One of the unique attributes of the Space Shuttle featured the ability to launch satellites into space and return them to Earth if needed. That capability was first demonstrated during the STS-51A mission in November 1984. Earlier in the year, the crew of STS-41B successfully deployed two communications satellites from Space Shuttle Challenger's cargo bay – Westar 6 for Western Union and Palapa B2 for Indonesia. The Payload Assist Module (PAM) upper stages of both satellites malfunctioned, leaving them in non-useable 160-by-600-mile high orbits instead of the intended 22,300-mile high geostationary orbits required for their normal operations. While both satellites remained healthy, their own thrusters could not boost them to the proper orbits. So NASA devised a plan to have astronauts retrieve the satellites during Extravehicular Activities (EVAs) or spacewalks using the jetpack known as the Manned Maneuvering Unit (MMU), after which the shuttle's Canadian-built Remote Manipulator System (RMS) or robot arm would grapple them and place them into the cargo bay for return to Earth. Astronauts had demonstrated the capability of the MMU during the STS-41C Solar Max satellite repair mission in April 1984 and NASA felt confident of its ability to capture and return Westar and Palapa.
In addition to the recovery and return of Westar 6 and Palapa B2, the astronauts' mission included deploying two communications satellites, Anik D2 for Telesat of Canada and Leasat 1 (also known as Syncom IV-1) for the US Navy.
In the weeks prior to STS-51A, ground controllers lowered the orbits of both satellites and reduced their spin rates from 50 to 1 rpm to enable capture by the shuttle astronauts. Engineers at NASA's Johnson Space Center in Houston developed the Apogee Kick Motor Capture Device (ACD), otherwise known as the stinger due to its appearance, to allow one of the astronauts to capture the satellites while flying the MMU. Once relocated over the payload bay, a second astronaut would remove the omnidirectional antenna with pruning shears and install an Antenna Bridge Structure (ABS) with a grapple fixture over the satellite's main antenna dish. The RMS would then grapple the satellite by this second fixture and lower into the specially-built cradle to secure it into the payload bay.
Space Shuttle Discovery launched on Nov. 8, 1984, to begin the first flight day of the STS-51A mission.
The second flight day involved the deployment via a spring ejection mechanism of the 2,727-pound Anik D2 satellite, which occurred on time and with no issues. As the first nighttime satellite deployment from the shuttle, photographs of the activity are somewhat less than clear. The crew also circularized the shuttle's orbit at 186 miles. The next day, the astronauts deployed the 17,000-pound Leasat 1. With the satellite deployments complete, the crew began to focus on the rendezvous maneuvers to bring them close to the Palapa B2 satellite.
On the fifth mission day, after Discovery was maneuvered to within 35 feet of Palapa. Astronauts Allen and Gardner exited the airlock to begin the spacewalk portion of the satellite capture. Allen donned the MMU mounted on the side wall of the cargo bay, attached the stinger to its arms, and flew out to Palapa. Once there, he inserted the stinger into the satellite's Apogee Kick Motor bell and using the MMU's attitude control system stopped Palapa's spin. Fisher then steered the RMS to capture a grapple fixture mounted on the stinger between Allen and the satellite. She then maneuvered the satellite over the payload bay where Gardner awaited to remove its omnidirectional antenna and install the bridge structure. However, Gardner was not able to attach the ABS to the satellite due to a clearance issue on the satellite that was unknown before flight. Using a backup plan, Allen undocked from the stinger, leaving it attached to the satellite as well as the RMS, and stowed the MMU in the payload bay. With Allen now holding the satellite by its antenna, Gardner attached an adaptor to the bottom end of the satellite to secure it in its cradle in the payload bay. This plan worked and Allen and Gardner completed the EVA in exactly six hours.
Between the two EVA days, the crew serviced the spacesuits, conducted routine maintenance on the shuttle, and prepared for the second rendezvous, this time to retrieve Westar. Allen and Gardner switched roles for the second EVA on flight day seven, with Gardner flying the MMU to capture Westar. The astronauts repeated the procedure from the first EVA, with the exception of not removing the omni antenna so they could use it as a handhold. With Westar secured in the payload bay, Gardner and Allen completed the second EVA in 5 hours and 42 minutes.
On Nov. 16, the astronauts closed the payload bay doors and fired the Orbital Maneuvering System engines to begin the descent back to Earth. Discovery glided to a smooth landing at KSC, completing a flight of 7 days, 23 hours, and 45 minutes.
What happened with the recovered satellites?
Hong Kong-based AsiaSat purchased the Westar 6 satellite, refurbished it, and relaunched it as AsiaSat 1 on April 7, 1990, on a Chinese CZ-3 rocket. Title to the Palapa B2 satellite returned to Indonesia after its relaunch as Palapa B2R on April 13, 1990, aboard a Delta rocket.