35. Cryogenic lines from the second stage were retracted prior to the spin up of the MHV.
The MHV guidance system solely tracked targets in the field of view of the infrared sensor, but did not determine altitude, attitude, or range to the target. Direct Proportional Line of Sight guidance used information from the detector to maneuver and null out any line-of-sight change. A Bang-bang control system was used to fire 56 full charge "divert" and lower thrust 8 half charge "end-game" solid rocket motors arranged around the circumference of the MHV. The half charge 8 "end-game" motors were used to perform finer trajectory adjustments just prior to intercepting the target satellite. Four pods at the rear of the MHV contained small attitude control rocket motors. These motors were used to damp off center rotation by the MHV.
Test launches[edit | edit source]
On 20 August 1985 President Reagan authorized a test against a satellite. The test was delayed to provide notice to the United States Congress. The target was the Solwind P78-1, an orbiting solar observatory that was launched on 24 February 1979.
On 13 September 1985, Maj. Wilbert D. "Doug" Pearson, flying the "Celestial Eagle" F-15A 76-0084 launched an ASM-135 ASAT about 322 km (200 miles) west of Vandenberg Air Force Base and destroyed the Solwind P78-1 satellite flying at an altitude of 555 km (345 miles). Prior to the launch, the F-15 - flying at Mach 1.22 - executed a 3.8g zoom climb at an angle of 65 degrees. The ASM-135 ASAT was automatically launched at 11.6 km while the F-15 was flying at Mach .934. The 13.6 kg (30 lb) MHV collided with the 907 kg (2,000 lb) Solwind P78-1 satellite at closing velocity of 24,140 km/h (15,000 mph).
NASA learned of U.S. Air Force plans for the Solwind ASAT test in July 1985. NASA modeled the effects of the test. This model determined that debris produced would still be in orbit in the 1990s. It would force NASA to enhance debris shielding for its planned space station.
Earlier the U.S. Air Force and NASA had worked together to develop a Scout-launched target vehicle for ASAT experiments. NASA advised the U.S. Air Force on how to conduct the ASAT test to avoid producing long-lived debris. However, congressional restrictions on ASAT tests intervened.
In order to complete an ASAT test before an expected Congressional ban took effect (as it did in October 1985), the DoD chose to use the existing Solwind astrophysics satellite as a target.
NASA worked with the DoD to monitor the effects of the tests using two orbital debris telescopes and a reentry radar deployed to Alaska.
NASA assumed the torn metal would be bright. Surprisingly, the Solwind pieces turned out to appear so dark as to be almost undetectable. Only two pieces were seen. NASA Scientists theorized that the unexpected Solwind darkening was due to carbonization of organic compounds in the target satellite; that is, when the kinetic energy of the projectile became heat energy on impact, the plastics inside Solwind vaporized and condensed on the metal pieces as soot.
NASA used U.S. Air Force infrared telescopes to show that the pieces were warm with heat absorbed from the Sun. This added weight to the contention that they were dark with soot and not reflective. The pieces decayed quickly from orbit, implying a large area-to-mass ratio. According to NASA, as of January 1998, 8 of 285 trackable pieces remained in orbit.
The Solwind test had three important results:
- It raised the possibility that the objects optical systems were detecting were large and dark, not small and bright as was generally assumed. This had implications for the calibration of optical and radar orbital debris detection systems.
- The test also created a baseline event for researchers seeking a characteristic signature of a hypervelocity collision in space.
- Awareness was raised about the orbital debris problem.
In the end, the Solwind ASAT test had few consequences for the planned U.S. space station as station completion was pushed beyond the mid-1990s. The record-high level of solar activity during the 19