Onwards to Uranus and Neptune! |
Onwards to Uranus and Neptune! |
Jan 12 2008, 09:40 PM
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#16
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Member Group: Members Posts: 813 Joined: 8-February 04 From: Arabia Terra Member No.: 12 |
As soon as MESSENGER gets to Mercury, the most poorly explored planets in the solar system will be Uranus and Neptune. Could this lead to a revival of interest in the ice giants and their retinue, in the same way that the existence of New Horizons is perhaps partly due to the Pluto stamp*?
*via Pluto Fast Flyby and later Pluto Kuiper Express |
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Feb 27 2008, 04:05 AM
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#17
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
My understanding has always been that gravity assists work by robbing a body of a bit of its rotational velocity by flying along with its rotating gravity field. The Sun rotates -- why ought this process not work with the Sun?
-the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Feb 27 2008, 05:18 AM
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#18
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Junior Member Group: Members Posts: 43 Joined: 10-December 05 Member No.: 605 |
Actually, this is not how gravity assists work - rather, they take advantage of an orbiting body's orbital motion relative to background space. Say a planet is orbiting with a speed V relative to the sun and a spacecraft approaches it (from the planet's point of view) from one side with a speed v. From the planet's perspective, the spacecraft ought to have the same relative magnitude of speed leaving it as approaching it, so the spacecraft leaves with speed v too. From, say, the Sun's point of view, though, the spacecraft approached the planet (which was moving at speed V) with some other speed z; by the time the spacecraft has left the vicinity of the planet, the planet has "dragged it along," and some significant fraction of the planet's orbital speed V is added to the original spacecraft velocity. (This can also be used to decelerate the spacecraft, too, by setting up the initial encounter differently.) The bottom line is that gravity assists depend on the mass and orbital velocity of the "assisting" body alone (robbing it of orbital, not rotational momentum), and have nothing to do with its rotation rate.
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