of Water in the LCROSS Ejects Plume,” Science 330 no 6003 (22 Oct 2010) 463-468,
  16. Li et al., “Direct evidence,” (2018).
  17. Sowers, G., Dreyer, C., “Ice Mining in Lunar Permanently Shadowed Regions,” New Space Vol. 7 #4. (16 Dec 2019),
  18. George Sowers et al., “Thermal Mining of Ices on Cold Solar System Bodies, NIAC Phase I report,”, 16.
  19. Ibid, 17.
  20. George Sowers, “The Business Case for Lunar Ice Mining,” New Space (24 Feb 2021),
  21. Ivett A. Leyva, “18 Spacecraft Subsystems I—Propulsion,” in Space Mission Engineering: The New SMAD, Ed. James R. Wertz, David F. Everett, and Jeffery J. Puschell, (Torrance, CA: Microcosm Press and Springer, 2018), 531.
  22. Calculations by author based on the dry and gross weight of the Saturn V stages and SLS Block 1 stages. Data from: “Space Launch System,” Wikipedia, April 9, 2021,; and “Saturn V,” Wikipedia, April 4, 2021,
  23. Sowers, “Business Case,” (2021).
  24. Ibid.
  25. Ibid.
  26. Sowers, G. (2016) “Transportation Enabling a Robust Cislunar Space Economy.” Presentation at the Space Resource Roundtable. Golden, Colorado.
  27. Sowers, “Business Case,” (2021).
  28. Sowers, G., “A cislunar transportation system fueled by lunar resources,” Space Policy, 37 (August 2016) 103-109,
  29. Bernard Kutter, et al., “A Practical, Affordable Cryogenic Propellant Depot Based on ULA’s Flight Experience,” AIAA 2008-7644. (9-11 September 2008),’s-flight-experience.pdf
  30. Sowers et al., “Thermal Mining,” (2020); Sowers, “Business Case,” (2021).
  31. “Chapter 8 Exploring New Frontiers in Space Policy and Property Rights,” in Economic Report of the President: Together with the Annual Report of the Council of Economic Advisers (Washington, DC: White House, 2021), 226-27,
  32. Bin Cheng, “Article VI of the 1967 Space Treaty Revisited: ‘International Responsibility,’ ‘National Activities,’ and the ‘Appropriate State.’”. Journal of Space Law, 26 No. 1 (1998) 23,
  33. Olavo de O. Bittencourt Neto, et al., Building Blocks for the Development of an International Framework for the Governance of Space Resource Activities: A Commentary, (The Hague: Eleven Publishing, 2020).
  34. Daniel Immerwahr. How to Hide an Empire: A History of the Greater United States. (New York: Farrar, Straus and Giroux, 2019).
  35. Mahan, “Sea Power,” 27.
  36. Gordon Roesler, “A Robotic Space Station for the 2020s,” ASCEND 2020, ASCEND, American Institute of Aeronautics and Astronautics, 2020,;Gordon Roesler, “The Robotic Space Station,” The Space Review, (August 6, 2018),
  37. Tracie Prater et al., “Nasa’s In-Space Manufacturing Project: Toward a Multimaterial Fabrication Laboratory for the International Space Station.” AIAA Space and Astronautics Forum and Exposition (12-14 Sep 2017),
  38. Ben Bouffard, “Naval Additive Manufacturing,” (December 17, 2018),
  39. John J. Klein, “Chapter 6 Celestial lines of communication,” in Space Warfare: Strategy, Principles and Policy (London: Routledge, 2006), 51.
  40. Missile Defense Advocacy Alliance. “Hypersonic and Ballistic Tracking Space Sensor (HBTSS)” (November 27, 2020),
  41. Department of Defense. Defense Space Strategy Summary. Washington, DC: Department of Defense, 2020.
  42. U.S. Spaceforce, “Spacepower,” 30.
  43. United Nations Office for Outer Space Affairs, Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, Article 1, (1967),
  44. Brad Townsend, “Strategic Choice and the Orbital Security Dilemma,” Strategic Studies Quarterly (Spring 2020), 79
  45. Mahan, “Sea Power,” 5-6.
  46. Mike Gruss, “Air Force Sent GSSAP Satellite to Check on Stalled MUOS-5,” Space News, (August 18, 2016),


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