In two posts in May (here and here) I reported on my telescopic observations of 2010-050B, the upper stage of the Chinese Chang'e 2 Lunar mission in a trans-Lunar orbit.
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This is not the only one of these objects observable (and sometimes mistaken for a Near Earth Asteroid, as 2010-050B in May was). The animated GIF above, shows you 2013-070B, the upper stage of the Chang'e 3 Lunar mission, imaged on July 5th using the 0.51-meter telescope of MPC Q65 Warrumbungle in Australia. It was at a distance of about 336000 km, roughly one Lunar distance, at that time
Unlike 2010-050B, which is stable in brightness, this objects is clearly tumbling and shows a marked periodic brightness variation as a result. There is a clear saw-tooth pattern with a steep ascending slope and more shallow descending slope, an amplitude of ~2.5 magnitudes and a period of about 420-425 seconds (or ~7 minutes).
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(click diagram to enlarge)
Observations of the same object from June 26 can be fitted to a very similar 7 minute period and ~2.5 magnitude amplitude, but with the descending instead of the ascending slope steeper and the ascending slope more shallow, the reverse of the July 5 observations.
The July 5 observations combined with the June 26 observations result in the following orbit for 2013-050B:
The orbit is more eccentric and has a smaller semi-major axis (and as a result, a perigee closer to Earth) and smaller orbital inclination than that of 2010-050B.
2013-070B and 2010-050B move in chaotic orbits: frequent close encounters with the Moon create sudden, drastic changes in eccentricity, inclination, perigee and apogee. It is possible that both objects will be ejected out of the Earth-Moon system in the future, into a Heliocentric orbit.
Below are the orbits for both objects as of July 6, 2015:
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(click to enlarge images)
posted by SatTrackCam Leiden at 23:24 on 08-Jul-2015
"2013-070B (Chang'e 3 r/b): a tumbling rocket stage at one Lunar distance"
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