The Space Reviewin association with SpaceNews

CubeSat launch
CubeSats deployed from the International Space Station. Such small spacecraft could pose a threat to critical national security spacecraft, but also be part of the solution to protect them. (credit: NASA)

CubeSat proximity operations: The natural evolution of defensive space control into a deterrence initiative

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Deterrence against CubeSat space control: Applying the doctrine of proportional response

The true danger of cubesat space control arises as a side effect of the uncertain environment of space and the inability to assign definitive attribution for hostile actions. While US space policy makes clear that any hostile act in space will be considered an act of war, without definitive attribution it is unlikely that the United States will have the political will to act. Combined with the high payoff of attacking space COGs, this creates a dangerous situation, with cubesats a potent weapon. Using defensive space control and proportionality doctrine to meet the deterrence initiative can help create a system for protection of the US space architecture from cubesat-based RPO incursions.

In the arena of space deterrence, each unique attack requires a unique response. The concept of proportionality drives any retaliatory action by the US.

The theory of graduated deterrence is centered on “active” defensive measures complementing the threat of force. One of the key factors for successful deterrence is the criteria of “proportionality, reciprocity and coercive credibility.” The more superior a nation’s available instruments to inflict harm, the larger costs for non-compliance it may credibly impose. Dissuasion of enemy escalation is accomplished through the threat of progressive retaliation, ultimately discouraging the enemy from an initial action. Nuclear deterrence theory makes good use of graduated deterrence, dating back to Robert McNamara and the Cold War. Proportionality reduces the force of response required to attain a retaliatory objective. The level of force is justified, the cost of such a response does not outweigh the benefits, and the political will to exert this response is never in doubt.

In the arena of space deterrence, each unique attack requires a unique response. The concept of proportionality drives any retaliatory action by the US. Three steps of escalating response and consequence are detailed below. This staged strategy ensures that the US response is proportional to the existing threat, while maintaining a strategic advantage and technological superiority.

Currently, the US space architecture is set up to respond proportionally to only the first two of these steps, leaving a need for additional deterrence policy and associated defensive space control system development.

No known deployment of RPO capability: Deterrence by ground detection

The base of the cubesat threat pyramid may be considered to be a state where there exists “a general threat of possible terrorist activity, the nature and extent of which is unpredictable.” This translates to no known deployment of RPO capability by an adversarial nation, or RPO missions in the first-time R&D regime only. Given this general threat level, a security posture of deterrence through ground detection and observation is proportional and appropriate.

This stance ensures that the status quo in space is maintained, that appropriate intelligence regarding another nation’s capabilities is gathered, and that there are no adverse effects to US space assets as a result of such experimentation. This level of response must be capable of being maintained indefinitely. Methods currently utilized today, such as the Space Fence, the Space Surveillance Network, and the Space-Based Space Situational Awareness system, are able tools for maintaining this ability to attribute.

Should adverse effects emerge as a result of a nation’s experimentation, either accidentally or deliberately, the US will then be able to galvanize the international community against further development or deployment of such technologies. An example is the Chinese Fengyun ASAT test: the resulting debris spread among operational orbits was widely condemned, and to this day, conferences and seminars discussing orbital debris use this test as an example of “what not to do.” Several nations subsequently adopted UN standards on limiting orbital debris, ensuring that the political climate is not conducive to similar demonstrations in the future.

Fielding of operational RPO capability: Deterrence by space detection

The next level on the cubesat threat pyramid is when “an increased and more predictable terrorist threat activity exists.” The threat increases when specific intelligence suggests the capability for possible aggression by a particular nation, though there is no specific information on a particular target of interest. This is realized when there is a known, operational RPO capability beyond the first-time R&D phase. An adversarial nation has tested and refined its RPO proficiency, and a satellite or constellation of satellites capable of proximity to US assets has either been fielded, or will be imminently.

