USA 186 is defying the schedule

Over the past months I have posted a number of analysis and prognosis with regard to the likely changes to the KH-11 Keyhole/CRYSTAL constellation of optical reconnaisance satellites, following the launch of USA 245 (NROL-65, 2013-043A) into the KH primary West plane on August 28, 2013. The most important of these posts can be found here (Sep 16, 2013), here (Oct 12, 2013) here (Dec 22, 2013), and here (Feb 1, 2014).

One of my predictions was that USA 186 (2005-042A) would be moved from the primary West plane to the secondary West plane, 10 degrees west in RAAN from the primary plane.

Indeed, it initially seemed to keep to my prediction as mid-November 2013 USA 186 made a manoeuvre that involved a 1-degree inclination change. As a result it lost its sun-synchronous precession rate and started to drift westward relative to the other KH-11 satellites, moving orbital plane out of the primary West plane towards the secondary West plane. Its precession rate was such that it would reach a 10-degree difference in RAAN with the new primary plane satellite, USA 245 (2013-043A) near Feb 6. I therefore expected USA 186 to manoeuvre near that date, a manoeuvre that should entail an orbit circularization including a significant lowering of the apogee (after which the orbit would be sun-synchronous again and the westward drift would stop). So as Feb 6th neared, we held our breath.

And nothing happened. USA 186 did not manoeuvre.

It is still drifting westwards, at a rate of  0.12 degrees/day relative to the other KH-11 satellites. My prediction failed.

click images to enlarge

Greg Roberts in South Africa did a good job in tracking USA 186 right up to February 12. As his southern hemisphere summer observing window was coming to an end, he could no longer follow it after that date. Luckily, it is coming in reach of northern hemisphere observers, and Cees Bassa in the Netherlands picked it up on February 21 with the first Northern hemisphere observations of 2014.

Now USA 186 has not manoeuvered, it is time to entertain my alternative scenario which I presented near the end of this post on Dec 22 and this post on Feb 1.

That alternative scenario is that the drift will continue until the difference in RAAN between USA 186 and USA 245 amounts to 20 degrees (instead of 10 degrees). This is a RAAN difference similar to that between the primary and secondary East plane satellites, USA 224 and USA 161. It would create a 90-degree angle in RAAN between the outermost, secondary East and West plane satellites (USA 161 and USA 186).

At the current drift rate, these values will be reached early May.

It is clear that the current, drifting orbit of USA 186 is not an intended end state. The orbit is not sun-synchronous, a must for an optical reconnaissance satellite. The inclination change it made mid-November 2013 is such that a manoeuvre into a ~380 x 400 km orbit similar to USA 161 in the secondary East plane will restore a sun-synchronous precession rate. So that appears to be the intended goal in the future. The current non sun-synchronous orbit is meant to let the RAAN drift up to a desired value. The question now is, what final RAAN value relative to the primary plane is intended.

My guess, now it has turned out to be not 10 degrees, is 20 degrees.

Meanwhile, another question is what they intend to do with the "old" secondary West plane satellite, USA 129 (see the post here).

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 Spaceweather.com 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 Spaceweather.com.

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.

An ISS transit over the moon, and supernova SN 2014J again

Yesterday evening 9 February near 23:38:30 local time (22:38:30 UT) the International Space Station (ISS) made a transit in front of the moon, as seen from Leiden.

click image to enlarge

While the pass itself was good (the transit occured at 45 degrees elevation),  atmospheric conditions were far from perfect. The evening started clear, but as I was setting up the Celestron C6 fields of clouds came in. There was a strong wind rocking the telescope tube.While focussing on the moon, I noted that the seeing was abysmal: the lunar disc trembled and shivered from atmospheric turbulence, and rolling waves went over it, as if it was reflected on the surface of water. Test shots showed a much more blurred moon image, even at 1/400s, than I am used to with this instrument.

The final minutes were tense. A field of clouds came in and covered the moon minutes before the transit would start. Near the horizon I could see even thicker clouds. In the last two minutes before the transit, a gap in the scattered clouds appeared. At the moment supreme, 22:38:29 UT, the moon was right in this clear gap!

