Friday, February 27, 2015

OT: another update on NEA 2015 CA40

 
Our Near Earth Asteroid discovery (see earlier post) 2015 CA40 is now past it's point of closest approach. It reached that point, at 6.3 lunar distances, on Feb 23 near 21:49 UT.



The animated GIF above shows the asteroid early on Feb 24, about 12 hours after closest approach, imaged with the 0.61-m F/10 Cassegrain of MPC G68 Sierra Stars Observatory in California, USA. The animation is made from 6 images taken over a 10-minute timespan. Each image was 30 second exposure, and the images were separated by 2 minutes.

The observed orbital arc of the asteroid now extends from Feb 15.93 to  Feb 24.58, or 8.5 days. Updated orbital elements from the MPC (MPEC 2015-D86, 26 Feb 2015):

Epoch 2014 Dec. 9.0 TT = JDT 2457000.5
M 298.05944              (2000.0)
n   0.84818796     Peri.  176.19408    T = 2457073.52693 JDT
a   1.1052859      Node   334.93169    q =     1.0044127
e   0.0912644      Incl.   15.06659    Earth MOID = 0.01553 AU
P   1.16           H   24.6
From 147 observations 2015 Feb. 15-24, mean residual 0".74.

13 observatories have now contributed to the observations, including our own MPC 461 Piszkéstetö where we discovered the object, and two observatories I used myself for 'remote' observations: MPC G68 Sierra Stars Observatory in the US and Q65 Warrumbungle observatory in Australia. The full list of contributing observatories (up to 24 Feb 2015) is:

461   Piszkéstetö Stn. (Konkoly), Hungary
J95   Great Shefford, UK
246   Klet obs. KLENOT, Czechia
J69   North observatory, Clanfield, UK
703   Catalina Sky Survey, USA
F65   Haleakala-Faulkes Telescope North, Hawaii, USA
C47   Nonndorf, Austria
G68   Sierra Stars Observatory, Markleeville, USA
474   Mount John Observatory, New Zealand
A48   Povegliano Veronese, Italy
B18   Terskol, Russia
Q65   Warrumbungle, Australia
W87  Cerro Tololo-LCOGT C, Chile


The asteroid is currently only observable from the southern hemisphere.

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Sunday, February 22, 2015

OT: An update on Near Earth Asteroid 2015 CA40

2015 CA40, the Amor Near Earth Asteroid discovered by Krisztián Sárneczky and me with the 0.60-m Schmidt telescope of MPC 461 Piszkéstetö (Konkoly) in Hungary on Feb 15, 2015 (see previous post) has now been observed for a week.



The animated GIF above shows the asteroid zipping through the FOV of the 0.61-m Cassegrain telescope of MPC G68 Sierra Stars Observatory in Markleeville, USA, in the morning of Feb 21. It was made from 5 images of 30 seconds exposure each, separated by 5 minutes each. A single frame from this sequence (taken 21 Feb 2015 at 09:45 UT) is below. Even at a relatively short exposure of 30 seconds, the asteroid has trailed:



With an observational arc of over 6 days, the orbital solution already is much better than it was when the discovery MPEC was issued. A number of observatories have now contributed to the observations. As of 22 February, these included, apart from our observatory MPC 461 Piszkéstetö (Konkoly):

246 Klet obs. KLENOT
703 Catalina Sky Survey
C47 Nonndorf
F65 Haleakala-Faulkes Telescope North
G68 Sierra Stars Observatory, Markleeville
J69 North observatory, Clanfield

J95 Great Shefford

The G68 observations are 'remote' observations by myself (see images above) on Feb 21.

Current orbital elements (source MPC, MPEC 2015-D57 of Feb 22):

Epoch 2014 Dec. 9.0      TT = JDT 2457000.5 
M 298.04783 (2000.0) 
n 0.84852056     Peri. 176.17901      T = 2457073.51198 JDT 
a 1.1049971      Node 334.93125       q = 1.0043903 
e 0.0910471      Incl. 15.04633  
P 1.16           H 24.5             Earth MOID = 0.01551 AU

From 104 observations 2015 Feb. 15-21, mean residual 0".54.

When we discovered 2015 CA40 on Feb 15 it was at 15.6 lunar distances. Tomorrow near 21:48 UT (Feb 23, 2015) it will have its closest approach, to 6.3 lunar distances. In the days following this it will move out of view of the Northern hemisphere, but I hope to be able to follow it a few days using the 50-cm telescope of MPC Q65 Warrumbungle Observatory in Australia.

NASA has placed 2015 CA40 on the NHATS page. This page lists objects in orbits suitable for potential future crewed space missions. NHATS stands for Near-Earth Object Human Space Flight Accessible Targets Study.

Last but not least, a picture of the 0.60-m Schmidt telescope at MPC 461 Piszkéstetö (Konkoly) in Hungary with which we discovered the asteroid (image Krisztián Sárneczky/Miclós Rácz):


For those able to read Hungarian (or use Google Translate), a nice story about the discovery in Hungarian is here. Stories in Dutch are here, here and here (and of course my previous blogpost).

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Tuesday, February 17, 2015

OT: the discovery of Near Earth Asteroid 2015 CA40 (updated)

Satellites is not the only thing I dabble with: as some long-time readers of this blog know, I am also involved in asteroid searches.

Since 2012 I am part of a small team that searches for asteroids with the 60-cm Schmidt telescope of Piszkéstető (MPC 461, Konkoly obs, Szeged university) in Hungary. The project is run by Dr Krisztián Sárneczky from the Szeged university.

My task in this project is to visually inspect the images for objects that have been missed by the automated (computerized) moving object detection routines. Typically, Krisztián sends the images to me via Dropbox within hours of the observing session. I then inspect them on my pc at home here in the Netherlands and measure any unidentified objects I encounter on the images. Over the years I have fished out a number of new main belt asteroids from our imagery.

This weekend, I found a Near Earth Asteroid in the imagery, my first NEA find in this project and my second in total (10 years ago I found NEA 2005 GG81 when I was a plate reviewer with the Spacewatch FMO project).

