Saturday 31 December 2011

Summary of 2011 observations

As the year is closing, it is time for a summary of the observations conducted in 2011.

Compared to the previous two years, 2011 saw slightly more observing nights, a larger number of  classified objects tracked, but a slightly lower number of positional estimates done:

Number of observing nights: 87
Number of obtained positions:  883
Number of classified objects tracked: 43

For 2009 and 2010, this were respectively: 77, 953, 32 and 78, 1084, 39

In the second diagram above, it can clearly be seen that the spring and late summer were very good (many clear nights), while winter, and especially December, were very poor.

The following tables give a summary of the objects observed (with the "obs" column refering to the number of positions obtained on the object):
(click tables to enlarge)

Just for fun, I plotted all obtained positions on an RA/DEC map:

click diagram to enlarge

New at SatTrackCam in 2011:

2011 saw several new additions to the equipment:

New lenses - new lenses added to the repertoire were the very fine SamYang f1.4/85mm and a Canon EF 2.0/35 mm. The SamYang allowed to target fainter objects in LEO and MEO, going clearly deeper than the EF 2.5/50 mm normally used on brighter objects in LEO. It's FOV is still large enough to capture full trails.
The Canon EF 2.0/35 was added to target fast moving objects in LEO such as objects near decay, Soyuz and Progress, and Keyholes in perigee passes. It has a similar aperture as the 50mm lens but a wider FOV.

Video - Video finally did it's entry at SatTrakCam Leiden in late 2011. The equipment consists of a sensitive WATEC 902H camera that can be equiped with a number of lenses (including the above mentioned Canon EF 2.0/35 and the SamYang 1.4/85). A GPSboxSprite2 time inserter from BlackBoxCamera in the UK is used for the imprint of accurate time signals, and the video feed is recorded on a HDD recorder.

Remote telescope - I have used remote rentable telescopes for some time for my work on asteroids. Starting mid-2011, I am also using them on satellites. The telescopes used are part of the SSON network and consist of a 37-cm and 61-cm Cassegrain located in California and Arizona. These received COSPAR station codes 8231 (Winer obs, MPC code 597) and 8438 (Sierra Stars obs, MPC code G68). I use them to target geostationary satellites visible from the western part of the USA. Two notable targets repeatedly imaged were the new SBIRS Geo 1 (11-019A) and the enigmatic Prowler (90-097E).

Observational highlights:

A few observational and other highlights of 2011:

Nanosail-D - This experimental NASA solar sail put on a fine show during late spring and summer. A study was made of the brightness variation of this object. See various posts here.

The last Space Shuttle missions - The truely last one was not observed, but the last flight of Discovery was imaged several times.

Spectacular IGS 1B flare - IGS 1B is a Japanese spy satellite that failed in 2007, will reenter in 2012-2013 and probably still has some fuel onboard. When I posted on the latter on this blog, this generated some interest, even from the White House.
On  September 2nd, I observed a brilliant flare produced by this satellite, one of the best satellite flares I have ever seen.

UARS and ROSAT - the uncontrolled reentries of these two satellites generated a lot of attention. ROSAT was actually observed twice by me shortly before its reentry, see here and here.

Fobos-Grunt - This Russian probe launched in November should have gone to Mars and the Martian moon Phobos for a sample return mission. A rocket engine failure however got it stuck in Low Earth Orbit, from which it will reenter mid-January. I observed, photographed and even filmed it a number of times.

Andre Kuipers to the ISS - on December 21st, a Soyuz with Dutch astronaut Andre Kuipers was launched for a six-month mission to the ISS. Just before the end of the year, I finally could see the ISS with Kuipers on board pass over Leiden and film it (between launch on December 21 and the sighting on December 30th, it had been very bad weather).

Andre's Soyuz 3rd stage decay - Due to untimely cloud cover I did not observe this event myself, but was involved in the identification of it. The spectacular decay in the evening of December 24th was seen by many people in the east, central and southern parts of the Netherlands (where it was clear, unlike in Leiden), as well as from Germany and France.
Ralf Vandeberg (B), Josep Remis (F) and me (NL) independantly were the first to identify the slow fragmenting fireball with the Soyuz 3rd stage used in the December 21 lauch to the ISS, disseminating our identifications on mailing lists, twitter and blogs within half an hour after the fireball apparition. Read more here.

Friday 30 December 2011

Footage of the ISS with Andre Kuipers on board passing over Leiden, 30 December

The footage above was shot by me this evening (30 December 2011, evening twilight, around 16:38 UTC = 17:38 local time). It shows the International Space Station (ISS) with Dutch astronaut Andre Kuipers on board, passing right over my observatory in Leiden, the Netherlands.

