Military Spaceflight Part 10 - Modern ASAT

Work on anti-satellite weapons began almost as soon as it became apparent that satellites had military utility, although initial work was driven by fears that the Soviets would put nuclear weapons in orbit. For a variety of reasons, this wasn't particularly well-founded, and it meant that the initial American systems, which used nuclear warheads of their own, were retired relatively quickly. Focus instead shifted to non-nuclear systems. The Soviets had preferred these from the start, designing coorbital systems that would come alongside and blow the target up from close range, while the Americans preferred to go straight up and intercept the target at high speed. The Soviets also looked extensively at in-space weapons, to the point of unsuccessfully launching a laser battle station in the closing years of the Cold War.

A DF-21 launcher

With the end of the Cold War, ASAT development quieted down for about 15 years before things began to heat up in the mid-2000s. China, who had had a quiet ASAT program since the 60s, began live tests of a direct-ascent missile in 2005, said to be based on the DF-21 ballistic missile with a different kinetic kill vehicle. These culminated in a hit on a weather satellite in 2007, which caused more debris than any previous event in the history of satellite tracking. 3,438 pieces were eventually tracked, and because the satellite was in an 850 km orbit, decay is slow, and NASA has estimated that 30% of pieces larger than 10 cm would remain in orbit past 2035. There was global outrage, and while China has run several subsequent tests, these have been against ballistic targets, which don't produce orbital debris. There have also been reports of more powerful ASAT systems, some of which are credited with capability against targets in GEO.

Lake Erie launches an SM-3 against USA-193

More proof of the minimal gap between ASAT and ABM came the next year, when the US conducted its first and only ASAT test since the end of the Cold War. In December 2006, USA-193, a radar satellite, malfunctioned shortly after launch, and by early 2008, its orbit had decayed to the point where it would reenter the atmosphere quite soon. The failed satellite had a tank full of toxic hydrazine, used as fuel by its thrusters, and there were concerns that it would survive reentry and harm those on the ground. There has been debate about the validity of these concerns ever since, with critics alleging that it was really a response to the Chinese test a few months earlier,¹ but ultimately President Bush decided to shoot USA-193 down with an SM-3 fired from the cruiser Lake Erie. The shootdown was successful, and because USA-193 was in low orbit, the vast majority of the debris entered the atmosphere within a few days, although some pieces persisted until late 2009.

India's ASAT missile heads for the sky

More recently, India and Russia got into the ASAT game, with India conducting a test in 2019 using its main ABM interceptor. The test was at low altitude (~300 km), to minimize the debris threat, although the last piece didn't deorbit until 2022. Russia ran its own test in 2021, using the new A-235 ABM on a Soviet-era SIGINT satellite. Although its orbit had decayed significantly over its four decades in space, the target satellite was about 475 km up, and the debris posed a significant threat to the ISS, requiring the crew to take shelter in the return capsule during the first few passes through the debris cloud. Fortunately, increased solar activity in the last few years has meant that these have cleared more rapidly than expected,² and by February 2023, only 300 of the initial 1,700 pieces of debris remained in orbit.

Cubesats launched from the ISS

Increased ASAT activity in recent years has turned the eyes of space warriors towards countermeasures, and they were helped a great deal by parallel developments in the broader space industry. During the Cold War, the US in particular relied on a small number of very sophisticated and very expensive satellites, which raised the obvious concern that the Soviets didn't have to kill very many targets to make a huge dent in US capabilities. But over the last decade, the broader space community has started to pivot towards "smallsats", making use of large constellations of small, cheap satellites, often launched as secondary payloads for larger satellites. Probably the first major user of this was Planet Labs, which uses CubeSats, each 30 cm x 10 cm x 10 cm, to provide daily imagery coverage of the Earth, although the current standard-bearer is Starlink, which operates about 6,000 satellites as of May 2024. To put this into perspective, the total number of active satellites in 2015 was a mere 1,364.³ As a result, the US and other powers have been getting on board, making plans for "proliferated constellations" which are simply too numerous to shoot down effectively.⁴

USA-193 moments after the SM-3 hit

All of which brings us to the state of affairs today. In 2022, the US voluntarily gave up testing of direct-ascent ASAT weapons that would leave orbital debris, a policy that is perhaps a bit narrower than it looks at first. Russia has continued work on coorbital ASAT, and on several occasions over the past few years has placed what appear to be killer satellites in the same orbital planes as big US recon satellites, although public information is that they've stayed at different altitudes and generally kept well clear. The most recent of these, Cosmos-2576, went up in mid-May 2024, into the same plane as USA 314, believed to be a KH-11 imaging satellite. More worryingly, the DOD has been reporting that the Russians are looking at nuclear ASAT weapons. Details are sketchy as they've been even more five-sided than usual in their statements, to the point that it's not even clear if they're saying it has a nuclear warhead or nuclear power of some kind, but it appears that the plan is to use the radiation from nuclear weapons in LEO to damage basically all satellites in those orbits. The Russians have launched several spacecraft in support of this, most notably Cosmos-2553, which was presumably intended to figure out the most efficient spot to detonate the weapons, although indications remain that the Russians haven't actually launched a nuclear warhead into orbit yet.

The future of ASAT?

ASAT remains an exciting and evolving field, although widely misunderstood by the general public and policymakers. As can be seen from this history, claims that current efforts are unprecedented are not well grounded in reality, and there is far less distinction between ASAT and ABM work than first appearances would have you believe. Unfortunately, militarization of space is probably inevitable, and defeating it will require a variety of countermeasures beyond just building more satellites. There's a (surprisingly readable)⁵ report on these countermeasures here.