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Space Forum / Space Flight / October 2003Chinese module at ISS?
What are the requirements for a Chinese module, using APAS as a docking adaptor, to be connected to ISS? Presumably, this module would be allowed if the Shenzhou serves as a transfer vehicle for ISS crews. Where could the module be located? > My greatest concern is whether/how long Cynthia might maintain a > stable, circular polar orbit. Not very long. The equatoral diameter of the earth is significantly larger than the polar diameter. The gravitiational pull towards the equator will tend to move the orbiting object into an equatoral orbit pretty fast. I could only guess at how long, though. I believe that the only reason our moon is not exactly in an equatoral orbit is because of the gravitational effect of the sun pulling it out of plane. ---- Michael Smith Mail address and GPG key available from www.netapps.com.au >> My greatest concern is whether/how long Cynthia might maintain a >> stable, circular polar orbit. [quoted text clipped - 3 lines] > equator will tend to move the orbiting object into an equatoral orbit > pretty fast. I could only guess at how long, though. Sorry, no. The physical mechanism that "equatorializes" an orbit is the slight transverse component of the tidal frictional torque created by the rotation of the Earth, =NOT= its oblateness per se. The tidal friction is approximately parallel to the _relative_ velocity of the satellite w.r.t. the ground. Because the Earth is rotating, the "drag" force on the satellite has a component in the direction of the Earth's surface velocity, which is transverse to the satellite's orbital velocity. This "drag" force exerts a torque that tips the satellite's angular momentum vector over until eventually it would be aligned with the rotation axis of the Earth (assuming it doesn't hit the ground first!). If the Earth were =NOT= rotating, the tidal "drag" would have no transverse component on a polar satellite, and no "tipping torque" on the satellite would result. > I believe that the only reason our moon is not exactly in an equatoral > orbit is because of the gravitational effect of the sun pulling it out of > plane. In a certain technical sense, the Moon is _not_ orbiting the Earth, since the force of the Sun's gravity on the Moon exceeds the force of the Earth's gravity on the Moon, so that unlike every other natural satellite in the solar system, the Moon's orbit is always "concave inward" and its velocity never goes "retrograde" relative to its primary. >From the Sun's point of view, the Moon and the Earth are in a rather peculiar form of "1:1 orbital resonance," something like Saturn's co-orbital satellites Janus and Epimethius --- the difference being that the period of the "do-si-do" is only about 1/13th of their common orbital period, instead of many times longer... -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' >In a certain technical sense, the Moon is _not_ orbiting the Earth, since >the force of the Sun's gravity on the Moon exceeds the force of the Earth's >gravity on the Moon... Not, however, in a very *useful* technical sense. What matters is not the absolute force the Sun exerts on the Moon, but how the Moon's resulting Sunward acceleration *differs* from the similar acceleration of the Earth. A more sophisticated analysis shows that the Moon most definitely orbits the Earth. When computing the Moon's motion, the errors introduced by ignoring the Sun are much smaller than the errors introduced by ignoring the Earth. (The surface where the two errors are equal is Earth's "sphere of influence"; it is approximately spherical and its radius is more than twice the average radius of the Moon's orbit.) >...so that unlike every other natural satellite in the >solar system, the Moon's orbit is always "concave inward" and its velocity >never goes "retrograde" relative to its primary. Both of which are mildly interesting facts which nobody considers to have any real importance. (In particular, astronomers do not feel that they make any fundamental difference to the status of the Moon.)  SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > Where could the module be located? At one of the PMA's. But I cant see why you would use that connection when there are few docking ports, and you more likely would connect the module to the russian segment. Otherwise (USOS) I think the CBM would be a better system. Sincerley Bjørn Ove The Chinese already own APAS units, but they don't have either probe/cone or CBM. Are you volunteering to ship them a CBM? > > Where could the module be located? > [quoted text clipped - 5 lines] > Sincerley > Bjørn Ove > The Chinese already own APAS units, but they don't have either > probe/cone or CBM. Are you volunteering to ship them a CBM? You seems to miss all points her. If the Chinese where to dock (more than for demonstration) to the USOS, they could most likely get hold of a CBM (althoug the docking metods nessesary for docking to CBM's is not in the scope of this reply) if they wished (because the PMA's is *per definition* American ground). Othervise it would likely (from both a technological and political standpoint) to dock with the Russian side of the station. To again feed you with the spoon, if they were allowed to do that they would be allowed on *russian ground*, and could most likely get hold of a russian docking adaptor. Sincerley Bjørn Ove |
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