Observing another doomed satellite: ROSAT

Shortly after the UARS reentry, which got wide attention, another scientific satellite is about to meet its demise by an uncontrolled plunge into the atmosphere. It is the German X-ray astronomical satellite ROSAT. This satellite is currently predicted to reenter about October 22 to 24.

This evening I watched it pass during twilight (sun at 8 degrees below the horizon, first stars just visible in a blue sky). It was fast, zipping across the sky, and bright: magnitude +1 and an easy naked eye object.

I used the new EF 2.0/35mm lens (a new purchase, first used last weekend during the Draconid meteor outburst, on which I will post in a later post), set to F2.5, making 5 second exposures at 400 ISO. The fast moving objects ran out of the frame of two of the three images. Below is the image thats shows the complete trail. The satellite was moving from left to right, across Cepheus. The streak in top is a streak of cirrus.

click image to enlarge

Tracking stations along UARS final track - a reconstruction [UPDATED TWICE]

click map (revised version) to enlarge

Above map provides an overview of groundbased tracking stations in the ESA ESTRACK and the US AFSCN network that are near or on the final trajectory of UARS. For relevant trackings tations, times of Advance of Sight (AOS) or Loss of Sight (LOS) are indicated. UARS is depicted at the point of reentry (see previous post) as indicated by SSC.

From the NASA talk by Johnson, they pinpointed the 04:00 +/- 1 minute UTC time and 14.1 S, 170.2 W location of UARS's demise using detections and non-detections by "a number of sensors".

As shown above, the last of these tracking facilties, the ESA station at Awarua, New Zealand, would have detected it and tracked untill it lost sight at 3:56 UTC. Next, there is an 11 minute coverage gap untill it could first have shown up at the Kaena Point tracking facility in Hawaii at 4:07 UTC. [EDIT: it appears that Awarua is a telemetry station only, not a true tracking station. As UARS was a dead satellite not sending telemetry, it then becomes unlikely Awarua played any tracking role: leaving nothing between Kerguelen and Hawaii. Thanks to Dan Fischer for querying me about the character of Awarua station]

As can be seen on the map, none of the regular tracking stations had direct coverage of the reported reentry location, begging the question where the "large number of detections" NASA's Johnson was talking about comes from. UARS could first have shown up at the Kaena Point tracking facility in Hawaii at 4:07 UTC. At that time, it would have been without groundbased tracking for quite some time already (over half an orbit).

Of course, we cannot exclude that a temporary tracking facility (e.g. an AEGIS ship) was employed in Polynesia at the time, providing additional data.

Also, a reader of this blog wrote to me with the suggestion that the US Navy's sensitive network of hydrophones could have picked up a signal when wreckage hit sea surface. I have no idea how feasible that is.

I still feel space-based observations were possibly involved (see my earlier post here), but are not being publicly acknowledged. The early warning satellites DSP F20, DSP F16 and SBIRS Geo-1 would have had coverage of the reentry location.

(note added: if anyone knows of additional tracking stations along the trajectory, info is welcome)

Infrasound?

Note added 29 Sept 2011
Dan Fischer raised the option in the comments that Infrasound detections could be involved. Indeed, this is a possibility (I consulted a Dutch infrasound researcher for an opinion here, and he thinks it is feasible, especially if sonic booms were involved) even though the distances to infrasound arrays involved are large.
A number of infrasound arrays are scattered over the Pacific area, listening for possible atomic detonations in breach of the Nuclear Test Ban treaty. A map of them can be found here. In the wider area, such arrays are located on Tahiti (French Polynesia), Hawaii, the Marquesas and New Caledonia. The UARS reentry location is within this triangular area. Below is a map of infrasound detection arrays located in the Pacific around the published UARS reentry location.

Edit late 29 Sept: Dutch infrasound researcher Läslo Evers just notified me he has checked the Tahiti and New Caledonia infrasound records for the reentry - he finds no sign of it.

click map to enlarge

UARS reentered over Samoa? [slightly updated]

USSTRATCOM, followed later today by NASA, has released a new reentry time and location estimate for UARS. It puts the time at 04:00 +/- 1 minute UTC and location at 14.1 deg South, 170.2 degrees W. This is over the south-central Pacific, in the vicinity of Samoa.