Three images out of a rapid burst series started a few seconds before the calculated transit time captured the ISS, as a ghostly dark bat in front of the moon. Nothwithstanding the bad seeing, wind and perhaps a slightly too long exposure time (1/400 second), structure is visible: the ISS solar panels are well visible for example.

The ISS was at a distance of 575 km over the British channel during the transit,  with an apparent size near 48". The transit took less than 1 second. As the ISS was not illuminated by the sun, it was visible as a dark silhouet (see the image above).


M82 and supernova SN 2014J

A few days earlier, in the evening of February 4, the sky was clear and I photographed galaxy M82 with supernova SN 2014J again. The wide field image below, a stack of 34 x 15 seconds at ISO 2000 also shows nearby spiral galaxy M81. The arrow points to the supernova:

click image to enlarge

USA 129 does a Mark Twain!

As I wrote in a previous post last week, the KH-11 Keyhole/CRYSTAL optical reconnaisance satellite USA 129 (1996-072A) had not been seen since January 27. We therefore presumed it might have been de-orbitted, as it is very old (17+ years, the longest operational lifettime of any of the KH-11's) and USA 186 is to take over its former orbital plane in two days from now.

We were wrong: USA 129  is still alive!

Greg Roberts observed it from S-Africa last night, after a dedicated 2.5 hour plane scan, and observed it over two passes. A quick fit to his observations by Ted Molczan suggests that the perigee of the satellite might have been brought significantly down, to 240 km (was 310 km). More observations are needed to say anything more about this.

This is something new. I really did not expect USA 129 to manoeuvre into a new orbit.

It should be noted that Ted Molczan already had a hunch about this: as USA 129 was running a bit late when Greg observed it on Jan 27th, Ted felt this could indicate it had made a manoeuver in the hours just prior to Greg's observation. It is now clear he was right: kudos to Ted!

The question now is: what does it mean? Do they have some new purpose for the satellite? At its age of 17+ years, that would be amazing! This is option #1 and perhaps the preferred option. The new orbit appears to be sun-synchronous, which is preferable for an operational optical reconnaissance satellite.

Or is this all in preparation for a de-orbit later (option #2)?

If they are running low on juice for example, they might have opted to bring the perigee of USA 129 down as far as possible and next use natural decay to bring down USA 129 even more, to say 150 km, and then do a final de-orbit burn (option #3). This is a scenario a bit similar to what NASA did with UARS in 2011 (except that they could not do a final de-orbit burn and had it re-enter uncontrolled, something which I don't expect for USA 129). But that is (extremely) wild speculation.

It will be interesting to see what happens with USA 129 the coming days, weeks and months.

Another interesting moment will be reached in two days from now: will USA 129's younger sister ship USA 186 (2005-042A), indeed be boosted into a more circular orbit, as I expect?

OT - Supernova SN 2014J in Messier 82

This is off-topic as it is not satellite related: but cool enough to warrant a post.

As about every astronomy afficionado will know by now, a Type Ia supernova was discovered in the relatively nearby bright galaxy M82 in Ursa Major (the Big Dipper) on January 21, 2014. The supernova, SN 2014J, was discovered from London (!), UK, by astronomy students of University College London during a teaching session. Being relatively near, it is relatively bright: about mag. +11.5 upon discovery, it currently is peaking at mag. +10.5.

Weather was very bad here in the Netherlands over the past two weeks: clouds, rainshowers, and strong haze (especially in the coastal region where I live). As my frustration grew, I scheduled a 'remote' image session using the 0.81-meter Ritchey-Chretien (the same telescope I frequently use for my asteroid observations) of Mt. Lemon Sky Center (MPC G84) in Arizona, USA. Below is a single 30 second exposure which I made with this telescope on January 29. The arrow points to the supernova:

click image to enlarge

Of course I was still hoping for clear skies in the Netherlands, so I could try to observe and image the supernova with my own Celestron C6 Schmidt-Cassegrain. As day after day of bad weather passed, my frustration grew. I was pretty miffed when a few days ago an evening started clear, but haze came in while I was setting up the telescope. Grrrrrrrrr!!!!!!

