Dawn Cruise |
Dawn Cruise |
Sep 27 2007, 12:31 PM
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#1
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Member Group: Members Posts: 100 Joined: 11-October 04 From: Oxford, UK (Glasgow by birth) Member No.: 101 |
Pushing out of Earth orbit now...........
-------------------- "There are 10 types of people in the world - those who understand binary code, and those who don't."
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Aug 31 2008, 02:59 AM
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#2
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
Regarding ion engines and circular orbits, one may make a qualitative non-mathematical argument why that is the case. We all know that for an elliptical orbit, firing engines at periapsis modifies the apoapsis (rising or dropping the apoapsis depending on the direction of the thrust), whereas firing the engines at apoapsis changes the periapsis. Now, for the case of a continuous low-thrust ion engine, it affects both apoapsis and periapsis. Let assume the case where both increase (as in Dawn). The spacecraft spends more time in the vicinity of the apoapsis that periapsis, as it is slower farther in its orbit from the center. Therefore the effect on periapsis is larger than the periapsis. The net effect is that with continuous thrusting, periapsis starts to catch up with apoapsis, i.e. the orbit becomes more circular.
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