The time and location is said to be based on a number of detections and non-detections of several "sensors", without clear indication whether these are groundbased or space based sensors (see my previous post here) but I do suspect the latter are involved. The more so since the only ground-based tracking stations in this wide area are on Oahu (Hawaii), Kwajalein and Guam, and none of these would be able to pinpoint this location so exactly as this location is out of their detection range [edit 28 Sep: plus, the final UARS track did not bring it in reach of Guam and Kwajalein anyway]. The description by NASA's Johnson in the video appears deliberately vague to me. [edit 28 Sep: there is of course always the possibility that they happened to have a tracking ship in the vicinity].

I have some lingering concern in the back of my mind about the "neatness" of a reentry at exactly 4:00 UTC (nice and round), but sometimes such coincidences do happen.

Below is a map of the now released reentry point.

click map to enlarge

Could the reentry of UARS have been monitored from Space?

One of the open questions regarding the inability to pinpoint the exact location and time of the UARS reentry, is whether the US military might have space-based detections from their infra-red early warning satellites.

The US military operates two constellations of such satellites, whose purpose is to detect and provide early warning for enemy ICBM launches using infra-red detection sensors. The older constellation is the DSP (Defense Support Program) series of satellites in geostationary orbit. There is also the newer SBIRS (Space-Based Infrared System) constellation, consisting of one geostationary satellite (SBIRS Geo-1) and two SBIRS sensors piggybacked on HEO satellites (USA 184 and USA 200).

We know that the DSP satellites have, in the past, frequently observed meteoric fireballs. It is therefore widely believed (and indeed likely) that the system should have been able to detect the UARS reentry fireballs as well. The problem is that post-9/11 the DoD has stopped declassifying meteor detections (which were previously shared with meteor scientists). Which makes you wonder whether, if they did detect the UARS reentry fireball, they would be forthcoming with that information. Probably not.

Would the UARS reentry have been visible from one of the DSP or SBIRS satellites? Would they cover the relevant areas? Yes they would.

Below map shows the location (for 4:16 UTC [edit 28 Sep: this was written before the reentry time was revised to 4:00 UTC, see here]) of UARS plus it's track, and the locations of the relevant satellites.

click map to enlarge

Yellow dots are the block 5 DSP satellites, white dots the SBIRS satellites. The green circle outlines show the coverage area of DSP F16, DSP F20, and SBIRS Geo-1.

The DSP's and SBIRS GEO-1 are geostationary and hence always above the geographic spot depicted in the map (with some minor latitudinal variation): for the HEO SBIRS platforms USA 184 and USA 200 the position plotted is for 4:16 UTC.At that time USA 184 was near apogee and basically almost in the same position (in geographic subsatellite point terms) for an hour on each side of 4:16 UTC. USA 200 was moving towards perigee, but would have UARS in view during the whole Africa pass of the latter.

DSP F16, DSP F20, SBIRS GEO-1 over the eastern Pacific as well as the SBIRS platform USA 184 over Siberia would cover the approach track over the Pacific and nominal center of the reentry window of UARS. Basically, they cover UARS on it's final track from New Zealand to over Canada.

Beyond Canada (would UARS have survived well beyond 4:16 UTC), DSP F17 over Brasil and the SBIRS platform USA 200 moving over Africa would have taken over, joined by DSP F18 plus DSP F21 and DSP F22 (all over Africa or the  Indian Ocean) once over Africa.

I also checked whether the experimental satellites in the STSS (Space Tracking and Surveillance System) series would have been able to capture it: turns out they would not have, as these satellites (in low earth orbits) were not near the relevant part of the UARS track at that time.

In conclusion: there is plenty of possibilities for the US military to have detected the UARS reentry from space, using their space-based assets (DSP and SBIRS) in GEO and HEO. Even if groundbased tracking facilities were sparse over UARS' final track, the space-based sensors should have been able to observe and pinpoint the reentry.

Yet, I suspect that if these observations exist (allowing the DoD a clear indication as to where UARS debris might have showered down), this information will not be released to the public.

(text slightly editted 27 Sep to clarify USA 200 movement)

"UARS crash" at Okotoks Alberta (Canada) now confirmed to be hoax

After all the hectic of the previous night, I spent yesterday out of house in the dunes and near the beach. Time to pick up now where I left.

NASA has held a teleconference. Basically, they did not report anything new regarding the potential reentry location than what I already reported here based on SSC and Harro Zimmer's conclusions. Note that this NASA map released is basically the same I posted here earlier.

