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

Michael Lorrey (
Mon, 14 Dec 1998 10:48:42 -0500

Spike Jones wrote:

> > > > 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.

It was me. Yes, I mentioned that cause that I what I am most familiar with. I expected the warhead to be on the short side, and considering that its on a suborbital trajectory, it should come in steep and fast.

> 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

At what altitude is the 20 second phase at? If its at 200,000-400,000 feet, then This tells me that the warhead has around a minute after reentry to get its bearings and make final course corrections before impact. The fact that the reentry phase is shorter than I thought actually makes GPS guidance easier.

Mike Lorrey