Military Spaceflight Part 9 - Cold War ASAT

The military utility of satellites quickly set the US thinking about ways to counter Soviet space presence. Given that this started in the late 50s and early 60s, it should be no surprise that the initial efforts, Project Mudflap and Program 437, were nuclear-tipped. But these, based on small islands in the Pacific, had limited engagement windows and using them would require accepting the rather dramatic consequences of high-altitude nuclear weapons on satellites and those on the ground.

This had been justified by fears of the Soviets putting nuclear weapons in orbit, but in the early 70s, Project 437 was shut down as it became increasingly clear that the Soviets weren't going to do that. As for other Soviet satellites, their recon birds had to return their film for processing, limiting their utility during a war, while communications was done from orbits far too high for the Thor missiles used in Project 437 to reach. But things began to change in the late 70s, as the Soviet ocean surveillance program ramped up, exposing US forces to real-time space surveillance and producing a resurgence of interest in ASAT. The downsides of using nuclear weapons in space meant that this version would involve getting a direct hit on the target satellite. And because the target had to be killed quickly, the weapon would need to be far more mobile than the old Thor, resulting in a return of the air-launched concept that dated back to Bold Orion, although this time with the high-performance F-15 as a launch platform.¹

ASM-135 ASAT on display at Udvar-Hazy

The result was the ASM-135 ASAT,² which used the first stage from the AGM-69 SRAM and the Altair second stage to boost a 16 kg "Miniature Homing Vehicle" up to intercept a satellite directly. There was no explosive warhead, so killing would require a direct impact, aided by an IR seeker. Using the F-15, which launched the missile in a supersonic zoom climb, as a launch platform meant that the missile only had to go essentially straight up, allowing the relatively small weapon (although it was still too big for most fighters) to intercept satellites at altitudes of 500 km or more. Development didn't go particularly smoothly, and there was significant Congressional opposition due to concerns about the ASAT program impacting arms control. The only operational test, carried out against the Solwind satellite,³ took place in September 1985, and resulted in a direct hit, the only time a satellite has been destroyed from an airplane. Shortly thereafter, a Congressional moratorium against destructive tests went into effect, and a few more tests were run with the MHV locked onto a star before the whole program was cancelled in 1988.

An F-15 launches an ASM-135 against Solwind

Opposition to the ASM-135 program was at least in part due to spillover from the public furor over Reagan's Strategic Defense Initiative, recently announced at the time of the Solwind test, and the connection wasn't entirely spurious. Satellites and ICBM warheads are both fast-moving targets that need to be engaged in space, and while there are significant differences, developments in one field are likely to be useful for the other. A year after the Solwind shootdown, the SDIO conducted another space test, known as Delta 180 after the rocket that launched it. This involved a deliberate impact between an orbital interceptor and the stage that launched it, intended to gather data for the development of in-space interceptors for SDI.⁴ Delta 180 was notable as the first in-space intercept test that took the debris problem seriously. It was conducted at low altitude (192 km), where drag would quickly deorbit the fragments, and was apparently successful in this.⁵

An artist's conception of an IS-type satellite

The Soviets had not been idle during all of this. American reliance on space systems had been obvious from early on, and the Soviets had begun their ASAT efforts in 1960. Although they experimented with an air-launched direct-ascent missile, even taking it to the point of flight tests,⁶ the Soviet preference for solving problems with big boosters instead of complicated electronics kicked in, and they selected the coorbital system under the name Istrebitel Sputnikov, which translates to "destroyer of satellites".⁷ The IS involved a radar seeker and a 300 kg warhead, with a lethal range of maybe a kilometer or so, and while it avoided the tricky timing required for a direct-ascent system, it was also likely to take an orbit or two to intercept the target, which gave the opponent time to avoid it. Various bureaucratic snafus meant that it wasn't until the late 60s that testing started in earnest,⁸ but by 1972, the Soviets were confident enough in the system to stop testing and keep the capability in reserve for war.⁹ Development continued on systems capable of making quicker interceptions, and by the late 70s, it had demonstrated the ability to intercept targets within the first orbit, and at altitudes from 160 km up to 1600 km. The only serious limitation was the inability to attack targets with inclinations lower than about 45°, which wasn't too much of a problem for the Soviets, as satellites in lower-inclination orbits wouldn't pass over the USSR.

Buran on its An-225 Mriya carrier aircraft

Other aspects of the Soviet ASAT program are shrouded in mystery. In the 80s, there were reports of a directed-energy weapon¹⁰ capable of damaging US satellites from the ground, although it appears that no such weapon actually existed. It is very much worth pointing out that the best lasers at the time would have been completely unable to do anything more than blind a satellite looking down at the surface, and it's not entirely clear that said blinding would have been from damage to the optical system instead of just not being able to see anything. Work on a similar system was reported around 2010, but little has been heard since then. There were also specialized systems designed to counter the Space Shuttle, which the Soviets thought would be a system for either bombing Russia out of a polar orbit or snatching satellites for inspection. In fact, they were so convinced of this that they essentially cargo-culted their own version, copying most of NASA's design for Buran, which flew one unmanned mission in 1988 and was then cancelled with the fall of the Soviet Union.¹¹ But having their own shuttle wasn't enough, and they are believed to have responded by designing Uragan, a spaceplane that was supposed to be armed with space-to-space missiles, although it was cancelled in the aftermath of the Challenger disaster.

Salyut 3

But the most interesting aspects of the Soviet ASAT program involved orbital systems beyond IS. Much liked the US, they had investigated manned inspection/destruction capabilities in the early 60s, producing a bewildering array of military Soyuz designs, none of which flew thanks in large part to internal politics. Instead, the winner was Almaz, a series of military space stations sent up to see if manned recon satellites would make sense, similar to the US MOL. Fears of US inspectors meant that the Almaz-2 station¹² (flown under the cover designation Salyut 3) was equipped with a 23 mm cannon, adapted from one used in the tail turret of the Tu-22 bomber. It was fixed to the station, which would have made aiming unwieldy, and concerns about vibration meant that it was only fired when the station was unmanned. It appears that the gun was not carried on Salyut 5, the last Almaz flight before the program was cancelled and a few spare spacecraft converted into big radar satellites. There are rumors that it was equipped with space-to-space missiles, but no details are available and it's likely that this wasn't the case. Soviet interest in space-to-space weapons increased during the 1980s, as they wanted a potential counter to the space-based elements of SDI, culminating in the 1987 launch of Polyus, a 100-ton spacecraft equipped with a megawatt-class CO₂ laser. It was launched using the massive Energia developed for Buran, but a glitch meant that instead of speeding the spacecraft up a bit into its final orbit, the last stage slowed it down, dumping it into the Indian Ocean.

Polyus was the last gasp of Cold War-era ASAT weapons, but while the end of the Cold War saw the brief slowdown in ASAT weaponry use, the field has seen a resurgence in recent years. We'll cover that next time.