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Modern military capabilities are becoming increasingly dependent on satellites, from communications to navigation, to reconnaissance and intelligence. This situation makes the space domain a crucial battleground in the future, and is incentivising the development of both offensive and defensive capabilities in this sphere.

Sixty years ago, a group of computer users at the Massachusetts Institute of Technology developed a primitive computer game that they dubbed Spacewar!. Run on the Digital Equipment Corporation PDP-1, a computer with a clock speed of 187 kHz, and only 9 Kb of memory, it featured two torpedo-armed spaceships under the control of rival players and able to dogfight while manoeuvring in the gravity well of a star located at the centre of the screen. Today, Spacewar! is a distant landmark in the history of computer games, but in the real world the techniques for space warfare have been explored by at least four nations. Satellites used for tasks such as communications, reconnaissance, and early-warning could be major targets in any future conflict.

US DoD Joint Publication 3-14 2018 titled Space Operations warned that adversaries were “developing, testing, and fielding capabilities in an attempt to deny the United States the advantages gained from space. Our adversaries’ progress in space technology not only threatens the space environment and our space capabilities but could also potentially deny us an advantage if we lose space superiority.”

Military satellites are not the only potential target. On 27 October 2022, a senior Russian foreign ministry official warned that as a result of military exploitation of commercial space systems such as SpaceX Starlink communications satellites and Maxar imaging satellites, these spacecraft “may become a legitimate target for retaliation.”

A Hostile Environment

Space is, and always will be, a hostile environment that challenges the spacecraft designer. It poses problems such as temperature-control, radiation, the absence of atmospheric pressure, residual atmospheric drag, spacecraft electrostatic charging, and the risk of meteoroid impact, or impact with man-made space debris. Although electromagnetic interference has the potential to disrupt spacecraft operation, this would be unintentional. However, intentional man-made threats include anti-satellite (ASAT) weapons, lasing and other forms of directed energy attack, as well as cyberattacks.

On 21 February 2008, the US Navy Aegis cruiser Lake Erie launched a single modified SM-3 missile which successfully engaged a defective US National Reconnaissance Office radar-imaging spacecraft. Credit: US Navy

The simplest form of ASAT weapon is the direct-ascent interceptor. After launch, these missiles fly suborbital trajectories that result in them intercepting a target spacecraft – a technique that requires a detailed knowledge of the target’s orbit and current position. There are two potential kill mechanisms. One relies on directly striking the target, relying on the interceptor’s mass and speed to create an impact that will at a minimum cause massive damage to critical components, and at best totally shatter its victim. The other approach uses a proximity-fuzed explosive warhead, and will remain effective if the attacker has less accurate knowledge of the target’s position. Both types of attack will create large debris fields which can be a hazard to other spacecraft, and increase the risk of a ‘Kessler syndrome’ scenario occurring, which would impede space exploitation for all.

Orbiting inspectors

An alternative engagement method involves placing a dedicated interceptor spacecraft into an orbit similar to that of the target. This allows the interceptor to make a slow approach to observe the other spacecraft. Images of the latter could show optical ports, antennas and sensors, features that would suggest the target spacecraft’s intended purpose.

To test the technology needed to allow one small unmanned spacecraft to close in on another, the US Air Force Research Laboratory gave Boeing a contract to develop the XSS-10 (eXperimental Small Satellite 10), a microsatellite weighing only 28 kg. Launched by a Delta II vehicle on 29 January 2003, the XSS-10 was released from Delta II’s second stage about 16 hours after lift-off. It then used its built-in guidance system (which included a television camera) to manoeuvre itself close to the spent second stage. The XSS-10 then backed away from the stage, and repeated the approach twice more. Under a follow-on project to demonstrate autonomous rendezvous and proximity manoeuvres, Lockheed Martin built a 125 kg spacecraft designated XSS-11. Launched by a Minotaur rocket on 11 April 2005, it spent more than 18 months in its primary orbit, before being manoeuvred into a graveyard orbit.

The spent Delta-K second stage of a Delta II rocket was photographed in orbit in January 2003 by the XSS-10 satellite that it had just launched.
Credit: USAF

Until 2014, the existence of a US satellite-inspection system able to perform rendezvous and proximity manoeuvres in geosynchronous orbit was classified, but the programme was publicly disclosed in February of that year. Built by Orbital Sciences, the Geosynchronous Space Situational Awareness Program (GSSAP) satellites are controlled by operators at Schriever Air Force Base in Colorado.