Part of one of the discovery images from Feb 15. Note the faint trail.

We had a run of several nights with the Piszkéstető Schmidt telescope last week. On Monday around lunchtime I was inspecting images taken Sunday-on-Monday night by Krisztián at high declination (+56 degrees) in Ursa Major. Usually, images at this high a declination are devoid of asteroids. But this time I noted a small moving streak in the images near RA 14h 22m 32.6s, dec. +56 16' 37". See above for (a part of) one of the images, and the animation below. Each frame in the animation below is a 5-minute exposure.

Animation of the discovery images.

Initially I was a bit cautious. As can be seen in the animation above, the object was very faint in the first two frames and brighter in the last two. This is a bit unusual (it can be due to rapid rotation of the object, or -most likely in this case- to changing sky conditions). My first thought therefore was a high altitude slowly flaring satellite: but checking the image times it was clear that this object moved much too slow for a satellite. So: a Near Earth Asteroid?!

I mailed Krisztián the positions noting that it looked like an FMO, a fast moving NEA. Krisztián remeasured the images (measuring is difficult with trailing objects, and certainly faint trails) and sent the observations to the Minor Planet Center (MPC) of the IAU in Harvard, under our temporary object designation "SaLa122".

It was then posted on the MPC's "NEOCP" page, a webpage that lists potential Near Earth Asteroid discoveries with a request to other observatories for confirmation. Due to a mistake it initially appeared as "SaLa123" there (see below) with only 50% of our data: this was however quickly corrected and soon it was on under the correct designation "SaLa122".


SaLa122 (under the erroneous designation SaLa123) on the NEOCP

At that moment we had a 30-minute observational arc, which is very short. It was vital that the object should be recovered over the next day, otherwise the object would be regarded as "lost" and would not count as a discovery.

Luckily, that recovery happened! The next night (16-17 Feb) Krisztián managed to relocate the object with the 60-cm Schmidt (see image below) and could follow it for several hours. In addition, astronomers at the Czech Klét observatory and British amateur astronomer Peter Birtwhistle at his private Great Shefford Observatory in the UK looked for the object too and could confirm it. This expanded the observational arc to 29 hours, enough for a preliminary orbit determination.

Stacked follow-up images from MPC 461 in the night of Feb 16-17

In the late afternoon of Feb 17 the MPC made the official discovery announcement in MPEC 2015-D10: the object now has the official designation 2015 CA40.

2015 CA40 is a borderline Amor/Apollo asteroid with [updated 22 Feb 2015] a semi-major axis of 1.1049538 AU, an eccentricity of 0.0910145 and an orbital inclination of 15.04 degrees. The perihelion is just outside the orbit of the earth at 1.004 AU. The aphelion is at 1.20 AU, well within the orbit of Mars. The orbital period of the asteroid is 1.16 years. With H=24.5 the asteroid is estimated to be about 45 meters in diameter.

Orbit of 2015 CA40

[Updated] 2015 CA40 orbital elements (MPC, from MPEC 2015-D47)

Epoch 2014 Dec. 9.0   TT = JDT 2457000.5 
M 298.04901 (2000.0) 
n 0.84857047     Peri. 176.17310     T = 2457073.50630 JDT 
a 1.1049538      Node 334.93131      q = 1.0043870 
e 0.0910145      Incl. 15.04278      Earth MOID = 0.01551 AU
P 1.16           H 24.5 

From 98 observations 2015 Feb. 15-21, mean residual 0".51. 

The theoretical minimum distance (MOID) of the asteroid's orbit  to the orbit of the Earth is 0.0155 AU or about 6 times the Earth-Moon distance. Closest actual approach of the asteroid to Earth this year, to about 6.3 times the lunar distance, is in the night of Feb 23-24 when it might reach mag. +16.6 and will be moving at a speed of 42" per minute.

Objects in this kind of orbit with a semi-major axis of ~1.0 AU (similar to the orbit of the Earth) are objects that already must have had one or more close encounters with the Earth and/or Mars.

We plan to follow the object over the coming nights, to expand the observational arc as much as possible, in order to increase the chances of it being found back during the next similarly close approach, which will be on 23 February 2066. There are some earlier dates at which the asteroid comes near Earth too (indicated in the diagram below: e.g. 2022, 2029, 2037, 2044, 2051 and 2058), but at a clearly larger distance than in 2015 and 2066. It will be much fainter and hence harder (but not impossible, given a big enough telescope) to detect during those years.


click diagram to enlarge: distance (in AU) of 2015 CA40 to earth over the coming century

Earlier close approaches to less than 0.1 AU over the past 200 years were in 1813 (0.0161 AU);  1849 (0.0429 AU); 1863 (0.0245 AU); 1899 (0.0773 AU); 1928 (0.0469 AU); 1950 (0.0503 AU); and 1979 (0.0665 AU).

2015 CA40 is  the 7th Near Earth Asteroid discovered by the Konkoly survey and my second NEA discovery (and my first in the Konkoly project).

More on my other asteroid discoveries here.

Update (21 Feb 2015): we are still following this object and the arc now includes observations from early Feb 21.


Acknowledgement: we thank Peter Birtwhistle and the people of Klet observatory for their follow-up observations.

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Saturday, February 14, 2015

ATV-5 'Georges Lemaitre' and the ISS chasing each other in a partly cloudy sky

ESA's ATV-5 'Georges Lemaitre' cargoship undocked from the ISS in the afternoon of February 14, 2015. A few hours later they made a fine zenith pass over Leiden, stille relatively close together, chasing each other in the sky.

Unfortunately, an untimely fields of clouds passed through the sky as the pass commenced. Still, the duo was well visible amidst the clouds. ATV-5 was an easy naked eye object at mag. +1. It was some 25 degrees (25-30 seconds) in front of the ISS.

ATV-5 near Capella

The image above shows ATV-5 amidst clouds near Capella. The image below shows both the ISS (top) and ATV-5 (bottom) descending to the east in a partly clouded sky. Both images were made with an EF2.0/35 mm lens.