I don't share some of the critique currently levelled at NASA. See discussion at the end of this post.


Okotoks, Canada: a HOAX
The Okotoks (Alberta, Canada) video and report of debris being found (see earlier post here) - news media now report  it is a HOAX. Seems I was right with having my reservations. [update 26 sep: more here. The report on wreckage was a hoax created by an aspiring film maker, apparently]

Aircraft contrails being mistaken for UARS

Meanwhile, simple aircraft contrails keep being mistaken for UARS as well: see the previous post and another case here.

Radar artefacts being mistaken for UARS

This one that is doing the rounds, is a mis-interpretation of a very common weather radar artefact. Note how the streak neatly points to the radar origin in the center.

Chinese lantern balloons being presented as "UARS"

As I pointed out in the previous post, footage of Chinese lantern balloons are either deliberately or mistakenly being passed off as "UARS" in the media as well.

Possible confusion with meteoric fireballs

To complicate the picture, there is also the point that "normal" meteoric fireballs appear and can be mistaken for UARS. Multiple such fireballs occur somewhere on this world every day.

Indeed, we had a very nice meteoric firebal (seen by amongst others myself while waiting for the UARS pass) of mag. -5 appear 5 minutes before the 1:37 UTC UARS pass on the 24th. Klaas Jobse has a nice all-sky image of that one here. Yet another one appeared a mere 17 minutes later (video of both fireballs here, again by Klaas Jobse). These were meteoric fireballs, little bits of asteroid or comet debris not related to UARS at all.

While it didn't fool experienced observers like me, laypersons could have easily mistaken it for UARS debris.

Some genuine reports of bright fireball phenomena seen around the predicted reentry time from a.o. Canada, could be such cases of meteoric fireballs. Without clear details on duration and character, it is difficult to discern between these and any potential real reentry observations.


Critique on NASA: I don't share that critique

There is currently a lot of critique on NASA that they can't pinpoint the point of reentry. I think those critiques are unfounded and stem from unrealistic expectations.

All I can say is: people expect too much of NASA and modern technology, notably under the influence of unrealistic TV-series that depict NASA as know-it-alls that can do anything (with just a few computer keystrokes and maybe a hack into a satellite feed here and there typically, according to the TV series that increasingly mold the public's "reality").

But even the best technology and best experts have their limits (and in terms of the actual tracking, this technology is not operated by NASA, but by the US Air Force, by the way), and with the last few UARS revolutions largely over empty ocean devoid of tracking stations, things simply get difficult. There are limits to what models can do when devoid of real-time tracking sensor input.

I might, given time and energy, elaborate on that later in a separate post

False "UARS" video's

Some video's are doing the rounds, some in respected news media, purporting to be showing the demise of UARS but in reality definitely something else.

This one posted on Space.com is an example. This clearly shows a Chinese lantern balloon, not UARS: you can see the bag and burner.

Another one is here (with thanks to Dan Fischer for pointing me to it): this British video on the website of The Telegraph simply shows an aircraft with contrail. As science writer Dan Fischer remarked in despair about this one on twitter: "don't you people ever watch the sky?!". Indeed, one would expect people recognize aircraft and contrails these days. Yet we see them pop up time and again in the media, as purported footage of "fireballs" and now as "UARS".

There is more of this stuff doing the rounds on the intarwebz currently. So be very careful with purported footage and images of "UARS reentering". A lot is not what it seems.

UARS update 24 Sept (2) - so where did it crash?!?

It is still not entirely clear where and when UARS met a fiery end. SSC issued a bulletin stating 4:16 +/- 53 minutes UTC. Harro Zimmer issued a final prediction of 4:15 +/- 9 minutes UTC.

The latter would place the reentry over an area defined by the Northeast Pacific and northern Canada.

 click map to enlarge

The problem is that the reentry was (according to a lack of reliable reports so far) not unambiguously observed, and probably that the last revolutions took UARS over areas (oceans and central Africa) where tracking stations are sparse. Perhaps the DoD might have space-based observations from their Infrared early warning satellites, but the question is whether those data will become public or not.

Okotoks video - UARS or not?

Meanwhile, a video from Okotoks, Alberta, Canada, hit the internet, purporting to show fireballs from the UARS reentry. However, to many people including me the video does not look right.

We feel it looks more like a series of  "Chinese lanterns", small toy hot air balloons. The individual "fragments" just don't show enough evolution over the video, they are too steady, amongst others (also, in the video the guy shooting it says it is "September 22nd", a wrong date).

