Cislunar Mission Concepts for the Department of Defense

Abstract

The United States has mobilized its civil and commercial space sectors to lead a multinational effort to establish and maintain a permanent human presence on and around the Moon. China is also pursuing its own competing objectives on the lunar surface, sparking fears that it may replicate its practice of seizing international territory for resource exploit. This fear is compounded because space operations are already hazardous due in part to natural debris, radiation, and near-vacuum pressures. The potential safety and security threats posed by China, Russia, or other spacefaring nations amplify the strategic implications of those hazards. In the face of these potential threats, the U.S. Space Force, working in conjunction with U.S. Space Command, other joint commands, government peers, space industry, and like-minded foreign partners, should apply the necessary technical skills and capabilities that would ensure operational success for the National Aeronautics and Space Administration and its mission partners in a contested, degraded, and operationally limited environment. This essay describes four Space Force lunar and cislunar mission concepts that would provide command, control, and communications; positioning, navigation, and timing; space domain awareness; and lunar surface awareness mission functions to civil, national, commercial, and international partners throughout the Earth-Moon system. If actualized, these mission concepts would support peaceful operations on and around the Moon in a matter analogous to current military-supported operations conducted in Antarctica and in international waters, thereby ensuring prosperity and stability throughout the Earth-Moon system in a manner consistent with the values of the United States and like-minded foreign allies and partners.

The new space race, also known as the second space race, is about establishing and maintaining economic benefits derived from space as opposed to the first space race during the Cold War, the goals of which were to orbit the Earth with the first spacecraft, place the first human being in space, and to safely bring the first humans to and from the Moon.[i] This new space race ushers in an era of lunar exploration, human expansion, and commercialization. Driven by promises of scientific, technological, and economic advancement, the United States mobilized the National Aeronautics and Space Administration (NASA) to establish and maintain a permanent human presence on and around the Moon.[ii] China also set its ambitions on the Moon, where it seeks to exploit lunar resources and pursue other competing scientific, technological, and economic objectives to further its own national objectives. 

As a spacefaring nation, sustained U.S. access to the lunar surface will be vital for prosperity and requires a space-based infrastructure that does not yet exist. This space-based infrastructure will service civil, commercial, and national security space sectors with the means to pursue mission and support operations throughout the Earth-Moon system and beyond with an ever-decreasing dependency upon terrestrial-based services.[iii] Examples of space-based infrastructure critical for extended or enhanced space operations include nodes for on-orbit servicing, propellant storage, in-space fabrication, in-situ resource utilization (ISRU), communications and navigation, space environment monitoring, space traffic management, inter-orbital transportation, and energy collection and distribution.[iv] NASA, its mission partners, and the commercial sector will depend upon an infrastructure that is persistent, accessible, and reliable in order to safely conduct extended-duration space operations on and around the Moon.

Upon deployment, this infrastructure needs to be defended should competing national objectives lead to conflict in the space domain. Established as the 11th combatant command, U.S. Space Command (USSPACECOM) is responsible for deterring aggression and conflict 100 kilometers above sea level and beyond as well as for defending American and allied freedom of action to, from, and through the space domain.[v]The U.S. Space Force (USSF) is the primary feeder service for USSPACECOM. The USSF Guardians would likely be called upon during conflict to support and defend the mission capabilities of NASA, its mission partners, and the commercial sector as they pursue objectives of scientific, technological, and economic value.

This article introduces four USSF lunar and cislunar mission concepts that would provide command, control, and communications (C3); positioning, navigation, and timing (PNT); space domain awareness (SDA); and lunar surface awareness (LSA) capabilities and services to NASA, its mission partners, and others operating on and around the Moon. The intent behind the design of these mission concepts is to establish space-based infrastructure that would support peaceful lunar and cislunar operations in a manner parallel to how the Department of Defense (DoD) employs military assets to support U.S. and multinational operations conducted in other international domains such as Antarctica and international waters. Other rationale for and details regarding these concepts will span a range of topics, including current events, space vehicle design, orbital mechanics, and military space operations methodology. This essay also proposes bilateral agreements between the DoD, NASA, and allies regarding roles, interoperability, and conduct in order to preserve and promote peace, prosperity, cooperation, safety, security, and stability throughout the space domain.

NASA Returns to the Moon

Pending any potential changes, Space Policy Directive-1 (SPD-1) directs NASA to lead a space exploration program with commercial and international partners to return to the Moon for long-term exploration and use.[vi] NASA’s response is the Artemis program, a multi-faceted effort aimed at fulfilling the objectives defined in SPD-1.[vii]As one of the first steps toward fulfilling SPD-1, NASA’s internally developed Orion space vehicle and Space Launch System (SLS) will soon lift off for the first time to field test critical components necessary for lunar surface access.[viii] The initial goal was to land the first American woman and next American man on the lunar south pole by 2024 and establish a sustained human lunar and cislunar presence by 2028, however, these dates may shift back by a year or so due to delays.[ix] 

The United States has committed to collaborating with government, commercial, and international partners on projects to develop space-based infrastructure to maintain a long-term human presence in cislunar space and on the lunar surface.[x] One such project is the Gateway, an Artemis program crewed space vehicle that will serve as a critical node connecting cislunar space to the lunar surface. NASA and its mission partners will assemble the Gateway in cislunar space over the next few years.[xi] The Gateway will provide habitation, logistics, communications, and experimentation support necessary for extended multinational crewed lunar operations.[xii] 

Several nations have signed the U.S.-led Artemis Accords, a set of guiding principles for bilateral, government-to-government agreements regarding multinational cooperation on the Moon, with the intent of participating with NASA under the Artemis program.[xiii] NASA’s Commercial Lunar Payload Services (CLPS) and Human Landing System (HLS) programs seek to contract companies to deliver experiments, technology demonstrations, operational equipment, and crewed landers to the lunar surface.[xiv] These and other initial lunar programs represent the beginnings of U.S.-led efforts to transform the Moon from a barren world into a region of strategic and economic importance.[xv]

Supporting American Spacepower

NASA and the DoD have a history of collaboration, resulting in dozens of space projects which have advanced U.S. spacepower. In September 2020, NASA and the USSF entered into a new Memorandum of Understanding (MOU) affirming a mutual interest in expanding upon the long-standing partnership between the military and civil space sectors. From this MOU, both entities affirmed to collaborate in eleven cooperative areas, such as establishing interoperable communications networks and supporting search, rescue, and recovery operations for human spaceflight.[xvi] More can and should be accomplished beyond the MOU’s limited defined cooperative areas to support certain aspects of NASA’s mission objectives on and around the Moon.

As an equal operator in the space domain, the USSF should leverage its role as the provider of organizing, training, and equipping military capabilities to look out and across the Earth-Moon system to provide direct lunar and cislunar mission support to NASA and its mission partners and to establish and maintain critical space-based infrastructure.[xvii]These efforts should include the development of new strategy and doctrine pertinent to USSF operations in cislunar space as a follow-on to the space capstone publication Spacepower: Doctrine for Space Forces, which briefly discusses cislunar space.[xviii]The 2020 NASA-USSF MOU along with the space capstone publication could serve as starting points for defining the employment of military spacepower around the Moon to support U.S. and allied objectives. 

The peaceful and nonaggressive application of military spacepower on and around the Moon is consistent with Article IV of the Outer Space Treaty: “the use of military personnel for scientific research or any other peaceful purposes shall not be prohibited.”[xix] However, Article IV specifically forbids “[t]he establishment of military bases, installations and fortifications, the testing of any types of weapons and the conduct of military maneuvers on celestial bodies.”[xx] There is much that the United States could do operationally around the Moon, and perhaps to a limited extent on the lunar surface, in furtherance of peaceful purposes. For example, instead of a military base, the United States can have a civilian-led lunar surface facility with military personnel detailed and residing within it. The USSF will have more latitude to operate in the regions above the lunar surface in orbit and across cislunar space.