The movie was shot using a sensitive WATEC 902H camera and F1.4/12mm lens (this is not the best of lenses in terms of sharpness, but it has a relatively wide FOV of 30 degrees that suited this case. This lens provides a reasonably good approximation of the typical visual view as well in that the limiting magnitude of the movie is similar to that with the naked eye).

I had actually almost missed this pass, as I was busy with another task and lost track of time. So I had to set up my equipment rather in a hurry, with no time to start up and synchronize the GPS time inserter. As usual (and also because I do not yet ahve a "routine"with this new equipment) I initially had an "issue" in getting an image on the laptop monitor: when I finally had an image and could focus, the ISS was already in the sky, ascending at 45 degrees elevation in the west.The sky was still a bit bright from twilight, and some hazy clouds were in the sky.

The footage picks up the ISS in northern Cygnus, shows the ISS as it ascends and goes through the zenith, passing over Pegasus and into Andromeda and next descends through the triangle towards the east, disappearing behind the roof of the house.

I am happy to have this footage at all, as the weather is abominably bad this month.

Tuesday 27 December 2011

Further confusion on Saturday's Soyuz r/b reentry

I earlier wrote about the confusion reigning in the press concerning the sky event over Europe of last Saturday evening. Initial confusion was over wether it was a meteor, "comet" or (and that was the correct explanation, but many Dutch and German news outlets failed to properly pick that up): the reentry of  a Soyuz rocket.

Now a new confusion has arrisen: some news outlets and weblogs, e.g. that of Physorg, mistakenly link the event to last Friday's failed Russian launch of the Meridian satellite. Due to a rocket failure, this never reached earth orbit but crashed in Siberia within minutes after the launch.

As I wrote earlier, what reentered and was seen over France, Germany and the Netherlands last Saturday evening, was the 3rd stage of last Wednesday's Soyuz launch to the ISS.

The confusion probably comes from the fact that both launches used a Soyuz rocket. The failed launch that crashed in Siberia on Friday got some press attention because fragments hit a house in Russia (see a.o. here (English), with pictures of a recovered fuel tank here (Russian)).

But again: that failed launch had nothing to do with Saturdays sky event over Europe. The reentry over Europe was the 3rd stage of the earlier Wednesday launch to the ISS, that included Dutch astronaut Andre Kuipers.

(More on Last Saturday's Soyuz reentry over Europe: here and here)

Monday 26 December 2011

11-078B Soyuz 3rd stage reentry: answers to some frequently asked questions

In the wake of the spectacular reentry over NW Europe of the Soyuz 3rd stage 2011-078B on Saturday 24 December 2011, several common questions popped up in comments, e-mails, on Twitter and in newspaper discussions. I will answer a few below.

Frequently Asked Questions:

(Q1): Are these things predictable and who makes such predictions?
(Q2) Does it really take a Soyuz rocket 3rd stage three days to fall back to earth?
(Q3) Why doesn't this happen with each Soyuz launch? Or: why not over the same location on Earth?
(Q4) has anything of the rocket stage survived to earth surface?


(Q1): Are these things predictable and who makes such predictions?

(A): It is "sort of" predictable. Using computer models which take into account many factors of influence, one can make a prediction yielding an indication of the time a rocket stage or satellite will re-enter the atmosphere. However, even very close to that actual time of reentry, the uncertainty in these predictions is still very large. Exactly when a rocket stage will start to burn up depends on many factors, including the exact condition of the atmosphere at that moment, the shape of the rocket stage, and whether it is tumbling or not. In practise,  this turns out to be very difficult to model, even with the best computer models.

Several organisations and individuals do such predictions (and you can even find software for it on the internet). However, one of the most authoritive sources of such predictions is USSTRATCOM, the American military organisation that tracks manmade objects in space (many people think NASA does that job. But that is incorrect: it is USSTRATCOM, better known as 'NORAD'). They publish these predictions as 'TIP' messages. Their first prediction is published 2 months in advance. These still have a very large uncertainty (think of: weeks). In the days close to decay, they publish new estimates as new TIP messages that gradually become more exact. But even these can have uncertainties of several hours, even for predictions made on the day of the reentry itself.

For example, the last pre-reentry TIP message issued only 2 hours before the Soyuz 3rd stage came down, still had an uncertainty window of six hours.....

