Comment by mandevil

The size being the same was not because of design reuse, but because that's the size limits imposed by the Space Shuttle payload bay. (1) Many of the contractors were the same, but that's because they won a competitive bidding process with a CCD design against a different set of contractors vidicon tube technology. Now, their experience with CCD's did come from the KH-11 process, but their bid did have competition.

1: Speculation but reasonably informed: in 1970 when the USAF was asked to set the size of the payload bay (in exchange for USAF political support on a program that had just survived by one vote, their parameters became the design guidelines for the STS) they basically went with their latest design at the time, the KH-10 Manned Orbiting Laboratory, which had already been canceled but was the latest thing anyone had. If the people at NRO who provided the specs had known how the future was going to go, they would have probably wanted a shorter but wider payload bay, so you could put bigger main mirrors into space. But, and this is total speculation, in 1970 when they are committing to this the KH-11 is far enough in the future that they don't have a good understanding of what it should be like. The KH-11 was designed to be carried into space by the STS, but the STS was delayed so its first flights were on unmanned rockets, and then after Challenger the NRO tried to get all of their satellites off the STS and go fully unmanned. A couple of satellites were far enough along that they were committed to the Shuttle after Return to Flight, but no more were committed after that point.