Close. They actually lower the perigee with the OMS deorbit burn, to where the perigee is below a dense enough portion of the atmosphere to allow a reentry capture, and then turn nose-forward and wait slightly less than half an orbit for entry interface. The moment they start encountering appreciable atmospheric drag, they are headed for the surface one way or the other and things start happening fairly quickly. But the key is that deorbit burn that puts the perigee right where they want it. There's no additional push other than atmospheric drag at entry interface. :)
(This is related to the reason why propelling something entirely from the surface, even firing something from an enormous cannon that propels the projectile far above the atmosphere, will never put it into orbit -- it will either escape Earth entirely or impact somewhere else on the surface. There has to be some horizontal acceleration at apogee for there to be a perigee afterward, which is why GEO sats have to carry an apogee kick motor with them to actually put them in GEO, a simple PAM boost from LEO won't do it. :)
On Feb 14, 2008, at 10:04 PM, Alan Sieg WB5RMG wrote:
I don't think orbital decay would be a good descriptor. Orbiter does the de-orbit burn about half-a-rev away, then a nose dive. The de-orbit burn puts the brakes on big time, then after it turns nose forward, a slight push towards the earth brings it on down fast.
"No nation was ever so virtuous as each believes itself, and none was ever so wicked as each believes the other." -- Bertrand Russell