With the Air Force’s Space Command going live this year, it’s worth kicking off 2022 with a timely piece by Air Force Reservist SQNLDR Michael Spencer. In this analysis, he delves into the known details of the Russian Anti-Satellite (ASAT) mission in November last year, examining how it was done and the ongoing ramifications of such an engagement. By doing so, he makes plain the enormous challenges that lie ahead for Space Powers to protect their orbital infrastructure and avoid a ‘scorched orbit’ policy.
My house is at the end of the street - so I don't know anything.
- Russian proverb
Figure 1. A belligerent space actor's indifference to generating a significant amount of uncontrolled space debris might be considered as a 'Scorched Earth' policy against the orbital space environment as a resource.
The Scorched Earth Policy
The 'scorched-earth policy' has its origins in early 20th-century military strategy thinking to weaken an attacking army's progress by tasking the retreating army to "destroy or devastate whole towns, facilities, agriculture, transport routes, and general infrastructure in order to deprive the advancing enemy forces or the belligerent population of food, shelter, fuel, communications, and other valuable resources that may be useful for them." The scorched earth strategy also presents uncontrolled risks and damages to the civilian population, and sustainability of the environment it depends on for critical infrastructure for many generations. Similarly, a state's indifference to conducting activities without debris mitigation might be viewed by other states as promoting a 'Scorched Earth-Orbit Policy' that wastes useful orbital altitudes and consumes the energy and efforts needed for space surveillance and orbital collision avoidance.
The Russian A-235 Nudol Anti-Satellite Missile
On 15 November 2021, the Russian military launched an A-235 PL-19 Nudol direct-ascent anti-satellite (DA-ASAT) interceptor missile. The DA-ASAT was launched in a test to verify its performance against the defunct Soviet-era Kosmos-1408 (COSMOS 1408) communications satellite. Space observation and tracking sensors have detected more than 1,500 new trackable debris objects in low-Earth orbit (LEO) resulting from the on-orbit destruction of the COSMOS 1408 satellite that may now threaten numerous satellites and the International Space Station.  General J Dickinson, US Space Command head, stated that the debris field would "likely generate hundreds of thousands of pieces of smaller orbital debris" beyond the 1,500 pieces that are too small to be detected and tracked.
The DA-ASAT missile was reportedly launched from a transporter erector launcher (TEL) located near the Plesetsk Cosmodrome, a Russian spaceport situated about 800 km north of Moscow and initially built by the Soviets as an intercontinental ballistic missile (ICBM) launch site. The ASAT mission requires a complicated integrated system of discrete systems covering different functions including space surveillance, target tracking, target intercept calculation, missile launch, missile guidance, and network systems integration (i.e. including uplinks for missile command signals). These sensors also measure the missile and satellite target positions (i.e. relative geometry), monitor range safety, and detect the post-attack results.
The Nudol DA-ASAT is a two-stage, long-range and trans-atmospheric rocket booster. It was launched from a mobile TEL in northern Russia to boost an exo-atmospheric hit-to-kill payload designed to intercept and disrupt a ballistic missile or a satellite in a LEO altitude. The success of the satellite intercept depends on the mission planning efforts needed to synchronise the time and location of the launch, the missile reaching the target, and the payload functioning correctly at the target. The Earth's rotation determines the launch event location and timing to align the missile's ascent trajectory with the satellite's orbit. Space surveillance provides the calculated predictions of when a missile trajectory can converge with the satellite orbit, and the missile can intercept the satellite speeding overhead at about 28,000 km/h.
Space surveillance systems may not immediately characterise a rocket launch as an ASAT mission or a benign spacelift event when both events appear to follow similar ascent trajectories to reach orbital altitudes. Similarly, both tasks need to follow a course and perform manoeuvres to rendezvous with an existing object already resident in orbit. It is only the broader understanding of the orbital space situation where the trajectory of a high-value satellite is predicted to overfly within reach of a launch site. When observations indicate a space launch event at that site, concerns will be triggered to assess the potential risk of an accidental orbital collision by a satellite rocket booster on a satellite rendezvous mission or a deliberate intercept by an attacking ASAT mission. A remote observer to a rocket launch cannot readily know if the launch is supporting a spacelift event or a direct ascent attack.
