Xref: utzoo sci.space:15439 sci.space.shuttle:4033 sci.astro:5672
Newsgroups: sci.space,sci.space.shuttle,sci.astro
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Future Space Missions
Message-ID: <1989Nov12.001720.6482@utzoo.uucp>
Organization: U of Toronto Zoology
References: <2086@jato.Jpl.Nasa.Gov> <5569@cbnewsh.ATT.COM>
Date: Sun, 12 Nov 89 00:17:20 GMT

In article <5569@cbnewsh.ATT.COM> lmg@cbnewsh.ATT.COM (lawrence.m.geary,ho,) writes:
>I have heard that Cassini will also use an Earth flyby to gain speed.
>I assume this means that these probes are using underpowered boosters
>and launching from the shuttle, as was the case with Galileo...
> WHY in heavens name is JPL sticking to this method for probes planned 
> for far in the future?...
>... Why aren't there plans to use appropriate boosters?

Because there are none.  Although it is fashionable to malign the Shuttle
as a planetary launcher, the Shuttle/IUS combination is the heaviest
booster available (outside the Soviet Union).  Titan/Centaur is in second
place by a considerable margin.  Shuttle/Centaur would be better,
Shuttle-C/Centaur would be still better, and a stretched-tank Centaur
fuelled in orbit would be better yet... but the first was cancelled, the
second is just a gleam in the planners' eyes, and the last isn't even
being planned.

The only available-now launcher that could do a better job on Cassini
would be Energia.  The Soviets have no superstitious fear of cryogenic
upper stages, and they will happily quote a price to put 200 tons --
eight times the Shuttle payload, enough for a lot of Centaurs -- in low 
orbit using an 8-strapon Energia.  If you're absolutely determined not
to use something that hasn't flown, they'll quote a price for 75 tons
or so using the off-the-shelf 4-strapon Energia.  NASA is not going to ask.
-- 
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