unruh wrote:
On 2011-09-22, David Woolley<[email protected]> wrote:
The orbit plane is fixed relative to the fixed stars, so, for the orbit
to cover the same ground each time, it has to have a period that exactly
divides the sidereal day. The period is between successive maximum
North points.
It is the sattelite you see, not the orbital plane. The sattelite goes
around its orbit in a much shorter time period than one siderial day.
David is correct, the GPS sats are in fact using orbits that have a
period of almost exactly half sidereal day, or about 11 hours 58 minutes.
This is not a requirement though, afaik the upcoming Galileo sats will
have significantly higher orbits/longer periods, but still a rational
factor of the sidereal day, so that they will return to the same point
after a number of days.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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