ISS (top) and ATV-5 (bottom)

Frustatingly enough, the clouds disappeared and it was completely clear just 5 minutes after the pass....

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Tuesday, January 06, 2015

Observing HEO objects

In wintertime at latitude 51 degrees North, satellites in Low Earth Orbit are mostly invisible except for twilight, as all their passes are completely within the Earth shadow.

This season is therefore the season that I focus on HEO and GEO objects. HEO stands for Highly Elliptical Orbit and is almost synonymous with the more informal name 'Molniya orbit', after a class of Russian communication satellites employed in such orbits.

Military SDS COMSAT USA 198 (SDS 3F5), imaged in Cassiopeia on 4 Jan 2014

Satellites in a Molniya orbit have an orbital period of about 2 revolutions per day, an orbital inclination near 63.4 degrees, perigee at a few hundred kilometers altitude over the southern hemisphere and apogee at altitudes near 36000 km over the Arctic. They spend most of their orbital time near their apogee.The 63.4 degree orbital inclination ensures that perigee keeps at a stable position over the southern hemisphere.

US military payloads and 'unknowns' in Molniya orbit

The advantage of a Molniya orbit is that it allows a good, long duration view of high northern latitudes, including the Arctic region, which are not well visible from a geostationary orbit. This is ideal for communications satellites serving these regions, for SIGINT satellites, and other applications (such as infrared ICBM early warning systems, e.g. SBIRS) that benefit from a long 'stare' and good view of high Northern latitudes.

The US military has several systems in a Molniya orbit (see image above): communication satellites (e.g. two components of the SDS system), several SIGINT satellites (TRUMPET and TRUMPET-FO), and components of the SBIRS system (piggybacked on three TRUMPET-FO SIGINT satellites). Identifiable payloads include:

- TRUMPET 1, 2 and 3 (SIGINT);
- TRUMPET-FO and SBIRS USA 184, 200 and 259 (SIGINT and SBIRS);
- SDS COM satellites USA 179 and 198

There are a couple more which we cannot (yet) tie to a specific launch and function (see note at end of post).

Near their apogee, satellites in Molniya orbit are located high in the sky for my location, and because of their high northern position, they are sun-illuminated and hence visible (typically at magnitudes near +9 to +12) even at midnight and in winter. They move very slowly when near apogee, creating tiny trails on the images.

On December 13, the NRO launched (as NROL-35) a new SIGINT and SBIRS platform into a Molniya orbit: USA 259 (see a previous post). It is currently still actively manoeuvering to attain its final orbit, which makes it an interesting object to track. The image below was taken in late twilight of Jan 4, when the satellite was past its apogee and on its way to perigee. It was 4 minutes early against orbital elements based on observations of only a few days old.

SIGINT/SBIRS satellite USA 259 (NROL-35) imaged in Andromeda in the evening of Jan 4

I image these objects with an old but good Zeiss Sonnar MC f2.8/180 mm telelens (made in the former DDR and sturdy -and heavy- as a tank). This lens has a 67 mm aperture at f 2.8, which means it shows faint objects. As these objects move very slowly, the relatively small FOV is no problem. My observational data from January 4th can be found here and here.

Note: the 'unknowns' in the orbital plot above are objects we track that are not in public orbital catalogues and which we cannot tie to a specific launch. Although some of them certainly are, not all of these need to be payloads: some might be spent rocket stages from launches into HEO.

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Tuesday, December 30, 2014

Observing USA 259 (NROL-35)

On December 13th, 2014, the NRO launched NROL-35 out of Vandenberg AFB into a Molniya orbit. The payload, USA 259 (2014-081A) is most likely a SIGINT, and possibly piggybacks a SBIRS sensor, according to analysts.

USA 259 (NROL-35) imaged by me on 28 December 2014

Our tracking network quite quickly picked up the payload. Peter Wakelin first picked it up from Britain on December 13, followed by Scott Tilley in Canada and Cees Bassa in the Netherlands a few hours later. In the two weeks since, the payload has been observed to be manoeuvering in order to get into its intended orbit.

My own first observations of the payload were done in the evening of December 28 (see image above, taken with the F2.8/180mm Zeiss Sonnar) during short clearings. It had been a clear day, but clouds rolled in around nightfall. The satellite was located high over the Northern Atlantic near aphelion at this time at an altitude of 34500 km, and situated high in the sky in Cepheus as seen from Leiden.

orbital position at time of the photograph
view from the satellite

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Monday, December 22, 2014

Analysis of the 2014-074B Soyuz r/b re-entry on 26 Nov 2014


In the early morning of 26 November 2014 between 03:35 and 03:40 UT, a very slow, long duration fireball was observed from the Netherlands, Germany and Hungary (see earlier post).

The fireball was quickly suspected to be caused by the fiery demise of a Soyuz third stage, used to launch ISS expedition crew 42, including ESA astronaut Samantha Cristoforetti, to the International Space Station on November 23.

Video still image from Erlangen, Germany (courtesy Stefan Schick)

Analysis

In this blog post, which is a follow-up on an earlier post, I will present some results from my analysis of the re-entry images, including a trajectory map, speed reconstructions and an altitude profile. The purpose of the analysis was:

1) to document that this indeed was the re-entry of 2014-074B;
2) to reconstruct the approximate re-entry trajectory;
3) to reconstruct the approximate altitude profile during the re-entry.


Data used

Three datasets were available to me for this analysis:

1) imagery from three photographic all-sky meteor cameras in the Netherlands, situated at Oostkapelle, Bussloo and Ermelo (courtesy of Klaas Jobse, Jaap van 't Leven and Koen Miskotte);

2) data from two meteor video camera stations (HUBAJ and HUBEC) situated in Hungary (courtesy of Zsolt Perkó and Szilárd Csizmadia);

3) imagery from a wide angle fireball video camera situated at Erlangen, Germany (courtesy Stefan Schick).

