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View Diary: Getting to Know Your Solar System (15): Asteroids (Vol. 1) (50 comments)

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  •  Maybe another way to look at it... (3+ / 0-)
    Recommended by:
    Troubadour, ER Doc, pucklady

    Imagine a trojan object in the same orbit as a planet, ignoring for a second the planet involved. It's happily orbiting the (very large) sun, all by itself, perfectly stable.

    Now, if the trojan is a trailing trojan, then the planet will pull the planet faster in its orbit.

    ... but, the effect of that is to widen/expand its orbit around the sun, slowing it down -- and this effect is larger than the pull of the planet. So the trojan moves outward in its orbit and slows. As it slows, it then starts to move backwards relative to the unperturbed trojan. (The unperturbed object is still in the original, smaller orbit. Being a smaller orbit, it has a shorter orbital period.)

    As it moves backwards (relative to the unperturbed object), however, the planet's force on the trojan diminishes. Eventually, it drifts to a position behind that of the unperturbed object, and its orbit crossing that of the unperturbed object, becoming closer to the sun. The sun's attraction/orbital dynamics then starts to speed it up... and the same dynamic takes place in reverse.

    ----
    The dynamics of bodies in orbits are strange, and apparently backwards. Attempting to speed up, e.g., with a rocket thruster firing in the direction of one's orbit, one moves to a larger orbit with a slower velocity(!). Attempting to "slow down" in orbit moves one to a smaller orbit, with a higher velocity(!).

    In the early space flight program this was tested in rendezvous between objects in orbit. If two (e.g., Gemini) capsules were in the same orbit, the trailing object would fire a thruster towards the leader (i.e., pushing it away from the leader). This shifted the trailing capsule into a lower orbit, and it would start catching up to the leader. Once caught up (and underneath), it would then fire a thruster in the direction of its orbit (as if to speed it up), and the capsule would then move into the larger orbit to rendezvous with the lead capsule.

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