More on the 21 September 2012 fireball: why it definitely was a meteor

I should have done this analysis earlier but did not have the time available until now. What follows now is a quick and back-of-the-envelope kind of calculation, but in my (not so) humble opinion it is adequate to the question at hand.

It concerns, of course, the splendid slow fireball seen widely over NW Europe near 21:55 UT on 21 September 2012. I posted on it before, focussing on saying "no" to the suggestion that this could have concerned a satellite reentry. In the post that now follows, I further strengthen the conclusion that it was not a satellite reentry, but a genuine meteoric fireball.

The map above gives a quick (and not particularly accurate) back-of-the-envelope reconstruction of the fireball trajectory. It is based on trajectory descriptions from Bussloo in the Netherlands and Dublin in Ireland: by taking reported altitudes (with respect to stars) and general directions of reported start and endpoints, and an assumed altitude of 50 km, the trajectory above is what approximately results. (update 19:10 UT, 24 Sep: an updated version of the map is at the bottom of this post).

The resulting trajectory is some 1000-1200 km long. In what now follows, I have taken 1100 km as the distance travelled by this fireball.

Observers near the western and eastern ends of the trajectory would probably not see the complete trajectory. Observers approximately mid-way, in mid-Britain, would potentially see most if not all of the trajectory (from experience I know you can see bright fireballs from distances of 500 km).

Observers report durations between 20-60 seconds: most video's on the web suggest a 40+ seconds duration.

It would take a reentering satellite travelling at 8 km/s (the orbital speed at decay altitudes) about 138 seconds or roughly 2.25 minutes to travel this distance. While the reported fireball durations are long, none of the reports nor videos comes even remotely close to that value.

A meteoric fireball travelling at the lowest speed possible for such an object, 11.8 km/s, would take 93 seconds to travel that distance. This is still longer than almost all of the reports suggest, but clearly getting closer.

If we take an estimated duration of 60 seconds, the 1100 km trajectory length results in a speed of  approximately 18 km/s.

18 km/s is a very reasonable speed for a slow, asteroidal origin fireball.

(it is, let me repeat, also way too fast for a satellite reentry).

Meteorite dropping fireballs typically have speeds between 11.8 and 27 km/s. A speed near 18 km/s sits squarely in the middle of that speed interval.

(update: diagram added 14:45 UT, 24 Sep)

(click diagram to enlarge)

The 60 seconds probably represents the upper boundary value for the duration of the fireball. If we take a shorter duration of 40 seconds, the speed already increases to 27.5 km/s.

This quick back-of-the-envelope reconstruction therefore shows that this must have been a meteoric fireball, quite likely of asteroidal origin, and we definitely can exclude a satellite reentry.

The fragmentation described and filmed is not unusual for meteorite dropping fireballs (see the video's of the Peekskill meteorite fall in my previous post). The object probably entered the atmosphere under a very shallow angle, which together with the slow speed explains the unusually long duration of the event.

Meteors of this kind are rare, but they have been seen before. Think of the Peekskill meteorite fall, but also the famous 1972 daylight fireball over the Grand Tetons (that had a duration of over 100 seconds) and the Cyrilid Meteor Procession from 1913 (that lasted minutes).

Note: a previous post gives a number of other lines of evidence which likewise suggest this fireball was not man-made space debris.

UPDATE: a further update is given in a new post: a very cautious orbital solution suggests an Aten orbit.

Note 2: on how I made this quick and (emphasis) rough trajectory reconstruction. I took observations that contain clear sky locations: e.g. a sighting from Dublin stating it went "through the pan of the Big Dipper"; the description from Bussloo observatory in the Netherlands; and later adding a.o. a photo from Halifax, UK, showing it just above the tail of Ursa Major. These descriptions can be turned into directions and elevations. Next, I drew lines from these sighting points towards the indicated directions, marking distances roughly corresponding to 30, 50 and 80 km altitude as indicated by the observed elevation [ distance = altitude / tan(elevation) ]. Near the start of the trajectory I marked 50 and 80 km, for Britain and Ireland I marked 30 and 50 km. These points then provide you with a rough trajectory.
From Dublin the object passed through North towards west. From Bussloo the object started NE (azimuth 60 degrees): these are important points of information too as it shows that the object started at least as far east as the Dutch-German border (and more likely over Sleswig-Holstein in N-Germany) and had its endpoint at least as far west as the northern part of Ireland.