I could be wrong though, and the general geographic area is in line with the predictions. So while I don't want to write off the video completely, I do keep my reservations about it.

UPDATE 11:25 UTC: there is now an UNCONFIRMED report of debris pieces having been found near where the video was taken. No details, no pictures, so could be bogus or mistake, no way to say. 

UARS update, 24 Sept (1)

UARS reentry update, 24 Sept 02:00 UTC
click here to check for more recent updates

We are now probably less than 3 hours from UARS reentry.

Using SatEvo software and the latest few orbital updates, re-entry is projected for 24 Sept 4:20-5:05 UTC: in essence, 4:45 UT +/- half an hour. [next sentence corrected] This would indicate Africa and possibly Australia as places which might get to see it.[/corrected]

Watched the 01:37 UTC pass here: this UARS pass was with the satellite completely in earth shadow. Nothing was seen, which means it is not glowing yet.

To make up for missing the decay (this was the last realisticly visible UARS pass for me in the Netherlands), I was treated on a beautiful meteoric fireball at 01:32:44 UTC, at least magnitude -5 if not brighter, appearing due south. It moved through Cetus ending some 10-15 degrees above the horizon. Mediumfast, and with a wake.

This is probably my last pre-reentry UARS update: I am very tired (it is 4:15 am here), the show is over as far as the Netherlands is concerned, so I am going to bed and will see tomorrow morning where UARS came down.

click image to enlarge 

 

UARS reentry update, 23 Sept (5)

UARS reentry update, 23 Sept 21:20 UTC
click here to check for more recent updates

SatEvo software with the latest orbital elements projects the re-entry at nominally 5:25 UTC (24th), so the time is slightly moving away again from 6+ UTC towards an earlier time.

Harro Zimmer predicts, using a more sophisticated model, 4:15 UTC +/- 90 minutes.

I covered the 21:05 UTC pass here, maximum altitude 57 degrees. It was a pass completely is shadow, so UARS would only be visible if it was already developing plasma phenomena. I did not see it (using both camera, and visually wityh 10 x 50 binoculars) so it isn't glowing yet.

click diagram to enlarge

UARS reentry update 23 Sept (4)

UARS reentry update, 23 Sept 18:30 UTC
click here to check for more recent updates

SatEvo software with the latest orbital elements now suggests re-entry at about 5-6 UTC (24th).

Harro Zimmer, using a much more sophisticated model, suggests 3:45 UTC, +/- 90 minutes.

click diagram to enlarge

UARS reentry update 23 Sept (3)

UARS reentry update, 23 Sept 13:30 UTC
click here to check for more recent updates

The nominal projected times for the UARS decay are moving forward again, to later times (which is less favourable for Europe). The latest three orbits at the moment of writing suggest times between 2 UT and 3:45 UT on the 24th.

click diagram to enlarge

UARS reentry update Sep 23 (2)

UARS reentry update, 23 Sept 8:45 UTC
click here to check for more recent updates

New orbital update, time shifted forward by 2 hours again. Shows that the uncertainty is still many hours. Nominal time now 24 Sep 02:00 UTC, but moving somewhat towards the right direction (for me in the Netherlands) . Here's hoping it will eventually move to near 23 Sep 21 UT.....

click diagram to enlarge

 

UARS reentry update 23 Sept (1)

UARS reentry update, 23 Sept 7:45 UTC
click here to check for more recent updates

The projected time of decay is still shifting considerabely with each orbit update: over the past 10 hours, it has hifted back and forth by several hours. The last few orbital updates tend to shift the projected reentry to a later time, early on the 24th, bringing a decay near the USA in view again

At the moment of writing, the nominal projected  reentry time using SatEvo and current solar flux data is 4:15 UTC on the 24th. This still has an uncertainty of a couple of hours, though.