Yesterday evening my luck finally changed: a nice clear sky at last! I set up the Celestron C6 and after some quick aligning, pointed it to M82 and M81 in the Big Dipper using a 38x magnification.

Both galaxies were easy to see, even from the middle of Leiden. And there it was: the cigar shape of M82 had a tiny but well visible star somewhat off-set from the center: supernova SN 2014J!

This was the second time I visually observed a bright supernova in another galaxy: almost exactly 15 years ago, in February 1989, I had seen supernova SN 1989B in M66 with my old 4.5" Newton.

After a satisfying visual look, I attached the Canon EOS 60D to the telescope and took a number of 10-second images (as my telescope had not been entirely well polar-aligned, longer exposures were not possible). Below is a stack (digital summary) of  33 images of 10 second exposure each, taken with my Celestron C6 15-cm Schmidt-Cassegrain (with F6.3 focal reducer) in the evening of February 1 near 22:55 UT:

click image to enlarge

[UPDATED] USA 129 de-orbitted [NO!]? And USA 186 about to manoeuvre?

UPDATE 04 Feb 2014: USA 129 was NOT de-orbitted! Greg recovered it on Feb 3. It appears to have manoeuvered into an orbit with a much lower perigee. More here.

USA 129, the oldest orbiting member of the KH-11/CRYSTAL optical reconnaissance satellites, appears to have been de-orbitted during the past week.

(click image to enlarge)

USA 129 on 28 September 2013
RIP ?

On January 27, Greg Roberts in South Africa observed USA 129 (1996-072A) and USA 186 (2005-042A), two of the west plane KH-11 satellites. When he observed again on January 30, USA 129 was gone. He could not spot it on two good passes that evening.

This non-observation raises the serious possibility that USA 129 has been de-orbited somewhere between Jan 28 and Jan 30, 2014. [Update 4 Feb 2014: it was not!]

A de-orbit fits into expectations. In September and October, I published a number of analytical posts on the past and future of the KH-11 KeyHole/CRYSTAL constellation. They detail how I think/thought the constellation of KH-11 satellites will be re-arranged following the lauch of a new satellite, USA 245 (2013-043A, NROL-65), into the primary West plane of the constellation on August 28, 2013. The two most pertinent of these posts are the ones here and here.

So far, my predictions seem to have been quite in line with what consequently actually happened. I suggest that this week will see the closing overture of this spatial spy satellite ballet.

I earlier predicted that after a few months of checkout of the newly launched USA 245, the older USA 186 would be moved from the primary West plane to the secondary West plane, by shifting the RAAN of its orbit 10 degrees more westward. In doing so it would take up the position formerly filled by USA 129 during its extended mission. I also predicted that USA 186 will at some point drastically lower apogee, slightly raise it perigee, and circularize it's orbit. I in addition expected USA 129, which was over 17 years old, to be de-orbitted near the moment those goals were attained.

The latter (the de-orbit of USA 129) seems to have happened in the past few days.

So far USA 186 has also been keeping to the plan. In mid-November 2013 (on or near 12 November), USA 186 made a manoeuvre that changed its inclination by 1 degree (see my post here), causing the satellite to temporarily lose sun-synchronisity and causing it to gradually drift in RAAN from the primary West plane towards the secondary West plane. It is nearly there now. At the current drift-rate (delta 0.12 deg/day relative to the sun-synchronous drift value of the other KH-11 satellites), it will reach the former orbital plane of USA 129 and a 10-degree separation in RAAN from USA 245 (now the sole satellite in the primary West plane) within a week from now, on February 6, 2014.

click image to enlarge

The image above shows how as a result of the Nov 12 manoeuvre, the orbital plane of USA 186 gradually drifted (and as of this writing on Feb 1 still drifts) from the primary West plane to the secondary West plane between November 12, 2013 and February 6, 2014. This is exactly what I predicted to happen back in September and October.

