Reentry of Soyuz rocket upper stage from Progress MS-03 launch seen from New Zealand, 19 Jul 2016

On July 19, 2016, near ~6:30 UT (~18:30 local time), a bright very slow and long-lasting fireball was reported by many people from New Zealand's South Island. Several images are available, e.g. here and here and here. The fine video below is from YouTube user Ralph Pfister:



Perhaps the most accurate time given for the event is 6:26 UT as given by amateur astronomer Paul Stewart from Timaru on New Zealand's South Island. Stewart captured  the fireball on several all-sky images. A fine animation of his images is on his weblog.

From the video's it is immediately clear that this is not a meteoric fireball, but the re-entry of an artificial object (i.e. artificial Space Junk).

Time, direction of movement  and geographical position moreover match well with an obvious decay candidate: the Russian Soyuz upper stage (2016-045B, NORAD #41671) from the July 16 launch of Progress MS-03 to the International Space Station. In other words: this was a Space Junk re-entry.

At the moment of writing, the elements that are available for the Soyuz rocket stage are almost a day old and not unproblematic. For unknown reasons the B* drag value of the elsets is zero and the NDOT/2 value unrealistic.

This hampers analysis slightly, but using the almost a day old elements face-value, the upper stage would have passed over New Zealand's Southern Island near ~6:33 UT (~18:33 local time). This is within minutes of the time of the New Zealand event. The direction of movement of the rocket stage also matches that in Paul Stewart's imagery.

The maps below show the predicted position and track of the Soyuz upper stage for 19 July 2016, 16:30 UT (18:30 local time in New Zealand). They are based on the almost a day old element set  16200.42841345.

click map to enlarge

click map to enlarge

The few minutes discrepancy between predictions and actual sighting from New Zealand is not unusual for a re-entering object. The last available elements (at the moment of writing) for the Soyuz stage are actually from many hours before the reentry, and during the last moments of its life the orbital altitude drops quickly (i.e. the orbit alters).

Old elements hence will place it in a too high orbit compared to the reality of that moment. As it drops lower in orbital altitude, the rocket stage will get a shorter orbital period and hence appear somewhat earlier,  "in front" of predictions made using the old element set. Discrepancies of a few minutes are therefore normal in cases like these.

When it is "early" on the ephemerids, the orbital plane will be slightly more to the east as seen from a locality. In this case, the nominal pass predicted for Paul Stewart's locality would have been a zenith pass: but the a few minutes earlier pass time compared to the predicted time and the lower actual orbital altitude at the time of the re-entry would result in a sky track that is shifted eastwards and lower in the sky. This matches Paul Stewart's all-sky imagery.

[Updated diagrams] GOCE is falling!

[diagrams updated 23 Oct 2013, 9:15 UT] 

GOCE, The European Space Agency's 1-tonne slick Gravity field and steady-state Ocean Circulation Explorer scientific satellite (2009-013A), is now truely coming down.

During the night of October 17-18, fuel reserves became so low that the pressure in GOCE's ion engine fuel system dropped below a critical 2.5 bar.  Next, between October 21.12 and 21.54, the ion engine stopped functioning, and as a result GOCE is now clearly losing altitude.

click diagrams [updated 23 Oct 9:15 UT]  to enlarge 

The first orbital determinations after the engine cut-off on October 21 are still inaccurate and as a result they are fluctuating, as the observational arc is still very short. But in the diagrams above, it can be clearly seen that the Mean Motion (the number of orbital revolutions per day that the satellite makes, i.e. how many times it circles the earth each day) jumps to much higher values. More orbital revolutions per day means that the orbit is getting smaller. The orbit getting smaller means the satellite is coming down.

This can be seen in the second diagram too. The apogee (the highest point in GOCE's slightly elliptical orbit) is steadily coming down since yesterday. The perigee (the lowest point in GOCE's slightly elliptical orbit) is dropping too.

GOCE's ion engine, when still working, provided a force countering the drag that the satellite experienced from the outer layers of the atmosphere in its low ~225 km orbit. As a result the drag parameter Bstar fluctuated around zero. When the ion engine cut out, the satellite suddenly experienced the full force of atmospheric drag. This can be seen in the lowermost diagram, which shows that the drag parameter Bstar made a strong jump to high positive values. The drag slows down the satellite, and as a result it drops in orbital altitude.

Over the coming days GOCE will rapidly lose altitude. So shortly after ion engine cut-off it is still too early to provide an accurate prediction about when it will truely re-enter and largely burn up: but as a ballpark figure this will happen somewhere between 2 to 3 weeks from now, somewhere during the first two weeks of November. In the days before re-entry, I will update re-entry forecasts on this blog.