Above: Updated map version, 24 Sep 19:10 GMT , also showing the principle of how it was reconstructed for three sighting locations. With thanks to Ramon van der Hilst for providing more detailed information on sky trajectory as seen from Bussloo (NL) on request.

FIA Radar 1 through the Pleiades, and Geostationary satellites in Orion

 click image to enlarge

The picture above (10s exposure taken with a Canon 450D and SamYang 1.4/85 mm lens) shows the classified military Radar reconnaissance satellite FIA Radar 1 (10-046A) sailing smack through the Pleiades last Friday.

Friday evening started clear, and I took the opportunity do so some observing. Using the SamYang 1.4/85 mm and the Carl Zeiss Jena Sonnar MC 2.8/180mm, I not only obtained the picture of FIA Radar 1 above, but I also targetted some geostationary satellites, imaging several of them in Orion.

Among the targets were the classified military communication satellite Milstar 5 (02-001A), the SDS data relay satellite USA 227 (11-011A) and the SIGINT satellite Mentor 2 (98-029A). Two other classified objects were captured as by-catch of these objects: the SIGINT satellite Vortex 6 (89-035A) and the object "Unknown 110623" (11-674A), an amateur-discovered object in GTO that is probably a spent rocket booster of a military launch. Note how it created a tiny trail in the image below as it was moving northwards through Orion.

The images below show these objects. Milstar 5, Vortex 6, UNK 110623 plus the two non-classified commercial communication satellites Eutelsat W2 (98-056A) and Intelsat New Dawn (11-016A) are all in the same 10-degree wide 85mm image. The stars of Orion's belt are visible in the top of the image, and Milstar 5 is close to the Orion Nebula. Orion's belt stars are visible at left in the Mentor 2 image as well.

click images to enlarge

 

In one of the other images taken last Friday evening, another commercial geostationary communication satellite, Intelsat 4 (95-040A) was captured while it briefly flared brightly at about 18:58:30 UTC (27 Jan).

The FIA radar and a number of geostationary objects (Mentor 2, Mentor 4) and the NOSS 3-3 r/b were imaged by me two weeks earlier as well, observations on January 14 and 15 which I had not reported here earlier. I also tried to relocate PAN, which recently has been relocated again but so far has not been recovered, although both Greg in South Africa and I in the Netherlands have tried.

Prowler

Among the family of classified satellites, three stand out as more mystifying than the rest: Misty 1 & 2, PAN, and Prowler.

The latter has long existed in the realm of rumours only. It was launched by Space Shuttle Atlantis on mission STS-38, which was a classified DoD mission launched on 15 November 1990. Officialy only one satellite, USA 67, was launched from the Atlantis payload bay. This is believed to be a geostationary SDS communications satellite, SDS 2-2.

STS-38 mission patch

USSTRATCOM released catalogue numbers (but no public orbit) for three objects connected to this launch: the SDS satellite USA 67 itself (90-097B, 20963) plus two rocket bodies (90-097 C & D, 20964 and 20965).

The latter was puzzling, as it is one too many (see the discussion by Ted Molcan here), This was the start of the idea that a second, unacknowledged object was launched by STS-38 as well.

In 2004 an NBC journalist referred to such a secret payload by the name of Prowler, in a news-item discussing a Senate debate about a classified spy satellite program drawing criticism for massive cost overruns. The same journalist, citing anonymous sources, did so again in 2007.

