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View Full Version : Flybys and gravity assists - interplanetary missions



Nereid
2006-Aug-10, 09:57 PM
The Galileo mission included many close flybys of the Galilean moons, made possible in no small part by the "gravity assist" of the flybys, to change to orbit of the probe.

The Cassini mission is similar, except that it is Titan which is providing almost all the gravity assist, and Jupiter helped Cassini get to Saturn in the first place.

Before them, Voyagers 1 and 2 got gravity assist from Jupiter, Saturn, and (for Voyager 2) Uranus and Neptune (though, strictly speaking, 2's 'assist' from Neptune, and 1's 'assist' from Saturn were more for the interstellar/heliopause parts of the Voyager mission).

And before them, Pioneers 10 and 11 used Jupiter's and Saturn's (for 11) gravity to change trajectory.

Ulysses got into its near-polar orbit (wrt the Sun) using gravity assist from Jupiter.

And so on.

Is there a single source for data on all the gravity assists used by interplanetary probes? I'm interested in details of those involving Mercury, Venus, Earth, Mars (are there any?), Jupiter, and Saturn (AFAIK, only Voyager 2 has visited Uranus and Neptune).

Also, close flybys of minor bodies - such as comets and asteroids - while interesting, are not what I'm after.

Finally, has any mission used the Moon's gravity, as an assist for an interplanetary mission?

FWIW, here's a list of the missions that I think might be included:
- Pioneer 10
- Pioneer 11
- Voyager 1
- Voyager 2
- Cassini
- Mariner 10
- Ulysses
- all the comet and asteroid missions - Giotto, Falcon, Deep Impact, Rosetta, ICE, (the Russian and Japanese Halley missions), Stardust, ... (but not NEAR?)
- New Horizons
- MESSENGER
- (none of the Mars missions?)

compton
2006-Aug-11, 09:26 PM
Finally, has any mission used the Moon's gravity, as an assist for an interplanetary mission?


I have a recollection of a mission which began with a slingshot around the earth (no idea which mission it was now) - I would expect that the moon is kind of redundant for gravity assist given that the earth is so much bigger, and, well, nearer

Stregone
2006-Aug-11, 10:52 PM
I have a recollection of a mission which began with a slingshot around the earth (no idea which mission it was now) - I would expect that the moon is kind of redundant for gravity assist given that the earth is so much bigger, and, well, nearer

That word (http://en.wikipedia.org/wiki/Gravity_assist), I do not beleive it means what you think it means. (I tried explaining it myself, but it sounded like gibberish :P)

compton
2006-Aug-11, 11:15 PM
heheh i had had a quick scan of that wiki article, after trying to see if i could quickly find the name of whatever it was that did a slingshot around the earth at the start (obviously) of its mission.

Maybe it doesn't mean what I thought it did! (haven't read the article in depth BTW)

I can just about visualise it if i assume the craft does an elliptical part-orbit, sort of dipping down closer to the planet to gain its speed - so fast that the planet's gravity won't recapture it, and bring it back into a full orbit. I guess it's more complicated than that in practice!

Stregone
2006-Aug-11, 11:34 PM
heheh i had had a quick scan of that wiki article, after trying to see if i could quickly find the name of whatever it was that did a slingshot around the earth at the start (obviously) of its mission.

Maybe it doesn't mean what I thought it did! (haven't read the article in depth BTW)

I can just about visualise it if i assume the craft does an elliptical part-orbit, sort of dipping down closer to the planet to gain its speed - so fast that the planet's gravity won't recapture it, and bring it back into a full orbit. I guess it's more complicated than that in practice!Well, something launched from the Earth can't immediatly get a gravity assist from the earth. It needs to enter solar orbit and come back around in order to get an assist from the Earth, however, it can get an assist from the moon before it leaves earth orbit.

I'm having a hard time thinking of how to explain the gravity assist, but you can probably visualise if much easier if you remember that the planets aren't stationary,t hey are orbiting the sun, and also that to get a gravity assist the spacecraft needs to approach the planet from 'behind'. If the spacecraft approached from the front it would slow down instead of speed up.

VanderL
2006-Aug-12, 11:43 AM
The Galileo mission included many close flybys of the Galilean moons, made possible in no small part by the "gravity assist" of the flybys, to change to orbit of the probe.

The Cassini mission is similar, except that it is Titan which is providing almost all the gravity assist, and Jupiter helped Cassini get to Saturn in the first place.

Before them, Voyagers 1 and 2 got gravity assist from Jupiter, Saturn, and (for Voyager 2) Uranus and Neptune (though, strictly speaking, 2's 'assist' from Neptune, and 1's 'assist' from Saturn were more for the interstellar/heliopause parts of the Voyager mission).

And before them, Pioneers 10 and 11 used Jupiter's and Saturn's (for 11) gravity to change trajectory.

Ulysses got into its near-polar orbit (wrt the Sun) using gravity assist from Jupiter.

And so on.

Is there a single source for data on all the gravity assists used by interplanetary probes? I'm interested in details of those involving Mercury, Venus, Earth, Mars (are there any?), Jupiter, and Saturn (AFAIK, only Voyager 2 has visited Uranus and Neptune).

Also, close flybys of minor bodies - such as comets and asteroids - while interesting, are not what I'm after.

Finally, has any mission used the Moon's gravity, as an assist for an interplanetary mission?

FWIW, here's a list of the missions that I think might be included:
- Pioneer 10
- Pioneer 11
- Voyager 1
- Voyager 2
- Cassini
- Mariner 10
- Ulysses
- all the comet and asteroid missions - Giotto, Falcon, Deep Impact, Rosetta, ICE, (the Russian and Japanese Halley missions), Stardust, ... (but not NEAR?)
- New Horizons
- MESSENGER
- (none of the Mars missions?)


This paper (http://xxx.lanl.gov/abs/astro-ph/0608087) describes anomalous flybys for several missions and there are references to other papers and databases. I think there is no single database, although JPL seems to be where most of the data come from. Have fun.

Cheers.