Below diagram depicts how the projected renetry time has fluctuated with each new orbit released over the past two days:

click diagram to enlarge

The following UARS related NOTAM was posted by the FAA:

!FDC 1/2095 FDC .. SPECIAL NOTICE .. EFFECTIVE IMMEDIATELY UNTIL 1109252359 UTC. AIRCRAFT ARE ADVISED THAT A POTENTIAL HAZARD MAY OCCUR DUE TO REENTRY OF SATELLITE UARS INTO THE EARTH'S ATMOSPHERE. FURTHER NOTAMS WILL BE ISSUED IF SPECIFIC INFORMATION BECOMES AVAILABLE. IN THE INTEREST OF FLIGHT SAFETY, IT IS CRITICAL THAT ALL PILOTS/FLIGHT CREW MEMBERS REPORT ANY OBSERVED FALLING SPACE DEBRIS TO THE APPROPRIATE ATC FACILITY AND INCLUDE POSITION, ALTITUDE, TIME, AND DIRECTION OF DEBRIS OBSERVED. THE DOMESTIC EVENTS NETWORK /DEN/ TELEPHONE 202-493-5107, IS THE FAA COORDINATION FACILITY.

UARS update, September 22 pm

UARS update 22 September 20:30 UTC

The projected decay time for UARS keeps shifting back and forth with each orbital update. Over the course of today, it has oscilated between 19:00 UT on the 23rd to 01:00 UT on the 24th.

The last few orbits tend to favour the later part of this time window, but it could as easily swing back to the earlier part of the window again over the course of tonight and tomorrow.

This just goes to show that the uncertainties are still large and still amount to many hours. Over the course of tomorrow, it will become gradually more clear. The current time window is however exciting, as we have passes visible from Europe including the Netherlands during that time span, notably around 21h UT.

click diagram to enlarge

UARS update, Sept 22 am

UARS update 22 Sept 08:45 UTC

Re-entry of UARS is now projected on the 23rd. Latest orbit plus current solar flux and Alan Pickup's fine SatEvo software suggest a nominal time near 19:00 UTC on the 23rd, but at this time that still has an uncertainty of several hours (I suggest up to at least 6 hours).

Areas with the best chances to see the reentry are currently for a swat that includes South-America, Europe, Russia, central Asia, southeast Asia and Australia, which all have passes in the hours around the nominal predicted time. It is increasingly unlikely that the USA will get to see anything of it.

UARS update, September 21 pm

UARS update, 21 Sept, 20:00 UTC

Based on the latest orbital elements from Space-Track, the projected reentry time is slowly moving earlier. The nominal value is now late September 23 (nominal 20:30 UTC, but with still many, many hours uncertainty). But within uncertainties, early September 24 (in UTC terms) is certainly not yet out of the picture. A lot can still happen in the two days left, e.g. changes in solar activity.

Below is an updated diagram of the observed and predicted  orbital evolution in terms of apogee and perigee altitudes.

click diagram to enlarge

UARS update 21 Sept am

Note: forecast and diagram now superceded by update here.

All eyes of the satellite world are now firmly on UARS. Unfortunately, I have no visible passes here these last few days of its existence.

The predictions for the moment of re-entry keep fluctuating between late September 23 and early September 24. Using Alan Pickup's SatEvo software and a 10.7 cm solar flux value of 145 plus this morning's latest elset, the nominal prediction is for the early hours of September 24 but this time still has an uncertainty of up to half a day.

Below diagram shows the changes in apogee altitudes (blue) and perigee altitudes (red) of UARS over September, plus a forecast of the future evolution of them (grey) untill re-entry.

click diagram to enlarge

UARS re-entry Update (and Nanosail-D, and IGS 1B)

UARS update: It seems that the re-entry moment for UARS, the defunct NASA Upper Atmosphere Research Satellite, is moving forward in time, as Harro Zimmer pointed out on the Seesat-L list.

NASA and SSC Space-Track both settle for a decay on or near 24 September, and so do independant analysis by Harro Zimmer as well as my own assessment (using Alan Pickup's SatEvo software with current 10.7cm flux values).

As the orbital development near decay is highly influenced by solar activity, there currently is an uncertainty of possibly up to a few days in these predictions. Yet it seems save to say that UARS has not much more than a week left.

Nanosail-D update: Meanwhile, that other NASA object up there slowly coming down, NASA's experimental solar sail Nanosail-D, seems not quite willing to give up. It's current orbit and current values for 10.7cm solar flux suggest it will hang on at least another month, untill late October. Same caveats as for UARS apply.

IGS 1B update: this defunct Japanese spy satellite which is steadily coming down (see earlier post here and earlier posts linked their in) since it malfunctioned in 2007, likewise seems intend on spending some more time up there. The current orbit plus solar activity now give a nominal re-entry prognosis for early 2013 instead of 2012. This date is certainly still going to shift back or forth considerably however, depending on how solar activity develops.

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.