The cislunar mission concepts proposed in this article would support peaceful operations around the Moon in a matter akin to current military-supported operations led by civilian agencies in Antarctica and in international waters.[xxi] In fact, the text of the Outer Space Treaty, signed by the United States in 1967, drew heavily from the language of the Antarctic Treaty, signed by the United States in 1959.[xxii] Since then, the DoD has provided several support functions to Antarctic research stations operated by the National Science Foundation (NSF). Terrestrial-based support is mainly provided by Joint Task Force-Support Forces Antarctica (JTF-SFA) via Operation Deep Freeze (ODF) in the form of logistical and meteorological services.[xxiii] Space-based support is mainly provided by joint elements under USSPACECOM in the form of PNT and satellite communications services.[xxiv] 

Legacy missions and units now organized under the USSF have supported terrestrial and low-Earth orbit (LEO) civilian operations for decades. Expanding existing USSF infrastructure and technical expertise to provide mission support functions throughout cislunar space would prevent NASA from “reinventing the wheel” by duplicating space-based infrastructure, such as communications and PNT services. Rather, the DoD providing space-based infrastructure frees NASA to concentrate its resources and efforts purely on science operations. As a member of the U.S. Intelligence Community (IC), the USSF should develop and deploy cislunar SDA capabilities to support intelligence-driven operations and to ensure safety and security for U.S.-led exploration and utilization of the Moon. In due time, these capabilities should also support the eventual missions to nearby asteroids, Mars, and beyond. 

Strategic Competition Among Great Powers

In 2016, the deputy chief of the Chinese military’s Equipment Development Department declared that cislunar space will be “strategically important for the great rejuvenation of the Chinese nation.”[xxv] The Chinese Communist Party (CCP) supports the desire of the Chinese military to create an economic zone on and around the Moon.[xxvi]Enabled by an emergent military-civil fusion (MCF) development strategy that fuses economic and social development strategies with security strategies, China seeks to establish a foothold on the lunar surface to secure resources for future exploitation.[xxvii] 

China’s lunar ambitions include seeking international partners to collaborate on a lunar research station near the lunar south pole as a Chinese-led alternative to NASA’s Artemis program.[xxviii]Thus far, only Russia has formally agreed to join the Chinese-led effort.[xxix]  However, current events in the South China Sea should cause potential international partners to approach the CCP’s space ambitions with caution. China has claimed sovereignty over a large region of the South China Sea, an area estimated to contain vast amounts of untapped oil and natural gas.[xxx] 

China maintains that the South China Sea is within its exclusive economic zone (EEZ) and has converted several islands in the region into platforms to support weapons systems which actively threaten any who might enter these international waters despite the Permanent Court of Arbitration’s 2016 ruling that China’s excessive maritime claims were “without lawful effect.”[xxxi] This ongoing situation demonstrates the lengths Chinese leadership and operators will go to achieve competing economic objectives and should serve as a warning for how China may conduct itself in cislunar space.

NASA and other parties have confirmed that the lunar surface contains useful amounts of water-ice, helium-3, titanium, silicon, aluminum, and other natural resources which have ISRU applications in power generation, life support, propulsion, and fabrication.[xxxii] Access to these valuable resources will be vital for the establishment of a new multi-trillion-dollar space-based economy.[xxxiii] If China were to duplicate aggressive and unjust behavior exhibited in the South China Sea on the Moon, then freedom of access to these vital resources and freedom of action on the lunar surface could be threatened for other spacefaring nations. This potential scenario would violate the Outer Space Treaty and would stand in direct opposition to the values of United States and its allies, creating tension that could escalate to armed conflict within the space domain.

Defending Against Threats and Hazards

China and other relevant-actors may one day deploy counterspace capabilities throughout the Earth-Moon system as the requisite technologies become increasingly accessible. These counterspace capabilities, as depicted in Figure 1 above, may allow nations or other parties to deny, disrupt, degrade, deceive, or destroy mission enabling services and capabilities provided by components of U.S. and allied spacepower with varying degrees of reversibility and deniability.[xxxiv] With deployed counterspace capabilities, such as anti-satellite (ASAT) missiles and directed energy weapons platforms, relevant-actors could resort to varying levels of aggression to achieve competing space objectives or to counter the space objectives of the United States and its allies with little-to-no warning.[xxxv] 

Figure 1. The Counterspace Continuum. Reproduced from the DoD.[xxxvi] 

The threats depicted in Figure 1 (above) could be deployed on or around the Moon, thus threatening the mission capabilities and objectives of NASA and its mission partners. Military space operations, led by USSPACECOM and alongside America’s foreign allies, must be integrated into national, civil, commercial, and multinational lunar and cislunar operations. By working closely with civilian counterparts, the DoD will effectively employ warfighting skills and capabilities to provide security and defense from all levels of aggression anywhere on or around the Moon. 

For example, the DoD should partner with the Department of State (DoS) to develop political advisor (POLAD) positions for cislunar space that would oversee interagency communication between the DoD and DoS and provide foreign policy expertise to senior decision makers serving at USSPACECOM.[xxxvii] Establishing POLAD positions for cislunar space would streamline coordination efforts between pertinent DoD elements and the DoS to ensure that U.S. partnerships and alliances are strengthened and would support communication efforts with other nations operating in cislunar space, such as China and Russia.[xxxviii] 

All USSF lunar and cislunar space vehicles should incorporate standard design features intended to mitigate or negate as many of the counterspace capabilities depicted in Figure 1 as possible.[xxxix] By incorporating counter-counterspace capabilities into all USSF lunar and cislunar space vehicles and by developing tactics, techniques, and procedures (TTPs) for the effective employment of those defensive design features, the United States and its allies will further influence relevant-actor actions and inactions to preserve freedom of action and freedom of access throughout the Earth-Moon system. The United States does have the innate right and the moral obligation to defend itself, its allies and partners, and others from acts of aggression even as it avidly tries to avoid conflict in space. 

The DoD should also develop and support capabilities necessary for U.S.-led emergency and search and rescue (SAR) operations throughout the Earth-Moon system.[xl] Space operations are inherently hazardous and with increased human lunar activity comes an increased probability that emergencies will occur on or near the Moon.[xli] Parallel to SAR services and capabilities provided by the U.S. Coast Guard and other support entities to those operating in Antarctica and on the high seas, the DoD, NASA, and foreign partners should collaborate to develop services and capabilities to assist astronauts in distress anywhere in cislunar space or on the lunar surface.[xlii] 

Concepts for USSF Lunar and Cislunar Missions

The United States and its allies depend on the full spectrum of national spacepower. To fulfill its role, the USSF will need to deploy lunar and cislunar space vehicles specialized to perform C3, PNT, SDA, and LSA operations and mission support functions and to establish and maintain a greater multi-provider, multi-user mission enabling space-based infrastructure. Four USSF lunar and cislunar mission concepts would perform these critical mission functions: one C3 mission, one PNT mission, and two intelligence, surveillance, and reconnaissance (ISR) missions conducting SDA and LSA operations. These missions will support NASA and its mission partners, and they will also operate synergistically to support one another. 

Cislunar C3 Relay System Concepts

Lunar operations would be impossible without C3 connectivity to mission controllers and other support entities on Earth. For this reason, NASA is developing a preliminary communications and PNT relay architecture named LunaNet, which is intended to provide connectivity between users operating on the lunar surface and in cislunar space to terrestrial stations.[xliii] This NASA-led program will be flexible and extensible with the intent of incorporating many mission partner systems and nodes into the greater LunaNet architecture over time.[xliv] The DoD should collaborate with NASA to integrate defense C3 services and capabilities into the LunaNet architecture via a USSF-owned cislunar C3 relay system in order to provide secure, survivable, and jam-resistant communications links to users operating throughout the Earth-Moon system. A notional cislunar C3 relay system is depicted in Figure 2 below. 

