Recommendation: NASA should study the benefits of designing spacecraft intended to operate around Earth or the Moon, or at the libration points for human and robotic servicing.

HUMAN SERVICING OF SPACECRAFT

NASA first began developing extravehicular activity (EVA) experience with the Gemini program in the mid-1960s. The early goals for these EVAs were to gain basic understanding of human operations in space and to develop better spacesuit designs for the purpose of eventually conducting EVAs on the lunar surface and for simple maneuvering and maintenance tasks in space. By the latter part of the Apollo program, astronauts conducted EVAs during the return from the Moon in order to retrieve film canisters from the Apollo Service Module’s Scientific Instrument Module.

Although the idea of having humans repair and upgrade spacecraft in orbit had existed for a long time (and in fact were a staple of 1950s science fiction movies), it was not until the first Skylab mission in 1973 that the usefulness of having humans perform spacewalks to repair a spacecraft was actually demonstrated. Skylab, launched in May 1973, sustained severe damage during its ascent, including damage to its micrometeoroid/sun shade and one of its solar panels. The launch of the first piloted mission to Skylab was delayed in order to develop repair techniques for the ISS. The astronauts were eventually launched into orbit with a special repair kit. During a series of difficult and largely unrehearsed EVAs, they successfully made substantial repairs, including the deployment of a parasol sunshade that cooled interior temperatures enough so that Skylab was habitable. Subsequent Skylab missions installed the twin-pole sunshade, repaired a malfunctioning antenna, and replaced film in the solar observatory. The Skylab experience successfully demonstrated that humans could conduct complex, challenging, and unplanned repairs to spacecraft in low Earth orbit.

From relatively early in its development, the space shuttle was designed to be capable of rendezvous with and capture of orbiting spacecraft, and the possibility of using shuttle crews to repair and upgrade spacecraft evolved out of these plans. The shuttle design evolved to include a robotic arm (the Robotic Manipulator System, or RMS, more commonly referred to as the Canadarm) and also equipment inside the payload bay to secure and support spacecraft as well as astronauts during EVA repair and maintenance missions. Many of the tools and techniques for servicing spacecraft were initially developed early in the shuttle program as an effort to demonstrate the shuttle’s ability to provide services that expendable launch vehicles could not. During the course of these operations, NASA learned a great deal about the development of EVA tools and techniques as well as about the importance of designing spacecraft for servicing.

In November 1984, the space shuttle Discovery (STS-51A) performed the first retrieval and return to Earth of a satellite for repair and relaunch. Two astronauts wearing jet-propelled manned maneuvering units retrieved two malfunctioning satellites, Palapa-B2 and Westar-VI, which were in improper orbits due to kick motor malfunction. A “stinger” was used to capture Palapa-B2 and Westar-VI.2 This mission was the last time that the Manned Maneuvering Unit, a backpack that allowed an astronaut to maneuver untethered from the shuttle, was used. It was also the last time that astronauts performed EVAs without a tethering system (besides the 1994 Simplified Aid for EVA Rescue [SAFER] test on STS-64).

The ability to improvise has proven to be a key asset in servicing satellites, as demonstrated with the rescue of Palapa-B2 and also with the attempted servicing of Leased Satellite (LEASAT) 3. LEASAT 3 was deployed in April 1985, and it immediately became apparent that its engines were not firing. Engineers theorized that an unreleased hook on the outside of the spacecraft was preventing the engines from working properly and advised the astronauts to push the hook down. No spacewalks had been planned for the mission, and there was the danger that upon releasing the hook the engines would accidentally immediately fire and injure anyone nearby. Further complicating matters was the fact that the satellite was rotating and could not be easily grabbed by the shuttle’s RMS. Four days after its deployment, the astronauts tried to repair LEASAT 3 by building a “fly swatter” (Figure 4.1)—created on the shuttle using a plastic document cover attached to the shuttle’s RMS. An astronaut was then able to carefully extend the arm toward LEASAT 3 and snag the hook in the “fly swatter.” Unfortu-



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