Wednesday, 28 September 2011

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


5 comments:

Daniel Fischer said...

Yet another way the reentry might have been detected directly from a distance could be microbarometry: you can record distant natural airbursts (due to exploding bolides) that way. I'm not sure though whether the gradual decay of a spacecraft in the atmosphere would generate a sharp enough pressure signal that could me measured hundreds if not thousands of kilometers away. And whether there is such a network at all around the Pacific (there is one in the continental U.S.).

Oh, and does the burn-up of a 6-ton spacecraft perhaps generate any - unique - EM radiation signal that might be picked up at a distance (just thinking while typing :-)? I'm still with you re. IR satellite sensors as the most likely source of information, of course, but wonder now whether a civilian wx satellite may have picked up something (a thermal flash, a smoke cloud etc.): After all the Sudan airburst from 2008 TC3 was imaged by a satellite.

Station operator SatTrackCam Leiden said...

Dan: you mean infrasound? That would be an option (meteoric bolides are sometimes detected by infrasound) but I have no idea whether an infrasound array is present in the wider area.

Station operator SatTrackCam Leiden said...

Okay, I did find a reference to a French infrasound setup in French Polynesia. Apparently these are used to monitor the ban on nuclear tests, so perhaps the US has something similar in their parts of the Pacific (to keep an ear on the French). I do not know.

Station operator SatTrackCam Leiden said...

Okay, there are infrasound arrays on Tahiti, Hawaii, Marquesas and New Caledonia. The reentry location is near the center of this triangle. Our resident KNMI infrasound scientists says that while distances involved are large, it could be feasible, especially in the case of strong sonic booms.

Ed said...

AOS: Aquisition Of Signal.

http://www2.jpl.nasa.gov/basics/glossary.php