OT ballistics question for Mr. Raab

[Aim to maim]

Sorry to be off topic, but it occurs to me that with your NASA background and reloading expertise, you are unusually well qualified to answer this puzzle.

I watched the Discovery launch this PM and like all Americans, was thankful to see they made it safely to orbit. The network I was watching showed views from the main fuel tank camera, together with a text box showing velocity, altitude, etc.

At the time of external tank separation, the velocity appeared to read approximately 15,000 mph. I'm guessing main engine shutdown follows very shortly after the external tank is jettisoned, since the shuttle itself could carry little fuel and most of that is required for retrofire for return to earth.

I seem to recall that the velocity required for near-earth orbit is somewhere aound 17,500 mph. My question is, how could the shuttle continue to accelerate from 15,000 mph to 17,500 mph, even in a vacuum, once the source of acceleration (main engines) is shut down.

There are several assumptions here on my part and any one of them being incorrect could make the question invalid. Could you help me out here?

[Rocky Raab]

You betcha.

Actually, the main engines shut down just before tank jettison. From there on, the shuttle is powered by the OMS (Orbital Maneuvering System) engines. Those are the two large "bumps" at the rear of the orbiter fuselage. Each of the two engines produces only 6,000 pounds of thrust, but that's more than enough in a vacuum to accelerate the orbiter the remaining amount, plus orbital maneuvers to the space station (or other target) and then out of orbit again at the end of the mission.

The OMS engines burn mono-methyl hydrazine and nitrogen tetroxide, which are hypergolic - meaning they self-ignite on contact. The nozzles of the OMS engines are the single largest pure beryllium objects ever made.

(I could go on and on with "gee whiz" stuff like that.)

Ask away, my friend! It feels like I'm still doing the launch commentary, even though that was 20+ years ago. Time flies even faster than the shuttle, it seems.

[Aim to maim]

Originally posted by Rocky Raab

(I could go on and on with "gee whiz" stuff like that.)

Ask away, my friend! It feels like I'm still doing the launch commentary, even though that was 20+ years ago. Time flies even faster than the shuttle, it seems.

Thanks very much for the informative reply. It's reassuring to know that Newton's Laws still apply. Nasty stuff, hypergolic fuel. As I recall the German ME-163 Komet pioneered the technology. Makes both pre and post flight handling a real adventure for all involved.

As for going on and on......our generation came of age with the space program. I fear it was probably the high water mark of the American race. Go on and on any time you feel the urge. It's a fine reminder of halcyon times, even for those of us who weren't directly associated with the program.