Once an object has reentered, USSTRATCOM does a post-analysis of the last orbital information, and publishes a "final' TIP message mentioning when and where the object came down (so this is done "after the fact"). These can be (but are not always, as it depends on how well the object was tracked during it's last hours of existence) very accurate. Sometimes, as was the case with this reentry of the Soyuz 3rd stage, they provide a time with an uncertainty of only minutes, plus a quite accurate position. In other cases, where less recent tracking data is available, the final uncertainty is much larger.

Note that a re-entering satellite or rocket booster has a speed of 7.5 km per second (4.7 miles per second)! So even if the predicted time has an uncertainty of just 15 minutes, this amounts to an uncertainty of 13,500 km (8,400 miles) in the position of the object when it reenters! This is why it is impossible to pinpoint the expected point of re-entry beforehand, when it is not a "controlled" re-entry. (in a "controlled" re-entry, the satellite operators send a command to the satellite to make a rocket burn at a precise time, kicking it down over a designated spot, usually the Pacific ocean. This Soyuz reentry was however not such a "controlled" reentry).

Many people mistakenly think that in this day and age of supercomputers, scientists (or the military) can predict everything. In reality, satellite/rocket reentries like this are so complex that even the best computer models can only give rough indications untill just minutes before the actual re-entry.

(Q2) Does it really take a Soyuz rocket 3rd stage three days to fall back to earth?

(A) Yes, it does. That last rocket stage is jettisoned that high above earth surface, that it does not just rapidly fall back on a ballistic trajectory (such as the 1st and 2nd stages do) but actually reaches Low Earth Orbit, and stays in orbit around the earth for several days. In effect, it becomes a satellite for a while in a very low orbit around Earth. Under influence of gravity and drag from the outer atmosphere, the orbit slowly evolves and becomes smaller and smaller. On the first day only gradually, but as it slowly comes down, this gradually goes faster and faster.

The influence of our atmosphere reaches several hundreds of kilometers up: even the International Space Station experiences some atmospheric drag, and would fall down within a year if its orbit was not regurlarly raised using the rocket engines of the Progress spacecraft docked to the ISS.

It takes about 3-4 days for a Soyuz 3rd stage from a launch to the ISS to come down. The exact amount of time is variable and different in each new case, as it depends on many factors. Our atmosphere is variable in extent and density, notably under the influence of solar activity. When the sun is active and many charged particles from solar outbursts reach earth, these interact with our atmosphere and the atmosphere slightly expands as a result of this. This means that objects at the altitude of the Space Station and below that (such as the Soyuz rocket stage) will experience a "thicker atmosphere", i.e. more drag from the atmosphere's outermost layers, and as a result they will come down faster. When it reaches at altitude of only 120 km (75 miles) it goes very quick: within minutes the rocket stage has dropped tens of kilometers, slowed down considerably, and finaly plunges straight down from that moment onwards.

The exact moment this happens, is highly dependant on these variations in extend of our atmosphere due to variations in solar activity. This is another reason why a satellite or rocket re-entry is so difficult to predict: one short but intense outburst occuring on the sun will next make a rocket stage fall back much quicker than expected.

Below diagram shows the orbital evolution of the Soyuz 3rd rocket stage that decayed last Saturday. It had to make 52 full orbits (full circles) around the Earth before it burned up. It's orbit was a bit "eccentric", which means that it was not a perfect circle but an ellipse. So on each revolution around the earth, there is a point where it is a bit higher above earth (called the "apogee") and a point where it is closest to the earth (called "perigee"). In the diagram, the values for these altitudes have been plotted as a red and blue line. Note how fast these altitudes change in the final hours before re-entry.

(Q3) Why doesn't this happen with each Soyuz launch? Or: why not over the same location on Earth?

(A) It does happen with each Soyuz launch to the ISS. The Soyuz 3rd stage always comes down some 3-4 days after the launch.

That reentry however is never over the same location on earth. The reasons for this, have already been outlined as part of the answer to question (2) above. An important factor of influence on how quickly a rocket stage comes down, is the variable earth's atmosphere, under influence of variability in solar activity. These factors are different for each new case. This is why the 3rd stages of Soyuz launches to the ISS never fall down near the same spot twice.

(Q4) has anything of the rocket stage survived to earth surface?

(A) Not that we so far know of. Usually, the rocket stage almost completely burns up in the atmosphere. Sometimes, a few smaller bits survive (quite often spherical fuel tanks). For example, an object that is likely a rocket fuel tank came down in Namibia in November and might be part of a rocket stage used in a Russian November  launch to the International Space Station.