Some example imagery is below:


Detail of one of the Bussloo Public Observatory (Netherlands) all-sky images, courtesy Jaap van 't Leven
Detail of the Cyclops Oostkapelle (Netherlands) all-sky image, courtesy Klaas Jobse
Detail of the Ermelo (Netherlands) all-sky image, courtesy Koen Miskotte
Stack of video frames from Erlangen (Germany), courtesy Stefan Schick
Stack of video frames from HUBEC station (Hungary), courtesy Szilárd Csizmadia and Szolt Perkó

Astrometry

The Hungarian data had already been astrometrically processed with METREC by Szilárd Csizmadia and came as a set of RA/Declination data with time stamps. The Dutch and German images were astrometrically processed by myself from the original imagery.

The German Erlangen imagery was measured with AstroRecord (the same astrometric package I use for my satellite imagery). An integrated stack of the video frames resulted in just enough reference stars to measure points on the western half of the image. As it concerns an extreme wide field image with low pixel resolution and limited reference stars, the astrometric accuracy will be low.

AstroRecord could not be used on the Dutch All-Sky images because of the extreme distortion inherent to imagery with fish-eye lenses. They were therefore measured by creating a Cartesian X-Y grid over the image, centered on the image center (the zenith). Some 25 reference stars per image were measured in this X, Y system, as well as points on the fireball trail. From the known azimuth and elevation of the reference stars, the azimuth and elevation of points on the fireball trail were reduced. While obtaining the azimuth with this method is a straight forward function of the X, Y angle on the images, obtaining the elevation is more ambiguous. Based on the known positions of the reference stars and their radius (in image pixels) with respect to the image center, a polynomial fit was made to the data yielding a scaling equation that was used to convert the radius with respect to the image center of the measured points on the fireball trail to sky elevation values.

Unlike meteoric fireballs, rocket stage re-entries are long-duration phenomena. The German and Hungarian data, being video data, had a good time control. The Dutch all-sky camera data, being long duration photographic exposures, had less good time control, even though the start- and end-times of the images are known. The trails for Oostkapelle and Ermelo had no meaningful start and end to the trails. Bussloo does provide some time control as the camera ended one image and started a new one halfway the event: the end point of the trail on the first image corresponds to the end time of that image, and similarly the start on the next image corresponds to the start time of that image. There was 7 seconds in between the two images. Time control is important for the speed reconstructions, but also for the astrometry (notably the determination of Right Ascension).


Data reduction and problems

The Azimuth/Elevation data resulting from the astrometry on the Dutch data were converted to RA/DEC using formulae from Meeus (1991). For these Dutch data, the lack of time control is slightly problematic as the RA is time-dependent (the declination is not). There is hence an uncertainty in the Dutch data.

The data where then reduced by a method originally devised for meteor images: fitting planes through the camera's location and the observed sky directions, and then determining the (average) intersection line of that plane with planes fitted from the other stations, weighted according to plane intersection angle. This is the method described by Ceplecha (1987). The plane construction was done in a geocentered Cartesian X-Y-Z grid and hence includes a spherical earth surface. The whole procedure was done using a still experimental Excel spreadsheet ("TRAJECT 2 beta") written by the author of this blog, coded serendipitously to reduce meteoric fireballs a few weeks before the re-entry.

I should warn that this method is actually not too well suited to reduce a satellite re-entry. The method is devised for meteoric fireballs, who's luminous atmospheric trajectory is not notably different from a straight line (fitting planes is well suited to reconstruct this line). A rocket stage re-entering from Low Earth Orbit however has a notably curved trajectory: as it is in orbit around the geocenter, it moves in an arc, not a straight line. This creates some problems, notably with the reconstructed altitudes, and increasingly so when the observed arc is longer. Altitudes reconstructed from the fitted intersection line of the planes come out too low, notably towards the middle of the used trajectory arc. The resulting altitude profile hence is distorted and produces a U-shape. The method is also problematic when stations used for the plane fitting procedure are geographically far removed from each other. In addition, the method is not very fit for long duration events.

The data were reduced as three sets:

1) data from the Dutch stations (independent from the other two datasets);
2) data from the German station combined with the two eastern-most Dutch stations;
3) data from the Hungarian stations (independent from the previous two datasets).

Dataset (2) combines data from stations geographically quite far apart. This is probably one of the reasons why this dataset produces a slightly skewed trajectory direction compared to the other two datasets.

The Dutch images have the event occurring very low in the sky (below 35 degrees elevation for Oostkapelle and below 25 degrees elevation for Bussloo and Ermelo). The convergence angles between the observed planes from the three stations is low (14 degrees or less). This combination of low convergence angles and low sky elevations, means that small measuring errors can have a notable scatter in distance as a result.


Results (1): trajectory

reconstructed trajectory (red dashed line and yellow dots)

The map above (in conic equal-area projection) shows the reconstructed trajectory as the yellow dots and the red dashed line. White dots are the observing stations.

The thin grey line just north of the reconstructed trajectory is the theoretical ground track resulting from a SatAna and SatEvo processed TLE orbital efemerid set for the rocket stage. This expected ground track need not perfectly coincide with the real trajectory, as the orbit changes rapidly during the final re-entry phase.

The reconstructed trajectory converges towards the theoretical (expected) ground track near the final re-entry location, above Hungary, but is slightly south of it earlier in time. The horizontal difference is about 30 km over southern England, 25-20 km over northern France due south of the Netherlands, 17-16 km over southern Germany and less than 3 km over Hungary.

This difference is most likely analytical error, introduced by the low sky elevations and convergence angles as seen from the Netherlands. On the other hand, the Hungarian observations (with stations on the other, southern side of the trajectory compared to the Dutch and German stations and reduced completely independent from the other data) place it slightly south too. So perhaps the deviation is real and due to orbital inclination changes during the final re-entry phase. Indeed, a SatEvo evolution of the last known orbit suggest a slight decrease in orbital inclination over time, although not of the observed magnitude.

The results from Erlangen come out slightly skewed in direction, likely for reasons already discussed above. The Hungarian results are probably the best quality results.


