Both Ulysses and Galileo were launched by the Space Shuttle and the Inertial Upper Stage (IUS). Yet Ulysses only took 16 months to reach Jupiter, while Galileo took 6 years. Is it because Galileo was heavier and needed to orbit Jupiter, while Ulysses was a flyby mission?

  • $\begingroup$ Thank you everyone!!!! That was a great answer...It is more difficult to orbit a planet than a flyby.. $\endgroup$ Jan 3, 2020 at 4:37

1 Answer 1



Ulysses was quite a light weight, only 370 kg. For comparison, the Galileo probe, which was put in to Jupiter's atmosphere, weighted almost that much, and that was a small part of Galileo, which in total weighed about 2562 kg. Much of that mass was to orbit the planet, also the communications was supposed to be better, as the prime part of Galileo was supposed to happen much further away than Ulysses, which could manage with just a moderate amount of radio communication that far out.

That lower mass allowed Ulysses to have an additional smaller booster, the McDonnell Douglas PAM-S (Payload Assist Module-Special), to give it a further kick to get to Jupiter faster.

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    $\begingroup$ It's worth noting that the faster Gallileo was moving when it got to Jupiter, the more delta-V it would have needed to enter Jupiter orbit. Also, perhaps that Gallileo was designed on the assumption that a more powerful upper stage would be available, but it was deemed to dangerous. $\endgroup$ Jan 3, 2020 at 0:01
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    $\begingroup$ Galileo was supposed to go directly to Jupiter, but due to the lower delta v, had to do some flybys. $\endgroup$
    – PearsonArtPhoto
    Jan 3, 2020 at 0:08

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