2013-070B (Chang'e 3 r/b): a tumbling rocket stage at one Lunar distance

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.



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).

(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:

Find_Orb
Perigee 2015 Jul 8.981227 +/- 0.0143 TT = 23:32:58 (JD 2457212.481227)
Epoch 2015 Jul 6.0 TT = JDT 2457209.5 
M 298.03225 +/- 0.15 
n 20.78598673 +/- 0.0509 

a 282763.321 +/- 462 km
e 0.7243890 +/- 0.00115 
Incl. 23.49157 +/- 0.0006 deg
Peri. 40.10428 +/- 0.055 deg
Node 141.35795 +/- 0.0017 deg
  
q 77932.6554 +/- 449 km   Q 487593.987 +/- 472 km
P 17.32d

24 of 29 observations 2015 June 26-July 5; mean residual 0".577. 

Chang'e 3 rb
1 00000U         15187.00000000  .00000000 00000-0 00000-0 0 05
2 00000 23.4899 141.5720 7239912 39.8984 298.3594 0.05732427 01 

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:

(click to enlarge images)