Most of GOCE's one-tonne mass will burn up on re-entry, but some 250 kg (in many small fragments) might survive re-entry. At this point, it is still impossible to predict where (and when) these fragments may come down as that is dependant on many contributing factors, some of which are difficult to predict (e.g. the effect of fluctuating solar activity on the density gradient of the atmosphere). It will only be possible to predict this with some confidence in the final hours directly before re-entry.

Although the satellite is now without propulsion, its scientific sensors are still working. GOCE will continue to gather important scientific data on the Earth's gravity field until very shortly before its final demise.

The satellite controllers at ESOC have told me they have put the satellite in Fine Pointing Mode: a series of magnetic torques which react to the Earth's magnetic field keep the satellite stable in attitude (orientation), preventing it from tumbling, even though it has lost propulsion.

Since 2009, the GOCE satellite has gathered highly detailed data on the Earth's gravitational field and ocean surface heights.

Note: the apogee and perigee altitudes in the 2nd diagram were calculated with a fixed Earth radius of 6378 km, ignoring Earth oblateness

My last view of GOCE, an image taken on 29 September 2013 during a twilight pass over Leiden (click image to enlarge)

Fireball seen over Eastern Australia, 13 June 2013 6:05 pm AEST, was NOT the decay of Molniya 3-53

On June 13, 2013, near 6:05 pm local time (AEST - corresponding to 10:05 UTC), many people in Eastern Australia observed a bright fast light falling down in the sky. It was even recorded by one of those new-fangled dashboard-cams (one of these days, I must get me one for my bike).

The Australian news website "The Chronicle" claims it was a satellite decay - more exactly, that of the Russian Molniya platform Molniya 3-53 (2003-029A).

It was however most definitely not a satellite decay.

All descriptions talk about a fast object. The dashcam video shows a pretty fast fireball indeed.

It is much too fast to be a decaying satellite. The latter move at relatively slow speeds - 8.5 km/s. At that speed, it takes them several minutes to traverse your sky, not just a few seconds. As low over the horizon as the dashcam video shows it, it would have been very, very slow, taking several tens of seconds to traverse the distance it does in the video.

In addition to it being too fast to be a satellite decay, the proposed connection to Molniya 3-53 can be rejected right away.

First: Molniya 3-53 did not decay on June 13. Orbital data by Strategic Space Command ("NORAD") show it was still in orbit in the early hours of June 15 - two days after the Australian fireball. At the moment of writing (12 UTC, June 15), the last available orbit is for epoch 13166.42726929 ( = 15 June 2013, 10:15 UTC). The moment of decay is currently predicted as 15 June 14:04 UTC, with an uncertainty of 2 hours. [Update 22/6: SSC's final TIP-message issued 15 June 15:30 UTC gives 15 June, 14:10 UTC +/- 26 minutes for the moment of decay)

Now, given that the apogee of the satellite was at a very low altitude already, could it have been the case that it briefly started to burn but survived after it passed perigee?

The answer is "no" in this case and brings us to a second point against the identification with this satellite: Molniya 3-53 was not over Australia at June 13, 10:05 UTC. It was at very high altitude over Northern Europe at that time (see map below). It would not pass over (central) Australia untill 10:55 UTC (6:55 pm AEST), i.e. a full hour later than the fireball sighting.

So what was it then? Given the speed, it is very clear this was a meteoric fireball, a small piece of cosmic rock or ice (debris from a comet or an asteroid) entering the atmosphere.

An update on IGS 1B - a spy satellite about to reenter this summer

(updated reentry prediction at the end of this post)

Last year I wrote extensively about the malfunctioned Japanese spy satellite IGS 1B (2003-009B) which is about to reenter, uncontrolled, into the atmosphere soon. The above footage of the object was shot by me last April 13 and 14 and shows two passes over Leiden.

This radar satellite, launched to keep an eye on North-Korea in 2003, malfunctioned in March 2007, halfway though its mission. Since then, it has been steadily coming down (see diagrams below) in a way that clearly shows that the satellite operators do no longer have control over it.

Last year, I pointed to the fact that the 1.2 tons  satellite will reenter in 2012 (so this year), and likely still has some remnant fuel onboard. A subsequent assessment by high-end amateur satellite tracker Ted Molczan showed that this amount of fuel is limited - probably about 14 to 50 kg, an order of a magnitude less than the infamous case of USA 193 in 2008. This assessment is important, as an uncontrolled reentry of a satellite with fuel onboard is a potential hazard (reason why I wrote about it last year) and authorities were (and are) very quiet about it. Ted's assessment, the only public one to date, helped to put the potential risks involved into proper context.

