Military Technology 05/2021

in the air and either stationary or moving. Uplink jamming, then, seeks to prevent the radio receiver aboard the spacecraft from receiving the intended signal, by transmitting a stronger signal of the same frequency into its antenna. As normal communications are restored when the jammer is switched off, and no damage is done to the satellite, the effects of such jamming attacks are regarded as reversible. The target organisation’s chances of attributing the attack to the attacker is modest, in CSIS’ estimation, be- cause equipment that can be used for jamming is readily available on the market, it may not be practical to geolocate the source of the jamming signal precisely in the time available and accidental ‘friendly fire’ jamming is quite common. While the satellite operator will be aware of uplink jamming, because it will interfere with commands sent up to the spacecraft, the end user of the data might not be, unless the satellite was serving as a relay between points on earth, which is often the case. Some satellites route both user data and command-and-control signals though the same receiving sys- tem, but others separate them. Unless the attacker has some other means of monitoring the actions of the satellite operator, or some of the data’s end users, they have no way of determining whether the attack was successful. Direct collateral damage from a jamming attack on an uplink is unlikely, as such an attack only disrupts the targeted signals, although it could spill over into adjacent frequencies. The same conclusions regarding attribution, reversibility, awareness, success assessment and collateral damage apply to downlink jamming, but here the geometry of the engagement is different, as the target of the jammer is on Earth rather than in space. GPS receivers, for example, are prime targets for this, as the signal from each satellite has to cover a large area with limited power, and is relatively easy to overwhelm locally with jammers of only modest power. Spoofing and Cyber Threats While jamming is intended to prevent the target from receiving the desired signal, spoofing is a more ambitious attack, whose purpose is to fool the receiver into accepting a fake signal as the real one, thereby With the US reportedly preparing to reveal the existence of a pre- viously secret space weapon programme, there is naturally a great deal of speculation about the kind of weapon it could be. The most spectacular are hard-kill missiles launched from aircraft, ground sys- tems or naval vessels, capable of obliterating any satellite whose or- bit they can reach. Such weapons, however, are inevitably messy, as they create fast-moving, high energy debris that can threaten other spacecraft in nearby or intersecting orbits. The ultimate worry is the Kessler Syndrome (named for NASA scientist Donald J Kessler who first described the danger in 1978) in which debris collisions create more debris in a cascade of destruction that wrecks every human-made object in orbit and effectively renders space unusable for an extended period. There are much more subtle options, how- ever, and it is possible that the about-not-to-be-secret-any-more US weapon is one of them. Easy Targets For all their importance to military operations – and to everyday life in the modern world – satellites are relatively easy targets for any nation or non-state actor with space or telecommunications capabilities of their own. Satellite orbits are predictable, and many are a matter of public re- cord, with freely accessible apps and websites catering both to amateur enthusiasts and professionals – perhaps unintentionally, but inevitably, providing initial targeting data. Stealth is extremely hard to achieve in space, since all objects are detectably hotter than the background, and few satellites have been designed with minimising their radar cross-­ section in mind, so detecting and tracking them with ground-based sen- sors is well established. Many have sensitive optics, and all rely on radio links for command and control, transmitting their data to Earth and for general housekeeping: the receivers of those links all have at least some susceptibility to electronic attack from jammers and cyber weapons. US think tank the Center for Strategic and International Studies (CSIS) carries out regular space threat assessments from an American perspec- tive, as does the US government itself, through the Defense Intelligence Agency (DIA), for example. While it can be assumed that potential adver- saries’ space systems are held at risk by US counter-space capabilities, it is still probably the case that they are less dependent on space for their overall military capabilities than is the US, although Chinese, Russian, North Korean and Iranian capabilities are all improving, according to the DIA. As the largest space power, however, the US has most to lose in this respect. As part of its assessment, the CSIS puts together a taxonomy of at- tacks, dividing them into physical attacks of the kinetic and non-kinetic varieties, electronic and cyber. It also assesses them against a set of con- siderations, including likelihood of attribution, whether or not its effects are reversible, awareness (how obvious it will be to the satellite operator and customers of the data, for example), ease or otherwise of assessment of success by the attacker and the nature of any likely collateral damage. Uplink and Downlink Jamming In electronic warfare, the target of any jamming attack is always a receiver. In a satellite uplink the receiver is aboard the spacecraft, while in a downlink the receiver is on Earth, generally either on the surface or Peter Donaldson Counter-satellite – Attack and Defence An artist’s impression, based on tracked objects in near Earth orbits, illustrates the potential for cascading collisions generating debris exponentially and cutting humanity off from space – the Kessler Syndrome. (Image: European Space Agency) 40 · MT 5/2021 · Special Supplement