Skynet 4 manufacture was carried out by British Aerospace Dynamics (BAe Dynamics) with Matra Marconi Space (MMS) providing the Communications payload. NATO adapted the design for the NATO IVA and IVB communication satellites, also manufactured by BAe Dynamics. The programme timescales were delayed, as initially Skynet 4 was designed to be launched from the Space Shuttle (STS), with chosen RAF officers to be part of each Shuttle Crew. However, following the 1986 Challenger disaster (STS 51-L), the programme slowed and all the Skynet 4 series satellites had to be modified to suit the changes needed to go on a disposable launch vehicle. As Skynet 4A build was advanced it needed significant modification, and its completion was overtaken by Skynet 4B which had not progressed as far, and hence more easily converted. Consequently, Skynet 4B was finished first and launched in 1988, with Skynet 4A next in early 1990, and Skynet 4C later the same year. As of 2020, Skynet 4C is still in operation, providing service to the U.S. Amundsen–Scott South Pole Station for up to six hours a day because its orbital inclination has increased to 10.3°.