Physical laws of items in orbit?

[Stranger_On_A_Train]

@Chronos

Indeed, the only reason I could think of to desire a retrograde orbit was if you wanted more impacts, whether for purpose of cleaning up space junk, or for attacking rival satellites. Why were the sparse handful you know of launched?

There are some global mapping/scanning satellites that have been launched in retrograde orbits. I believe JPL’s SEASAT satellite was in a slightly retrograde orbit. At least one Soviet FOBS test involved a retrograde trajectory (presumably to conceal the origin of launch, although by that time the U.S. had the capability to discriminate rocket launches within seconds). The Soviets also performed a number of retrograde launches for various reasons (some still unknown). Several orbital/ASAT defense proposals have suggested launches to retrograde orbit to increase coverage, and most boost-phase and mid-course ICBM interception launches are necessarially retrograde, although obviously these aren’t satellites to orbit. The ERCS (Emergency Rocket Communications System), a short-term dwell satellite that would be launched over the United States in the case of a commucations loss (i.e. from a nuclear attack) was launched in a dramatically retrograde profile; the original booster was intended to be a Blue Scout Junior, but ended up being a Minuteman II.

In general, however, most retrograde launches are polar orbits that are just barely retrograde, and the vast bulk of launches are well inside the prograde orbit profile.

Stranger

[Mangetout]

@Chronos

It’s inherent in the nature of the Dope: If you (or I) omit anything for the sake of simplicity, someone else will inevitably pop in to include it.

I understand that, it’s just the way they were presented as if correcting an error rather than elaborating detail. I suppose I should have stated that I was simplifying.

[Malacandra]

@Mangetout

I understand that, it’s just the way they were presented as if correcting an error rather than elaborating detail. I suppose I should have stated that I was simplifying.

Sure. And I said that you could put an artificial satellite into (very high) Earth orbit so that it would have an orbital period of one solar year, giving it an apparent transit time of one solar day, and had a stab at the orbital radius. It’d be hard to see at that distance but an easy object to track. You want to get sniffy about that, it’s all right with me.

[Stranger_On_A_Train]

@Malacandra

Sure. And I said that you could put an artificial satellite into (very high) Earth orbit so that it would have an orbital period of one solar year, giving it an apparent transit time of one solar day, and had a stab at the orbital radius. It’d be hard to see at that distance but an easy object to track. You want to get sniffy about that, it’s all right with me.

Uh, no, you can’t. A satellite in a roughly circular orbit about the Earth with an orbital period of 365.25 days (~8765 hours) would have a semi-major axis of a=2.16*10[sup]6[/sup] km, which would be well outside the Earth’s sphere of influence. This object would be in orbit of the Sun. A highly elliptical orbit that is synchronized to be coinfluenced by the Earth might be possible, but then it’s not going to appear to make a smooth retrograde transit of a day, it’ll be bobbing back and forth across the sky in an irregular apparent orbit.

Stranger