Results (2): altitudes and speed

altitudes (in km) versus geographic longitude

As mentioned earlier, the altitudes resulting from the fitted linear planes intersection line come out spurious due to the curvature of the trajectory. Altitudes were therefore calculated from the observed sky elevations and known horizontal distance to the trajectory. The horizontal distance "d" between the observing station and each resulting point on the trajectory were calculated using the geodetic software PCTrans (software by the Hydrographic Service of the Royal Dutch Navy). Next, for each point the (uncorrected) altitude "z" was calculated from the formula:

         z = d * tan(h),

where "h" is the observed sky elevation in degrees.

This is the result for a "flat" earth. It has hence to be corrected for earth surface curvature, by adding a correction via the geodetic equation:

        Zcr - sqrt (r 2 + d 2)     [all values in meters],

where "r" is the Earth radius for this latitude, "d" the horizontal distance between the observing station and the point on the trajectory, and "Zc" the resulting correction on the altitude calculated earlier.

The results are shown in the diagram above, where the elevation has been plotted as a function of geographic longitude. It suggests an initial rapid decline in altitude from ~125 km to ~100 km between southern England and northern France, an altitude of ~100 km over southern Germany, and a very rapid decline near the end, with altitudes of 60-50 km over Lake Balaton in Hungary. Whether the curvature in the early part of the diagram is true or analytical error is difficult to say, although it is probably wise to assume it is analytical error.

Apart from the match in trajectory location, speed is another measure to determine whether this was the decay of 2014-074B or not. Meteors always have an initial speed larger than 11.8 km/s (but: for extremely long duration  slow meteors deceleration can decrease the terminal speed considerably below 11.8 km/s later on in the trajectory). Objects re-entering from geocentric (Earth) orbit have speeds well below 11.8 km/s, usually between 7-8 km/s depending on the orbit apogee. When speed determinations come out well below 11.8 km/s, a re-entry is a likely although not 100% certain interpretation. When speed determinations come out at 11.8 km/s or faster, it is 100% certain a meteor and no re-entry.

By taking the distance between two points on the trajectory with a known time difference, I get the following approximate speeds:

- from the Hungarian data: 7.0 km/s;
- from the Dutch data: 9.0 km/s;
- from the German data: 9.4 km/s.

These are values that are obviously not too accurate, but nevertheless reasonably in line with what you expect for a re-entry of artificial material from geocentric (Earth) orbit.

It should be noted that if the southern deviation (see trajectory results above) of the trajectory data is analytical error, the speed of the Dutch and German observations is a slight overestimation, while the Hungarian results will be a slight underestimate. This would bring the speeds more in line with each other, and even closer to what you expect from a rocket stage re-entry from Low Earth Orbit.


Discussion and Conclusions

The trajectory and speed reconstructions resulting from this analysis strongly indicate that the fireball seen over northwest and central Europe on 26 November 2014, 03:35-03:40 UT indeed was the re-entry of the Soyuz  third stage 2014-074B from the Soyuz TMA-15M launch. Although there are some slight deviations from the expected trajectory, the results are close enough to warrant this positive identification.

The deviations are easily explained by analytical error, given the used reduction method and the not always favourable configuration of the photographic and video stations with regard to the fireball trajectory. Notably, the large distance of the Dutch stations to the trajectory resulting in very low observed sky elevations and low plane fitting convergence angles for these stations is a factor to consider. Nevertheless, and on a positive note, the final result fits the expectations surprisingly well.

The data suggest that the object was at an altitude approaching 125 km (close to the expected final orbital altitude on the last completed orbit) while over southern England and the Channel, had come down to critical altitudes near 100 km while over southern Germany, and was coming down increasingly fast at altitudes of 60 km and below while over Hungary.

The Hungarian observations show that the rocket stage re-entry continued beyond longitude 19.3o E and below 46.45o N, and happened some time after 03:39:20 UT. It likely not survived much beyond longitude 21o E.

The nominal re-entry position and time given in the final JSpOC TIP message for 2014-074B are 03:39 +/- 1 min UT and latitude 47o N longitude 17o E, with the +/- of 1m in time corresponding to a +/- of several degrees in longitude. This is in reasonable agreement with the observations.

Acknowledgements

I thank Zsolt Perkó, Szilárd Csizmadia, Stefan Schick, Jaap van 't Leven, Klaas Jobse and Koen Miskotte for making their images and data available for analysis. Carl Johannink contributed some mathematical solutions to the construction of the spreadsheet used for this analysis.

Note: another Soyuz rocket stage re-entry from an earlier Soyuz launch towards the ISS was observed from the Netherlands and Germany in December 2011, see earlier post here. As to why it takes such a rocket stage three days to come down, read FAQ here.



Literature:
- Ceplecha Z., 1987: Geometric, dynamic, orbital and photometric data on meteoroids from photographic fireball networks. Bull. Astron. Inst. Czech. 38, p. 222-234.
- Meeus J. (1991): Astronomical Algorithms. Willmann-Bell Inc., USA. 



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Thursday, November 27, 2014

[UPDATED] Re-entry of Soyuz third stage 2014-074B from Soyuz-TMA 15M launch observed from the Netherlands and Hungaria.

Update 23 Dec 2014: further analysis of imagery in new post
(28 Nov 2014, 10:45 UT: updated with more imagery)

click image to enlarge

Today Carlos Bella alerted the seesat list that Hungarian amateur astronomers had captured imagery of a re-entry in the early morning of November 26.

It concerns the re-entry of 2014-074B, the Soyuz third stage from the launch of Soyuz-TMA 15M which launched expedition crew 42 to the ISS on 23 November 2014.

Below is one of several casual phone-camera video's also shot from Hungaria Serbia, showing the fragmenting fireball:


(video by Aleksandar F, Belgrade)

According to the TIP message of  JSpOC, the re-entry happened near 3:39 UT on the early morning of 26 November, 2014, near 47 N,  17 E. This perfectly fits the Hungarian observations. See also the map above, which shows the predicted trajectory of 2014-074B resulting from processing the last known orbital elements with SatAna and SatEvo.