(in the images above, the grey line is the orbit of USA 245, the white that of USA 186, and the red that of USA 129)

The next step is that I expect a large manoeuvre by USA 186 on Thursday February 6th, in which it lowers it's apogee (currently at 975 km) to ~390-400 km, and slightly raises its perigee (currently at 260 km) to ~380-390 km, attaining a much more circular and on average lower orbit with eccentricity close to 0.00055 (currently 0.05) and Mean Motion near 15.59 revolutions/day.

The current orbital inclination of  96.91 degrees is already very close to the 96.99 degree value with which such a 390 x 400 km orbit is sun-synchronous. Lowering apogee and perigee to these values hence would restore a sun-synchronous orbit and stop the drift in RAAN relative to the other satellites in the constellation. As such, the 1 degree inclination change in the satellite's orbit introduced mid-November might be a strong clue that indeed a 390 x 400 km orbit (similar to USA 161, in the secondary East plane) is intended.

click image to enlarge

The image above shows the KH-11/CRYSTAL constellation as of 28 January 2014, and excluding USA 129 which was de-orbitted on or very shortly after that date. The small yellow arrow perpendicular to the orbital plane of USA 186 indicates that I expect it to shift by an extra 0.6 degrees over the coming week.

The image below shows how the constellation will look like after the apogee-perigee changing manoeuvre which I expect USA 186 to make on Feb 6. Note the lower, more circular orbit of the latter compared to the image above:

click image to enlarge

click image to enlarge

As a caveat, there is a very small, alternative possibility that USA 186 will not manoeuvre on Feb 6th. In that case, it will keep drifting another 2.5 months untill the RAAN (orbital plane) difference with USA 245 reaches 20 degrees (and the RAAN separation of the outermost, secondary E and W planes 90 degrees). My hunch is however that this will not happen, and USA 186 will manoeuvre on Feb 6th into a sun-synchronous orbit with RAAN 10 degrees from the RAAN of USA 245, as explained above.

Note: many thanks to Greg Roberts, South Africa, for keeping an eye on the KH-11 satellites during the Northern hemisphere winter blackout!

ISS and Orbital-1 Cygnus, 5 hours before docking

click image to enlarge

This morning near 6:56 local time (5:56 UT) I had a visible pass of the International Space Station ISS and the Orbital-1 Cygnus commercial cargoship bringing supplies to the ISS, five hours before the latter would dock to the first. The pass had a maximum elevation of 28 degrees, in the S-SE.

The Cygnus was faint: for most of the pass it was not visible by the naked eye (nor visible in my imagery, taken with an EF 2.0/35mm lens at F2.2 and 500 ISO).

Near 5:57:05 UT however, it briefly flared to mag. +2 and the duo ISS-Cygnus then became  well visible as a result, low in the sky at about 23 degrees elevation. They were quite close, with a pass-time difference in the order of 8 seconds. As always, seeing two spacecraft this close was an impressive (if brief) sight!

click image to enlarge

An unknown object in (near) Geostationary orbit: Express AM-5?

The evening of December 29 2013 started clear, so I did a small survey of a part of the geostationary belt. Main focus of the session was PAN, as well as Mentor 4 and 6.

Inspecting the images I found an unidentified object in near-Geostationary orbit some 4 degrees east of PAN, between Mentor 6 and NSS 5, on several images (positions here). The image below shows it near M42, the Orion nebula, near 19:17 UT:

click image to enlarge

In addition to the UNID you can also see a classified satellite at left, Mentor 6 (2012-034A), a SIGINT satellite also known under the code name Advanced Orion. At right are two commercial geostationary satellites, NSS 5 (1997-053A) and Galaxy 26 (1999-005A).

Cees Bassa in the Netherlands and Greg Roberts in South Africa also observed what is likely the same UNID object later that night. While it is not easy to fit a reliable orbit to such a relatively short span of observations, the suggestion is an object with an inclination near 0 and a Mean Motion of about 0.92 revolutions per day, i.e. an object near Geostationary altitudes.

The Mean Motion could suggest an old object being moved to a Graveyard Orbit. If this is the case, we haven't been able to identify which 'old' object it is yet.

