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From: desj@brahms.BERKELEY.EDU (David desJardins)
Newsgroups: net.space
Subject: Re: Ulysses probe
Message-ID: <12089@ucbvax.BERKELEY.EDU>
Date: Fri, 28-Feb-86 00:39:39 EST
Article-I.D.: ucbvax.12089
Posted: Fri Feb 28 00:39:39 1986
Date-Received: Sat, 1-Mar-86 02:52:47 EST
References: <8602280148.AA08000@mitre-bedford.ARPA>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: desj@brahms.UUCP (David desJardins)
Organization: University of California, Berkeley
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In article <8602280148.AA08000@mitre-bedford.ARPA> jrv@MITRE-BEDFORD.ARPA (James R. Van Zandt) writes:
>>>Ulysses is a European probe, to  be  launched  from  the  Shuttle,
>>>which will go over one the Sun's poles ...
>>>How can it go over one pole but not both?
>
>It *will* go over both poles.
>It can't leave the solar system because it doesn't have enough energy. 
>It'll be in an elliptical orbit around the sun like any planet, but the
>plane of the orbit will be tilted with respect to the plane of (for
>example) the earth's orbit.  If it were easy to supply the delta V to
>place the probe far out of the plane of earth's orbit, we wouldn't have
>to use Jupiter in the first place.  As it is, Jupiter is a convenient
>place to "turn a corner" in space.
>   ...  Does anyone know what the period and inclination of the probe's
>orbit will be?

   While I don't have the information necessary to give a definitive
answer (hopefully someone with better information can do that), I feel
I can add something to the above.  The use of Jupiter is to deal with
momentum problems; in order to pass over the pole of the sun one needs
(1) to cancel the orbital momentum of the Earth and (2) to add momentum
out of the plane of the ecliptic.  Passing around Jupiter is a convenient
way to change the momentum vector in almost any way desired, subject of
course to certain energy constraints.
   Since presumably after the Jupiter encounter the spacecraft will not
pass near any other planets, the path that it takes will be completely
determined by its velocity after the Jupiter encounter.  If its kinetic
energy is greater than the depth of the solar potential well it will
pass by the Sun and follow a hyperbolic path out of the solar system.
If its kinetic energy is below this threshold it will enter an elliptic
orbit (with aphelion at least as far from the Sun as Jupiter and thus a
period of several years) and so eventually will indeed pass over both poles.
   A quick computation (mv^2/2 = GMm/r) gives an escape velocity of about
1.9 x 10^4 m/s, or 11.6 mi/s, which is high but possible.  If Ulysses'
velocity after the Jupiter encounter exceeds this (in any direction) it
will escape.  I think that it will leave the Jupiter encounter at a
*slower* speed than it arrived due to the use of Jupiter to kill its
angular momentum (the opposite of the "slingshot effect"), so it would
have to arrive at a higher velocity.  For comparison, the Earth's orbital
velocity is 3.0 x 10^4 m/s, but of course the spacecraft will lose energy
in moving from Earth's orbit to Jupiter's.
   If anyone does have definitive information (so we can end all of this
silly speculation :-)) the numbers I would most appreciate are the actual
velocity after the Jupiter encounter and the distance the spacecraft will
pass from the solar pole.  But any reliable data would be appreciated.
Thank you...

   -- David desJardins