It has now been confirmed that this was a US Trident SLBM test launched from an Ohio-class submerged submarine! So I was right!
(note added 25 Sep 2013: a post with more info subsequently come to light and an update on the probable launch trajectory is available here)
click image to enlarge
In the evening of September 10, 2013, German astrophotographer Jan Hattenbach was taking images with an f2.8/24mm lens near the GranTeCa dome, at 2300 meter altitude at the Roque de los Muchachos observatory on La Palma in the Canary Islands. His camera was looking due west, out over the Atlantic Ocean, in the direction of Bootes and Virgo. The intention was to create a time lapse movie.
Between 21:16 and 21:20 UT, he captured something unexpected on his images. A strange fuzzy bright object moved over the images, spouting cloudy puffs. Above is a stack of the images: it shows the GranTeCa dome, star trails, a normal satellite (Kosmos 1410)...and the strange cloudy phenomena coming under an oblique angle from the horizon. Below is a short movie made from the images (5 second images with a 2 second interval). Note that it is a time-lapse that speeds up the event: the whole phenomena took about 2.5 minutes in real time:
Jan wrote about his strange observation on his own blog (in German) and posted his story on the AKM forum and on Twitter. Rainer Kresken forwarded it to the SeeSat-L mailinglist, and science writer/journalist Daniel Fischer tweeted to Jonathan McDowell and me whether we could explain the phenomena. Next, Jan was so kind to make his original imagery available to me.
Initially Jan reported that the images were taken near 21:23 UT (Sept 10, 2013). However, it turned out that his camera clock was off by several minutes. The event in reality happened earlier.
Luckily, a "normal" satellite is visible in the image sequence too, briefly flaring, and Cees Bassa and me could identify that satellite as Kosmos 1410 (82-096A). As the orbit of this object is known, astrometry I performed on the trail yielded the correct image times. Jan's camera clock was off by 6m 17s, as it turned out. The phenomena took place between 21:16 and 21:20 UT.
After seeing the images, my first thought was that this could be a fuel vent by a rocket booster in Earth orbit. The time and trajectory did however not match any known object, unclassified or classified.
Another option was a satellite launch. There were however no launches scheduled for this date (and this includes launches of classified objects, which you really cannot keep secret. They are publicly announced as it involves temporary restrictions to airspace down te launch trajectory, and a very visible rocket ascent from Vandenberg or Canaveral).
At that point, I started to suspect that it could perhaps be a hush-hush suborbital ballistic missile launch test, similar to the September 2, 2013, US-Israeli missile test in the Mediterranean. Harvard space historian Jonathan McDowell communicated a similar suspicion, noting that the particular part of the Atlantic has seen Poseidon SLBM tests in the past.
The thing is, that no such test was announced for this date. For example, I have found no NOTAM's restricting airspace over parts of the Atlantic because of a missile launch. That does not mean it is not a missile test though. It just means that whoever did the test, doesn't want to acknowledge it and preferred no-one to know about it. The September 2, US-Israeli test in the Mediterranean was not announced either (it came to light because it was detected by a Russian Early Warning Radar).
If the event seen from La Palma was indeed a clandestine Medium Range Ballistic Missile test (such as I believe is the case), the primary suspects are the Unites States or Great Britain, who both operate the Trident Submarine Launched Ballistic Missile (SLBM); or the French, who operate the M45 and M51 SLBM.
Several points in the observation fit a SLBM test. The US/British Trident and the French M45/M51 are 3-stage missiles. In the stacked image and movie above, there are two sudden bursts of brightness in the trail, both accompanied by an expanding puffy cloud. I interpret these as the moments of jettison of the 1st stage and ignition of the 2nd stage (note: but see update here); and ejection of the 2nd stage and ignition of the 3rd stage. I have marked these moments, taking place at 21:17:08 and 21:18:43 UT (so with a 1m 35s separation), in below detail of the stacked image. The corresponding astrometric positions of these points are RA 205.061, Dec -3.950, and RA 211.366, Dec -6.153 degrees.
click to enlarge
Below are details from the single still images from those moments:
click image to enlarge
Below is a detail from a single frame just after what I interpret as the 3rd stage ignition, showing a bright fuzzy trail and expanding vapour clouds on both sides:
click image to enlarge
The duration of the event fits what is known of the Trident missile: from launch to 3rd stage ignition takes less than 2 minutes with the Trident. The 2nd stage ignites at about 70 km altitude, the 3rd at about 150km altitude.