The target for the DA-ASAT was the Soviet military communications satellite of the type known as Tselina-D and catalogued as COSMOS 1408. It was a 1,750 kg satellite launched into LEO in 1982. Initially, it formed one component of a two-satellite Tselina electronic intelligence satellite reconnaissance system. Tselina-D was used to gain more detailed observations of radiofrequency sources initially detected by a smaller-sized Tselina-O satellite.  The Soviets launched 137 Tselina satellites, including 63 Tselina-D variants.  For the DA-ASAT trial, COSMOS 1408 was an appropriate choice as a representative target for a large-sized non-cooperative satellite travelling in a polar low-Earth orbit. 
The period when Tselina-D and -O were designed was still in the early orbital space operations. There was little regard or appreciation for the risks of accumulating debris to space sustainability. There was no recognition for space debris mitigation to influence satellite designs, and satellites remained in situ on-orbit if they failed or their mission system expired. Today, satellites are designed to carry a reserve fuel to de-orbit after their mission expires to clear the orbital trajectory for re-use. Thus, the Soviets had initially intended for COSMOS 1408 to be abandoned on-orbit as uncontrolled space debris after it expired.
The TEL is a valuable tactical manoeuvring advantage to relocate the launch event, increasing the challenges for observers seeking to monitor and predict where and when the launch event might occur. The TEL does not signify a manoeuvre to engage any satellite on-demand quickly. The mission planner needs to predict an opportunity for the missile and satellite trajectories to converge and the satellite transit within the missile engagement range.
The satellite may not be visible for several orbital passes. The mobile TEL crew needs to deploy and wait until the orbiting satellite comes into range. The satellite overflights or 'revisit period' depends on the observer's location and the design of the orbit. A satellite following a polar orbital trajectory might be visible about every 90 minutes to an observer near the north pole or approximately every 24 hours to an observer near the Equator.
Figure 2. The A-235 PL-15 Nudol DA-ASAT missile and transporter erector launcher.
The Space Debris Legacy of an ASAT Test
The A-235 Nudol can hit an exo-atmospheric target (e.g. satellite or ballistic missile) at a range of up to 1,500 kilometres. The test missile is estimated to have been launched to intercept the overflying satellite from behind. The design of solid-propellant booster rockets does not allow for speed to be controlled during the ascent; the rocket functions to accelerate the warhead to an orbital speed faster than the satellite.
The orbital intercept occurred above the North Sea at the height of about 480 kilometres. The attack is likely to have been controlled from the ground tracking station sending missile guidance commands to steer the command/inertial-guided missile. The ground station is critical to using the missile-target relative positions and speed vectors for calculating the flight corrections needed to steer the missile towards the intercept position. When the missile closes within the sensor range of its target, it breaks from the command guidance from the ground station and switches to using its onboard short-range seeker to self-guide directly to impact the orbiting target.
The physics of orbital dynamics dictate that the object's speed determines its kinetic energy that equates to a unique altitude. A missile travelling slower than the satellite will not reach the same height. Conversely, a missile travelling faster than the satellite will pass through the satellite's altitude to achieve a stable orbital trajectory at a higher altitude. Thus, if the missile travels faster than the satellite (e.g. greater than Mach 23), it will fly a course that ascends through the orbital trajectory of the satellite and, if synchronised correctly, can intercept the satellite. The payload can rapidly manoeuvre at high hypersonic speeds without air and aerodynamic resistance.
The boosted Nudol payload intercepts its target at a closing speed equivalent to high hypersonic at about Mach 10. The overmatch in speed provides the kinetic energy for the attacking payload to destroy the target satellite.
Little is publicly known about the payload designs and their damage mechanism. Although the debris resulting from high-speed interaction with the target suggests a direct hit, this may result from a self-guided unitary warhead travelling at high hypersonic speed to impact a single orbiting target or a fragmenting payload increase the probability of a hit by a single-shot missile attack. The customary use of a combined sensor-fuzed explosive warhead is challenged when considering the lead-time needed for the payload to sense, detonate, and distribute a fragmentation pattern with a density adequate to strike a unitary target approaching at high hypersonic speed.
The Soviets had previously developed 'Shchit-2 (translation: Shield-2)" as a self-guided spinning projectile for the active space defence system. Shield-2 was a self-guided payload with a 'hedgehog' configuration of projectiles fired outwardly in a radial pattern to increase the size and volume of the attack effect against a single, high-speed small-sized unitary target. The Soviets were motivated to develop Shield-1, a projectile firing space gun, and Shield-2 as self-defence options in a conceptual design for the orbiting military Almaz OPS-4 space station. Shield-1 and -2 were likely designed to defend a spacecraft against relatively slow-moving co-orbital objects on an incoming attack trajectory rather than chasing passing orbital targets.