Launched into in drift orbits just above or below Geostationary orbit (GEO) or Geosynchronous orbit (GSO), GSAAP satellites are able to position themselves close to selected non-US spacecraft, then use optoelectronic sensors to observe these, so that ground-based intelligence analysts can assess the target’s likely role. It has been speculated that GSSAP spacecraft may also carry electronic intelligence (ELINT) receivers able to monitor radio transmissions to and from the satellite being observed. Given their method of use, GSSAP satellite are likely to carry a large enough quantity of propellant to allow frequent orbit adjustments and station-keeping manoeuvres.

During a press briefing in September 2015, Gen. John Hyten, commander of Air Force Space Command, revealed that the first two GSSAP satellites to be launched had been temporarily taken out of test mode to make observations of specific objects in GEO/GSO. “The users that requested the information are extremely pleased with the pictures we gave them,” he stated, describing them as “truly eye-watering”.

This artist’s rendition shows two US Geosynchronous Space Situational Awareness Program (GSSAP) satellites in orbit.
Credit: USAF

Since US military satellites have been monitoring other inhabitants of GEO/GSO since the 1990s, it is hardly surprising that Russia and China have joined this orbital ballet, using their own specialised satellites to observe US spacecraft. For example, soon after China’s Shiyan-12-01 and Shiyan-12-02 satellites reached geostationary orbit early in 2022, the US manoeuvred its GSAAP-3 to take a close look at the newcomers, which responded by conducting counter manoeuvres during which Shiyan-12-02 is reported to have positioned itself in a good location to observe the US satellite.

Potential Means of Attack

Given its slow approach speed, an orbital interceptor will be unable to use kinetic impact in order to obtain a kill. The easiest solution might be to equip the interceptor with a warhead, or with a rocket-powered sub-missile that it can fire at the target. An alternative kill mechanism might be some form of chemical spray that could damage optical windows, solar panels, or antennas of the victim.

Robotic Arms – a Cause for Concern?

Some spacecraft designed for rendezvous missions are also being fitted with robotic arms. Working under a contract from the US Space Force, Northrop Grumman is developing a spacecraft fitted with a robotic arm that could be used to repair or relocate other satellites. Due to make its debut in 2024, the Mission Robotic Vehicle (MRV) is equipped with a robotic arm, and will be able to install propulsion packs on failing or failed satellites.
Sometime in 2026 or later, NASA plans to launch OSAM-1 (On-orbit Servicing, Assembly, and Manufacturing-1), a spacecraft equipped with robotic arms and all the tools and equipment needed for a planned repair mission intended to refuel the Earth-observing satellite Landsat 7. In orbit since 1999, Landsat 7 was not built with refuelling in mind, so OSOM-1’s ground-based engineers will direct one of robotic arms to use the tools needed to cut away the satellite’s multi-layer insulation thermal blanketing, then expose and unlock the propellant fill/drain valves so that these can be accessed by a refuelling hose.

This artwork shows how NASA’s On-orbit Servicing, Assembly, and Manufacturing 1 (OSAM-1) spacecraft (bottom) will grapple Landsat 7 before giving the latter a fresh supply of fuel.  Credit: NASA

Servicing existing satellites, or removing life-expired examples from GEO/GSO are useful activities, but the ability to manoeuvre one satellite close to another or even to connect up the two has obvious military applications. The technology that makes one class of mission possible also enables the other. Although a valuable tool for use on satellite-repair missions, a robotic arm gives a spacecraft the potential ability to conduct a docking manoeuvre against a non-cooperative target, or even to render the latter inoperable by inflicting damage by degrading or disabling individual components of its victim such as solar panels, antennas, or optical ports.

Directed Energy – the Multi-Shot Threat

Often ground-based, directed-energy weapons use high-powered beams of laser or microwave energy to damage or destroy the targeted spacecraft. Their effect is scalable, so that the damage inflicted to the victim can be either temporary or permanent. Interceptor satellites are essentially single-shot systems, but a directed-energy weapon would be capable of engaging multiple targets.

