Transcript

The F15 Satellite Killer

In the early 1980s, an interesting new program was proposed for the F-15. With an assumption that future warfare would involve low orbit satellites, a proposal was made to develop a set of weapons capable of being launched from standard fighter aircraft toward space targets. This program, known as F-15 ASAT, would produce a missile capable of shooting down satellites in orbit.

HISTORY

In the 1970s, with the strategic advantage of satellites becoming increasingly important, the United States, and presumably other nations, began to plan for the possibility of space warfare. They foresaw the rise of what they called ‘killer satellites’, designed to intercept and destroy American satellites, and perhaps eventually be capable of attacking targets on the earth’s surface. In 1978, it was also claimed that the Soviets had begun working on an anti-satellite program. Thus, the move to formulate a new missile system that could be carried by fighter aircraft and launched at space targets with a high degree of accuracy.

The groundwork for anti-satellite (or ASAT) missiles dates back to the late 1950s. In 1958, Lockheed and Convair jointly designed the WS-199C (or High Virgo) an-aircraft launched ballistic missile. Launched from a B-58 Hustler at Mach 2, the High Virgo missile would travel at Mach 6 to its target, being guided by an advanced inertial guidance system. On September 22 1959, after three previous launches, the fourth missile would be used to track and destroy a satellite. Attempting to lock-up the Explorer 4, the High Virgo missile was launched, complete with cameras and data transmitters to monitor accuracy. However, soon after launch, the missile lost telemetry signal and the test failed.

During this same period, Martin Aircraft researchers had been working on a similar air-launched ballistic missile. The missile produced (known as WS-199B, or Bold Orion) was designed to be dropped from a B-47 in a zoom climb. On October 13, 1959, an anti-satellite test was conducted. Climbing to 35,000 feet, the B-47 released the missile. Soon thereafter, the missile successful tracked and approached the Explorer 6 satellite at an altitude of 251 kilometres, passing within a range of 6.4 kilometres. This was considered a success, as an anti-satellite missile in combat would have been equipped with a nuclear warhead, thus easily destroying the target at such a close range.

Despite this success, both programs were closed down, but the research data would prove foundational in the later Skybolt program – an effort to produce an even more advanced air-launched ballistic missile.

ASAT

In earlier programs, the general concept was to simply deploy a nuclear warhead to destroy the target within a certain range. However, missile targeting computers were becoming far more accurate, and propulsion systems could propel missiles to upwards of Mach 12. Therefore, kinetic energy at this speed could completely destroy a satellite, without the repercussions of detonating a nuclear weapon in space and being much safer for nearby friendly satellites.

From the 1960s onwards, various anti-satellite programs were run with a focus on surface-to-space tactics. One of the first widely known programs was the Zeus program, which would create the Nike-X anti-ballistic missile system in the mid 60s. In 1963, an early iteration of the Zeus missile, program 505, successfully intercepted a satellite. The centrepiece of the later Nike-X system was the “Sprint”, a hypersonic missile capable of rapidly intercepting re-entry vehicles in the upper atmosphere, with extreme kinetic energy. By the late 60s, anti-ballistic missile systems fell out of favour with the public who lived in the vicinity of launch sites, believing that it simply made their towns targets for soviet missiles. Thus, the Nike projects were shelved in favour of the new “Sentinel” defence program.

In 1978, the first hypersonic air launched anti-satellite missile, the ASM-135 ASAT was developed. Due to its high thrust-to-weight ratio, the F15-A was chosen for the role of carrying and launching the missile. Modifications were made to its computer and head-up display, which would help guide the pilot into the best launch position.

The first stage of the missile would use the Boeing AGM-69 SRAM, powered by a Lockheed LPC-415 solid propellent two pulse rocket engines.  The second stage would use the ATV Aerospace Altair-3, powered by the Thiokol FW-4S solid propellent rocket engine. This second stage was to be equipped with thrusters to begin orienting the missiles course towards the satellite. Before separation into the third stage, this second stage would also be used to accelerate the missile into a 30-revolutions-per-second spin, using a Honeywell ring laser gyroscope.

MHV final stage

The third stage – also designed by ATV Aerospace – was known as the Miniature Homing Vehicle interceptor, or MHV. Closing in, the target was tracked by an infrared sensor, designed by Hughes Research Laboratory. Using a strip detector; consisting of four strips of crosses and four strips of logarithmic spirals of Indium Bismuth, the infrared sensor could track the target as it crossed the strips. This infrared unit required liquid cooling. To do this, two liquid helium systems were developed. The first was located in place of the F-15’s gun ammunition drum. The second was inside the second stage of the missile and would disconnect once the MHV was released.

Finally, before detonation, the MHV final stage would fire 56 full charge ‘divert’ solid rocket motors, and then, for final trajectory correction, 8 half charge ‘end-game’ motors around the circumference of the missile. During this process, four pods located at the back of the missile were used to stabilise any centre rotation of the missile.

