Re: GPS BASICS: WAS:Re: BASICS: Property Rights

Spike Jones (
Sun, 13 Dec 1998 20:52:50 -0800

> > > Michael Lorrey writes:
> > >
> > > I'm not sure, but don't you get EM shielding during atmospheric
> > > reentry due to the plasma screen?
> Yes of course, but only for a minute or two during the most intense part of reentry.
> Interpolation techniques along with some accelerometers can take up the slack for the
> interim.

im not sure who wrote what above, but i must comment upon the "minute or two" of em shielding during reentry. we are talking about two different things. the reentry of a manned vehicle is very shallow so as to not place too much strain on the occupants with g forces. in a long shallow reentry, sure, you have a minute or two of signal loss by ionized atmosphere around the vehicle, as we see with the shuttle and the earlier manned capsules. the shuttle has a gentle peak of around 3 g during reentry.

the original comment was about reentry vehicles to be used as weapons. these come in steep and fast. i can assure you, the entire reentry event (interaction with sensible atmosphere) is very short, on the order of 20 seconds, and not all of that is necessarily in the em signal loss regime.

typical weapon-use reentry bodies would come in 20-40 degrees from vertical and the velocity would go from around 8-10 km/sec down to 3-4 km per second, experiencing 60-80 g during that phase. these are not extremes, these are typical numbers. spike