Recently, a friend of mine working on a different project has waved me into his office. It turned out that he wanted to visualise the orbit of one of space probes, and the orbital elements he had were not pretty: in fact, they resembled a sawtooth in one of the axes (and were seemed normal in the other two). He asked for my suggestion regarding fixing the flight path for the presentation purposes; I typed up a quick and dirty implementation of a moving average smoothing algorithm that was enough for a last-minute fix.
After walking home from my work I first spent a couple of minutes thinking whether I should have applied a different approach (such as fitting polynomials or local regression, or whatever jumped to my mind at the moment), but moments later I realised I have no idea why do the data look that way. Any explanation for such a sawtooth for being there? It is too regular to look like constant engine corrections. Do any of you have a clue?
Tomasz, the observation of this signature in the absence of pertubations of the other axes strikes me too. If there had been gravitational forces - or even regular engine corrections, you might have expected pertubations on at least two axes. Therefore I strongly suppose some artifacts in the measured orbital data.
Thanks for the suggestion, dr Lingner. This seemed plausible enough to me too, but I keep wondering whether this is the case... Perhaps somebody has a different explanation to offer?
Hi Tomasz.
Objects orbit in a plane, so you would not expect any motion in the axis perpendicular to that plane...unless the orbit is precessing. Perhaps the sawtooth pattern represents a periodic correction of drift caused by nodal precession?
But I'm kind of guessing in the dark, because I don't know the nature of the system in question. Some more detail would help guide us towards the answer...
- By referring to it as a space probe and not as a satellite, do you mean that it is not in Earth orbit, but rather elsewhere in the Solar system? What is its purpose?
- What sort of orbit is it in? Low, medium, geostationary, polar, heliosynchronous, Lagrange point, highly elliptical, transfer, ...?
Hello Dr Butler,
Our case actually involved a space probe on an escape trajectory. The calculations used heliocentric coordinates.
For the purpose of discussion, we could generate a very similar case with the interface available to the general public at https://omniweb.gsfc.nasa.gov/coho/helios/heli.html and generating the XYZ Solar ecliptic output for the entire range available for Voyager 1 or 2 with a daily resolution. The output seems to be influenced by the same effect.
Best regards,
Tom
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