From: amon@elegabalus.cs.qub.ac.uk
Subject: Re: Drop nuc waste into sun
X-Added: Forwarded by Space Digest
Organization: [via International Space University]
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU
Distribution: sci
Date: Fri, 9 Oct 1992 18:46:34 GMT

> Earth plunging into the Sun its orbital velocity.  uh-huh.  And  
if we placed a
> satellite in an identical orbit as the earth, but at a slower  
orbital velocity
> (by firing it off in an opposite direction to that way which the  
earth is
> going) what will happen.  Will its orbit decay until it falls  
into the sun, or
> will its orbit merely change to a different one.  Either way we  
have an
> advantage.  If it falls into the Sun (or indeed hit Venus,  
Mercury or some
> other body) the problem is gone forever.  And if it settles into  
a different
> 


I'm virtually certain there must be an FAQ on this. Everyone has  
been repeating it anyway. You are orbiting the Sun at 93M miles.  
You must kill virtually all of that orbital velocity (kinetic  
energy) to fall into the Sun close enough to "aerobrake" and "hit"  
the sun, although you'd probably melt long before that. If you  
miss, the object will return to Earth orbit, since in the process  
of falling towards the Sun it has picked up the kinetic energy of a  
93M mile free fall. Since space is frictionless (ignoring a bit of  
dust, and such) you will go around the Sun and reach a ApoSol about  
where you started.

You ask about the orbit "decaying". Why should it decay? Do you  
think the Earth's orbit is decaying? The truth is, that it is...  
but by the release of gravity waves. We should get down to the Sun  
in a few billions of billions of years, if not lots longer...  
(Assuming of course that gravity waves actually do exist, a  
reasonable certainty at this time.) But I don't think that has  
anything to do with what was being asked, and besides which the  
loss of energy by gravity wave is even less significant to a few  
hundred kilos of satellite than it is to the planet Earth. There is  
the Poynting-Robertson effect, but that will not have much effect  
on an object as large as a satellite.

From Space Digest v10N74:
	... A particle 1 mm in diameter that originates in the  
region of the
	asteroid belt spirals into the Sun in only 10 million  
years. Even
	a particle 10 cm across at the Earth will spiral in given  
10^8 years.


So just think pure Newtonian physics. An object in motion tends to  
stay in motion. A satellite will stay in the orbit it was placed in  
unless acted on by a third body or its own thrusters. Launching it  
away from Earth opposite the Earth's orbital motion subtracts from  
the kinetic energy at ApoSol. The object falls to a new PeriSol,  
trading potential energy for kinetic energy all the way down. And  
then goes back up, trading kinetic energy to potential energy...  
and so on until interfered with.

Of course the orbit can get randomized by near passes to Earth,  
Venus and Mercury. If you have enough of these objects in play in  
this Solar Pin ball game, eventually one of them will come right  
back and hit us. Just like asteroids. As a recent post noted, we  
can expect a hit from a 50-100m object once a century. If we make a  
habit out of tossing nuclear waste towards the Sun, we'd run the  
same risk. Maybe not very high, but high enough to eventually drop  
one on the heads of our distant descendants.

Now of course we could do a circularization burn, but if we're  
doing that, it hardly matters whether we park it between  
Earth-Venus or Mars-Earth or anywhere else.

If the nucleopaths on Earth won't agree to the best solution, which  
is the hole in the ground on Earth, then the next best solution  
might be a lunar hole in the ground. Lots of them are ready made  
anyway. No tectonics, no leaching, not much more chance of impact  
damage (after trading off gravitational focusing for the impacts of  
smaller bodies) and less problem even if one happens...

And after all, by the time they actually BUILD a repositary, the  
construction plus environmental impact statements will probably  
have cost MORE than Apollo did. :-(



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