How many shuttles are left?

How many shuttles are left in the U.S. fleet? The only other one I can remember doing a mission is Atlantis. Enterprise was more of a protoype, wasn’t it? I don’t think it’s ever done a mission?

Three: Discovery, Atlantis, Endeavour.

Enterprise was indeed the non-launching prototype. She was carried aloft on a 747 and did the landing trials. She is currently on display at Dulles airport outside D.C…

History of * Enterprise*

Im sorry but I have to ask this.
What about a collision with space junk?
With the speed the Shuttle travels and the amount of debris from past missions on a low earth orbit, this possibility is screaming at me!

There is supposed to be an agency within the gov’t that is tracking all the space junk floating around. I suppose that with the thousands of pieces of crap floating around up there that they could miss a piece now and again. Not comforting when you’re traveling at 17,000+mph.

Low Earth Orbit is generally defined as 160 nautical miles to 300 miles above the earth.

The Columbia exploded at 40 miles altitude, far below LOE. Any space junk it encountered would itself have been already on its way down, fast, not merely orbiting.

And I would think that the physics of a 90-ton shuttle hitting a piece of space junk at 12,500 miles per hour would mean that the space junk would be, basically, pulverized. Think “car hitting beer can”, not “car hitting deer”.

And yes, the United States Space Command has the job of monitoring space junk.

If there were a piece of space junk falling out of LOE along the shuttle’s flight path big enough to impact the shuttle the way a deer impacts a Toyota, Space Command would have said something.

The junk didn’t have to cause the shuttle to explode on impact!
It may have damaged the crafts integrity causing a malfunction during re-entry!

It dosen’t take the colision with a large object to do serious damage at the speeds we are talking about.
MACH 16.

While there’s a lot of space junk up there, and it’s moving pretty fast, most of it is in a very similar orbit. So the relative speed at collision is likely to be fairly low. Regardless, though, anything big enough to cause a catastrophic failure is tracked. There is some debris which isn’t tracked, but it’s all things like flecks of paint, which do minor, easily-repaired damage on every flight.

Theoretically possible, but unlikely. This is one of those cases where effects scale very fast. And even if the shuttle could survive a significant impact, it would be noticed.
As Chronos says, minor damage is routine and fully accounted for. The only other data point is the case where a satellite was probably destroyed by space junk. Even empirically, there’s nothing in between.

Incidentally, from memory, the limit on trackable objects in orbit is about 1 cm. That’s somewhat more dangerous than a fleck of paint.

A fleck of paint caused a one-inch pit in one of Discovery’s front windows a while back, IIRC. When you’re going 17,500 MPH it doesn’t take anything at all to cause serious damage. NORAD, the agency responsible for tracking space debris, can only track objects up to the size of a softball. However, were it to strike at the right place and speed, an object much much smaller than that could result in a catastrophic failure.

Duck Duck Goose is half right. It’s extremely unlikely that the shuttle collided with anything on its way down, because anything big enough to do damage to the shuttle would have been tracked and anything small enough to escape detection would have vaporized long before even coming close to the shuttle’s altitude. However, the “car hitting beer can” analogy isn’t exactly correct. It’s more like “car hitting beer can at 17,500 MPH” :slight_smile: Just a slight difference there.

LOL. Yeah, NORAD’s radar prevents them from tracking any large objects. Haha, no…

I meant to say “down to the size of a softball.”

By the way, a beer can going 17,500 MPH has roughly 62,000 times more energy than a beer can going, say, 70 MPH on the highway. Energy goes up with the square of the velocity, which is why even the tiniest object can do SO much damage.