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.

Small unusual artificial object WT1190F will impact in a few hours [UPDATED with imagery of actual impact]

click image to enlarge

(for an update with imagery of the actual impact of this object from a research plane, see bottom of post)

The animated GIF above was made from images which I took just a few hours ago with the 0.61-m Cassegrain telescope of MPC G68 Sierra Stars Observatory in Markleeville, California.

The moving object is WT1190F, discovered on October 3 this year by the Catalina Sky Survey. This small peculiar object will impact in a few hours from now (near 6:18 UT, Friday 13 November 2015) just south of Sri Lanka.

It is an unusual object that is not a Near Earth Asteroid but almost certainly a small (1-2 meter) artificial object. It is moving in the Earth-Moon system (i.e. in a very elliptic orbit around earth) and its orbit is under influence of Solar Radiation Pressure, which shows that it is very light weight for its size. This fact, and the geocentric rather than Heliocentric orbit with apogee at twice the distance to the Moon, suggests it is some piece of hardware from a past Lunar mission.

image credit: Bill Gray, Project Pluto

It is not clear from which Lunar mission this object is a relic: it could be from one of the American missions, but also Russian or Chinese. The object in question turns out to have been sporadically observed since 2009, as it is probably the same object earlier designated 9U01FF6 in 2009 and UDA34A3 and UW8551D in 2013.

Shortly after its (re-) discovery on October 3, Bill Gray noted that the orbit yielded impact solutions on November 13 near 6:18 UT. The predicted impact point is over the Indian Ocean, just south of Sri Lanka. Bill Gray has put up a FAQ for this object with maps of the orbit and impact location here.

image credit: Bill Gray, project Pluto

As this is a small, 1-2 meter sized and lightweight object, the impact is harmless. It will burn up in the atmosphere and likely nothing will reach the water surface. It provides scientists with a good opportunity though to observe what happens during a small asteroid impact, as the speed and entry angle of this object is quite similar (see also the project page here).

The astrometry obtained from my images makes, along with data by many other observers, a modest contribution to  establishing the impact point and time as good as possible.

1st UPDATE, 13 Nov 2015, 09 UT:  WT1190F is now toast for a few hours. South Sri Lanka seems to have been clouded out, but there are reports on Twitter of sonic booms from the re-entry heard in Sri Lanka. 

In response to some of the comments, I want to point out that WT1190F is/was not the only artificial object in a trans-Lunar orbit which we were/are tracking. Here you can find an earlier post (out of several) on tracking 2010-050B and 2013-070B, two rocket boosters in trans-Lunar orbits from the Chinese Chang'e 2 and Chang'e 3 Lunar missions.

2nd UPDATE,  13 Nov 2015, 13 UT:  The first imagery (below, three stills and the video) has just appeared of the actual impact near Sri Lanka, shot from a research aircraft organized by IAC / UAE Space Agency / NASA / ESA:

The tumble periodicity of the Chang'e 3 upper stage (2013-070B) revisited

click image to enlarge

Brightness variation due to tumbling of the Chang'e 3 upper stage (2013-070B)
stack of 15 images taken with the 0.51-m telescope of MPC Q65 Warrumbungle
11 September 2015

I have written before on this blog about tracking very distant space debris: the CZ-3C upper stages of the Chinese Lunar missions Chang'e 2 and Chang'e 3, which move in chaotic trans-Lunar orbits. I have embarked on a long-term project to follow these objects.

Apart from positions to keep their orbits up to date, these observations also provide information about the tumbling behaviour of these objects. Both objects have a periodic variation in brightness: a very rapid one for 2010-050B, the Chang'e 2 upper stage, and a slow one for 2013-070B, the Chang'e 3 upper stage.

Earlier, in July 2015, I had established a tumbling periodicity of  ~7 minutes for 2013-070B. I have now been able to refine that value much better, to only a few hundreds of a second.

With the help of Peter Starr from Warrumbungle Observatory (MPC Q65) in Australia and Krisztián Sárneczky from Szeged University's Piszkéstető Observatory (MPC 461) in Hungary, I could obtain two nice series of data the past week. The data were gathered on September 11 (Warrumbungle 0.51-m telescope) and September 14 (Piszkéstető 0.60-m Schmidt telescope).

The first set, taken by Peter from Warrumbungle, is a set of 15 exposures of 30 seconds each, taken in ~1 minute intervals. The image at the top of this post is a stack of these images. The brightness maxima can be clearly seen.

