Herb Schaltegger wrote:

Interestingly, at the tail end of Space Station Freedom, as it was
morphing through Space Station Alpha on it's way to ISS, the final
"restructure/rephase" was to consider the option of using a
Lockheed-designed "service module" to perform the task later given to
FGB. It was not divulged how and why Lockheed had designed such a
module nor were we encouraged to ask; it was enough that we were told:
"It works and this is what it can do . . ." Obviously (moreso now than
in the summer of 1993), this was a core vehicle used for various
classified NRO payloads that NASA was essentially begging for permission
to use for early attitude and orbital control.

This probably gives the recon satellites the ability to change their
orbital parameters on-station; both to evade interception and to make
their time of passage over interesting photo targets less predictable.

It's unclear if NRO
simply refused or if they place so many roadblocks in the way of its use
that NASA was forced to go to the Russians on this aspect of the program.

It would have meant people would get a detailed look at its design, and
a lot of its capabilities could have been deduced from that.

Pat