Deployment and retrieval

In February 1984, during the STS 41-B mission, two Comsats were successfully deployed by the crew from the payload bay of Challenger using the Payload Assist Module (PAM) upper stage system. The Indonesian Palapa B2 and Western Union Westar VI were not able to reach their proper orbits, however, due to failures on each of the PAM Perigee Kick Motors (PKM). Each engine firing ended prematurely and stranded both satellites well below their intended geosynchronous orbits. Fortunately both PKM were successfully ejected from the satellites and each of them appeared to be undamaged, if useless, in their new orbits. Despite all crew activities being performed flawlessly (as with the TDRS-A/IUS deployment from STS-6 the previous April), the media were quick to highlight the expensive failures.

Even before STS 41-B had landed, NASA and Hughes officials (the makers of the satellites) began to study the possibility of retrieving both satellites on a future Shuttle mission. By May, both satellites had been placed in the same circular parking orbit about 1,000 km above the Earth by means of the solid fuel contained in the Apogee Kick Motor (AKM) on each satellite. This was also an essential safety procedure in the event of a rescue mission taking place, disposing of the fuel prior to either the Shuttle or any astronauts approaching the stranded satellites. Over the next few months, Hughes controllers initiated a series of manoeuvres to rendezvous both satellites in the same orbit. By August, both were stable, within 0.03 degrees of each other though 180 degrees apart and by early October, a programme of further manoeuvres was completed to both close the separation distance of the satellites to approximately 965 km and to lower their orbits to 360 km, within range of the Shuttle. Over a three-week period, more than 100 orbital adjustments were made for each satellite. By the end of October, their spin stabilisation rates had been slowed and they were ready for recovery. As both satellites were commercial, they had been insured against loss by underwriters, represented by Merrett Syndicates of London and International Technologies Underwriters of Washington DC. In August, after discussion with NASA and Hughes, a contract for $10.5 million was agreed for a dual satellite recovery.

With the satellites ready for retrieval and the cash to support a mission, NASA looked to the manifest to determine which flight and crew would be best prepared to

Joe Allen about to enter the mid-deck of Discovery prior to starting his second flight into space.

attempt the task. Despite the loss of the two satellites, STS 41-B had flawlessly demonstrated the use of the Manned Manoeuvring Unit (MMU) for the first time. The successful EVA repair of the Solar Max satellite (on STS 41-C in April) had given great confidence to the NASA team that satellite retrieval and repair was indeed possible. The mission would have to be completed as soon as possible while still giving the crew (and engineers) about six months to develop techniques and hardware to capture two satellites that were not designed to be returned to Earth. It was too late in the cycle to add the task to the crew training for the twelfth and thirteenth missions, and the fifteenth was a classified DoD mission, so the required media openness for the dramatic satellite rescue would not be possible on that flight. The flights of Spacelab 2 and 3 could not support returning a satellite payload as well as the Spacelab equipment and with the June abort of STS 41-D, the subsequent combination of 41-D and 41-F payloads, and the reassignment of the 41-F crew to a new mission (51-E in 1985), this left the Hauck crew, due to launch in the spring of 1984. The crew would now be dispatching two satellites before attempting to retrieve two more. This would be a daunting mission and a challenging one.

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