US policy is clear: if a hostile act is discovered against American space assets, our response will be quick and sure. However, if an adversary is aware that their technology is sufficiently advanced that it may be able to attack and escape undetected, this can create an incentive to act. Dissuading an adversary nation from exercising mature RPO capabilities requires an escalation in the ability by the US to detect and respond to such an action.

US policy is clear: if a hostile act is discovered against American space assets, our response will be quick and sure.

The operative logic of “flexible response” doctrine seems to dictate that the US must first develop the full range of retaliatory capabilities. However, the possibility of rapid weaponization of space becomes a concern, particularly if there is no information to indicate a directly hostile action, merely the possibility of such an action. Deterrence can be achieved here by removing the enemy’s incentive to act. Amputating the veil of invisibility around co-orbital RPO cubesats can have a sizable impact on the political will to act, and is a proportional response.

To do so, the United States must develop a range of detection capabilities tailored to the specific threat of cubesatellite incursions on its space assets. The small size and limited detectability of inbound cubesats implies that currently space situational awareness capabilities are likely inadequate to accomplish the objective of dissuasion by detection. The onus for dissuasion and deterrence against a nation with a developed RPO capability falls on the shoulders of space-based space situational awareness mission sets.

The implementation of a similar policy can be inferred with regard to recent news reports concerning the GEO Space Situational Awareness Program (GSSAP, once a classified program. “GSSAP will bolster our ability to discern when adversaries attempt to avoid detection,” Gen. William Shelton, then head of Air Force Space Command, said at the 2014 Air Warfare Symposium, “and to discover capabilities they may have which might be harmful to our critical assets at these higher altitudes.”

By alerting foreign entities to the increased likelihood of their detection, the culpability for hostile action, if detected, becomes more possible, increasing the likelihood of subsequent socio-political ramifications. Graduated deterrence doctrine dictates that the threat of rapid escalation, to the possible flash point of a space act of war against the United States, will dissuade an adversary from initiating an action that could be construed as hostile, such as proximity operations around or approaching a US space asset. The knowledge that the United States can respond with exactly the same action around that nation’s space assets will cause justifiable unease, and dissuade operational use of developed RPO capabilities against the US.

Known inbound deployment of RPO capability: Deterrence by awareness of local space

The protection of space assets in the event of more direct threats is the focus of this section. The final level on the threat pyramid has larger geopolitical consequences that can directly impede or cripple servicemen in harm’s way. While space-based space situational awareness capabilities, such as GSSAP, are suitable to deterring nations that have susceptibility to socio-political pressure, and would not like to be caught red- handed, this is far from a sufficient strategy to fully ensure the safety of United States space assets. Nations with less accomplished space programs are capable of developing cubesat technology, and are also less likely to adhere to the classic psychology of deterrence. An understanding of US space situational awareness capabilities, combined with the anonymity of cubesat size, can encourage rogue actions against concentrated COGs of space power.

For example, a cyerattack could take command of a co-orbital satellite, at which point it becomes an unintended ASAT weapon. Alternately, a cubesat already tracked could have an alternate purpose, and later exploit holes in US detection capabilities to maneuver into a new orbit. By the time this satellite is reacquired, it could have caused harm to a high-value asset, causing a critical gap in capability.

Dissuading this level of attack is an entirely different matter. For such situations, current US deterrence policy, as well as tracking capability, is inadequate. To assign attribution, respond proportionally, and deter this kind of threat, US space situational awareness assets must increase the probability that an inbound hostile vehicle will not just be detected, but tracked. The US must be able to characterize the motion, intent, and capability of inbound cubesats, assign attribution, and avoid imminent harm to space COGs in a responsive manner.

Cubesats designed for RPO can ensure the safety and sanctity of local space, while simultaneously performing as a contributing sensor, providing information for global space situational awareness systems.