Moreover, the speed determination by the Hungarian meteor camera network, 7.4 km/s, confirms this is not a meteor but a re-entry. The speed is too low for a meteor (which are always faster than 11.8 km/s, the earth escape velocity) but matches the speed of an object re-entering from Low Earth Orbit.

Realizing that the rocket stage made a pass over the Netherlands/Belgium only minutes earlier,  I asked the operators of the DMS All-Sky meteor cameras to check their imagery of that morning. As it turns out, three Dutch All-sky stations did capture the re-entry: Bussloo (Jaap van 't Leven), Oostkapelle (Klaas Jobse) and Ermelo (Koen Miskotte).
 
Detail of the Bussloo Public Observatory all-sky image (courtesy Jaap van 't Leven)

Detail of the Cyclops Oostkapelle all-sky image (courtesy Klaas Jobse)

Detail of the Ermelo image (courtesy Koen Miskotte)

Parts of the three Dutch images (courtesy Jaap van 't Leven, Klaas Jobse and Koen Miskotte) are shown above. All stations have it very low above the horizon at elevations of 20 degrees or lower.

The Oostkapelle image shows that the incandescent phase of the re-entry already started over the UK, as the image shows the trail well to the west (and Oostkapelle is on the Dutch West coast).

As soon as I can find some time, I will analyze the imagery to see whether I can get altitude data from them. It would be nice to document the last minutes of this rocket stage in this way!

So stay tuned for an update....

UPDATE 23 Dec 2014: new post with a further analysis with trajectory and altitude reconstructions based on observations from the Netherlands, Hungaria and Germany now available

(I thank Jaap van 't Leven, Klaas Jobse and Koen Miskotte for permission to use their imagery)

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Monday, November 10, 2014

Live blog from ESOC, Darmstadt: Philae (Rosetta) Landing on comet Churyumov-Gerasimenko:

 LIVE BLOG

 
I (am) was on-site at ESA's European Space Operations Center (ESOC) in Darmstadt for the Philae landing on comet 67P/Churyumov-Gerasimenko
This blog-post will be live updated as the events unfold. 
Be sure to hit refresh upon a new visit!
 I will also  be tweeting through @Marco_Langbroek)

15 Nov

01:45 The communications link has broken. This is it. Philae has gone to sleep, perhaps to never wake up again...or will it? So far it has kept amazing us all, after all...!

01:29 Philae has been switched into standby mode. All instruments powered off, but communications llink still active. Time to go to sleep now, brave little friend....

01:00 Battery power is dropping fast but Philae is not giving up! More and more data is being received. This is History written large, with a capital H. Truely epic science History!

00:28 Philae's rotation, over 35 degrees, was successful.
https://twitter.com/philae2014/status/533393729156308992

00:20 Philae is alive and the drill has worked! At the moment, they are trying to rotate the lander to get more sunlight on the panels. I think we can safely say now that nothwithstanding all that went different from what was planned, the mission has become a resounding success!

14 Nov

15:10 Brief recap of the Google+ briefing of this afternoon: Matt Taylor apologizes for #shirtgate. Contacts Rosetta-Philae are very stable. 80% of the most important science data from the first science sequence are now in. Rosetta has not imaged Philae on the surface yet, but there are still images in the pipeline and the search continues.  Holger Sierks suggests that in fact, they should have caught the lander just before touchdown at 500 meter above the surface, and during the first bounce in the images from the first two hours after touchdown, which have not been downloaded yet. These images should give the direction of the rebounce.
Lomatsch told that Philae has not moved at all since finally settling. Philae is in a difficult position however, surrounded by walls, limiting sunlight reaching the solar panels.From what she said, I get the impression that hopes for a lander revival once 67P/ is closer to the sun, should not be too high.
During the Q&A Ulamec indicated that it is unlikely that cometary jets will blow the lander from the surface as activity increases, as it has a too high density.
The DS2 drill is already extended 25 cm below base plate, but as there is a (scheduled) loss of contact right now, it is unsure whether it can/has reached the surface yet. New (and perhaps last) contact with Philae near 22 CET this evening. A command to go into low power mode did however not reach Philae, so it is going to get really close wether the next contact will be successful.


9:55 Philae's batteries will run out of power tomorrow. Coming night the operators will try to rotate the lander such that the largest solar panel will be facing the sun (via @elakdawala)https://twitter.com/elakdawalla/status/533179905610371073

4:55 Although it will be under "very risky conditions", SD2, the core drilling tool, will be employed. it will take subsurface samples that will be analysed by COSAC and Ptolemy, two instruments that o.a. look for organic compounds and determine the isotopic composition of water in the comet. The latter will yield information whether water may have been brought to Earth by comets.
https://twitter.com/rosettasd2/status/533056385819607040

00:45 MUPUS is communicating the first "science" temperatures (but not subsurface yet) https://twitter.com/philae_mupus/status/533040327058534400

13 Nov

23:25 After first attempt failed, second upload attempt of MUPUS commands succeeded!
https://twitter.com/philae_mupus/status/533021560593219584

21:58 The commands to deploy MUPUS failed to upload: https://twitter.com/philae_mupus/status/532998982193397762

20:55 Tonight the MUPUS  (MUlti-PUrpose Sensors for Surface and Sub-Surface Science) instrument will be deployed, for about 20 cm of its 30 cm length. The probe, which contains several temperature sensors, will be slowly hammered into the subsurface. The goals are amongst others to gather data on subsurface consistency, and a subsurface temoperature profile. It also provides calibration data for the thermal mapper onboard the Rosetta orbiter. 

    19:40 More details have been released. Philae bounced twice, at 15:34 GMT (first contact of lander with comet) and 17:25 GMT, before settling on the cometary surface at 17:32 UT. It rotated around the Z-axis (the vertical axis) after the first bounce (this rotation was the first sign yesterday evening that the lander did not settle at first contact). It is working though, although there are indications that some of the solar panels are in shadow (perhaps due to a nearby boulder? [update: it's a cliff]). It hence does not have full power. 