Figure 3. A Soviet-era Shchit-2 anti-spacecraft guided weapon designed for deployment from an orbiting space station.
There is no useful analytical model to predict the consequences of the hittile-target interaction or the resulting breakup of the target, distribution of space debris, or their separate mass and velocity vectors needed to validate the implications for the orbital environment and other orbiting satellites.
The size and shape of the space debris fields resulting from an on-orbit impact are determined by the momentum imparted from the two colliding objects to each piece of debris. Since the tail-chasing DA-ASAT follows an intercept trajectory that closely aligns with the target's trajectory, it follows that the centroid of the space debris field will generally be split into two main groups following along the original orbits of the satellite and the interceptor missile.
Following Newtonian physics, fragments that are slowed by the impact will have a decreased momentum, naturally descend to a lower orbital altitude, and move ahead of the satellite datum with a faster radial velocity. Fragments with the same speed after the impact will continue at the same speed and altitude as the original satellite datum. However, the fragments accelerated to a higher momentum after the impact will ascend to a higher altitude and begin to lag behind the satellite datum with a slower radial velocity. The velocity of the debris object determines its orbital altitude, which remains unchanged until an external unbalanced force acts to change that velocity (e.g. on-orbit collision, solar wind, gravity anomaly, aerodynamic drag, etc).
The sizes and shapes of the two new debris fields are dynamic. The debris is generated instantly from the missile intercept, and each debris piece quickly settles on separate orbital trajectories corresponding to their speed and kinetic energy. Once stable on orbit, the debris field is subjected to environmental effects that slowly retard the objects to descend at different rates, further dispersing the size and shape of the debris fields.
There is air in the thermosphere, the region above the atmosphere, extending up to about 1,000 km. The atoms and molecules of different gases are thoroughly mixed in the atmosphere by atmospheric turbulence. In the thermosphere, the air density is so thin that gas particles rarely collide. Space objects in LEO collide with these gas particles, causing aerodynamic drag and retarding their speed. The accumulative effect of this drag, extended over months and years, will cause the debris object to slowly descend until it is eventually captured by the denser atmosphere at the lower altitudes and burned up on re-entry.
The lower-altitudes of the LEO environment are popular with space actors deploying low-cost nanosatellite missions, assured they will slowly descend and clear the orbital environment after their short mission life has expired. As the orbital altitude decreases, the debris objects will cross the trajectories commonly used by other satellites. The LEO environment is also more readily accessible than the higher altitudes and popular with crewed space stations (i.e. International Space Station and Tiangong-2), and a growing number of new satellite constellations such as WebOne, Amazon, led by the SpaceX Starlink (about 1,800 deployed for a planned total of 42,000). Also, spacelift rockets must necessarily ascend through the LEO environment to ascend to the higher orbits and interplanetary space missions.
ASAT Mission 'Scorches' Earth Orbital and Terrestrial Resources
Coming back down to Earth, the DA-ASAT test may have been necessary to verify the correct functioning of a complex integrated system and space mission. Attacking a satellite may be useful for an immediate tactical effect for a period spanning until the opposing force replaces the damaged satellite or adapts to function without it. However, the unwanted new space debris generated as collateral from the attack impacts different space actors. Space users, military and non-military, will be affected by the new orbital space debris for years beyond the cessation of the hostilities that initially inspired the attack against the satellite.
The Russian military may have thought it adequate to manage safety by restricting activities within a volume of air and space situated over a controlled sea area at a specified time and location to address potential damage risks from a failed missile and falling debris. However, the orbital space environment cannot be subdivided or physically separated from the space commons accessed and used by all space actors, including military, commercial, scientific, and amateur space actors.
The new space debris occupies a volume of space that clutters the orbital altitudes above and below the original target satellite's altitude, introducing unknown risks of on-orbit collisions with current and future satellites and ascending spacelift rockets. Many satellite orbits are deliberately designed for the mission payload to perform optimally from a particular altitude and travel along a specifically oriented trajectory to access Earth stations and mission target(s). The competition and congestion of the orbital environment give value to an orbital trajectory where some are more in demand and more valuable than others. Space actors might view the orbital environment as a valuable and finite resource and that the debris contamination of an orbit is destroying a valued shared resource.