According to these stories, Prowler was an experimental satellite used for close inspection of other (non-US) satellites in geostationary orbit (see discussion here), reportedly coming to within decimeters of some satellites. There are suggestions that it was a test of technology which, in wartime, could be used to sabotage enemies' space assets. It was also said to employ stealth technologies to evade easy detection.

Meanwhile, US amateur observers Ed Cannon and Mike McCants had discovered an unidentified near-geostationary object in July 1998. As time progressed and more and more ISON and amateur-discovered objects could be identified with specific launches, this one was one of few left unidentified. This in turn led to suggestions that the object in question was the rumoured unacknowledged STS-38 launch, Prowler. It was likely discovered only after its active lifetime ended, and it was put in a disposal orbit (see below).

Since then, a long term analysis by Ted Molczan has strengthened this identification. The object has al the right characteristics in terms of brightness behaviour and orbital behaviour. It currently is in an unusual librating disposal orbit that seems devised to keep it out of reach of Soviet tracking facilities (see discussion in depth by Ted here). In a second analysis, Ted showed that STS-38 indeed had the opportunity to launch this object and some tell-tale clues to that are present in the manoeuvering history of STS-38 Atlantis. The whole history of the object, from launch onwards but also including the final disposal orbit when the stealth character of the object was lost, was designed with low detectability by Soviet tracking facilities in mind (see Ted's discussion here).

The object now resides in a currently 13-degrees inclined orbit librating between 73 W and 136 W, putting it over the eastern Pacific, with visibility from the western United States. Over the past two weeks , I imaged it a number of times, using the 0.61-meter "remote" telescope of Sierra Stars observatory in California. Below is one of the better images, shot on the morning of July 6th:

click image to enlarge

Flaring Keyholes in a moonlit sky, and a BWGS meeting

The "Supermoon" of yesterday was not my only observational target. The sky was very transparent, and hence even with this full "supermoon" low in the southeast, conditions were fine for satellite observations.

I imaged two Lacrosses and two KH-12 Keyholes: Lacrosse 3 (97-064A), Lacrosse 5 (05-016A), USA 129 (96-072A) and USA 186 (05-042A). In one of the images, Rubin 4/SL-8 (03-042B) was captured as a faint stray.

Both of the Keyholes and one of the Lacrosses (Lacrosse 3) flared: KH-12 USA 129 did so while the camera was open, yielding the picture below (note the Hyades at the bottom):

click image to enlarge

Flare times:

USA 129: 20:29:08 UTC
USA 186: 20:14:40 UTC
Lacrosse 3: 19:52:40 UTC

Below images show Lacrosse 3 ascending and brightnening over the chimney (with Canis minor in the upper right corner: this was just before it flared), and Lacrosse 5 descending through the tail of the Big Dipper (the fuzzy arc is a reflection from a nearby lightsource):

click images to enlarge

These observations were all done just after returning from a trip to Belgium, where we had a meeting of the BWGS (Belgian Working Group Satellites). It was a small but nice gathering (six attendants, including this author). Below some pictures showing me (left) and Leo Barhorst (right): and BWGS president Bram Dorreman (all pictures taken by Koen Geukens):

click images to enlarge

On the agenda were amongst others the future of flash observations; the observations of flaring geostationary satellites earlier this month; while I did a very short photo-presentation on the recent PAN relocation story (see also here). Our host that day was Koen Geukens.

The FIA Radar, USA 179 (SDS 3-3) and more

On the 5th, 9th, 10th and on the 16th of January, the skies shortly cleared in the evening and I observed the FIA 1 Radar (10-046A) making some nice passes through the winter sky. On the 16th it was a particularly close race with clouds coming in (the last image in the series has clouds in the image frame).