See Figure 2. Notional Cislunar C3 Relay System. (above)

Because Lagrange points are stationary within a rotating frame, as the Moon moves through its 27-day orbit, Earth-Moon Lagrange point 2 (EML2) remains fixed beyond the Moon at a mean distance of 61,500 kilometers.[xlv] This affords C3 relays stationed in halo orbits centered on EML2 with continuous visibility of the lunar far-side and intermittent visibility of either lunar pole, making EML2 strategically important. The halo orbits depicted in Figure 2 would have approximate periods of one to two weeks, which would allow a single C3 relay to provide coverage to either lunar pole for a few days at a time before dropping below the local horizon.[xlvi] By employing multiple evenly spaced C3 relays to EML2, both lunar poles could receive continuous coverage. As seen in Figure 2, a full system of cross-linked C3 relays in halo orbits around both EML1 and EML2 could provide continuous C3 connectivity to the entire lunar surface and to the full volume of lunar orbit. 

The USSF cislunar C3 relay system would likely take advantage of existing technologies and capabilities by using the same or similar frequencies currently used for wideband commercial and military satellite communications (MILSATCOM) services, which offer robust signals with high data rates to thousands of users on Earth.[xlvii] Cislunar C3 payloads would likely provide these signals through a combination of phased-array antennas, which can steer and shape multiple beams, and gimbaled-dish antennas, which generally require less electrical power to operate. Where possible, cislunar C3 payloads should utilize defensive techniques such as frequency-hopping and adaptive beamforming to mitigate unintended signal detection and interception, and to nullify the effects of electromagnetic interference (EMI).[xlviii] 

The DoD should work with NASA and other approved mission partners to develop requirements and standards for all elements necessary to integrate DoD-provided functions into LunaNet and to co-develop a common space-based communications network for the Artemis program and other future deep space mission programs. These efforts could include the development of common user terminals and interfaces, interoperable architecture, standardized waveform properties, and shared encryption methods. USSPACECOM would manage DoD cislunar C3 operations, which could include oversight of user scheduling and service deconfliction, coordination of over-the-air rekeying, and implementation of responses to EMI incidents. 

In addition to supporting primary high throughput cislunar C3 payloads for routine lunar and cislunar space operations, the relay space vehicles should also support a secondary communications payload reserved for use during emergencies such as SAR operations and vehicle anomaly and recovery operations that could involve potential loss of life or mission capability. Taken to the fullest potential, all space vehicles belonging to the DoD, NASA, and interested mission partners would support secondary emergency and SAR communications payloads to provide maximum coverage to operators throughout the Earth-Moon system. USSPACECOM would oversee this communications network and should ensure its use for the entire international community to promote safety and encourage the responsible use of space. 

Lunar PNT System Concepts

Spacefaring nations will benefit from PNT services expanded for use throughout the Earth-Moon system as lunar and cislunar operations become routine. For example, PNT signals provided by the Global Positioning System (GPS) can support space operations in LEO, which enables operational capabilities such as precision orbit determination, attitude correction, enhanced payload pointing, time synchronization, formation flying, and launch vehicle tracking.[xlix] However, because GPS payloads are strictly Earth-pointing and their side lobes are not as reliable for use as main lobes, GPS cannot fully support lunar or cislunar users. LunaNet is intended to provide relayed GPS PNT signals to users operating near the Moon, albeit with limited levels of accuracy or resilience to EMI.[l] Although LunaNet would provide users with initial partial PNT services, the USSF should deploy a dedicated lunar PNT system (LPS) to provide lunar and cislunar users with highly accurate and robust PNT signals. Figure 3 above depicts a notional LPS constellation. 

See Figure 3. Notional LPS Constellation. (above)

Referencing Figure 3, a full LPS constellation would likely comprise several space vehicles stationed across lunar orbit and cislunar space. Analogous to the cislunar C3 relay system, LPS vehicles operating in halo orbits around EML1 and EML2 would have continuous visibility over large portions of the lunar surface, lunar orbit, and cislunar space. However, users operating on the lunar surface would have limited-to-no visibility on many of these LPS vehicles due to the consequences of orbital geometry combined with the lunar horizon and local topography, which could potentially lead to degradations to user selenolocation, pointing, navigation, and timing functions. Stationing additional LPS vehicles in elliptical orbits in low lunar orbit (LLO) as seen in Figure 3 could provide additional coverage to the lunar surface, particularly for the lunar poles, which could in turn provide users operating there with visibility on at least four LPS vehicles at any given time with suitable angular separation.[li] 

Users moving through cislunar space would have the advantage of near-continuous visibility of several LPS vehicles compared to users operating on or near the lunar surface. However, these users could be positioned at any angle relative to each LPS vehicle. This would require LPS payloads to be capable of radiating PNT signals in any direction, not just nadir with respect to the Moon. Because omnidirectional antennas suffer from poor range, engineers should design PNT payloads to incorporate multiple steerable directional transmitters mounted in opposing directions to provide maximum angular coverage.[lii] 

The USSF should develop future LPS PNT signals to be common with modern GPS PNT signals in order to optimize and standardize PNT operations for all users throughout the Earth-Moon system. With LPS and GPS emitting the same L1C, L2C, and L5 signals using a common civil navigation (CNAV) message format, users operating throughout the Earth-Moon system would be able to utilize the main lobes and side lobes of both PNT systems simultaneously.[liii] LPS should also transmit a version of M-code signals, which would secure high-value users against EMI.[liv]As with modern GPS payloads, LPS payloads could transmit these signals via dedicated high-gain gimbaled-dish antennas to provide specific users with jam-resistant PNT signals.[lv] Without robust PNT signals, vital mission operation functions such as secure communications, accurate payload pointing, or autonomous precision landing could be jeopardized by accidental interference or hostile electronic attacks.

LPS vehicles could not use their own signals to determine their present location and, because natural trajectories in cislunar space are generally chaotic and unstable, future trajectories may rapidly diverge from their initially projected paths by a substantial degree, both of which will require the USSF to rely on vehicle tracking and signal monitoring services provided by automated remote tracking and monitoring (ARTM) stations positioned across the lunar surface.[lvi] Stations operating on the lunar surface would be physically closer to the LPS constellation than Earth-based stations and would remain fixed with respect to a lunar coordinate frame.[lvii] The DoD should partner with NASA to operate the ARTM stations to ensure that U.S.-led space operations remain consistent with Article IV of the Outer Space Treaty. These NASA-operated stations could be co-located with and powered by other NASA-owned lunar surface assets such as remotely operated observatories and manned research facilities. 

Equipped with laser rangefinders and signal detectors, ARTM stations would collect orbit and signal data from the LPS constellation and feed that data back to the Master Control Station for error correction and performance optimization. Each ARTM station would ideally be placed in view of multiple LPS vehicles to optimize tracking and would likely operate under moderate-to-heavy duty cycles to maintain ephemeride accuracy and precision in response to the chaotic and unstable trajectories followed by each LPS vehicle. All LPS vehicles would be equipped with a retro-reflector array to interface with the laser rangefinders used by the ARTM stations to improve their space vehicle tracking capabilities, which in turn would increase the quality of the PNT signals provided by the LPS constellation. 

Cislunar Space Domain Awareness System Concepts

SDA is defined as the identification, characterization, and understanding of all factors associated with the space domain and requires the employment of a variety of sensors, such as those provided by ISR space vehicles.[lviii] As the 18thmember of the IC, the USSF should operate cislunar SDA sensors to provide policymakers, warfighters, NASA, and other IC partners with access to real-time awareness regarding all natural and man-made aspects of the space domain, especially in regions leading up to or located around the Moon. Current SDA sensors are not designed to overcome the extreme distances involved in observing space vehicles operating beyond Earth orbit, which would leave cislunar space and lunar orbit largely overlooked.

