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From: rogers@SRC.Honeywell.COM (Brynn Rogers)
Newsgroups: sci.space.shuttle
Subject: Re: Galileo Gravity Boost
Message-ID: <36082@srcsip.UUCP>
Date: 24 Oct 89 05:13:35 GMT
References: <12027@eerie.acsu.Buffalo.EDU> <34700003@uxh.cso.uiuc.edu> <18630@pasteur.Berkeley.EDU> <10150@thorin.cs.unc.edu>
Sender: news@src.honeywell.COM
Reply-To: rogers@src.honeywell.com (Brynn Rogers)
Organization: Honeywell Systems & Research Center
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Okay, related to gravity boost there is something I would like to ask.

   I think that the best (most efficient) time to make a course 
correction or add delta-V is when a spacecraft is closest to a planet
(moon,star,asteroid, or gravity well).  Any small changes made
in course or speed of the spacecraft are much more effective than
changes made in deep space.

   Why doesn't Galileo (or future craft) use this fact to shorten its
trip time?   (Other than the fact that it dumps the IUS close to
Earth.)  If there were a small kick motor on Galileo that fired on the
closest approach to Venus (apogee or perogee, I forget which), wouldn't it
give a great improvement to the trip time, at small cost?

   Isn't the reason Galileo goes to Venus, then back to Earth, then to
Jupiter, still taking 6 years due to the fact that the IUS has a
significantly smaller amount of specific impulse than the Centaur upper
stage?  (that sentence is too long.)  How long would the trip take with
a Centaur upper stage as originally planned?  Did that trajectory bring
it around Venus?




 Brynn Rogers    Honeywell S&RC        rogers@src.honeywell.com
 home 612 874-7737