RE: Um, eh? (Orbital Mechanics for Dummies)

The projectile will have a velocity vector of the intial satellite, plus
whatever thrust you applied to the projectile.	Since you are in orbit,
the planet's gravity will exert a continous and slowly increasing vector
towards the planet.  The projectile will spiral inward towards the
planet.

The best visualization of this is the giant funnels that people drop
coins into.  The initial oribiting vector would be the rail but the
track that launches the coin is slanted in slightly, effectively
providing thrust towards the center.  Gravity pulls the coin towards the
center, but it still has a forward velocity vector and so moves in a
slowly closing spiral.

One reason you don't want Thor projectiles in geo-synchronous is that it
takes a long time for them to fall.  You'd probably want them in LEO
(Low Earth Orbit) where they are only 100-200 miles up.  They probably
need to be coated in thermal shielding (like the shuttle) to survive
re-entry since most metals can't go above a few thousand degrees temp. 
Another issue is that re-entry will always be in the orbital direction
of the satellite. Which means targets on the far side of a mountain are
going to be pretty safe.  This can be offset by having a bunch of
satellites in different directions (which you would need anyway to get
decent coverage of the planet using low orbit satellites)  

--Binhan

> -----Original Message-----
> From: Tomb [mailto:tomb@dreammechanics.com]
> Sent: Tuesday, March 12, 2002 10:15 AM
> To: gzg-l@csua.berkeley.edu
> Subject: Um, eh? (Orbital Mechanics for Dummies)
> 
> Okay, I'm an idiot. Let's start by assuming I know very little. 
> 
> I'm in orbit (ignore drag). I launch a Thor Javelin by applying thrust
> directly towards planetary centre of mass. What will happen to my
> projectile? With thrust applied, it should move away from the