This gap in SDA would leave space vehicles blind to potential hypervelocity collisions with untracked space debris and could allow relevant-actors to threaten U.S. and allied space operations with impunity. To close this gap, the USSF should deploy ISR space vehicles equipped with proper SDA sensors to operating locations in cislunar space in order to detect and characterize natural or man-made transient and resident space objects throughout the Earth-Moon system. A notional cislunar SDA system is depicted in Figure 4 above.

See Figure 4. Notional Cislunar SDA System. (above)

Cislunar space spans hundreds of thousands of kilometers, and objects moving through cislunar space are difficult to detect and track because they are relatively faint and slow compared to objects in Earth orbit and because they are subject to optical exclusion zones that may be long in duration and complex in nature.[lix] Overcoming these challenges will require the deployment of new SDA payloads incorporating technologies and techniques optimized for distant detection and characterization of space objects moving to, from, and around the Moon.[lx] This will ensure that new objects are identified and cataloged and that previous identified objects are re-found as they move through cislunar space and around the Moon. 

Once detected, analysts would scrutinize data collected from these SDA sensors to characterize each object. With knowledge of an object’s current trajectory, its future location could then be predicted with a certain degree of accuracy, and should the object’s trajectory change from a maneuver, analysts could use knowledge of previous trajectories and activities to infer the object’s new location.[lxi] Over time, consecutive observations will yield intelligence necessary for analysts to determine mission related details of all cislunar space vehicles, including their activities, mission objectives, system capabilities, patterns-of-life, and the status of their consumables and expendables.[lxii] This information would allow the DoD and IC to identify hazards, threats, and violations to international agreements and treaties so that mitigation actions may be taken and violators or aggressors may be held accountable for their actions.

SDA payloads should employ combinations of sophisticated remote sensors such as narrow-angle high-definition imagers, wide-angle imagers, radar systems, and passive radio frequency detectors to detect as many kinds of signatures as possible. Imagers, which are capable of precision distant viewing and are also used for broad area coverage, collect data with relatively low energy requirements. However, many imagers rely on ideal lighting conditions for object illumination, limiting their use according to the consequences of orbital geometry. By comparison, active sensors such as radar systems operate independently of lighting conditions, but at the cost of higher electrical power requirements. Passive radio frequency detectors, which are used for collecting signals intelligence (SIGINT), also operate independently of lighting conditions, but must be precisely positioned within the beam of interest. If possible, SDA space vehicles should host mission partner ISR payloads to further integrate international allies and partners into U.S.-led space operations for increased cooperation, expanded interoperability, improved space traffic management, and streamlined data sharing. 

The gravitational topography and orbital geometry of cislunar space and lunar orbit combined with the extreme distances separating regions within the Earth-Moon system will require SDA sensors to be positioned in specialized operational orbits. For example, the Cislunar Highway Patrol System (CHPS) demonstration mission, orchestrated by Air Force Research Labs (AFRL), may utilize a variety of halo family orbits about EML1 and EML2 to assess its ability to observe objects near the Moon thanks to the chaotic and unstable nature of the dynamics of the Earth-Moon system, which can best be described according to the three-body problem (3BP).[lxiii]Another orbit that may be advantageous for SDA sensors is known as a distant retrograde orbit (DRO). Because DROs are repeating natural orbits, space vehicles operating in a lunar DRO as depicted in Figure 4 would steadily drift around the Moon approximately every two weeks.[lxiv] Such an orbit would grant a constellation of SDA sensors full views of the orbital regions around the Moon, EML1, and EML2 as well as the approach vectors from Earth so that all space vehicles and space debris located in those regions may be continuously tracked.[lxv] 

Another mission area that cislunar SDA sensors should support is planetary defense because the technologies and techniques necessary to detect active space vehicles and space debris are similar to those necessary to detect nearby asteroids and comets classified as Near-Earth Objects (NEOs). In 2005, Congress mandated that NASA shall discover and characterize 90 percent of all NEOs 140 meters in size and larger by the end of 2020.[lxvi] However, a lack of adequate funding combined with the technical challenges associated with surveying objects scattered across the solar system resulted in NASA’s NEO observations program falling short of this goal.[lxvii] Because surveys for planetary defense and SDA overlap similar portions of the sky, NASA and the DoD should share sensor data and, when possible, the DoD should utilize cislunar SDA sensors to perform planetary defense observations. Cislunar SDA platforms could also host planetary defense sensors as a secondary payload as another way to support NASA.

Lunar Surface Awareness System Concepts

Spacefaring nations and organizations will eventually send crewed and uncrewed missions the lunar south pole to pursue competing scientific and economic objectives. Decision makers, mission planners, warfighters, and the IC must have awareness of all factors associated with the lunar surface to secure surface operations for NASA and its partners against hazards and threats.[lxviii] Analogous to the cislunar SDA system, the USSF should deploy ISR space vehicles to lunar orbit equipped with LSA sensors to collect intelligence, support NASA’s science objectives, and perform other remote sensing operations as applicable. A notional LSA system is depicted in Figure 5, above.

See Figure 5. Notional Lunar Surface Awareness System. (above)

LSA payloads should comprise combinations of imagers, radar systems, and radio frequency detectors to sense all aspects of the lunar surface. Because these sensors will likely operate near areas and objects of interest, sensitive imaging technologies and techniques that are generally less suitable for viewing distant objects will be viable for use to support a variety of applications. Multispectral imagery, which collects data across a few specific bands of the electromagnetic spectrum, could be used to produce separate large-area thermal infrared, visible-light, and ultraviolet maps of the lunar surface.[lxix] Hyperspectral imagery, which collects data across hundreds of narrow contiguous spectral bands, could be used to detect subtle changes to surface features, facilities, and equipment in order to build a better understanding of surface activity.[lxx] LSA payloads should also employ lidar systems, which would precisely measure ranges using pulsed lasers to produce highly detailed topographic maps for navigation and landing zone selection.[lxxi] The effectiveness of LSA sensors will be coupled with their operating orbit. 

The gravitational topography of lunar orbit is different than that of Earth orbit, presenting challenging constraints, but also opportunities. The primary constraints are caused by the Moon’s highly uneven mass concentrations (mascons), which limit the number of stable inclinations, and the Earth’s third body effects, which severely perturb space vehicles operating at altitudes above 500 kilometers.[lxxii] Since the Moon lacks an atmosphere, this creates an opportunity for LSA sensors to operate just above the lunar surface. NASA’s Lunar Reconnaissance Orbiter (LRO), for example, operated at an altitude of 25 kilometers, a distance which allowed its primary sensor to resolve the tracks from the Lunar Roving Vehicle (LRV) used for Apollo 15 with relatively high levels of detail.[lxxiii] The DoD should deploy a system of LSA space vehicles to specialized orbits to take advantage of the characteristics of the lunar gravitational topography. From the configuration depicted above in Figure 5, LSA sensors could periodically observe facilities located at the lunar south pole at varying operating altitudes and viewing angles.

LSA sensors will offer the DoD, IC, NASA, and other mission partners with advantageous views of the lunar surface, particularly with regard to the lunar far-side and the interiors of craters. As a result, the LSA system would be able to collect different forms of intelligence from regions of the lunar surface currently inaccessible to other sensors.[lxxiv]These forms of intelligence will provide analysts with the information necessary to monitor lunar surface activity and to assess the capabilities and mission objectives of all surface equipment, vehicles, and facilities. 

As with the proposed cislunar SDA system, the DoD should utilize LSA sensors to support science objectives wherever possible. Over the course of their operational lifetimes, LSA sensors will overfly many regions of the lunar surface. Products from selenospatial intelligence (SELENOINT) and other forms of intelligence should be routinely declassified and released by the DoD to provide NASA and other mission partners with the means to analyze and exploit imagery and information pertaining to the lunar surface. This would allow for the creation of comprehensive surface maps detailing selenological features, valuable resources, the interiors of permanently shadowed craters, and other features of interest and would also be used to ensure that the Apollo landing sites are not disturbed by surface activity so that these historical sites may be preserved for posterity. Timely access to imagery of the lunar surface would also provide SAR teams with critical information necessary to rescue astronauts in distress on the lunar surface. 