Another option is that this is a new object. The only likely candidate in that case is the Russian satellite Express AM-5 which was launched on December 26th. This object seems to have been temporarily "lost" by JSpOC: as I write this (Jan 2),  Space-Track does not list orbital elements later than December 26th (when it was still in  a temporary transfer orbit).

For the moment, Mike McCants has given it the name UNK 131229 (with the acronym UNK meaning "Unknown").

This observing session also served to check on PAN (2009-047A). PAN is a highly mobile satellite and often moves position in May and December (I have written on the mystery of this satellite before). Not this time, it seems: it is still at the position it has been in for several months, forming a trio with the commercial satellites Yahsat 1B and Intelsat 10:

click image to enlarge

Other classified objects imaged this night were the old SIGINT Mercury 1 (USA 105, "Advanced Vortex", 1994-054A), and the SIGINT Mentor 4 (USA 202, 2009-001A). Mercury 1 was placed at 48 E and recovered by me about a year ago.

click images to enlarge

During this observing session, I captured a bright irregular orange light moving across the sky: a 'Thai Lantern' ( a miniature hot-air balloon). They are the cause of many false fireball and re-entry reports. Here it is, moving through Orion while carried by the wind:

Two days earlier, on December 27, I also did my periodic check on Prowler (90-097E), using the 61-cm Cassegrain of Sierra Stars Observatory in Markleeville, California (MPC G68).

I concluded the evening of the 29th by making some shots of M31, the Andromeda Galaxy. Unfortunately, some thin haze came in after a while. The image below is a stack of 16 haze-free images of 30 seconds exposure each, with a CLS filter (against light pollution - the images were taken from Leiden town center)) and Zeiss 2.8/180mm lens piggyback on the mount of my C6:

click image to enlarge

Guest post at ESA's Rocket Science blog

On request of one of the editors I have written a long guest post for ESA's Rocket Science blog titled:

  "Predicting GOCE re-entry: a citizen- scientist’s view"

The post details how I tried to forecast GOCE's re-entry time and position, using Alan Pickup's SatAna and SatEvo software. It provides some information about what factors are involved, and what problems you bump into. Basically, it is a consolidation and extension of posts that earlier appeared on this SatTrackcam blog.

Read the post on ESA's blog here.

USA 186 (Keyhole KH-11/Advanced CRYSTAL) is moving orbit, as expected

In a series of previous posts culminating in the October 12 summarizing post here, I scetched a scenario of what I think will happen to the Keyhole/KH-11/Advanced CRYSTAL constellation of high-resolution Optical reconnaissance satellites following the launch of USA 245 on August 28.

The first part of that scenario now seems to be happening: USA 186 has moved orbit.

This happened slightly earlier than I anticipated, but it does seem to be the first change in a series of changes right along the lines I expected.

The KH-11's are currently almost inobservable from the northern hemisphere (and hence my location) due to the "winter blackout". In the southern hemisphere, where it is summer, South African observer Greg Roberts has however been tracking them.

On December 10, Greg failed to recover USA 186 (2005-042A) in its old orbit. Earlier I predicted that this would happen at some point, as the satellite would likely be moved several degrees in RAAN from the primary West plane to the secondary West plane, which are 10 degrees apart in RAAN. See my earlier post here for a discussion of primary and  secondary orbital planes.

This made Greg next search for USA 186 in orbital planes more west of the original one. Indeed, on Dec 17 he recovered USA 186 in a more westward plane.

The new orbit as calculated by Ted Molczan from Greg's orbservations shows that the satellite lowered its orbital inclination by almost a degree, to 96.9 degrees. This manoeuvre probably happened on or near November 12th.

As a result of the inclination change the orbit is no longer sun-synchronous and hence its rate of precession changed. As a result its RAAN is currently shifting westwards relative to the other KH-11's. On December 17 the RAAN of USA 186 had already shifted westwards by 4 degrees. I suspect it will keep precessing until it reaches a value 10 degrees west of what it initially was (see my earlier predictions here, where I predicted this shift in RAAN), close to the aged West plane secondary satellite USA 129 (1996-072A). This shift will have been accomplished by early February at the current rate of precession (0.868 degrees/day or -0.12 degrees/day relative to the sun. Taking into account the RAAN precession of USA 245, they will have a separation of 10 degrees in RAAN by February 5).

