# Tag Info

### Lowest possible lunar orbit and has any spacecraft achieved it?

The lowest orbit achieved would probably be PFS-2, a small satellite deployed from Apollo 16's service module. It was intended to go into a 55x76-mile orbit (88.5x122 km), but due to variations in ...
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### Why is the sidereal period of the Earth 362.392667 days?

Why is the sidereal period of the Earth 362.392667 days? It's not. You are doing three things wrong: You are using the solar system barycenter and assuming that is an object (it isn't). You are ...
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### Lowest possible lunar orbit and has any spacecraft achieved it?

"Lowest possible lunar orbit..." As pointed out in comments and in answers to the linked questions Are low, polar lunar orbits in general relatively stable? Moon orbit station-keeping delta-...
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### How do satellite trackers work when showing a "satellite"?

How do satellite trackers work when showing a "satellite"? Satellite "tracking" websites do not "track" anything. You could blow up the satellite, and that little dot ...
• 148k
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### Can the Right Ascension and Argument of Perigee of a spacecraft's orbit keep varying by themselves with time?

You are correct to a point that the RA of the ascending node and argument of perigee won't change over time without some external force acting upon the satellite. In a simplified gravitational field, ...
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### Will crewed vehicles ever follow multi-flyby trajectories?

Given the mass costs in terms of consumables and the risk and support costs of keeping humans in space for longer, it seems unlikely that the multiple Earth-Venus flybys used by a lot of robot probes ...
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### How to get semi-major axis from TLE?

The TLE gives mean motion ($n$) in $\frac{rev}{day}$. This needs to be converted to $\frac{rad}{s}$ which can be accomplished by multiplying the $n$ TLE value by $\frac{2\pi}{86400}$. Therefore, to go ...
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### How (the heck) are military satellites with (apparently) classified TLEs still showing up on sat map websites?

There is an international network of observers of classified satellites, organized around the Seesat-L mailing list: http://www.satobs.org/seesat/seesatindex.html They typically look for satellite ...
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### Deriving the changes in Keplerian Elements induced by small impulses

If we assume a perfect two-body problem, absent perturbations from external bodies or non-spherical gravity sources (i.e., perfect conic orbits with no precession or variation), your constraints ...
• 17.3k
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### Determine orbit type from TLE

According to Wikipedia, field 8 of TLE line 2 is the "mean motion in revolutions per day"; you can determine the orbital period from this. For geosynchronous orbit, you should expect 1.0 ...
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### Is it possible to plot the ground track of a satellite with just azimuth & elevation angles without range?

Yes. This is a classical astrodynamics problem of orbit determination. The technique you would use is called Gauss' method. It allows you to determine an approximate orbit from three timed ...
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