Conclusion

Access to the Moon and lunar resources will be vital for spacefaring nations. Ideally, all nations would collaborate in space in the pursuit of peace and mutual prosperity. However, history has time and again shown that when great powers have competing visions and objectives, conflict can arise.[lxxv] With several imminent crewed and uncrewed missions to the lunar surface belonging to United States, Artemis partners, China, Russia, other nations, and commercial operators, the United States should deploy space vehicles beyond Earth’s orbit to establish, maintain, support, protect, and defend vital space-based infrastructure critical for the mission objectives of NASA and its mission partners. The technical skills and operational capabilities provided by the DoD will prove vital for the success of the United States and international allies and partners during times of peace and conflict. 

Therefore, the United States ought to develop national-level policy directing the USSF to organize, train, and equip space forces to support and defend the mission capabilities of NASA and its mission partners on and around the Moon. Demonstration missions such as CHPS and the Defense Deep Space Sentinel (D2S2) program represent the necessary first steps toward the realization of the mission concepts introduced in this article.[lxxvi]However, in the near future the DoD should fund more demonstration missions validating key technologies and techniques necessary to perform space operations throughout cislunar space and across the lunar surface. The new space race has already begun, presenting with it an opportunity for the United States and allies to establish a rules-based international order throughout the Earth-Moon system that promotes peace, stability, and prosperity. 

Captain Tyler D. Bates, USSF, is serving as a Flight Commander in the 3rd Space Experimentation Squadron. This paper represents solely the author’s views and do not necessarily represent the official policy or position of any Department or Agency of the U.S. Government. If you have a different perspective, we’d love to hear from you.

NOTES

[1] Josh Carlson, “Reflecting Core American Values in the Competition for the Final Economic Frontier,” The Space Review, February 2021, https://www.thespacereview.com/article/4124/1 (accessed April 2, 2021).

[2] Specific goals for NASA returning to the Moon have shifted over the years with each new Administration. Though NASA’s Artemis program is publicly supported by the White House and has a degree bi-partisan support in Congress, it is possible that strategic objectives and relevant timelines proposed by the previous Administration may shift or change in accordance with the priorities of the current Administration and the actions of the current Congress. For more information, reference Jeff Foust, “White House Endorses Artemis program,” SpaceNews.com, February 2021, https://spacenews.com/white-house-endorses-artemis-program/ (accessed March 13, 2021). ­

[3] James A. Vedda, “Cislunar Development: What to Build–And Why,” The Aerospace Corporation, April 2018, 3, https://aerospace.org/sites/default/files/2018-05/CislunarDevelopment.pdf (accessed April 2, 2021).

[4] Ibid, 3-8.

[5] General John W. Raymond said “This combatant command has an area of responsibility that’s 100 kilometers above mean sea level, globally, and higher,” C. Todd Lopez, “Spacecom build for Today’s Strategic Environment,” U.S. Department of Defense, September 2019, https://www.defense.gov/Explore/News/Article/Article/1973953/spacecom-built-for-todays-strategic-environment/ (accessed April 2, 2021) and USSPACECOM is a regionally focused COCOM akin to the other terrestrial-based commands, “Defense Primer: Commanding U.S. Military Operations,” Congressional Research Service, February 2020, https://crsreports.congress.gov/product/pdf/IF/IF10542/8 (accessed April 2, 2021).

[6] Though SPD-1 is still valid and current as of the date of this publication, all SPDs put forth by the previous Administration are open to review by the current Administration for possible changes, see “Presidential Memorandum on Reinvigorating America’s Human Space Exploration Program,” The White House, December 2017, https://trumpwhitehouse.archives.gov/presidential-actions/presidential-memorandum-reinvigorating-americas-human-space-exploration-program/ (Accessed April 3, 2021).

[7] NASA’s Artemis program is the actionable response to the directive to return to the Moon. It will involve multiple systems and the coordination of government, private, and international partners over the course of many years to complete. The Artemis program represents the critical first step towards establishing and maintaining a permanent human presence beyond low-Earth orbit to the Moon, Mars, asteroids, and further, Brian Dunbar, “Humanity’s Return to the Moon,” NASA, https://www.nasa.gov/specials/artemis/ (accessed April 2, 2021).

[8] U.S. space policy defines “space vehicle” as satellites, space stations, launch vehicles, separable upper stages, or any other type of spacecraft. These space vehicles will deploy astronauts to the Moon and back for the first time in half a century once fully tested and certified for human spaceflight. See “Memorandum on Space Policy Directive-5—Cybersecurity Principles for Space Systems,” The White House, September 2020, https://trumpwhitehouse.archives.gov/presidential-actions/memorandum-space-policy-directive-5-cybersecurity-principles-space-systems/ (accessed March 13, 2021); 

“National Space Exploration Campaign Report,” NASA, September 2018, 4, https://www.nasa.gov/sites/default/files/atoms/files/nationalspaceexplorationcampaign.pdf (accessed March 13, 2021).

[9] Delays caused by COVID-19 and uncertainties in funding and the future of the Artemis program lead NASA to delay certain components of the program, see Elaine Slaugh, “FY 2020 Budget Overview,” NASA Human Exploration and Operations Mission Directorate (HEOMD), May 2019, 3, https://www.nasa.gov/sites/default/files/atoms/files/nac_budget_charts_final_updated_pfp.pdf (accessed March 13, 2021) and Jeff Foust, “NASA to Delay Decision on Artemis Lunar Landers,” Space News, February 2021, https://spacenews.com/nasa-to-delay-decision-on-artemis-lunar-landers/ (accessed April 3, 2021).

[10] Cislunar space is generally defined as the region between and around Earth orbit and lunar orbit. Lunar orbit is the volume of space immediately around the Moon, not to be confused with the Moon’s orbit, which is the path the Moon takes as it orbits around the Earth.

[11] Melvin J. Ferebee, Kevin R, Antcliff, “Lunar Gateway,” NASA, https://sacd.larc.nasa.gov/smab/smab-projects/lunar-gateway/ (accessed March 13, 2021).

[12] “National Space Exploration Campaign Report,” NASA, September 2018, 7, https://www.nasa.gov/sites/default/files/atoms/files/nationalspaceexplorationcampaign.pdf (accessed March 13, 2021).

[13] As of June 2021, 12 Nations have signed the Artemis Accords: Australia, Brazil, Canada, Italy, Japan, Luxembourg, New Zealand, the Republic of Korea, Ukraine, the United Arab Emirates, the United Kingdom, and the United States. See Brian Dunbar, “The Artemis Accords,” NASA, June 2021, https://www.nasa.gov/specials/artemis-accords/index.html (accessed June 24, 2021).

[14] Cheryl Warner and Brian Dunbar, “First Commercial Moon Delivery Assignments to Advance Artemis,” NASA, January 2020, https://www.nasa.gov/feature/first-commercial-moon-delivery-assignments-to-advance-artemis (accessed March 13, 2021) and Erin Mahoney, “NextSTEP H: Human Landing System,” NASA, January 2021, https://www.nasa.gov/nextstep/humanlander2 (accessed April 3, 2021).

[15] The United States and other countries intend to utilize the space domain to their benefit economically and strategically. This challenge will require a whole-of-government approach that includes the U.S. Space Force and other elements of the Department of Defense, particularly as strategic competition among great powers extends from terrestrial domains into cislunar space. Brien Flewelling, “Securing Cislunar Space: A Vision for U.S. Leadership,” SpaceNews.com, November 2020, https://spacenews.com/op-ed-securing-cislunar-space-a-vision-for-u-s-leadership/ (accessed April 29, 2021) and Sandra Erwin, “U.S. Military Eyes a Role in the Great Power Competition for Lunar Resources,” SpaceNews.com, August 2020, https://spacenews.com/u-s-military-eyes-a-role-in-the-great-power-competition-for-lunar-resources/ (accessed April 29, 2021).

