March 1983:space activities report

SUCCESS FOR PAM

The fifth mission of the Space Shuttle saw the first use aboard the reusable spacecraft of an important new addition to the family of rocket stages: the Payload Assist Module (PAM). The new stage was privately developed by the McDonnell Douglas Astronautics Company as the first commercial space launch vehicle. The first PAM was pushed out by springs from the cargo bay of Columbia precisely on schedule on 11 November. It drifted with its SBS communications satellite payload for 45 minutes while the Shuttle moved to a safe distance. Then it began an 83 second rocket burn to boost SBS-3 towards geostationary orbit, approximately 22,898 mi (36,851 km) above the Earth.

Twenty-four hours later, the launch was repeated with Telesat Canada's ANIK-C3 satellite. Both satellites were moved into their final operational circular orbits of about 22,300 mi (35,887 km) by built-in "apogee kick motors" a few days later. The specially designed cradles that held the PAMs and their payloads in the cargo bay were returned to Earth by the Shuttle for use on future missions.

The mission aboard STS-5 marked the ninth and tenth launches for PAM since 1980. On the first eight, PAM operated as the third stage of the Delta launcher.

The next Shuttle mission for the Payload Assist Module will be aboard STS-7, scheduled for launch next April. Telesat Canada will use PAM again with the ANIK-C2 satellite, accompanied by a second PAM carrying the Indonesian communications satellite Palapa-B1. Altogether, more than 60 PAM missions aboard the Shuttle may fly over the next five years. In addition to the PAM-D's 2750 lb (1274.5 kg) Delta-class payload capacity, McDonnell Douglas is offering two other PAM configurations to handle large Shuttle payloads: the recently announced PAM-D2 for satellites of up to 3500 1b (1587 kg) and the PAM-A (Atlas Class) for those weighing up to 4400 lb (1996 kg).

SHUTTLE ENGINES

The three main engines from Shuttle Orbit,er Col¬ umbia will next fly into space aboard a new Shuttle craft. According to Judson Lovingood, manager of the Space Shuttle Main Engine Project at the Marshall Space Flight Center, the engines will undergo a complete overhaul before they are reused again on Orbiter Atlantis, due for delivery late next year. These engines, which were operated at 100 per cent of rated thrust on Columbia, will be modified and retested to certify them for operation at 109 per cent aboard the fourth Orbiter. The engines have been removed from Columbia and shipped back to the manufacturer (Rocketdyne Division of Rockwell International in Canoga Park, California).

The first order of business was to carefully disassemble them. Then every part was to undergo inspection to determine wear and reusability. "We know that some parts will have to be replaced because of the increased temperatures and pressures they will see at the higher power level,” said Lovingood. "But we would also like to see if the flight environment has a different effect on the hardware that we have seen in ground testing."

The engines will be reassembled and thoroughly checked before being shipped to the Marshall Center's engine test facility at the National Space Technology Laboratories for a series of acceptance test firings. These firings, tentatively schedule for autumn 1984, will include ignition, calibration and endurance tests. The engines underwent similar test firings before they were installed in the Columbia. After the engines have been accepted for flight by the Marshall Center they will then be installed in Atlantjs in time for its first mission in 1985. Columbia will receive three brand new engines for its next flight, the Spacelab mission in September.

JAPAN'S THIRD METSAT

Japan's Geostationary Meteorological Satellite (GMS) programme will take a further step forward in August 1984 when the third satellite (GMS-3a) will be launched using the sixth N-2 vehicle. GMS-3a will be placed in geostationary orbit at 140° East longitude covering the Japanese segment of the World Weather Watch, writes Nicholas Staggall. The GMS-2 prototype model will be used as the GMS-3a flight model although some refurbishing will be required. This work will be based on the experience gained from the flight model of the GMS-2 now orbiting the Earth.