SATELLITE RENDEZVOUS TACTICS

Rendezvous Operation: “involves attaching one satellite to another. This could pose a threat as the intercepting satellite could potentially be used to manipulate, damage or even destroy its target.” [Ministry of Defence [United Kingdom]. 2022 Joint Doctrine Publication 0-40, UK Space Power. Ministry of Defence]

SATELLITE ARCHITECTURE

Unlike the Tsiolkovsky Spherical Spaceship designed as an omnidirectional craft with controllers for each facet controlling a different direction [Tsiolkovsky, K.E. 1883 Free space. Manuscript], satellites are designed, depending on the craft’s configuration, with Earth and Space facing ends, and effectively windward, or leeward sides. Typically the satellite housing (the outside container) will be rectangular with solar panels mounted on pivoting spars from opposite sides, so these can always stay in direct path of light rays no matter how the craft is pointed. If the satellite has a spin stabilization system its housing will be cylindrical, with solar cells mounted on the cylinder surface. The antenna will be connected on one end/side of the body by a rotating bearing to keep it pointed in a fixed direction. Antenna system have two functions: (a) receive and transmit telecommunications signals; (b) provide tracking, telemetry, and command functions which maintain the satellite’s operation in orbit. Thruster nozzles placed on alternate sides to the rear-end main motor with its nozzle, allow for station keeping: ensuring the satellite stays in its orbit, and for manoeuvre. The system relies on a fuel supply, the amount of which determines the useful life of a satellite till it is depleted▼.

GRAPPLING MANOEUVRE (SPACE-BASED GRAPPLING COUNTERSPACE WEAPONS)

One satellite approaching another to dock or join will be positioned pointing towards the other, using thruster firings to keep lateral motion in check and slow the approach to a few centimetres per second, for its final approach, contact and docking/joining the two craft.

(1) Penetrators: In 2020, Northrop Grumman’s Mission Extension Vehicle – a robotic repair satellite, rendezvoused with Intelsat 901 to attach a new propulsion and stabilization capability. Historically, few satellites were constructed with features designed as grapple points allowing a robotic arm to grab and hold onto. The approaching satellite attached via the existing propulsion system (the apogee kick motor nozzle), by manoeuvring behind the craft inserting a probe into the nozzle, which expanded so it could grab the craft via the thrust chamber. Retracting the probe, pulling the craft together, locked these into one unit. Once the two craft were mated, the rear satellite is able to use its motor to push the captured satellite into a new position; which is what the Mission Extension Vehicle was used to do, giving Intelsat 901 an extra four to five years of mission time.

(1.1) Orbital Warfare Penetrator Attack: In an Orbital Warfare scenario, the capture and mating of RED (attacking) with the BLUE (target) satellite would likely end its mission if it were a non-manoeuvrable type, and perhaps the RED satellite ground controllers could take control of the captured BLUE satellite. The Mission Extension Vehicle was also designed to detach from Intelsat 901, and perform the same mission on another target satellite, and this could lead to an Orbital Warfare scenario where RED manoeuvrable robotic satellites raid and steal opponent BLUE satellites, perhaps reducing the capability of Disaggregated, Distributed or Proliferated Constellations. The main difference between on-orbit servicing and military application, is this occurs with an uncooperative or uncontrolled space object:

“While several commercial companies are developing capabilities for on-orbit servicing, a distinguishing feature of a military defensive capability is the ability to conduct remote proximity and docking operations with an uncooperative or uncontrolled space object. For example, the Northrop Grumman Mission Extension Vehicle on-orbit serving satellites can attach themselves to a cooperative host satellite. They use their propulsion systems to maneuver the host satellite to a new orbit and take over station keeping—maintaining position in a desired orbit — for the remainder of the satellite’s life. Docking with an uncooperative satellite — either without the operator’s consent or where control has been lost — is more difficult because the satellite could make unexpected movements, may be tumbling out of control, or may react to the docking in unexpected ways if its automatic control system remains engaged. Docking with a satellite under these conditions may require more advanced capabilities, such as a robotic arm, harpoon, deployable net, or other device.” [Harrison, T. Johnson, K. Young, M. 2021 Defense Against the Dark Arts in Space: Protecting Space Systems from Counterspace Weapons. A Report of the CSIS Aerospace Security Project. Rowman & Littlefield (February)]

(2) Robotic Arm Use: to overcome the problem of grabbing/grappling an uncooperative or uncontrolled space object a robotic arm could be used. It has been noted:

“countries have experimented with several ways of disabling adversary satellites. One of them is a Co-Orbital Anti-Satellite system … [with] … a … satellite that … [can] … use a robotic arm to grab or destabilise the target satellite.” [Joshi, M. 2024 A New Frontier: Space Warfare. Observer Research Foundation (27 February)]

It is also possible to disorient satellites, “by shifting their orbits using satellites with robotic arms.” [Joshi, 2024] Earlier in 2019, it was noted:

“The concept of using a robotic arm as a potential weapon in Space has created a brand-new environment of ‘Space warfare’ that has not been encountered before. Current international and national laws do not prohibit the use of robotic arm, nor prevent satellites conducting Rendezvous and Proximity Operations, and thereby leaving any potential ‘attack’ on Allies’ spacecraft in the legal grey area.” [Wong, A. 2019 Robotic Satellite Servicing: Enabler or Threat? The Three Swords Magazine. Volume 35]

Use of a satellite fitted with a robotic arm may also point to a transformation of Orbital Space Manoeuvre Warfare:

“Due to the outcome of direct ascent attack using missiles, the robotic arm sabotaging could be the next generation Space weapon without causing the Kessler Syndrome, which will potentially be damaging all Space-based assets in the nearby altitude. The use of the robotic arm is also more subtle as satellites could hide between the current Space debris field for months as a sleeper satellite and strike when their existence in Space has been forgotten.” [Wong, 2019]

It should be noted, however, in Chinese military literature it is an open question, “if grappling would be intended to enable permanent or reversible satellite interference, or if such activity would be debris generating.” [Burke, K. 2023 PLA Counterspace Command and Control. China Aerospace Studies Institute (December)]

In 2021, it was reported: “one notable object is the Shijian-17, a Chinese satellite with a robotic arm.” [Dickinson, J. 2021 Senate Armed Services Committee Hearing Transcript (21 April); Competing in Space (Second Edition). 2023 A Joint Product of The National Space Intelligence Center and The National Air and Space Intelligence Center (December); Burke, 2023; Williams, C. 2024 Dynamic Space Operations: An Overview and Assessment. National Security Space Association (2 April)] Adding, Space-Based robotic arm technology, “could be used in a future system for grappling other satellites” [Dickinson, 2021; Williams, 2024; Headquarters Space Force Intelligence. 2024 Space Threat Fact Sheet (16 July)]. In 2022, a Chinese satellite Shiajin-21 was able to manoeuvre to capture Compass G2 and move it to a high graveyard orbit. Compass G2, “was tumbling near the Geosynchronous Orbit Belt and this operation demonstrated China’s ability to capture a non-cooperative target.” [Williams, 2024] Shiajin-21 also demonstrated China’s Rendezvous and Proximity Operations, tactics, and capture techniques on its apogee kick motor, where it matched the motor spin rate, captured it and moved it to the graveyard [Williams, 2024].

GRAPPLING SATELLITE CONCEALMENT

The Concealment and Space Situational Awareness relevance to grappling satellites:

“From a technical standpoint, Chinese on-orbit grappling satellites are currently large and detectable, and as such, in the near term, they are probably only capable of on-orbit servicing, not approaching undetected to grapple an adversary satellite. In the near-term, the People’s Liberation Army might be more likely to use these large satellites in what it calls a ‘space-blockade’ to complicate adversary satellite communication links and ability to manoeuvre, simply by moving in the way, not by grappling nor electronically jamming adversary satellites. In the future, however, the People’s Liberation Army will probably miniaturize these systems and achieve what they call ‘stealth satellites’ or ‘nano-spy satellites’, concepts which the People’s Liberation Army primarily intends for Intelligence, Surveillance, and Reconnaissance missions, but which hypothetically could enable grappling of foreign satellites in Geosynchronous Orbit, with lower likelihood of immediate detection.” [Burke, 2023]

It should be noted, Shiajin-17 has a mass of nearly 4,000 kilograms [Burke, 2023; Krebs, G.D. 2024 SJ 17. Gunter’s Space Page], while Shiajin-21 is thought to have a launch mass of 5,000 kilograms, and dry mass of 2,500 [Orbiting Now reporting]. In 2024, it was estimated the relative sizes of Shiajin-17, and Shiajin-21, were:

“Chinese satellites with robotic arms are currently easily trackable with ground-based telescopes because they are very large. The Shijian-17 satellite is approximately 4,000 kilograms —larger than Milstar and just smaller than AEHF. The launch vehicle that carried Shiajin-21 to Geostationary Transfer Orbit has a launch capacity of approximately 5,000 kilograms, indicating that Shiajin-21 may be as large, if not larger than Shiajin-17. When the Chinese have successfully miniaturize satellites with robotic arms, they may have more counterspace applications, as argued in a recent report.” [Burke, K. 2024 PLA On-Orbit Satellite Logistics. China Aerospace Studies Institute (March)]

A 2006 Chinese research paper gives an early account of the basic configuration of a mobile satellite, carrying a micro target satellite, that can be released and captured again by the robot arm, with six-degrees of freedom, with a fixed gripper, that is around two meters long (fully extended), mounted and folded on the underside of the cubic satellite housing, facing towards the front of the craft [Gao, X.H. et al. 2006 Development of the Chinese Intelligent Space Robotic System. IEEE/RSJ International (9 October)]. It should be noted, China’s 2018 design for its On-Orbit Gas Station is equipped with two robotic arms, “[and] … requires a two-meter rendezvous with the customer satellite for the robotic arms to connect.” [Burke, K. 2024 PLA On-Orbit Satellite Logistics. China Aerospace Studies Institute (March)]

► Robotic arms (manipulators), for example designs like the NASA Restore-L satellite is shown with a pair of robotic arms [NASA. 2016 Artist’s View of Restore-L].