Saturday 24 December 2011

[Updated] Breaking News: Decay of Soyuz r/b stage from André Kuipers' launch to ISS observed from the Netherlands!

UPDATE - the final TIP for Soyuz r/b 38037 / 2011-078B has been released by USSTRATCOM near 18h GMT and it indeed shows that this was the Soyuz r/b: reentry time is quoted as 16:25 +/- 1 minute GMT at 49 deg N, 7 deg E. This fits the observations well.
In the Dutch press, there meanwhile appears to be a lot of confusion. The Dutch National Police claims that they talked to "NASA" who apparently said it was a "meteor" (or "comet"). So THAT is widely claimed in the press now, to the point of calling the identification with the Soyuz 3rd stage "speculation". Which it is not: it is based on factual data and now clearly confirmed by the USSTRATCOM JSpOC TIP message. What more do you want?!

I have no idea to whom (or even where: NASA is big...) the Police spoke, but for all things it could have been the JPL janitor....
At any rate: appart from my analysis below (which is already clear), the USSTRATCOM TIP message mentioned above makes unambiguously clear that this was the Soyuz 3rd stage.
Note that to access the USSTRATCOM TIP message via the link above you need an approved account. USSTRATCOM is the US military Command responsible for tracking manmade objects in space, and perhaps better known under their former name NORAD.
- end of update

Multiple reports are coming in, among others by experienced Dutch meteor observers Carl Johannink (Gronau) and Arnold Tukkers (Denekamp), of a bright and very slow fragmenting object seen low in the west-southwest near Venus at 16:26 UTC, 24 December.

From the descriptions it clearly was a reentry of an artificial object (space junk), as the event was too long in duration and too slow to be a meteoric fireball.

And it was not "just" a random bit of space debris, it turns out:

The observations fit with 2011-078B (#38037), the last stage of the Soyuz rocket that brought Dutch astronaut Andre Kuipers up to the ISS earlier this week. It was already predicted to decay near this moment by USSTRATCOM.

Below is the  predicted trajectory of the Soyuz  3rd stage for the Gronau/Enschede area (and below that, the ground trajectory). It is based on an orbit with an epoch near noon of 24 December (epoch 11358.49032868. Source: USSTRATCOM), so a few hours old, which will introduce some minor discrepancies (a few seconds in time). But it fits the descriptions very well in terms of time and trajectory in the sky.
click images to enlarge

[UPDATE 7 October 2017]:

I recently modelled the re-entry of 2011-078B in GMAT, using the MSISE90 model atmosphere with actual Spaceweather of that time. Drag surface was set at 60% of the maximum drag surface for a Soyuz upper stage: this yields a decay position and decay time well in agreement with the JSpOC TIP position and is close to what the drag value for a tumbling, fragmenting object would be.

As seen from Gronau in Germany, it yields the following sky trajectory. Compare with Carl Johannink's description below: it matches his description well.

click map to enlarge
- end of update

- continuing original post:

Some quickly translated descriptions by two experienced Dutch meteor observers (compare to the sky trajectory map above for their area):

Arnold Tukkers, Denekamp (Netherlands):

At 17:26 CET (=16:26 UTC) I looked out of the window and saw a strange phenomena just above the rooftops behind us. It looked like a very, very slow meteor fragmented in several pieces. Like Peekskill but less bright.
Multiple fragments. Because it was so low in the sky, I walked upstairs and could still see the last part from the bedroom window. So it at least took 20 seconds. [...]
What a sight! Trajectory for me (did not see initial part) southwest-southeast. Altitude maximum 20 degrees. Colour brown-red.

Carl Johannink, Gronau (Germany):

Just was looking at Venus in evening twilight.
Left of it an object appeared from behind a cloud that I first thought to be an aircraft, but next I found something was not right. The thing sometimes brightened and became fuzzy, trailing a circa 8 degree long tail. Maximum brightness about -4.
The object roughly moved from SSW to SE at an elevation of about 15 degrees. The whole phenomena took over half a minute.

To see the second part of the trajectory I had to walk to a different room. Called in Elisabeth, together we saw the object fragment into pieces (each individual piece about mag. 0 to +1) and then fade out.

The whole event looked much alike to the New Years Eve satellite decay of 1978, albeit being somewhat less bright.
A number of video's from Germany have surfaced which likely show the event. Here are a few:
video 1
video 2
Video 3 (on the Bad Astronomer's blog)
Video 4
Video 5


Read the answers to Frequently Asked Questions for this reentry case I published later here.