[16] “Memorandum of Understanding Between the National Aeronautics and Space Administration and the United States Space Force,” NASA, September 2020, 3, https://www.nasa.gov/sites/default/files/atoms/files/nasa_ussf_mou_21_sep_20.pdf (accessed March 13, 2021).

[17] While today’s military is focused on “look down” capabilities, the U.S. should also develop capabilities to look out and across cislunar space and the lunar surface as the U.S. and other nations move to explore and utilize those regions of the space domain. Mir Sadat and Michael Sinclair, “A Pentagon Strategy for Elevating the Space Mission,” Politico, February 2021, https://www.politico.com/news/2021/02/11/pengtagon-space-lloyd-austin-468659 (accessed April 30, 2021).

[18] The first USSF capstone mentions cislunar space only three times, focusing purely on its existence as an orbital and gravitational regime with minor mention of the fact the national and commercial ventures will extend beyond geocentric regions. “Spacepower (SCP),” Headquarters United States Space Force, June 2020, 6, 14 & 24, https://www.spaceforce.mil/Portals/1/Space%20Capstone%20Publication_10%20Aug%202020.pdf (accessed March 13, 2021).

[19] “2222 (XXI). Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies,” United Nations Office for Outer Space Affairs, December 1966, https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/outerspacetreaty.html (accessed March 13, 2021).

[20] Ibid.

[21] There are numerous examples of the U.S. military supporting civilian scientific and exploration missions. These examples include expeditions to other nations, research missions to Antarctica, and NASA’s astronaut programs. For a detailed snapshot of some of these examples, see Carl Poole and Robert A. Bettinger, “The Cosmic Sandbox: An Advocated Military Role in Future Space Commerce and Exploration,” Space Force Journal, January 2021, https://spaceforcejournal.org/the-cosmic-sandbox-an-advocated-military-role-in-future-space-commerce-and-exploration/ (accessed April 29, 2021).

[22] The Antarctic Treaty was signed by the United States in 1959, affirming an agreement to limit the activities of military and land acquisitions as well as encouraging the peaceful and cooperative use of resources and terrain in the Antarctic region. This treaty served as a model for several future “non-armament” treaties, to include the Outer Space Treaty of 1967, “Antarctic Treaty,” U.S. Department of State, https://2009-2017.state.gov/t/avc/trty/193967.htm#treaty (accessed April 2, 2021) and “2222 (XXI), Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies,” United Nations Office for Outer Space Affairs, December 1966, https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/outerspacetreaty.html (accessed April 2, 2021).

[23] Mikaley Kline, “Joint Task Force Kicks Off 64thYear of DoD Antarctic Mission Support,” Pacific Air Forces Public Affairs, September 2019, https://www.pacaf.af.mil/News/Article-Display/Article/1956772/joint-task-force-kicks-off-64th-year-of-dod-antarctic-mission-support/ (accessed March 13, 2021).

[24] “Defense Satellite Communications System (DSCS),” National Science Foundation United States Antarctic Program, https://www.usap.gov/technology/4298/ (accessed March 13, 2021).

[25] “2019 Report to Congress of the U.S.-China Economic and Security Review Commission,” US Government Publishing Office, November 2019, 362 https://www.uscc.gov/sites/default/files/2019-11/2019%20Annual%20Report%20to%20Congress.pdf (accessed March 13, 2021).

[26] The Chinese Communist Party, also known as the Communist Party of China, has increasingly publicly stated its space ambitions. Namrata Goswami, “China in Space: Ambitions and Possible Conflict,” Strategic Studies Quarterly 34, no. 2, 77, https://www.airuniversity.af.edu/Portals/10/SSQ/documents/Volume-12_Issue-1/Goswami.pdf (accessed March 13, 2021).

[27] “Military and Security Developments Involving the People’s Republic of China,” Office of the Secretary of Defense, August 2020, 1-6, https://media.defense.gov/2020/Sep/01/2002488689/-1/-1/1/2020-DOD-CHINA-MILITARY-POWER-REPORT-FINAL.PDF (accessed March 13, 2021).

[28] China is attempting to establish its own lunar surface presence, Andrew Jones, “China is Aiming to Attract Partners for an International Lunar Research Station,” SpaceNews.com, August 2020, https://spacenews.com/china-is-aiming-to-attract-partners-for-an-international-lunar-research-station/ (accessed March 13, 2021).

[29] Andrew Jones, “China, Russia Enter MOU on International Lunar Research Station,” Space News, March 2021, https://spacenews.com/china-russia-enter-mou-on-international-lunar-research-station/ (accessed April 2, 2021).

[30] “Territorial Disputes in the South China Sea,” Council on Foreign Relations (CFR), October 2020, https://www.cfr.org/global-conflict-tracker/conflict/territorial-disputes-south-china-sea (accessed March 13, 2021).

[31] Ibid. See also Perm. Ct. Arb., The South China Sea Arbitration, Award of 12 July 2016, ¶278, https://docs.pca-cpa.org/2016/07/PH-CN-20160712-Award.pdf (Accessed March 13, 2021) and Jack H. Burke, “China’s New Wealth-Creation Scheme: Mining the Moon,” National Review, June 2019, https://www.nationalreview.com/2019/06/china-moon-mining-ambitious-space-plans/ (accessed March 13, 2021).

[32] Jack H. Burke, “China’s New Wealth-Creation Scheme: Mining the Moon,” National Review, June 2019, https://www.nationalreview.com/2019/06/china-moon-mining-ambitious-space-plans/ (accessed October 11, 2020).

[33] Space should be considered as an economic frontier. Emergent technologies and activities are poised to establish space-based economic ventures totalling in trillions of dollars over the next few decades. This prospect may result in a renewed global competition among nations and coalitions of nations in the near future. Bruce Cahan and Mir H. Sadat, “US Space Policies for the New Space Age: Competing on the Final Economic Frontier,” NewSpace New Mexico, January 2021, 11, https://www.newspacenm.org/wp-content/uploads/2021/01/US-Space-Policies-for-the-New-Space-Age-Competing-on-the-Final-Economic-Frontier-010621-final.pdf (accessed April 2, 2021).

[34] The “Five D’s” of possible desired effects when targeting an adversary’s space capabilities, “Offensive Space Control,” Curtis E. Lemay Center for Doctrine Development and Education, June 2012, 1, https://fas.org/irp/doddir/usaf/3-14-annex-osc.pdf (accessed April 2, 2021).

[35] Both China and Russia intend to field counterspace directed-energy weapons and China tested an anti-satellite missile in 2007, generating over 3000 pieces of trackable debris that remain in orbit, “Competing in Space,” the National Air and Space Intelligence Center, https://media.defense.gov/2019/Jan/16/2002080386/-1/-1/1/190115-F-NV711-0002.PDF (accessed April 2, 2021).

[36] Department of Defense, June 2020, 4, Counterspace Continuum [Infographic], in “Defense Space Strategy Summary,” https://media.defense.gov/2020/Jun/17/2002317391/-1/-1/1/2020_DEFENSE_SPACE_STRATEGY_SUMMARY.PDF (accessed March 13, 2021).

[37] “About Us – Office of State-Defense Integration,” U.S. Department of State, https://www.state.gov/bureau-of-political-military-affairs-office-of-state-defense-integration-pm-sdi/ (accessed April 30, 2021).

[38] The United States should be prepared should communication efforts breakdown.

