Monday 14 December 2015

Something (a fuel leak?) happened to the Chang'e 3 booster (2013-070B) late September-early October

Over the past year I have frequently reported on my observations of very distant space junk: objects orbiting at trans-Lunar distance. One of these objects, 2013-070B, the CZ-3C upper stage of the Chinese Chang'e 3 Lunar mission from 2013, is now showing something interesting.

flash cycle of 2013-070B on 11 Sep 2015 (click to enlarge). Stack of multiple images

2013-070B is tumbling and shows a very slow flash cycle (see various previous posts). Observations during the summer months of 2015, up to 14 September 2015, suggested a stable flash period of  about 423 seconds.

But somewhere between mid-September and late October 2015, things have changed. The first indication was from this fine series of data points which Krisztián Sárneczky obtained for me on 24 October 2015, using the 0.6-m Schmidt telescope of MPC 461 (Piszkéstető station of Konkoly Observatory, Hungary):

click diagram to enlarge

The flash period had suddenly dropped, to 384 seconds on 24 October 2015, and has further dropped to 364 seconds on 6 December 2015, based on a series of images I obtained with the help of Peter Starr from Warrumbungle Observatory (MPC Q65) in Australia.

2010-013B 2013-070B is hence suddenly tumbling at a faster speed than it used to do. The value is still dropping further, but the drop appears to be slowing down, as can be seen in the diagram below:

click to enlarge diagram

Such a sudden drop from a stable flash period to a shorter flash period can have a number of causes. A close approach to the Moon can result in a tumble periodicity change: but 2013-070B did not experience such a close approach during the relevant weeks, so that is not an explanation. The most likely explanation is that the booster developed a fuel leak.

Rocket stages always contain some remnant fuel in their tanks. Rocket fuel is often quite corrosive and slowly eats its way through the metal of the tank and booster. In addition, a meteoroid impact can puncture the rocket stage and tanks. When one of these two things happen, fuel vapor escapes from the rocket stage, and acts as a mini rocket engine, giving the object some extra momentum. This can either speed up or slow down he tumbling speed of the object.

We have seen this happen a number of times with rocket stages in Low Earth Orbit as well, and there is no reason why this could not happen to a rocket stage in a trans-Lunar orbit.

Imaging Geostationary satellites, and PAN's past relocations

Last week saw some clear evenings, and I used one of them to image some geostationary satellites. It concerned "the usual suspects": MENTOR's, MERCURY's and the enigmatic, probably SIGINT satellite PAN (2009-047A). The latter satellite has not been moved for quite a while now: since the end of 2013 it is at longitude 47.7 E, parked close to a number of commercial comsats. In the past it was frequently relocated, taking positions next to various commercial COMSATS. In four years time between 2009-2013, it moved at least 9 times (which is a lot) to various longitudes between 33 E and 52.5 E.

PAN amidst several commercial COMSATS on 9 December 2015 (click to enlarge)

The diagram below charts these frequent movements of PAN. Relocations typically took place about once every 6 months. Late 2013, they stopped. PAN however must still be operational, as active station-keeping is necessary for it to stay at 47.7 E.

relocations of PAN over time, 2009-2015 (click to enlarge)

Four other SIGINT satellites and a military comsat were imaged as well: Mentor 4 (2009-001A) and Mentor 6 (2012-034A), Mercury 1 (1994-054A) and Mercury 2 (1996-026A), and the military comsat Milstar 5 (2002-001A).

Mentor 4, next to commercial comsat Thuraya 2 on 9 Dec 2015 (click to enlarge)

Mentor 6 and a number of commercial satellites, close to the Orion nebula, on 9 Dec 2015

Using the remote telescope at Warrumbungle (MPC Q65) in Australia, I recently (4 December 2015) also checked-up on the recently launched US Navy COMSAT MUOS 4 (2015-044A). It is still at its check-out location over the Pacific at longitude 172 W, but some recent press statements suggest check-out has been successfully completed, and it will be moved to its operational position at longitude 75 E near India in the spring of 2016.