USA 186: old orbit (red) and new orbit (white, December 17 plane)

The new orbit is still precessing westward over time. I expect

this will stop once it reaches the RAAN of USA 129 (grey)

I also suspect that next the satellite will reduce apogee altitude to attain a near-circular 390 x 400 km orbit, after which it will be sun-synchronous again. Indeed, the change in inclination to 96.9 degrees indicates as much as this inclination value fits a 390 x 400 km sun-synchronous orbit. As a result, USA 186 would start to move in an orbit very similar to USA 161 (2001-044A) in the secondary East plane in terms of apogee, perigee, inclination and eccentricity as well as in ground-track repeat patterns.

The initiation of these moves comes two months earlier than I expected, suggesting that USA 245 (2013-043A) which was launched into the primary West plane last August 28, needed less check-out time after launch than was the case with USA 224 (2011-002A).

As USA 186 is now moving to take the place of the aged USA 129 satellite, I expect the latter to be de-orbitted any moment.

Below diagram depicts the current constellation (December 17th), with USA 186 on the move westwards between the primary West plane (now occupied by USA 245) and secondary West plane (occupied by USA 129). See my earlier post here for a discussion of primary and  secondary orbital planes.

It will be interesting to see whether the drift in RAAN of USA 186 relative to USA 245 indeed stops at a 10 degree difference (the former separation of the orbital planes of USA 186 and USA 129), or whether it perhaps continues up to 20 degrees (the separation of the orbital planes of USA 161 and USA 224 in the East plane).

Gaia launch event, Noordwijk SpaceExpo

On 19 December at 9:12 UT, a Soyuz rocket with a Fregat upper stage carrying ESA's 2-tonne astrometric space telescope Gaia lifted off from Kourou in French Guiana. It's destination: the L2 Lagrange point of the Sun and Earth, some 1.5 million kilometer from the latter.

Gaia artist impression (ESA)

  (wikicommons)

ESA, the Dutch Research School for Astronomy NOVA, the Netherlands Space Office NSO and TNO organised a launch event at Noordwijk SpaceExpo on the morning of the launch, and Marieke Baan of NOVA was so kind to invite me for this event. As part of the event we all watched the launch Live on a big screen, with live narration by Juan de Dalmau, and next awaited confirmation of the separation of Gaia from the Fregat upper stage and the crucial last bottleneck, the deployment of Gaia's folded sun shield.

At the launch the audience was 'as silent as a mouse' as we say in Dutch. Applause was there following successful separation from the Fregat stage, and again upon confirmation of the solar shield deployment. The short video below shows the first two of these three moments:




  
The audience largely consisted of people from the Space Industry and journalists, and apart from watching the launch live on the big screen, they were treated on small lectures by a few of the people involved in the project. Marieke Baan (NOVA) acted as a moderator of the talks.

After an introduction by Juan de Dalmau we first watched the launch broadcast. This was followed by a very fine lecture by ESA astronomer Rene Laureijs, who detailed what work Gaia will do and what techniques it will employ. Next, Leiden astronomer Simon Portegies  Zwart told us what 'revolution' Gaia will bring to astronomy. This was followed by a technical talk about the development of the equipment by TNO's Wim Gielesen.

 Renee Laureijs (ESA) lecturing

Over the next five years, this telescope will record positions, distance and proper motion characteristics of one billion stars, creating a detailed 3D map (or 4D, given that movement in time is involved...) of our galaxy. It will do so 50 to 100 times more accurate than previous efforts, and for about 10 000 times as much stars.

In the course of this work, the satellite is expected to also record positional data on some 300 000 asteroids in our solar system, detect the tell-tale signs of exoplanets with other stars, as well as record Quasars and transient phenomena such as supernovae in other galaxies, not to speak of providing more insights into stellar evolution. It is also expected to measure the bending of starlight by the sun's gravitational field and in this way test Einstein's General Theory of Relativity.

The only thing it does not seem to do is brew a decent cup of coffee...

