Sunday 23 February 2014

Mystery object in Alaska sky night Feb 20-21 was a fuel vent connected to the USA 248 (GPS 2F-05) launch

Yesterday an intriguing photo shot  from Pedro Dome near Fairbanks, Alaska (USA) by Dennis Mammana appeared on the website. It showed a butterfly-like cloud in the starry sky, in the Pegasus square. The image can be seen here (scroll down a bit) and was taken near 6:15 UT on February 21, 2014, from a location near 65.04 N, 147.457 W.

The cloud. Image (c) by Dennis Mammana,
reproduced with permission

The cloud looks very much like a satellite or rocket booster fuel vent. But what satellite/rocket was responsible? Early suspicion was that it could be connected to the launch of a new GPS Navstar satellite, USA 248/Navstar 2F-05 (2014-008A) from Cape Canaveral a few hours earlier.

Upon seeing the image and checking a few things, I could quickly confirm that this indeed was a fuel vent related to this launch.

The satellite was launched near 01:59 UT on Feb 21 (evening of Feb 20 local time in the USA) from Cape Canaveral in Florida using a Delta IV medium rocket. It separated from the second (final) rocket stage 3h 33m 05s after lift-off, i.e. around 5:32 UT (Feb 21) while coasting just east of Hainan, China. This was some 43 minutes before the observations from Alaska by Dennis Mammana.

Upon separation the satellite was placed in a 54.98 degree inclined orbit at an average altitude of 20470 km. The rocket stage moves in a quite similar orbit.

At the time of Mammana's observation, barely 45 minutes after separation, the satellite and rocket stage were still close together (they were only some 30 km separate in space) coasting over Beijing, China, at an altitude of 20 482 km and moving northwards. As seen from Pedro Dome in Alaska the two objects were within a few arcminutes of each other low in the Western sky, at a range of 24 300 km to the observer.

click map to enlarge

click images to enlarge
The rocket stage and the GPS satellite's sky positions agree closely to the position of the butterfly cloud photographed by Mammana (compare the map below with Mammana's photograph).
click map to enlarge

click image to enlarge. Image (c) by Dennis Mammana,
reproduced with permission

As seen from Pedro Dome, Alaska, the rocket stage was at an elevation of 17 degrees almost due West in the sky (az 290 degrees) at 6:15 UT (Feb 21), near RA 23h44m57s, dec. +23 47'. This is in the square of Pegasus, indicated with red lines in the map above. The satellite was near RA 23h44m26s, dec. +23 43'. This is based on Space-Track elements for epoch 14052.70 (Feb 21.70 UT) for the rocket stage and epoch 14052.27 (Feb 21.27 UT)  for the satellite.

For the object on Mammana's images I measure (with an accuracy no better than 1 arc-minute due to limited resolution of the published image) RA 23h 44m, dec +23 42' (2000.0) using AstroRecord and the image posted on

Object             RA         Dec
Mammana cloud *    23h 44m   +23 42'  meas.
Satellite          23h 44m   +23 43'  pred.
Rocket stage       23h 45m   +23 47'  pred.

These positions are within arcminutes of each other. The position I measure for the approximate center of the butterfly cloud has a smallest miss-distance to the track of USA 248 of only 0.13 degree. These are values so close (particularly giving the measurement uncertainties and epoch differences) that the identification with a fuel vent from the GPS launch can be put forward with strong confidence.

Update: a second image by an observer in Canada, David Cartier, has now appeared (with thanks to Tony Philips for pointing me to it).

I thank Dennis Mammana for his permission to reproduce his photographs.

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