In an April 2022 presentation to the US Senate Armed Services Committee, General James H. Dickinson, the Commander of US Space Command noted that “Russia also has several ground-based low-power lasers designed to temporarily blind US missile warning and imagery satellites, and high-power lasers developed to damage US satellites.” He also warned that China has “multiple ground-based laser systems of varying power levels that could blind or damage satellite systems.”

Light from three green lasers is sent skywards from facilities at the Starfire Optical Range on Kirtland Air Force Base, New Mexico. Deformable optics are used to minimise optical distortions caused by the Earth’s atmosphere. The Starfire lasers are used for research, but similar technology might allow the creation of a laser-based weapon for direct attacks against satellites.
Credit: USAF

Hacking the Satellites

In May 2022, Secretary of State Antony J. Blinken reported the US assessment that Russia had launched cyberattacks against commercial satellite communications networks in late February of that year in order to disrupt Ukrainian command and control during the early stages of the Russian invasion if Ukraine. This activity had disabled very small aperture terminals in Ukraine, but had also affected tens of thousands of terminals outside of Ukraine, he claimed.

Protecting the spacecraft

Some of the potential methods of defending satellites from attack are similar to those used to protect aircraft and UAVs from attack – manoeuvrability, passive and active countermeasures, and stealth. Spacecraft manoeuvres might be used to create problems for the enemy’s targeting system. Speaking at the 2019 Aspen Security Forum, former Secretary of the US Air Force Heather Wilson revealed that the Boeing X-37B unmanned recoverable spacecraft can fly at altitudes low enough to allow the use of atmospheric drag to change its orbital parameters in order to temporarily confuse the space-surveillance systems of other counties.

In a 2015 documentary on the US CBS TV channel, General John Hyten, at that time head of Air Force Space Command, was asked if US military satellites could manoeuvre to counter an anti-satellite weapon. “It depends on a huge number of variables”, he replied. “It depends on the satellite. It depends on the mission. It depends on when [the satellite] was built, depends on how old it is. It depends on when we know the threat is coming.”
Given the high level of secrecy associated with many types of military spacecraft, almost nothing is known about their configuration and payload. While most if not all will use thrusters for orientation and orbital positioning, the capacity of their propellant tanks, and thus the degree of potential manoeuvrability available for defensive purposes is unknown. In the case of high-value space assets such as large reconnaissance, sigint, and early-warning spacecraft that are expected to have a long service life, it might be possible use an orbital-repair capability to top up the thruster propellant stock, or to attach a module containing decoys and obscurant launchers. A New York Times article published on 3 November 1987 claimed that “Future spy satellites will be capable of being refuelled, dramatically extending their range and lifespan.”

KH-11 imaging satellites use a hydrazine-powered propulsion system when making orbital adjustments, and it has been suggested that this could have been refuelled during classified missions by the Space Shuttle. The Block III satellites (KH-12) have a reported lifetime of 15 years, which may have been made possible by larger fuel reserves and unmanned refuelling missions.

Potential Countermeasures

If an incoming direct-attack interceptor has achieved lock-on, this could be broken by the deployment from the satellite of a cloud of obscurant, while the release of several decoys could create problems when the attacker tries to regain lock. Another way of defending satellites would be to equip these with electronic and optical countermeasures intended to jam or spoof enemy kill vehicles, or even to use kinetic shoot-back weapons based on unguided or guided projectiles. An alternative approach would be to mount such hardware on separate guardian satellites, or even to use guardian satellites able to rapidly reposition themselves between the enemy threat system and the satellite the guardian is protecting.

Is Stealth the Answer?

Stealth technology is being applied to military spacecraft – a concept described in a 1963 memorandum which the US National Reconnaissance Office declassified in 1997. This document described the need for a satellite featuring a “reduction in radar and optical cross-sections below the detection threshold” and stated that “as no vehicle to ground transmissions are permissible, any ground command system envisaged must operate without verification of commands received.”

As part of its celebration of the 40th anniversary of the first successful mission of a Corona spy satellite, in August 2000 the US National Reconnaissance Office (NRO) honoured 10 individuals who had played a major role in creating the US space-based reconnaissance capability. One of these was Dr. Edward Purcell, whose main contribution “involved methods to make these vehicles, if not invisible to radar, hard to observe with radar.” During the 1980s a special security classification named ‘Zirconic’ was set up to control access to information on US programmes involving stealth satellites.

