Let’s see, we have Discovery, Columbia, Endeavor, and Challenger (RIP). Is there any difference, or are they all exactly the same? I was just wondering since wo only fly one at any given time, so are the rest just sitting around being checked-out until their number comes up?
The four orbiters are slightly different. The original Columbia was completed in '79, and the newest orbiter Endeavour was completed in '90. Orbiters are continually being upgraded, so most of the features in the newer orbiters have been incorporated into the older ones. The most visible upgrade is the drag chute - watch an early footage of a Shuttle landing and you won’t see it. But I believe the newer ones are still lighter than the older ones, which means more payload capacity. Check this site for details and upgrade histories of the four orbiters.
It takes a huge amount of ground support to fly a Shuttle. Teams of engineers, technitians, doctors, etc. are monitoring the flight around the clock. Even if it’s possible to fly two Shuttles at the same time, it would be very difficult and expensive. Besides, after you prepare and launch one Shuttle it takes some time to get the next one ready, and they can only stay up for about a month.
Food for the crew, if nothing else, I imagine.
Ranchoth
The main restrictions on mission length for the Shuttle are air, water, food, and orbital manuevering fuel, in roughly decreasing order of importance.
I thought there were five orbiters. Wasn’t there an Atlantis too?
Oops, you’re right. That is, there have been five total. But Endeavour was built to replace the Challenger, so there were never five at the same time.
In fact, Columbia, the oldest shuttle in the fleet, may soon be retired because it is too heavy to fly construction missions to the space station. Since that’s pretty much all NASA is using them for now, they have no use for it.
Because the outer shell’s so critical to high-speed aerodynamics the Shuttles remain about the same shape, but today’s are vastly more sophisticated than the first off the line.
Upgrades are frequent, but the same upgrades aren’t necessarily applied to every Shuttle. Certainly not at the same time. As noted, Columbia is too heavy for some missions, and therefore would receive different upgrades.
The relative weights of the empty shuttles circa 1996 is a clue how different they are:
Columbia 160,393 lbs
Endeavour 152,570 lbs
Atlantis 152,314 lbs
Discovery 151,090 lbs
(Source “Space Shuttle: The History of Developing the National Space Transportation System”)
There have been upgrades to the engines, the fuel pumps, the onboard computers, the tiles, the boosters, etc.
The primary thing stopping the shuttles from flying more often is money. Or you might see it as lack of “appropriate” missions, compared to manless rockets. There were plans, for example, to put boosters inside the shuttle bay, so they could launch satellites to geostationary orbit, but the thought of an explosion dampened enthusiasm.
Actually, the Boeing Inertial Upper Stage (IUS) booster has been carried on the Shuttle several times. It is used to place satellites like the Chandra X-ray Obseratory into higher orbit and to send probes on interplanetary flights.
Yes, scr4, you’re right. I was thinking of another program that was cancelled.
Ahh, Atlantis. Sorry 'bout that. Carry on.
Thanks for the info. So, really, do we need so many of the same thing?
As a corrollary to the OPs question, are there significant differences between the Enterprise and the other orbiters, other than from upgrades? Were there significant design differences between Enterprise and Columbia, for example?
Well Enterprise, as you’ll remember was a prototype that couldn’t reach space. Quoting from “Space Shuttle”, again (which has 100 wonderful pages of early shuttle and Buran development I’d forgotten about): “Enterprise contained no Main Propulsion System plumbing, internal fuel lines or tankage, and the Space Shuttle Main Engines and their expansion nozzles on the tail were mock-ups…”
“All other Orbiters…would use windw and a mid-fuselage significantly stronger…and some aluminium castings in other areas of the fuselage were changed to titanium…”
The Columbia, when built, had no heads up displays. There’s a picture in the book of three phases of shuttle instrument panels, the first looks quite a lot like an 1970s airplane, the Phase 1 of the MEDS program replaces b&w LCD displays for color, and Phase 2 (which I guess is complete now) has almost all LCD displays.
Modifications after Challenger allow the side hatch on the mid deck to be explosively blown.
Atlantis was modified to accept the Orbiter Docking System to hook up with the Mir.
Anything in particular you’re interested in?
MarkyDeSadeI think there’s been talk about getting rid of Columbia, because it’s so heavy. But considering how much the shuttles cost, and how long they take to build, I think NASA’s hedging its bets in case the financial climate or scientific climate changes suddenly. For example, if the Chinese start making great strides in their manned flight, it would probably light a fire over a few congressmen…
from Mark Wade’s site at www.astronautix.com/craft/mancraft.htm :
CUS was a version of the Centaur stage used in Atlas and Titan boosters, a controllable, restartable, “hotter” booster for faster, more direct launches of larger, heavier GSO satellites and of interplanetary probes w/o so much slingshotting around the inner planets.
Enterprise (OV-101) was built solely as a test platform, for landing aerodynamics, systems and procedures. Challenger was originally STA-99, the full-dress structural/ mechanical/ systems test platform, and converted to full space-worthiness.
As to the others, from Wade’s site :
A second to JRDelirious’s recommendation about http://www.astronautix.com/craft/mancraft.htm. Many hours of happy browsing, there.
Argh! Since the SDMB submission turned that into a hot link I didn’t intend, which doesn’t work, let me follow up with this link, and describe what you’ll find.
A large index of manned spacecraft and related items such as space planes and space suits, emphasizing American and Russian developments. Each of the links goes to a page that’s been custom-written for the site, which always includes some text description and bibliography. Often there are small graphics.
I put it in my favorites. Thanks JR.