[39] Examples of defensive design features include but are not limited to: hardening against directed energy weapons, high-thrust evasive thrusters, encryption, jam-resistant waveforms, and antenna nulling and adaptive filtering of electromagnetic interference (EMI). The ability to command, communicate with, and control forces and assets is of vital importance in warfare and in times of peace. This concept will remain true for U.S. and allied operations in cislunar space. A variety of methods have been developed to protect signals from interference, whether it be intentional or accidental. For a detailed report of how the DoD might protect communications networks, see Elham Ghashghai, “Communications Networks to Support Integrated Intelligence, Surveillance, Reconnaissance, and Strike Operations,” RAND Corporation, 2004, https://www.rand.org/content/dam/rand/pubs/technical_reports/2004/RAND_TR159.pdf. (accessed April 29, 2021). With the advent of more destructive counterspace capabilities, space vehicles themselves must also be protected. For a comprehensive report concerning defense against a variety of counterspace capabilities, see Todd Harrison et al., “Defense Against the Dark Arts in Space: Protecting Space Systems from Counterspace Weapons,” Center for Strategic Studies & International Studies, February 2021, https://www.csis.org/analysis/defense-against-dark-arts-space-protecting-space-systems-counterspace-weapons (accessed April 29, 2021).

[40] Other collaborative areas between the DoD, NASA, and other potential civilian mission partners should also be investigated wherever possible to promote safety, security, and stability.

[41] Incidents such as Apollo 13 and the Columbia disaster show how dangerous space operations are and there are few existing capabilities to save astronauts in distress. Megan Ray Nichols, “How Astronauts Deal With Emergencies,” Discover Magazine, September 2018, https://www.discovermagazine.com/the-sciences/how-astronauts-deal-with-emergencies (accessed April 30, 2021).

[42] Search and Rescue is a major function of the U.S. Coast Guard, which performs search and rescue operations on the high seas globally. “U.S. Coast Guard Office of Search and Rescue (CG-SAR),” U.S. Coast Guard, https://www.dco.uscg.mil/Our-Organization/Assistant-Commandant-for-Response-Policy-CG-5R/Office-of-Incident-Management-Preparedness-CG-5RI/US-Coast-Guard-Office-of-Search-and-Rescue-CG-SAR/ (accessed April 30, 2021). Search and Rescue operations in Antarctica are performed by a variety of organizations and many research stations have their own search and rescue teams ready on stand-by should researchers and other personnel require emergency assistance. Michael Lucibella, “Podcast: The Search and Rescue Team,” The Antarctic Sun, U.S. Antarctic Program, November 2020, https://antarcticsun.usap.gov/features/4438/ (accessed April 30, 2021).

[43] LunaNet is a NASA-led space-based communications and navigation architecture that will support the Artemis program. The intent is for LunaNet to comprise of space vehicles and surface stations owned and operated by a combination of NASA, commercial partners, international partners, and other mission partners to establish a networked system that connects users across cislunar space and the lunar surface to support exploration and science objectives, David J. Israel, et al., “ LunaNet: A Flexible and Extensible Lunar Exploration Communications and Navigation Infrastructure,” NASA Goddard Space Flight Center, March 2020, https://ntrs.nasa.gov/api/citations/20200001555/downloads/20200001555.pdf (accessed April 29, 2021) and Katherine Schauer, “LunaNet: A Flexible and Extensible Lunar Exploration Communications and Navigation Infrastructure,” NASA, September 2019, https://esc.gsfc.nasa.gov/news/_LunaNetConcept (accessed April 29, 2021).

[44] Ibid.

[45] See M. J. Holzinger, C. C. Chow, and P. Garretson, “A Primer on Cislunar Space,” Air Force Research Labs, May 2021, 7, https://www.afrl.af.mil/Portals/90/Documents/RV/A%20Primer%20on%20Cislunar%20Space_Dist%20A_PA2021-1271.pdf?ver=vs6e0sE4PuJ51QC-15DEfg%3d%3d (accessed June 24, 2021). See also Steve Stich, “Asteroid Redirect Mission and Human Space Flight Briefing to National Research Council Committee for Study on Human Space Flight Technical Panel,” NASA, June 2013, 5, https://www.nasa.gov/pdf/756678main_20130619-NRC_Tech_Panel_Stich.pdf (accessed March 13, 2021).

[46] Ibid.

[47] Wideband signals are higher frequencies than narrowband and many other radio-frequency signals. In general, higher frequencies accommodate greater bandwidth which in turn translates to higher data rates. Wideband transmitters require higher power levels than lower frequency signals to minimize signal-to-noise-ratio performances, but not so high as to be impractical for space vehicle design or for the design of user terminals and equipment, Jack Browne, “Comparing Narrowband and Wideband Channels,” Microwaves & RF, February 2018, https://www.mwrf.com/technologies/systems/article/21848973/comparing-narrowband-and-wideband-channels (accessed April 2, 2021).

[48] Ghashghai, Elham, “Communications Networks to Support Integrated Intelligence, Surveillance, Reconnaissance, and Strike Operations,” RAND Corporation, 2004, 21-23, https://www.rand.org/content/dam/rand/pubs/technical_reports/2004/RAND_TR159.pdf (Accessed March 13, 2021).

[49] “Space,” GPS.gov, 2006, https://www.gps.gov/applications/space/ (accessed March 13, 2021).

[50] David J. Israel, et al., “ LunaNet: A Flexible and Extensible Lunar Exploration Communications and Navigation Infrastructure,” NASA Goddard Space Flight Center, March 2020, https://ntrs.nasa.gov/api/citations/20200001555/downloads/20200001555.pdf (accessed April 29, 2021) and Katherine Schauer, “LunaNet: A Flexible and Extensible Lunar Exploration Communications and Navigation Infrastructure,” NASA, September 2019, https://esc.gsfc.nasa.gov/news/_LunaNetConcept (accessed April 29, 2021).

[51] Higher degrees of angular separation between satellites results in the least amount of errors for users in view of satellites, “Global Positioning System,” U.S. Department of the Interior Bureau of Reclamation, Engineering Geology Field Manual, Volume II, Chapter 25, 444, https://www.usbr.gov/tsc/techreferences/mands/geologyfieldmanual-vol2/Chapter25.pdf (accessed April 2, 2021).

[52] An Isotropic antenna, also known as an omnidirectional antenna, emits signals even ly in all directions. By contrast, a directional antenna focuses directed energy into a specific direction, increasing its gain to increase output signal up to the limit of an ideal isotropic antenna, Shahin Farahani, “RF Propagation, Antennas, and Regulatory Requirements,” Science Direct, reproduced from ZigBee Wireless Networks and Transceivers, 2008, Elsevier Ltd, https://www.sciencedirect.com/topics/engineering/isotropic-antenna (accessed April 2, 2021).

[53] “New Civil Signals,” GPS.gov, August 2020, https://www.gps.gov/systems/gps/modernization/civilsignals/ (Accessed March 13, 2021) and Joel J. K. Parker, “An Introduction to High-Altitude Space Use of GNSS (For Timing People),” GPS.gov, September 2018, 2-4, https://www.gps.gov/cgsic/meetings/2018/parker.pdf (Accessed March 13, 2021).

[54] “Lesson 9: GPS Modernization,” Penn State, https://www.e-education.psu.edu/geog862/print/l9.html (accessed March 13, 2021).

[55] Ibid.

[56] PNT payloads cannot use other PNT payloads to update their own ephemeris. This requires monitor stations to track GPS satellites to collect navigation signals and to track spacecraft and feed these measurements back to the master control station to update the ephemerides of the constellation. See “Control Segment,” GPS.gov, January 2021, https://www.gps.gov/systems/gps/control/ (accessed April 2, 2021). See also M. J. Holzinger, C. C. Chow, and P. Garretson, “A Primer on Cislunar Space,” Air Force Research Labs, May 2021, 5-11, https://www.afrl.af.mil/Portals/90/Documents/RV/A%20Primer%20on%20Cislunar%20Space_Dist%20A_PA2021-1271.pdf?ver=vs6e0sE4PuJ51QC-15DEfg%3d%3d (accessed June 24, 2021).