A suitable strategy may be derived from NATO doctrine, which dictates that the force structure include the “deliberate integration of dual-use weapons platforms.” Though this strategy is derived for the nuclear enterprise, i.e., arming missiles with nuclear payloads, it is directly applicable to the cubesat threat. Following this theory, the dual-use platform dissuasion dictates two tenets:

1) That the United States make a concerted and dedicated effort toward developing cubesat RPO technology for utility in the operational realm, and exert deterrence through its possession of such space control capabilities and capability to respond to threats proportionally.

2) That these RPO-capable cubesats be used in a defensive posture to perform proximity operations around high-value assets designated as critical space centers of gravity, and monitor their local space.

Enabling “awareness of local space” can ensure that any object, even cubesat-sized, will be detected and characterized if it is in the vicinity of a high-value asset. If justified and directed, interception attacks by the RPO cubesat performing the protective action may even be needed to ensure safety of the asset. In other words, given a paradigm of cubesat technology used as space control weapons against space COGs, the ultimate deterrent is the presence of a similar asset in the vicinity of such COGs, i.e., “fight fire with fire.”

Such assets enable the almost certainty of detection. Cubesats designed for RPO can ensure the safety and sanctity of local space, while simultaneously performing as a contributing sensor, providing information for global space situational awareness systems. Designed for passive, autonomous proximity operations, such cubesats would not interfere with the primary asset’s mission. The presence of a responsive communication link between the orbiting cubesatellite “Guardian” and its high-value asset gives the COG sufficient time to maneuver out of the way of an interception. The Guardian would also be able to image the interceptor, provide orbital tracking information, deliver responsive intelligence regarding the source of the attack, and provide a post-event battle damage assessment. The protective security function of the Guardian, the high likelihood of failure of a hostile action, and subsequent negative consequences combine to dissuade the adversary from ever attempting the action. Perhaps as importantly, they also provide the US the ability to respond to such an attack in a timely and proportional manner.


The emerging threat of agile, maneuverable, easily fabricated cubesats capable of offensive space control actions raises several questions regarding current deterrence strategy. Dissuading hostile cubesat actions, particularly those directed at high-value assets critical to United States national security and warfighting apparatus, may be achieved by modifying existing, proven theories of graduated deterrence and proportional response.

Currently, there is a critical gap in the ability of the military space enterprise to respond proportionately and swiftly in the event of a cubesat RPO attack. The United States must reinforce a commitment, at the policy and senior leadership levels, to developing and fielding operational cubesat systems in a protector role to fill this crucial gap, which would protect and maintain US space superiority and the high ground.

Deterrence by uncertainty can be achieved when adversarial nations are unable to determine if a particular target may be hosting protector cubesats.

The natural evolution of such a paradigm becomes a truly revolutionary change to the status quo. Once the capability for guardian cubesats is established, and policy direction favors their continuous and rapid employment for high value asset protection, deterrence may be provided as a function of uncertainty. In this scenario, Guardians are not deployed as continuous orbiters, but rather on demand. Designs exist for ride-along cubesats within the spare storage space aboard commercial telecommunications satellites. High-value assets could be similarly adapted to fit not one, but multiple RPO-capable cubesats within their volume.

In response to an increased threat, or intelligence hinting at an impending attack, the high-value COG can deploy one or more of its Guardians to assess local space, determine threats, ensure safety, and provide responsive battlespace awareness. Deterrence by uncertainty can be achieved when adversarial nations are unable to determine if a particular target may be hosting protector cubesats. With the knowledge that these Guardians are RPO-capable, autonomous, and responsive to threats, the risk to invade the local space of a high-value asset becomes too high to justify action.


Opinions expressed in this work are those of the author and do not in any way represent the official views of the US Air Force or the US Government. A special thanks is due to Lt Col Joseph Nance for detailed feedback that helped refine this work. Thanks to Ms. Grace Persico and Ms. Christina Doolittle for their thoughtful comments. The author gratefully acknowledges support from the National Defense Science and Engineering Graduate Fellowship.