Radar cross-section and visual detectability are largely dictated by the size of the basic structure of the spacecraft and of its external components such as solar panels or antennas. But there is very little information in the public domain on how a satellite’s signature might be minimised. In some ways the situation is similar to that of half a century ago, when the existence of first-generation stealth aircraft was known, but there was almost no accurate information on how signature reduction had been achieved.

Clues to possible methods for creating a stealthy spacecraft have been given in several US patents. A 1994 patent filed by Teledyne Industries (now Teledyne Technologies) proposed using a large inflatable cone-shaped balloon made of Mylar or Kapton coated with a film of radiation reflecting material such as gold or aluminium, which would be mounted on a rotating arm on the body of the spacecraft. This arm could be moved into position to conceal the satellite when such measures were needed, with the balloon intended to deflect radar energy and light away in harmless directions. According to the patent, this was intended “to suppress the laser, radar, visible and infrared signatures of satellites to make it difficult or impossible for hostile enemy forces to damage or destroy satellites in orbit”. At times when the satellite needed to observe targets on the ground, the device could be moved out of the way of the spacecraft’s sensors.

This diagram from a US Patent awarded to Teledyne Industries shows how a movable arm (40) could position a conical anti-radar shield (10) in the general direc¬tion of a threat if an attack on a satellite (12) seems imminent, then move it back to a parked position when the satellite is ready to resume its normal functions.
Credit: Teledyne Industries

Another scheme based on inflatable hardware was patented by Bigelow Aerospace in 2005. This combined a multi-layer inflatable shell with a core able to house mission-specific payloads, an attitude-control device, a power source, and a controller. The shell could incorporate radar absorbing materials and/or geometries that reflect radar waves at angles that make detection of the craft difficult, but may also have radio or microwave characteristics that allow specific radio frequencies to pass through the shell without substantial attenuation, allowing the mission payload to transmit and receive information. The shell could also incorporate a window to be used by optical equipment inside the craft such as a camera. The shell could be coloured as to make visual detection more difficult, while its shape would conceal the function of the spacecraft.

Stealth in action

Press reports in 2007 claimed that in November 1990, the US had used the space shuttle Atlantis to launch a highly-classified satellite designed to rendezvous with Russian and other satellites in GEO/GSO. Reported to be optically stealthy, and to have the nickname ‘Prowler’, it was said to have the ability to home on its target autonomously rather than relying on data and commands sent by its ground-based users. Once in position close to a satellite, ‘Prowler’ was credited with the ability to capture visual imagery of the target, measure its size and RCS, and detect the radio frequencies that the target used.

The US is thought to have used stealth technology in a classified programme with the reported codename of ‘Misty’. This designation has been associated with satellites launched on 28 February 1990 and 22 May 1999. Following both launches, ground-based amateur observers were initially able to track the satellite, but shortly afterwards could find only a group of smaller multiple objects. Since it is unlikely that both satellites had suffered from catastrophic failure, it is possible that these satellites had released multiple decoys before moving off towards their operational orbit. Although a follow-on stealth satellite programme was reported in 2004, shortly after becoming the United States Director of National Intelligence in 2007, vice admiral Mike McConnell was understood to have cancelled it, but this has never been confirmed.

Large Constellations – a Novel Solution

If the would-be attacker is faced with only a relatively small number of satellites that need to be targeted, only a modest number of ASAT weapons will be required. So an obvious countermeasure is to significantly increase the number of satellites, forcing the other side to increase the quantity and/or size and cost of its threat systems.

India became the third country to demonstrate ASAT capability when it launched its Ballistic Missile Defence (BMD) Interceptor missile to engage a target satellite in Low Earth Orbit (LEO) on 27 March 2019.
Credit: DRDO

One simple way of complicating the situation for a would-be attacker is to deploy a larger number of similar satellites to in order to perform missions. A less-expensive defensive measure might be avoid the use of multi-mission satellites, and deploy a larger number of separate mission-specific spacecraft which operate in parallel to provide the same total capability. This approach is known as disaggregation.

Set up in March 2019, the US Space Development Agency (SDA) favours the use of large satellite constellations based on low-cost spacecraft. It envisages a network of satellites in low-earth orbit that would be deployed in layers tasked with different military capabilities such as reconnaissance, surveillance, global navigation, and communications. These individual spacecraft would be interlinked by a secure command and control network using laser-based communications.