The lead-time needed to detect and determine the potential risk of a catastrophic collision requires an observation system that measures both physical and temporal characteristics of the Earth orbital environment as an ecosystem. The space surveillance system measures the orbital trajectories of satellites and debris to understand the state of the ecosystem at the time of observation. Temporal surveillance is then used to support calculations to project forward in time to predict future conditions of the ecosystem and the potential for catastrophic on-orbit collisions.
The speed of satellite motion is too fast, the orbital trajectory is too curved, and the satellite size, weight and power constraints limit the viability of using an onboard 'seek and avoid' flight control system. Satellite collision avoidance relies on the space surveillance network (SSN) and processors to understand the orbital ecosystem. However, there are system limitations to the numbers and frequencies of observations that can be achieved and processed by the SSN when it has limited coverage of the orbital ecosystem. The SSN relies on a network of sensors spread around the globe that has gaps in its skyward looking coverage – there are not enough sensors to provide continuous coverage for all of the orbital ecosystem nor the availability to see all space events.
Satellite collision risks need to be constantly re-evaluated, necessarily using a priorities list for tasking the sensors and updating satellite track data. Space surveillance and understanding the situation in the orbital ecosystem are resource-intensive activities. Space surveillance and collision avoidance predictions are valuable resources for safeguarding the continued safe use and availability of orbits and satellites. However, the unnecessary introduction of a significant number of space debris objects will unnecessarily increase the demands on these finite resources, potentially degrading the level of protection previously provided to protect valuable satellites. The space debris risk is further exacerbated by the introduction into orbit of more objects that are too small to be detected and tracked to support collision risk assessments.
The burden of space debris on SSN resources has follow-on consequences that bring additional resource burdens. A satellite must burn fuel from its limited onboard fuel supply to perform a collision avoidance manoeuvre. The fuel is a finite resource that determines the satellite mission's life based on its ability to hold its orbit. Additionally, suppose the satellite does manoeuvre to avoid a collision. In that case, it changes the status of the orbital ecosystem, and the new state of the ecosystem needs to be recalculated for the new risks of on-orbit collisions, burning resources to keep these calculated predictions up-to-date.
Indifference to Generating Space Debris equates to "Scorched Earth Orbit" Policy
The Russian proverb quoted at the beginning of this paper indicates when a person is indifferent about their situation by denying their relationship to the world. The expression describes a person who is not caring about the happenings around them or the consequences of their actions or inactions. This Russian expression encourages people to be proactive and interested to engage in the important issues arising within their social environment.
This proverb aptly depicts the Russian military as the protagonist displaying indifference to the global community's efforts to control the generation of unwanted space debris in the shared orbital space commons. The consequences of the DA-ASAT test performed on 15 November 2021 served to validate the system's functioning, in a momentary event, to the satisfaction of the Russian military. It also served to validate to the rest of the world the realisation of collateral risks to the continuing availability and viability of orbital trajectories that are valuable resources to global space actors. The new debris contamination of the orbital ecosystem has increased burdens on the finite limits of resources needed to monitor and support space situational awareness and space safety.
Together, the Russian attitudes to the results of the Russian DA-ASAT test and the follow-on consequences to the orbital environment that endure for years to come are analogous to a scorched Earth policy being applied to critically valuable Earth orbital resources. The irony is that the DA-ASAT might provide an immediate tactical advantage for those who launch it. Still, they will not be divorced from sharing the increased risks and burdens resulting from the 'scorched' orbital ecosystem that affect all space users for many years, including the Russian people.
Squadron Leader Michael Spencer is currently serving in the Air Force Reserve. He transitioned after a career in the Permanent Air Force, starting as a Navigator flying in long-range maritime patrol missions on P-3C Orions. The experiences gained from operational flying were transposed into a career in writing future air concepts, air capability development, and project acquisition management for air and space capabilities. He is currently working with the AFHQ RPAS (MQ-9B SkyGuardian) Team and the Defence COVID-19 Taskforce.
Additional readings on space debris issues can be found in the papers contributed to Project Asteria 2019: Space Debris, Space Traffic Management and Space Sustainability by a team of writers, including the author. Available at https://airpower.airforce.gov.au/publications/project-asteria-2019-space-debris-space-traffic-management-and-space-sustainability
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