Below are two images: one from the 10th showing the FIA 1 Radar passing close to the Pleiades; the other showing it passing through the alpha Persei association on Jan 16th.

click images to enlarge

I also observed the Molniya orbit satellite USA 179 (SDS 3-3) on the 16th, which was close to the alpha Persei association too. As it was too faint for the 50mm lens, I used the Carl Zeiss Jena 180mm lens for it (brightest star in image is alpha Persei):

click image to enlarge

Other objects observed include PAN (09-047A) on the 9th of January. It is still in the fixed position at 49.0 E where it is since December 24 (see earlier post here). That same evening, Mentor 4 (USA 202), Mentor 2 and the Milstar 5 r/b were observed as well. A flashing H2A rocket, 06-059A, was captured as a stray. On the 5th of January, the IGS R2 r/b was captured in twilight, being very fast and very bright.

A second NROL-41 (FIA Radar 1) patch

Grey overcast skies and snow do not allow observations currently. South-African observations by Ian Roberts show that PAN was still drifting as off 21 December. Will be interesting to see where the drifting stops (if it continues this way, it will soon drift out of my reach).

In a week or so from now, I will be preparing my overview of 2010 observations. For now, I want to fill the weather-induced lul in observations by showing a recent addition to the patch collection.

A patch for NROL-41, the FIA Radar 1 launch (2010-046A), was shown earlier on this blog here. Recently I however acquired a second patch, which is of much better design:

click image to enlarge

Patch designs of the black space program have become a bit generic and bland lately, perhaps as the result of this NRO Director's memo, but the NROL-41 patch above is beautiful. And, with hindsight, offering some clues (to what we now already know from our own observations).

The clue is in the heroine archer. She is aiming for the setting sun (i.e., westwards). I feel this could very well be an allusion to the unusual retrograde (westward) orbit of the FIA 1 Radar.

The purple 'vermicelli' pattern in the nighttime earth actually includes a few character combinations, i.e. acronyms, of units and organizations connected to the launch. Recognizable are amongst others 'NRO', and what appears to be '4 SLS' and 'LRS' or 'LRSW'.

It would be interesting to know what the three white stars in the patch rim signify.

When did PAN start to drift?

click diagram to enlarge

Answer: on December 1st. Which tallies with it still being at her old position at 38.0 deg E on November 28.

Update on the UNID geostationary: Greg observed it too!

On the evening of December 8, while imageing PAN, I captured an unknown object, apparently in a geostationary orbit, close to the commercial geostationary objects Turksat 2A and Turksat 3A. See my earlier report and pictures here.

Since then, I have been completely clouded out. However, Greg Roberts in South Africa had clear skies yesterday, and managed to recover the object. It has moved closer to the Turksat duo.

Greg is in some doubt whether this really is the "lost" SCS 3-11 (2000-001A ) as he feels it is too bright.

To be continued!!!!!

Senegalese skies

I spent the first half of this month in Africa, in Senegal, where I took part in the 2010 PANAF/Safa conference (PANAF = Pan-African Archaeology Conference) in Dakar. After the conference my girlfriend, two friends/colleagues and me added a few days of tourism through the country.

During the conference field excursion to the Saloum delta, and later during our private trip to the Lompoul sand dunes, I took a few shots of the Senegalese night sky. I didn't have my regular astrophoto lenses with me, so used my Tamron 2.8/17-50 mm zoom (not an ideal choice for astrophotography) at 17mm. The camera was fixed on a tripod, no guiding, exposure times ranged between 10 and 20 seconds, ISO 1600.

Below are some of the resulting pictures, plus a photograph of me taken at a megalithic site during the conference field excursion.

click images to enlarge

Another Keyhole flare

Although the skies were somewhat hazy, observations were conducted on the evenings of April 15th and 16th. Targets were the various IGS objects (1B, 5A, 5r/b), the Lacrosse 5 r/b, and the KH-12 Keyholes USA 129 and USA 186.

USA 186 was so friendly as to flare in my camera image on the 16th. The flare occurred at 20:43:40.75 UTC (Apr 16). Below is the image, and the resulting profile (with saturation at the peak). The two bright stars are the front stars of the pan of the Big Dipper, alpha and beta Uma.

click images to enlarge