    So that first bounce took two hours, while the second bounce appears to have been mild. As the harpoons did not work, Philae is not well anchored to the comet. This will interfere with some of the planned activities (e.g. coring the subsurface).

    See also: http://blogs.esa.int/rosetta/2014/11/13/philae-the-happy-lander/

    17:20 (This post comes belated as I am still travelling homewards...)
    ESA has released the first panoramic image by Philae. It is obviously a rather dark world out there... Of all the extraterrestrial landscapes imaged, I feel this one beats them all! This truely is a Primeordial world... (photo: ESA)



    16:30 (back on Dutch soil, but stil in the train) The place where Philae finally landed has been located. It is about 1 km offset from the original location. In the image below, the cross is the original landing site, the box where it finally ended up.


    (image: ESA)

    12:05 News now is that Philae is on the comet, but not anchored well. This means the coring of the subsurface cannot happen, which is a bummer. Still, no doubt much new scientific data will be gathered. Given that we knew this landing effort was very risky, we can say Philae is a big success anyway!

    I am at Darmstadt railroad station currently, about to return home to the Netherlands, so this will be my last blog update today for now.

    11:50 CET  Great news! Philae is alive and has send the first images of the comet' surface!
    below you can see one of the lander legs, and part of the surface. The image is a composite of two images taken by Philae's CIVA camera.



    Image : ESA


    12 Nov

    20:25 Gist of the press briefing: some data might indicate that Philae briefly left surface again after touchdown, i.e. it bounced and then settled again at a slightly different spot. Data need to be evaluated now. Next briefing is tomorrow 14:00 CET. No word about those images shown by the French...

    19:10 This is reportedly the first image of the comet's surface (but image is unconfirmed, at least it has not been shown yet here at ESOC):



    18:12 Ulamec just told reporters that a lot is still uncertain about the spacecraft condition and safety. Also said option to try to re-fire harpoons is risky, as the non-working gas thruster cannot produce the counterforce necessary. This mean the counterforce of (re-) firing the harpoons could result in Philae being ejected from the comet surface.

    17:42 Flight controller Geurts reports that the gas thruster indeed did not work, and that the anchors did not fire. Incredible that the landing nevertheless still seems to have been succesful!
    Geurts mentioned they might retry to fire the anchors.

    17:04 Philae has landed!!!!! They are receiving telemetry. Harpoon has been fired, landing gear is in. Its on the surface!!!!

    16:50 Nailbiting at ESOC!



    16:28 Touch down window has started.....fingers crossed!

    15:52 https://twitter.com/spaceflight101/status/532546694593126400 cool image of Philae on its way down as imaged by the Rosetta orbiter! note the three extended landing legs.
    Think about what this image exemplifies: To boldly go where no-one has gone before! Exploration!



    15:18 Image of Rosetta imaged by Philae has been shown now. Descend so far is "going as planned". Image is here:  https://twitter.com/esa_rosetta/status/532537918557265921

    12:33 Deployment of Philae landing gear confirmed.

    12:07 Datalink Philae-Rosetta confirmed! Datalink with both objects is healthy. This is an important moment! Over the next hours Philae data from the descend phase will be relayed to the control center. In about 5 hrs from now, Philae should touch down.

    11:00 My ESOC source tells me that for the cold gas thruster to work, a membrane was to be punctured. And this might actually have happened, but the returned sensor data that should confirm this was "contradictory". So the system might actually work, but it is not certain.

    10:20 First data relay from the still descending lander expected about 2 hours from now. Telemetry plus a picture of th orbiter seen from the lander. The lander will reach the cometary surface in about 7 hours from now. The big wait has started.....

    10:20 Dr Churyumov:


    10:04 Separation confirmed!!! Alea Jacta est, to quote old Julius

    9:50 Matt Taylor: "This is our Longest Day" 

    9:36 Separation of the lander is actually happening now, but we won't know for a while as it takes the confirmation signal 28 minutes to reach us

    9:30 The problem with the cold gas system means they have to land without it. This introduces the risk that the lander will bounce back from the cometary surface because of opposite forces when they fiire the anchor harpoon.

    8:15 We have a GO!

    8:00 CET - The go/no of last night has been delayed. The cold gas sytem of Philae has a problem. This cold gas drives the small thruster on top of Philae that pins the lander to the comet surface in the first few minutes.

    11 Nov - The go/no go decision of this evening has given a 'go' as verdict. Early tomorrow morning there will be a second, and last, go/no go moment.




     (player provides a live stream from ESOC by ESA)

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    Announcing a Live Blog from ESOC during the Philae landing on 67P/Churyumov-Gerasimenko

    On Wednesday November 12, Philae, the lander of ESA's Rosetta mission, will attempt to land on comet 67P/Churyumov-Gerasimenko.

    I will be at ESA's Space Operations Center ESOC when this happens. If the WiFi doesn't fail on me, I will attempt to live-blog the events of that day on this blog, as well as live tweet the events via my Twitter account (@Marco_Langbroek).

    So stay tuned here (or on Twitter) next Wednesday!

    Meanwhile, here is a nice interactive 3D model (model courtesy of ESA) of the comet to play with (requires WebGL enabled browser: might not work in iOS):


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    Saturday, November 01, 2014

    Brightness variation of the USA 198 Centaur rocket stage on October 30, 2014

    Earlier today I posted this image of the USA 198 Centaur rocket (2007-060B) passing close to M33 galaxy in Triangulum:

    click image to enlarge
    I noted a slight but clear brightness variation in the trail segments on subsequent images (the stack above is a stack of 19 individual images). I therefore decided to use the images to create a brightness variation profile.

    click diagram to enlarge

    The result is the diagram above (grey crosses are individual pixel values; the blue line is an 11-point sliding average; the red dotted line a sinusoid with a period of 37 seconds). This is the result of combining measurements of the trail brightness variation on 20 images. The individual pixel values are noisy, the result of using a high ISO setting of 2000 (which results in noise) but a pattern is visible, even more so in the 11-point sliding average.

