X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
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Subject: Re: Asteroids as weapons of mass destruction
In article <oZEo=Xu00WI4E784gT@andrew.cmu.edu> kr0u+@andrew.cmu.edu (Kevin William Ryan) writes:
> If the asteroid is already in an elliptical orbit crossing Earths, then the
>delta vee needed is that which changes the period of the asteroids orbit just
>enough so that it crosses Earths orbit when the Earth is there, some time in
>the future. I'm not knowledgeable enough to say how much delta-vee this
>requires...
Potentially almost zero. Potentially zero, in fact, given that there is
a significant chance of a natural impact if you wait long enough. Humans
do tend to be impatient, however... :-)
> Second, concerning propulsion of said asteroid - nobody has mentioned mass
>drivers! ...
Probably because (a) they are slow, and (b) they're not a fully-developed
technology yet. Just kicking the thing with H-bombs can be done with
off-the-shelf technology, and the thrust-to-weight ratio is better.
--
A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology
megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
------------------------------
Date: 23 Oct 89 14:47:56 GMT
From: bunny!krs0@husc6.harvard.edu (Rod Stephens)
Subject: Re: Galileo Schedule
In article <1940@jato.Jpl.Nasa.Gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
>
>
> Galileo Schedule of Events
:
:
> 02/15/90 - Venus Flyby
> 10/**/90 - Venus Data Playback
:
:
What is "Venus Data Playback?" Why is it so long after the Venus flyby?
Rod Stephens
GTE Laboratories, Inc
40 Sylvan Rd
Waltham, MA
02254
(617)466-4182
------------------------------
Date: 24 Oct 89 00:27:04 GMT
From: gem.mps.ohio-state.edu!wuarchive!mailrus!jarvis.csri.toronto.edu!utgpu!radio.astro!helios.physics!griffin@tut.cis.ohio-state.edu (Prof. A. Griffin)
Subject: Cleaning up LEO
Disclaimer: I am NOT professor Griffin. If you use "F", please check the
attribution against the signature.
Over the past couple of weeks we've seen a few ways to clean dust and
grit out of low earth orbit, where it could damage satellites, shuttles, or
the space station. Two of the more memorable ones were the ice cube in an
opposing orbit, and the giant flypaper. I submit that there is an easier
and more selective way to do the same thing.
According to some calculations I made this afternoon, and which I'm
still having trouble believing, it's very easy, assuming that most of the
grit is going spinward, in the direction of most satellite launches. This
grit goes from west to east as seen by an observer on the ground. A mirror
is placed in the sunlight in the east as seen by a terrestrial observer.
The mirror reflects sunlight across the sky, from east to west, so that it
is shining directly into the path of the orbiting grit.
The scenario I used was a mettalic flake 1mm in diameter, and 0.1mm
thick, in a circular orbit 300km above the surface of the earth. It turns
out that the photon pressure on the flakes lowers the perigee of the orbit
to 100km, at which time it can be said to be braking in the atmosphere and
out of our way, in only 1.6 hours of exposure to the beam, or roughly two
days, where the orbit passes into the beam every ninety minutes for four
minutes.
The same flake in a Clarke orbit would enter atmosphere after about
twenty months.
The advantage to this approach is that it works best on small objects. A
communication satellite would suffer a delta-v of only about 1m/s, which I
presume is within the tolerance of the onboard thrusters to compensate.
An alternative solution is to put a giant sunshade which blocks light
reaching orbit as they cross from day to night, while still letting the
particles get the sun in their faces as they go from night to day. I favor
the first approach because it is easier to stabilize the mirror than a
sunscreen, since solar pressure on the mirror acts to oppose the earth's
gravity, while solar pressure on the sunshade adds to the earth's gravity.
Also, a mirror can be easily aimed to sweep different orbits, while a
sunshade or a retrograde ice cube would require a lot of effort and time to
do the same.
If anyone finds these results unlikely, send me e-mail and I'll send you
the parameters I used. I checked the results a few different ways, so I
don't think they're wrong.
--
Christopher Neufeld....Just a graduate student | "Scotty..now _would_
cneufeld@pro-generic.pnet01.crash | be a good time!"
griffin@helios.physics.utoronto.ca | - Pavel Chekov