In the autumn of 2011 we temporarily lost track of IGS 1B because it entered winter invisibility for the Northern hemisphere (where most of our observers are located). Early April this year, it emerged from this winter blackout again. I did a failed attempt to recover it on the evening of April 2, and then Russell Eberst successfully recovered it a day later on the evening of April 3. Since then, I observed it on April 13, 14 and 22 (see video footage above of the April 13 and 14 passes) and other amateurs have observed it as well.

Below is a 35-second integration of video frames from the April 13 video (upper right are tail stars of the Big Dipper):

click image to enlarge

Orbital evolution over the winter blackout

When IGS 1B was lost in the winter blackout in the autumn of 2011, it was in a 453 x 455 km orbit. Since then, it has come down considerably: as of 2012 May 1 it is in a 366 x 368 km orbit, almost 100 km lower (and now below the orbital altitude of the ISS). It is coming down at an increasingly fast speed, as the diagrams below show (based on orbital calculations by Mike McCants, derived from amateur observations which include my observations):

click diagrams to enlarge

 

Current Decay Prediction

Using Alan Pickup's SatEvo software with the current orbit and solar activity, I expect the reentry of IGS 1B to occur somewhere during a window that spans from June until August. As the orbit is evolving fast, it is pertinent that we keep close track of the object in order not to lose it (a few days old elements already results in several minutes uncertainty in pass time).

April 20 Brazilian fireball was NOT the reentry of an Atlas Centaur r/b

A beautiful, slow, long duration, fragmenting fireball was filmed from Brazil in the evening of April 20 (20 April near 20-21h UT). Movies can be seen here and here.

Soon after the apparition, the question came up: meteoric fireball, or a reentry of "space junk"? Based on the visuals of the two movies available, I noted that it looked like a meteoric fireball, not a reentry.

Subsequently, a piece appeared in Universe Today, claiming it was a reentry: that of an Atlas Centaur rocket, #16102, 85-087B, which launched Intelsat 512 in 1985.

That conclusion is simply wrong however. According to USSTRATCOM the object in question decayed 18.5 hours earlier than the fireball, over the western Pacific at 1:23 UTC (20 April) near 18N, 161 E. It reentered nowhere near Brazil. It did pass over northern Brasil on its final pass an hour before reentry, but that would have been at 00:30 UTC, not 20-21 UTC. Moreover, even that pass would have been too much north to see it from the southern Brasilian location where it was filmed from: it would have passed below the horizon as seen from there.

And even if pieces would have survived longer (highly unlikely in this case), these could not have caused a fireball over Brasil 18.5 hours later: the orbital plane of the r/b was wrongly oriented for that. Around the time of the fireball, any surviving objects in the Centaur orbit would not pass over Brasil but much more north, over Mexico and the Caribean (see below. Note: the object was no longer in orbit at that time!).

So, the object that was filmed was most likely a piece of asteroidal debris, a very nice, very slow and very long duration meteor grazing through the upper atmosphere and breaking to pieces.

Watch UARS - it's dropping!

Several news outlets are abuzz (e.g. here and here) about UARS, the defunct Upper Atmosphere Research Satellite, which is in the last days of its life.

click image to enlarge

Launched on Space Shuttle STS-48 in 1991, it was shut down in 2005 and it's orbit lowered to speed up decay.

That moment of decay is now near, with the 6 tonnes satellite expected to re-enter into our atmosphere in the last days of September or first days of October. At this moment , it is not possible to predict the moment of decay more exactly than this, and hence it is impossible to say where (over which part of the world) the re-entry will take place. At the moment of writing, the satellite already has come down to a 244 x 275 km orbit. The nominal decay date is currently projected to be around September 28-29 but has an uncertainty of several days.

UARS is that big, that parts of it might actually survive re-entry and impact on land or sea. Modelling by NASA suggests up to 532 kg of material, broken up into tens of pieces, might survive re-entry, with the biggest piece being perhaps in the order of just over 150 kg. The odds of this debris hitting someone are small however.

UARS is a large satellite that can be quite bright and easily seen by the naked eye: in the past, I have seen it attain brightnesses up to  mag. +0.5, as bright as the brightest stars in the sky.

The image above shows UARS photographed by me on 16 June 2010 from Leiden, the Netherlands, when it showed a small flare.