[57] These attributes make the lunar surface an ideal location from which to track LPS vehicles.

[58] Sandra Erwin, “Air Force: SSA is No More; It’s ‘Space Domain Awareness’,” SpaceNews.com, November 2019, https://spacenews.com/air-force-ssa-is-no-more-its-space-domain-awareness/#:~:text=The%20memo%20defines%20SDA%20as,or%20environment%20of%20our%20nation.%E2%80%9D (accessed March 13, 2021).

[59] The Moon is an average distance of 384,402 kilometers away from the Earth. It took the command module Columbia three days to reach lunar orbit, Jonti Horner, “This Simple Explanation Puts Into Perspective Just How Far Away the Moon Really is,” Science Alert, July 2019, https://www.sciencealert.com/this-is-how-big-and-far-away-the-moon-actually-is (accessed April 2, 2021). There are a number of challenges associated with detecting and tracking objects moving through cislunar space. This will require the development of new technologies and techniques specifically intended to perform and support cislunar SDA. See also M. J. Holzinger, C. C. Chow, and P. Garretson, “A Primer on Cislunar Space,” Air Force Research Labs, May 2021, 11-18, https://www.afrl.af.mil/Portals/90/Documents/RV/A%20Primer%20on%20Cislunar%20Space_Dist%20A_PA2021-1271.pdf?ver=vs6e0sE4PuJ51QC-15DEfg%3d%3d (accessed June 24, 2021).

[60] To detect small space objects moving through space at any relative distance or angle, these SDA sensors will need to continuously scan through a wide field-of-view in a short amount of time, all the while discerning man-made objects from the backdrop of distant stars and other celestial objects.

[61] This process would involve accurately resolving an object’s relative position and velocity as well as identifying unique signatures and patterns pertaining to the object and its actions.

[62] “Spacepower (SCP),” Headquarters United States Space Force, June 2020, 39, https://www.spaceforce.mil/Portals/1/Space%20Capstone%20Publication_10%20Aug%202020.pdf (accessed March 13, 2021).

[63] The CHPS is an experimental mission intended to demonstrate space domain awareness concepts in cislunar space, “Cislunar Highway Patrol System,” Air Force Research Labs, https://www.afrl.af.mil/News/Photos/igphoto/2002556344/mediaid/4752579/ (accessed April 2, 2021). See also M. J. Holzinger, C. C. Chow, and P. Garretson, “A Primer on Cislunar Space,” Air Force Research Labs, May 2021, 5-6 and 17, https://www.afrl.af.mil/Portals/90/Documents/RV/A%20Primer%20on%20Cislunar%20Space_Dist%20A_PA2021-1271.pdf?ver=vs6e0sE4PuJ51QC-15DEfg%3d%3d (accessed June 24, 2021).

[64] William Gerstenmaier and Jason Crusan, “Cislunar and Gateway Overview,” NASA, https://www.nasa.gov/sites/default/files/atoms/files/cislunar-update-gerstenmaier-crusan-v5a.pdf (accessed April 2, 2021). See also M. J. Holzinger, C. C. Chow, and P. Garretson, “A Primer on Cislunar Space,” Air Force Research Labs, May 2021, 17, https://www.afrl.af.mil/Portals/90/Documents/RV/A%20Primer%20on%20Cislunar%20Space_Dist%20A_PA2021-1271.pdf?ver=vs6e0sE4PuJ51QC-15DEfg%3d%3d (accessed June 24, 2021).

[65] Distant Retrograde Orbits result from gravitational perturbations of a third body. In this case, the third body is the Earth with the other two bodies being the Moon and the space vehicle. DROs are studied via the planar circular restricted three-body problem and Hill’s problem. DROs have been proposed for use around many moons, including the Earth’s Moon and the Jovian Moon Europa, see Try Lam and Gregory J. Whiffen, “Exploration of Distant Retrograde Orbits Around Europa,” NASA, 2014, https://trs.jpl.nasa.gov/bitstream/handle/2014/37526/05-0195.pdf?sequence=1 (accessed April 2, 2021).

[66] “Subtitle C–George E. Brown, Jr. Near-Earth Object Survey,” George E. Brown Jr. Near-Earth Object Survey Act, 2005 § 321, https://www.congress.gov/109/plaws/publ155/PLAW-109publ155.pdf (accessed April 2, 2021).

[67] NASA’s NEO observation program has a history of being underfunded. This problem has made it difficult for NASA to procure resources necessary to conduct sky surveys capable of scanning the sky for all NEOs in the span of 15 years. Advanced sensors require more funding, Casey Dreier, “How NASA’s Planetary Defense Budget Grew by More than 4000% in 10 Years,” the Planetary Society, September 2019, https://www.planetary.org/articles/nasas-planetary-defense-budget-growth (accessed April 2, 2021).

[68] Within the context of this article, LSA is defined as the identification, characterization, and understanding of all factors associated with the surface of the Moon.

[69] “What is the difference between multispectral and hyperspectral imagery?,” Mapasyst, Extension, August 2019, https://mapasyst.extension.org/what-is-the-difference-between-multispectral-and-hyperspectral-imagery/ (accessed March 13, 2021).

[70] Ibid.

[71] “What is lidar?,” NOAA, August 2020, https://oceanservice.noaa.gov/facts/lidar.html#:~:text=Lidar%2C%20which%20stands%20for%20Light,variable%20distances)%20to%20the%20Earth (accessed March 13, 2021).

[72] Mamta Patel Nagaraja, “Bizarre Lunar Orbits,” NASA, November 2006, https://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit/ (accessed March 13, 2021) and Todd Ely, “Stable Constellations of Frozen Elliptical Inclined Lunar Orbits,” Research Gate, The Journal of Astronautical Sciences, Vol. 53, No. 3, July-September 2005, 301-302, https://www.researchgate.net/publication/264815005_Stable_Constellations_of_Frozen_Elliptical_Inclined_Lunar_Orbits (accessed March 13, 2021).

[73] Mark Robinson, “Follow the Tracks,” Arizona State University, March 2012, http://lroc.sese.asu.edu/posts/491 (accessed March 13, 2021).

[74] Forms of intelligence that LSA sensors could collect include SIGINT, imagery intelligence (IMINT), measurement and signatures intelligence (MASINT), and selenospatial intelligence (SELENOINT). Within the context of this article, SELENOINT is applied with respect to the Moon in a manner equivalent to how geospatial intelligence (GEOINT) is applied with respect to the Earth. Akin to Geospatial Intelligence (GEOINT), the term Selenospatial Intelligence (SELENOINT) is applied within this article to mean the exploitation and analysis of imagery and information pertaining to the lunar surface to describe, assess, and visually depict physical features and activity occurring across the Moon, “NGA’s Mission,” National Geospatial-Intelligence Agency, https://www.nga.mil/about/1596052185524_Mission.html (accessed March 13, 2021).

[75] The term “great-power competition” is a relatively new term that describes a scenario that has played out numerous times throughout human history. When two or more powerful nations or alliances have differing views with regards to common or competing objectives, tensions can rise and lead to armed conflict. One example is the “Great Game” between the Russian and British Empires in the 19th century. “The Great Power Competition Narrative,” University of South Florida, https://www.usf.edu/arts-sciences/great-power-competition/about/the-great-power-competition-narrative.aspx (accessed April 29, 2021). See also Alexander Boroff, “What is Great-Power Competition, Anyway?” Modern War Institute at West Point, April 2020, https://mwi.usma.edu/great-power-competition-anyway/ (accessed April 29, 2021).

[76] The D2S2 satellite is the first DoD mission to demonstrate lunar surface observation capabilities, Theresa Hitchens, “Space Force, AFRL to Demo Mobile Lunar Spy Sat,” Breaking Defense, November 2020, https://breakingdefense.com/2020/11/space-force-afrl-to-demo-mobile-lunar-spy-sat/ (accessed April 2, 2021)