Mass-produced and comparatively inexpensive due to the use of commercial satellite technology, these networked satellites would total more than 1,000 by 2026, so would be numerous enough to saturate the capabilities of the ASAT weapons deployed by potential opponents. Individual satellites would be relatively short-lived, so the production programme would use spiral development to steadily improve their capabilities.

DARPA’s Blackjack programme is intended to develop and demonstrate the critical elements for a global high-speed network of satellites deployed in low Earth orbit (LEO). A constellation of this complexity would be difficult target for a non-nuclear ASAT attack.
Credit: DARPA

Following its realignment underneath the US Space Force, on 23 January 2023 the Space Development Agency (SDA) renamed its National Defense Space Architecture (NDSA) to the Proliferated Warfighter Space Architecture (PWSA).

Speaking during a Space Symposium 365 event in February 2022, Space Systems Command Executive Director Joy White stated that as a result of growing concerns over evolving on-orbit threats, Space System Command had set 2026 as the target date for delivering “maximum operational capability” in the form of new, more resilient space systems.

Each of the planned tranches of the PWSA is essentially one generation. Planned for Fiscal Year 2022 (FY22), Tranche 0 is seen as the minimum viable product able to demonstrate the feasibility of the PWSA in terms of cost, schedule, and scalability. Tranche 1 in FY24 will be expected to provide an initial warfighting capability in terms of regional persistence for tactical data links, advanced missile detection, and beyond line-of-sight targeting.

Tranche 2 in FY26 will expand the system to provide global persistence. In March 2023, the SDA released a request for industry feedback on a tranche 2 low Earth orbit Tracking Layer architecture able to provide global surveillance and targeting for missile warning, missile tracking, and missile defence. Information was sought regarding “mature infrared payloads for space-based sensing, constellation architecture(s), resiliency methods, and mission data processing parameters”. Contract award was planned for FY24, leading to first launches in mid-FY27.

Tranche 3 in FY28 is expected to include better sensitivity for missile tracking, better targeting capabilities, additional positioning, navigation and timing (PNT) capabilities, plus advances in blue/green laser communications and protected RF communications. Tranche 4 (FY30) should incorporate whatever additional capabilities have been identified as being needed to meet current or future threats.

The SDA uses the term ‘layer’ to indicate a particular function of the architecture, but this function may not have its own dedicated constellation of satellites. Some layers will deliver capabilities with sensors, processors or other technologies hosted on another layer’s satellites. An example of this approach is the Battle Management Layer whose software and processing capabilities will be hosted on most or even all PWSA spacecraft.

The Tracking Layer and Custody Layer will provide sensing functions for advanced missile threats and time-critical land and maritime targets, but will be connected to the Transport Layer – a network of communication satellites that connect to one another and to other space vehicles and ground stations via optical inter-satellite links (OISLs). Threat indications and targeting data will be transmitted to the ground in real time.

The growing use of large constellations of Low Earth Orbit (LEO) telecommunications satellites has changed the way that these spacecraft are launched. Iridium’s constellation of more than 80 satellites involved missions in which a single launch vehicle carried ten satellites, but this was eclipsed in May 2019 when SpaceX began to use its Falcon 9 launch vehicle to orbit 60 satellites at a time.

On 23 October 2022 India’s LVM3 launch vehicle carried a total of 36 OneWeb communications satellites into low Earth orbit. The total weight of the combined payload was 5,796 kg, and the individual spacecraft were dispensed over a period of 1 hour and 15 minutes.
Credit: ISRO

While using a launch vehicle weighting hundreds of tonnes may be a viable method of orbiting such a large number of satellites simultaneously, a similarly-sized missile able to release a similar number of ASAT kill vehicles would not be a viable weapon for use against a numerically-large satellite constellation.

Secrets of the ‘Black’ World

Given that details of the KH-7 Gambit photo-imaging satellite remained classified until 2011, more than four decades after the system was taken out of service, it is likely that details of systems such as Misty will remain ‘under wraps’ for several decades more, especially information relating to its low-observable features. Russia and China are likely to be equally cautious is releasing this class of information, so the full story of ASAT systems, satellite inspectors, stealth spacecraft, and the orbital game of move and counter-move is unlikely to be told in the foreseeable future. Yet from available information it seems clear that the cosmic arms race is already well under way.

Doug Richardson