    The diagram shows a modest but clear semi-regular brightness variation with a peak in brightness approximately each 37 seconds. There is perhaps also a regularity visible in that each second valley in the curve is more shallow than the first. The pattern suggests a slow tumbling motion.

    Below is one of the original individual images:

    click image to enlarge

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    USA 198 r/b passing the M33 galaxy

    click image to enlarge


    Last Thursday evening was very clear. I tested a clip-in CLS filter on my Canon EOS 60D, employing the 2.8/180mm Zeiss lens and a motorized tracking mount.

    One of the targets was M33, a big galaxy in Triangulum. As it happened (it was not planned), I captured a classified object in the series: the USA 198 r/b (2007-060B). It can be seen passing M33 in the image above, which is a stack of several 20-second images (breaks in the trail represent short moments inbetween consecutive exposures).

    As the images do not have the timing accuracy of my usual tracking images, they are probably of little use for astrometry. But I do seem to see some slight brightness variation, so I might try to construct a brightness curve.

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    Sunday, October 19, 2014

    Imaging the North Korean Kwangmyŏngsŏng (KMS) 3-2 satellite

    Yesterday evening was initially clear. Using the SamYang 1.4/85 mm lens, I imaged an object that has been on my "to do"-list for a (too) long time: the North Korean satellite Kwangmyŏngsŏng 3-2 (KMS 3-2, 2012-072A), visible as a very faint trail on this image:

    click image to enlarge

    Kwangmyŏngsŏng ("Brilliant Star") 3-2 was launched under much international tension almost two years ago, on 12 December 2012, from Songhae. It is the first and so far only successful North Korean launch.

    On 8 Dec 2012, just days before they launched KMS 3-2, the N-Koreans actually visited this weblog, looking for information on US IMINT satellites (specifically Lacrosse and Keyhole). As I wrote at that time, very few North-Koreans have access to the internet. Those who do, have close ties to Kim Jung Un or are among the top military. So that visit was surprising.

    The reason became quickly apparent. Post-launch, I made an analysis of the KMS 3-2 launch time, showing that the North Koreans picked a carefully determined one-hour gap in Western space-based IMINT coverage to launch their satellite.

    Later that month, on 21, 22 and 23 Dec 2012, the North-Koreans popped up again, visiting my launch time analysis post, and searching for TLE's of their own satellite! (one would expect that the Chinese could provide these to them, so this was surprising again). The visits came from another IP than the Dec 8 visits.

    Another visit to this blog was made two weeks later, on 8 Jan 2013, from the same IP as the Dec 8 visit (but another computer perhaps, as the Dec 8 visitor used Windows Xp, but this visitor Windows 7). This time the subject of the visit was my analysis of the tumbling behaviour of the satellite which I made late December 2012 using Greg Roberts' 20 Dec 2012 footage of a KMS 3-2 pass (as it was in the dead of the Northern hemisphere winter, it was not possible for me to image the satellite myself at that time). They might have been interested in my analysis in order to assess the character of this tumbling, which was probably not intended and might indicate a failure to stabilize the satellite after orbit insertion.

    Then it was quiet for 1.5 years. But last summer, I got another surprise N-Korean visit to this blog. This happened on June 9, and it was this visit which reminded me that it might be fun to try to image the satellite this summer. For various reasons, I only succeeded last night.

    The June 9 N-Korean visitor visited posts about the SDS and SBSS satellite systems. The first (SDS, Satellite Data System) is a system of geostationary US military data relay satellites which (a.o.) relays IMINT data from other satellites to the US. The other (SBSS, the Space Based Space Surveillance system) is a satellite in Low Earth Orbit for detecting and tracking objects orbiting in space (i.e., other satellites - like those of North Korea).

    This visit came while upgrade activities of the launch installations at Sohae were documented by the 38 North blog. The upgrade seems to point to Sohae being readied to facilitate a heavier launch vehicle. How a North-Korean interest in SBSS and SDS would fit into this picture, is however not entirely clear, apart from that it could indicate that they might aim to avoid SBSS tracking of their payloads during the initial orbit insertion.

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    Sunday, September 28, 2014

    Observing HEO objects

    Friday evening I missed the LEO window because of a dinner. When back home near midnight, conditions were dynamic: intermittent clear skies and roving cloud fields.

    A HEO (Highly Elliptical Orbit) object called "Unknown 051230" (2005-864A) was well-placed near the zenith, in Cepheus. I targetted it using the 2.8/180mm Zeiss Sonnar MC lens, snapping pictures during clear spells. It shows up well, as a tiny but clear trail (indicated by the arrow in the image):

    click image to enlarge

    This object is one which our analysts cannot link to any particular launch - hence the designation "Unknown". It is being tracked by us for quite a couple of years now (since Greg Roberts discovered it on 30 December 2005). It could be either a (defunct) payload, or an old rocket booster.

    At the time of my observations it was at an altitude of 36650 km, close to its apogee, situated over the Arctic circle roughly above Iceland:


    orbital position of Unknown 051230 at the time of observation
    click image to enlarge

    Nadir view from orbital position of Unknown 051230 at the time of observation
    click image to enlarge

    Highly Elliptical Orbits (also called a Molniya orbit) typically have an orbital inclination near 63.4 degrees, an apogee near 36000 km, and perigee at only a few hundred km altitude, usually over Antarctica.

    63.4 degree orbital inclination of Unknown 051230
    click image to enlarge

    The ~63.4 degree inclination with these orbital parameters ensures that the perigee is stable, i.e. always stays over the southern hemisphere.

    An object in this orbit has a period of 0.5 day, so it makes 2 revolutions per day. Its residence time in perigee over the southern hemisphere is only brief: most of the time it is at high altitude over the northern hemisphere, allowing many hours of  continued presence above that area (see image above).

    Objects in these orbits are therefore typically used to provide communications at high Northern latitudes, or for SIGINT and infra-red surveillance.

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