[rainbowzootsuit]

From some distant memory the dimensions of the Space Shuttle cargo bay was specifically matched to accommodate the launch and servicing of the Hubble Space telescope. I'm not sure which design drove which.

[vkou]

The HST was a close variant of various military spy satellites. The difference is that it was pointed into space, as opposed to towards Earth.

Consider that a large number of Shuttle missions were classified, then put two and two together...