The sensor of the satellite is equivalent to a 1000 megapixel CCD. For about 1 billion stars, Gaia will determine on average 70 positions per object (and in some selected cases more), measured over a 5 year operational period. It will measure their positions, do photometry and determine the object's radial speed. It does so by means of parallax measurements with an accuracy of 0.026 milli arcseconds (!). To give you an idea of this accuracy: it means the positions are pinpointed with no more leeway than the diameter of a Euro coin at the distance of the moon.

Starting in May 2014, the satellite will produce 40 Gb of data per day, for five years. In other words: an incredible amount of data.

A Dutch-Italian girl named Gaia was a special guest

The Netherlands plays an important role in this mission. Part of the initial data processing will be done here. Much of the spacecraft's frame and optical assembly were developed and built by TNO, while Dutchspace built a crucial Real-Time Simulator (RTS).

GOCE re-entry photographed from the Falklands?

This has just appeared on Twitter:

@BBCAmos We saw GOCE satellite burn up over East Falkland at about 9.20pm last night. pic.twitter.com/KpFGAYALkY
— Bill Chater (@Cheds23) November 11, 2013

Reported time and geographic location seem a match (21:20 Falkland time is 00:20 UT)!

Alas, poor GOCE, I knew him well...

click map to enlarge

Last night just after 0h UT, GOCE, ESA's Gravity Field and Steady-State Ocean Circulation Explorer, died an heroic death, plunging into the atmosphere while passing over the ice cold wastes of Antarctica, within minutes of passing over the Falkland islands.

ESA reported the decay time as "close to 01:00 CET on Monday 11 November" (= close to 00:00 UT, Nov 10-11).

USSTRATCOM gives a final TIP placing decay at 11 Nov 00:16 UTC +/- 1 m near 56 S 60 W.

My initial last pre-decay forecast, made in a haste late last evening after returning from a full day surveying in the field (later more on that...), was too early.

This was before the final few orbits for GOCE were published, and before I learned from Alan Pickup of a secret setting in SatAna and SatEvo that makes it possible to tweak details that are important in the last few orbits at very low altitude. My tweet at that time:

Reentry forecast #GOCE: Nov 10, 22:10 UT +/- 25 min #GOCEreentry
— Dr Marco Langbroek (@Marco_Langbroek) November 10, 2013

As this window was including a pass over Australia, I also tweeted:

Observers in mid-Australia: watch if #GOCE is perhaps reentering above you NOW @drspacejunk
— Dr Marco Langbroek (@Marco_Langbroek) November 10, 2013

ESA however next reported having received telemetry from a GOCE pass at 22:42 UT from Troll station on Antarctica, making clear GOCE was still alive and functioning while only just above 110 km altitude!

So my 22:10 UT forecast was wrong. We now know it was wrong by an hour two hours, actually.

Alan Pickup mailed me around that time about some 'hidden' experimental options in SatAna and SatEvo that take into account spacecraft dimensions and some dimension-related effects that are significant at very low altitudes only.

Together with the addition of two more orbital updates that have since appeared, I have therefore re-done the exercise, as an "aftercast".

With solar flux at 154, a 0.3 day tle arc (the last 5 available orbit updates) processed in SatAna and the result then fed into Satevo, and setting the length of GOCE at 5.0, I get re-entry at:

11 Nov 00:13 UT +/- 14 m
69 S, 52 W

This is only 3 minutes from the time given by USSTRATCOM.

In the map on the top of this post, the blue dot gives the USSTRATCOM position, the red dot and red line give the SatAna + SatEvo nominal  prediction and window.

Below is the SatEvo result in 3D, looking towards the south polar region:

I am rather surprised about how well (after tweaking some internal settings) the final SatEvo result compares to USSTRATCOM's final TIP. Kudo's to Alan who wrote the software! (of course, and Alan agrees, the near-perfect match can be a lucky coincidence).

The diagram above shows how quickly GOCE dropped in the end. The last available orbital elements from an epoch about an hour before reentry, are for a perigee altitude of only 110 km! A day earlier the perigee was still at 150 km altitude.

