|Quoting seachaz (Reply 15):|
Wasn't the shuttle originally designed to be a fair amount smaller then what it ended up being? Thought I read that to get the Air Force on board with the program (which was a way around a funding shortfall) the cargo bay had to be expanded to its current size in order to launch the big spy satellites. How much smaller/lighter would it have been in the original config?
It’s hard to give an exact number, since there was no single definitive design before the USAF
requirements were brought on board. One of the earliest concepts, dating back to the mid-sixties, would have had a four man crew and 20,000lbs lift to LEO. Mind you that this was long before the boost configuration was even remotely settled, everything from a winged booster to an S-IC
were considered along the way, and there was lots of growth. In retrospect, starting with a small X-20/Dynasoar class vehicle, just as an R&D vehicle, would have been a much better idea.
The Shuttle ended up with about at 53,000lbs lift to LEO. A reasonable ballpark is that the USAF
requirements were about a third of that (IOW, NASA was in the 35klb range before, USAF
requirements added about 50%). Much of the actual mission requirements were concentrated in high inclination flights, but that’s mostly a matter of how you report the number (IOW, the USAF
was less interested in flying 50,000lbs to LEO, than they were 25,000lbs to a polar orbit). So significant, but not game changing.
A bigger impact was on the size of the wings. USAF
requirement appear to have significantly increased the bring-back mass, and the USAF
definitely wanted a lot more cross range capability than NASA was planning*, both of which required significantly more lift. Of course NASA was looking at landing speeds nearer 250kts, than 190, which does raise some issues, too.
The dimensions of the cargo bay also increased significantly, probably netting something on the order of a 100-150% increase in volume (a certain USAF
requirement was to launch spy satellites – those simply require large mirrors, and large, but empty tubes – basically Hubble-style vehicles**), but not a lot of mass increase.
So, for a rough estimate, the overall mass of the orbiter approximately doubled.
And I like to point out that the USAF
, while interested in the Shuttle’s planned capabilities (the Shuttle did draw on a number of USAF
studies of reusable vehicles during the sixties too), was not actively pushing for those increases. They were told to wind down the expendable programs, as all future launches *would* be on the Shuttle, and then their requirements had to be met. Of course the USAF
never really go to use the polar or cross range capabilities of the Shuttle, despite blowing $4B building SLC
-6 (to add insult to injury, Challenger was lost only about nine months before the first scheduled flight from Vandenberg (Discovery would have made the first manned flight*** to polar orbit).
had a set of once-around and back to the launch site missions they wanted to fly, since the launch site moves 1500+ miles, you better be able to fly that much off to the side, especially during a polar flight.
and friends would probably correct me and call Hubble a KH-11 size/style vehicle.
***we’re still waiting for that milestone.