The second set, obtained in twilight by Krisztián from Piszkéstető at the end of a run of the Szeged Asteroid Survey, is a set of 18 exposures of 3 seconds (!) each, in ~20 second intervals, with a brief pause halfway the series.

Single sinusoid fit to data from Sep 11 (lef) and Sep 14 (right)
click diagram to enlarge

The data allow to fit a sinusoid to both sets simultaniously, and from that get a very accurate periodicity. The double diagram above shows this sinus-fit to the data. It allows to establish a peak-to-peak periodicity of 423.01 ± 0.03 seconds for the tumbling of 2013-070B.

Rapid tumbling of the Chang'e 2 r/b (2010-050B) and Rollercoaster orbital evolution

(click image to enlarge)

Recently, I have posted several times about my tracking of two extremely remote pieces of space junk: 2010-050B and 2013-070B, the CZ-3C upper stages of the Chinese Chang'e 2 and 3 Lunar missions. These orbit in orbits with (currently) perigee just within, and apogee beyond one Lunar distance, i.e. a trans-Lunar orbit.

In a recent post I discussed the tumbling behaviour of 2013-070B, the Chang'e 3 booster. At that time, I stated that by contrast the Chang'e 2 booster, 2010-050B, appears steady.

I can now say that is not true: 2010-050B is tumbling too. And very rapidly, which is why I didn't notice it earlier.

My earlier imaging sessions were done while 2010-050B was at well over one Lunar distance (beyond 400 000 km), towards its apogee. On July 18th I imaged it from MPC Q65 Warrumbungle while it was only a few hours from its perigee, at a distance of 280 000 km (about three quarter of a Lunar Distance), moving at 47" per minute. The result is a much longer trail on the image than in earlier imaging sessions.

Rather than being a trail, suddenly the trail is resolved in a series of dots: typically three (and in one image two) per 30 second exposure. See the image in the top of this post. The reason this was not visible during earlier imaging sessions, was that the trail was so short (a  few arcsecs) when imaging the object at larger distance, that the dots merge into one trail.

The 3 dots per image, and once two dots, indicate a flash period of ~15 seconds, testifying to a rapid tumble. This is close to the period determined by Peter Birthwhistle (MPC J95 Great Shefford) in 2010 shortly after the launch.

I also imaged 2013-070B that night, at a distance of about 479 000 km (1.25 Lunar Distances). This object is tumbling much slower than 2010-050B: the brightness variation in the animated GIF below fits nicely with the 7m 05s flash period determined from June 26 and July 5.

The orbits of 2010-050B and 2013-070B are changing extremely fast, in a chaotic way, notably as a result of Lunar perturbations. As you can see in the table that is part of my SeeSat-List post here, the apogee of the 2010-050B orbit for example changed from about 550 000 km to about 446 000 km between May 7 and July 18. The perigee changed from about 350 000 km to about 280 000 km, i.e. from about 1 Lunar Distance to about 0.73 Lunar Distance, during that same period. The orbital period was shortened by almost 10 days.

While the apogee and perigee distances are currently decreasing for this object, a new Lunar perturbation might make them increase again in the future. The orbital inclination also widely varies over time. Such changes are very sudden, especially in connection to close Lunar encounters. These objects are on a true Rollercoaster ride through the Earth-Moon system.

As it turns out, this kind of chaotic orbit is very difficult to model, even over relatively short time scales. Attempts using GMAT show that very small variations in the determined orbit yield very different outcomes within only a few years. Variations in the order of a few hundred meters (!) in apogee and perigee will already do it, i.e. variations well within the uncertainties in the determined orbital parameters.

GMAT-simulated chaotic orbital evolution of 2010-050B over a 1.5 year period. Grey is the Moon orbit, red is 2010-050B orbit, blue grid is earth equatorial plane. In reality, the orbital evolution might be different as small variations in initial conditions (see text) yield large differences after 1.5 years.

So we have to observe these objects to see how their orbits evolve in the future. And this is what I will do: keep following them, over the coming years.

Basically, three eventual future fates are possible for these objects: one is eventual ejection into a Heliocentric orbit (so it will leave the Earth-Moon system); two is an eventual Earth impact (i.e. a decay in the Earth atmosphere); and three is an impact on the moon.

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)