Throughout this process, the missiles infrared system relied purely on direct proportional line of sight guidance. It did not compute radar specifics such as range to target, altitude, and so forth. Instead, line of sight was adjusted via the infrared sensor and strip detector.

TESTING

With the missile showing potential, the first tests would begin in 1982. Using an F-15A, a series of captive tests were performed. These proved that the missile was capable of successful launch from the F-15.

The first proper launch of the missile would occur on January 21st, 1984. Simulating an actual combat launch, the F-15 would be directed by controllers at NORAD, who, in a real situation, would have tracked the position of the target satellite. In this case, there was no physical target, instead the F-15 was vectored onto a point in space and ordered to climb and launch. The test was conducted over the Pacific Ocean, and the first order of the day was to perform zoom climb tests. Two different F-15s from the 6512th test squadron would successfully do this. Then, the missile – ASM-135A – was loaded onto Major Ralph B Fillburn’s aircraft, from which it was fired at a specified point in space. The missile performed well, although it was launched without the final stage.

The next hurdle would be locking an IR signature. Over the following year, three more tests were conducted. The technique was to lock onto a specific star in space, to simulate the IR signal from a satellite. The only live-fire test of this kind (conducted on November 13th 1984), unfortunately failed to produce a lock on the star.

Solwind P-78-1 satellite

Finally, it was decided that the missile would be used in a live fire test to destroy an actual satellite. After hearing of the plan, NASA intended to develop a small test target, which could be sent into space to test the missile without producing harmful debris. However, this would take time, and the Air Force, correctly, feared that congress would soon outlaw any such space tests. Consequently, the green light was given to shoot down the already orbiting satellite Solwind P78-1, on September 13th, 1985. This operation would be codenamed “Celestial Eagle Flight”. The Solwind satellite was considered a good test subject; as with many soviet recon and surveillance satellites, it flew in a polar orbit. It was also deemed by the decision makers to be an outdated satellite.

Flying to a location 300 kilometres west of Vanderberg Air Base, Major Wilbert “Doug” Pearson would be responsible for the launch. Vectored onto target, Pearson bought the F-15 up to Mach 1.22, before pulling into a 65 degree zoom-climb. At 38,100 feet, Mach 0.93, the missile was launched. Rapidly speeding up to 24,000 km/hr, the hypersonic missile successfully destroyed the satellite at an altitude of 555 kilometres. However, and unsurprisingly, political issues immediately confronted the operation. Just as the Air Force had predicted, political intervention led to congress banning such tests in October that year, as well as claiming that it contradicted a joint American-Soviet treaty on use of weapons in space. There were also claims that data from the satellite was still being used for research purposes before it was blown up.

For this test, NASA worked with the department of defence to monitor any debris from the intercepted satellite. This was done with two orbital debris satellites and a re-entry radar. Contrary to NASA’s prediction, the debris was not bright and reflective, and only two pieces of debris could be seen, the remaining being dark vaporised plastic and, metal fragments coated with black soot. Using infrared telescopes from the Air Force, NASA eventually accounted for all 285 pieces of debris.  NASA believed debris would affect future satellite and space station projects, forcing the space industry to spend on reinforced anti-debris systems for existing satellites.

As such, the ASAT program was blocked from further live tests, with an official ban on its use on space targets placed in December 1985. This threw a spanner into the works, as the Air Force had just launched specially made target practice vehicles into space to avoid further debris. From this point on, the ASAT program would be slowly scaled back. Air Force passion for the project was waning, and the original budget had over-run by an estimated $500 million, resulting in a total cost of $5.5 billion. Two final launches were conducted in 1986. Both of these would stay within the newly established restrictions, with the missiles once again being launched at the infrared signal of distant stars.

Without real targets, it was difficult to gauge effectiveness in real-world scenarios. Nevertheless, plans were made for 112 such missiles for possible use, to be deployed by two F-15 squadrons: the 48h Fighter Interceptor Squadron at Langley Air Base Virginia, and the 318th Fighter Interceptor squadron in Washington. F-15s from both squadrons underwent airframe modifications to accommodate these new missiles in anticipation of the provision of these missiles.

However, by 1987, the Air Force, experiencing an increase in technical difficulties, asked to shut down the program, and by 1988, the Reagan administration would officially end the program, citing technical issues, budget, and delays. Thus, the ASM-135 ASAT would never see service.

CONCLUSION

Despite its shortcomings as a program, the SM-135 ASAT proved the lethality of advanced air-to-air munitions at long ranges; something which would become increasingly important in the decades following, albeit not against satellites. Now relegated to the history books, often as nothing more than an interesting side note, the ASAT program nevertheless demonstrated what can be achieved in a relatively short time when there’s high level of motivation.