Newsgroups: sci.space
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Solar Impact Mission.
Message-ID: <1991Feb5.215055.21771@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <1991Feb4.111437.9283@helios.physics.utoronto.ca> <1991Feb4.172846.3706@zoo.toronto.edu> <1991Feb5.154205.29266@engin.umich.edu> <1991Feb5.185021.10001@lonex.radc.af.mil>
Date: Tue, 5 Feb 1991 21:50:55 GMT

In article <1991Feb5.185021.10001@lonex.radc.af.mil> disprep@lonex.radc.af.mil (Disaster Preparedness) writes:
>     These are very interesting ideas that, I agree, would allow a probe
>to change its direction in a hurry.  The problem I see is that when the 
>vehicle enters an atmosphere, it loses kinetic energy in favor of thermal
>energy.  The idea of using this aero-assist method would seem to work okay
>for a solar impact mission, but I don't see how a probe could reach Pluto
>in four years after losing kinetic energy...

You lose some energy to air drag in the waverider concept.  However, you
are doing a turn around a *moving* planet, and there is momentum transfer
from planet to probe (or vice versa), just like with a gravity-assist
maneuver.

>... Does it kind of bounce off
>of the Martian atmosphere and gain a whole bunch of kinetic energy somehow...

Viewed from a distance, either a gravity-assist maneuver or a waverider turn
looks very much like bouncing off the planet.  Remember, the planet is moving,
so bouncing off it can give you a velocity gain or loss, depending on which
direction you come in from and the angle of the bounce.  The waverider's
advantage is that it can give you a much more drastic bounce, because the
aerodynamic forces are much stronger than gravity.
-- 
"Maybe we should tell the truth?"      | Henry Spencer at U of Toronto Zoology
"Surely we aren't that desperate yet." |  henry@zoo.toronto.edu   utzoo!henry