A careful look at the stacked image shows that after what I interpret as the 3rd stage ignition, the trajectory clearly starts to deviate from the previous more or less straight line:
click image to enlarge
This is not an effect of lens distortion, as I will show below. It is a real deviation, that fits a missile launch. It shows unequivocally that the phenomena is not a fuel vent by a rocket booster in earth orbit. Such an object (moving in a Great Circle) would move in a straight line when positions are plotted in a Gnomonic projection. I did this for Jan's object: I astrometrically measured points on the trail and converted and plotted the measured RA/DEC in a gnomonic projection system. The same deviation that should not be there if this was an object in Earth orbit is visible in the RA/DEC data:
click diagram to enlarge
This makes very clear that Jan's object was not in orbit around the earth, but on a launch/ballistic trajectory. So we can definitely exclude a rocket booster orbiting the earth from a previous launch and venting fuel.
Just to support my previous argument further: here is what the trajectory in RA/DEC looks like for an object in an eccentric GTO orbit observed near perigee over a similar time span as Jan's object. The comparison object is the USA 40 rocket (1989-061D):
Assuming the La Palma event indeed was an unacknowledged Trident SLBM test by the USA or the British, the known specs of the Trident provide a (very) rough indication of where the launch took place.
As mentioned earlier, the 2nd stage of a Trident SLBM ignites at about 70 km altitude, the 3rd at about 150km altitude. As mentioned too above, I interpret two points in the trail to represent these moments. By measuring their astrometric position and calculating the corresponding azimuth and elevation in the sky, we can get a rough indication of distance and direction at these moments. I did this as a (please note) very rough back-of-the-envelope calculation. It suggests the launch took place near latitude 23-25N and a longitude several degrees West of 40 W. This is right in the middle of the Atlantic, at least 2000-3000 km from any coast in any direction. Again, that points to a Submarine launched missile. The launch azimuth is roughly 80-85 degrees, towards the African coast at a distance of over 3000 km. (note added 25 Sept: but see update here that somewhat changes the picture)
The USA was testing missile intercepts near Kwajalein in the Pacific that same September 10. It is however highly unlikely that the launch that Jan seems to have captured is directly related, for the simple reason that a Trident launched in the Mid-Atlantic does not have the necessary reach to get to Kwajalein.
It is a busy time with missile tests: after the September 2 test in the Mediterranean, the September 10 tests near Kwajalein, and this potential unacknowledged test captured by Jan Hattenbach that same date, there was also a missile test in New Mexico on September 13. The Kwajalein tests were scheduled well before, but the unannounced September 2 test in the Mediterranean and perhaps also this unacknowledged September 10 test in the Atlantic might be part of ad hoc military practise exercises in connection to the continuing situation with Syria.
One question some might raise: why a Medium range Ballistic Missile launch? Why can't this not be an unacknowledged launch into Earth orbit? First: it would not be possible to keep such a launch from a US landbased site a secret. It would be seen over a wide area (like the New Mexico test) and necessitate temporary closure of parts of airspace. Moreover, altitudes and directions really point to a launch in the Mid-Atlantic. The only way to launch into Earth Orbit over the Mid Atlantic would be by an airborne launch using a Pegasus rocket.
All in all, and given the context of the situation in Syria and the September 2 test in the Mediterranean as well, it is much more likely that this is an unacknowledged SLBM test, launched from a US, British or French submarine in the Mid-Atlantic.
UPDATE 24 Sep 2013 18:00:
It has now been confirmed that this was a US Trident SLBM test launched from an Ohio-class submerged submarine! So I was right!
Update 25 Sep 2013: New post with new info here, including re-assessment of the launch trajectory
(note: I thank Jan Hattenbach for making available his original imagery and for his permission to use it on this blog. And I thank Cees Bassa, Jonathan McDowell, Rainer Kresken and Daniel Fischer for discussions. Conclusions and any errors are solely mine).
APPENDIX - added 24 Sept 2013, 19:50
Below are the astrometric data I used in my analysis. I did not measure every image, but enough to describe the track of the object. Measurements were done with AstroRecord astrometric software. Only the start of each trail segment was measured, except for IMG_1848 where the point where it brightens (3rd stage ignition) was measured as well. The observing site is at 28.7564 N, 17.8889 W and 2300 meter altitude. Times are accurate to ~1 second.
IMG UT RA DEC
1835 21:17:08 205.061 -3.950
1838 21:17:29 206.335 -4.418
1840 21:17:43 207.272 -4.737
1843 21:18:04 208.731 -5.228
1846 21:18:25 210.137 -5.743
1848 21:18:39 211.071 -6.089
1848_ign? 21:18:43 211.366 -6.153
1850 21:18:53 212.081 -6.416
1852 21:19:07 213.008 -6.790
1853 21:19:14 213.489 -6.977
1855 21:19:28 214.450 -7.388
1856 21:19:35 214.907 -7.585
1857 21:19:42 215.493 -7.786
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