One of the most amazing things about the re-entry of GOCE is that the spacecraft retained its drag-reducing attitude right up to the end. The designers of the spacecraft deserve some serious kudo's for that.

Of all the ways a spacecraft can go, GOCE died gracefully and heroically!  GOCE, clutching on to life to the bitter end, victim of the same forces that it helped map in so much detail. Now let us mourn our brave little spacecraft...

R.I.P.
GOCE

(17 Mar 2009 - 11 Nov 2013)

(here imaged 1.5 months before it's re-entry)

Brief update on Goce (9 Nov): one day from reentry!

My current re-entry forecast for GOCE, made with Alan Pickup's SatAna and SatEvo software, is re-entry in a 11.3 hr window centered on Nov 10.806 UT.

Any deviation from the nominal value is more likely to be towards the later part of that window (i.e. up to the early hours of Nov 11 is possible) unless attitude control fails earlier, in which case it will come down earlier.

Due to circumstances I will not be able to update my forecasts tomorrow. I will do an "aftercast" on Monday.

Another brief update on #GOCE, 8 Nov 2013

The average orbit of GOCE is now below 172 km altitude, with perigee below 170 km. It is hence approaching the critical value of 150 km.

 
Due to the effects of several recent solar outbursts on the atmosphere, drag levels went up and fluctuated over the past 1.5 days (see ESA's blog here and the diagram below). This makes forecasting difficult. Forecasts at different times today varied as a result, but they all are somewhat earlier in time than they were yesterday.

The forecast at the moment of writing (SatEvo prediction on a 1-day SatAna arc up to Nov 8.55 UT) is for a 1-day window centered on Nov 10.7 UT. With the same caveat as in my previous posts: this forecast assumes GOCE will keep its drag-reducing attitude up to re-entry, which is by no means certain.

USSTRATCOM has issued two first TIP-bulletins for GOCE, yesterday and today. The last of these forecasts is re-entry at Nov 11.12 UT, +/- 48 hours.

Brief GOCE update, 7 November

This morning the average orbital altitude of GOCE had dropped to 181 km. The orbital droprate is now near 6 km per day. There is no sign yet that attitude control is failing.

The nominal re-entry forecast is slightly shifting backwards. My current forecast using Alan Pickup's SatAna and SatEvo software is re-entry in a 1.5 day uncertainty window centered on Nov 11.17 UT. This is assuming that the attitude control will hold until decay (see discussions in previous posts).

Brief (semi-) daily GOCE update, 6 November

GOCE's perigee is now below 183.5 km, the average orbit has dropped to 187 km (from 227.5 km originally). The orbital droprate is now close to 5 km/day.

The nominal forecast re-entry window is currently a two-day period centered on Nov 10.90 UT. However, see the caveat in my previous post. If GOCE loses its current drag-reducing attitude (flight orientation), the re-entry forecast above will turn completely obsolete.

A more elaborate explanation of factors involved can be found in my previous post, including an explanation on why re-entry forecasts for GOCE must be approached very cautiously.

Forecasts were made using Alan Pickup's SatAna and SatEvo software: for an explanation on the workings of this software and factors of influence, see an earlier post here.

GOCE update (5 Nov 2013)

GOCE, ESA's Gravity Field and Steady-State Ocean Circulation Explorer, is still steadily coming down (see previous posts). This morning, the average orbital altitude had dropped below 191.5 km (from originally 227.5 km before Oct 21) and perigee is already down to 188 km. The orbital altitude has dropped 36 km in 15 days and it is currently coming down at a rate of 4.5 - 5 km per day, and increasing.

The nominal center of the re-entry forecast window, a period of several days, is still hovering near November 10-11. My latest forecast (issue date Nov 5.22 UT) has it nominally at Nov 10.97, +/- 1.2 days. This is the approximate date the satellite would re-enter, if it remains in its current drag-reducing attitude (orientation).

The latter caveat is an important point to note in this case and its implication should not be ignored. The special aerodynamic design of GOCE means that (much more so than for other satellites) there is a large difference in the amount of drag it is experiencing in drag-reducing attitude compared to what it will experience when that attitude is lost. If the attitude control mechanism (magnetic torques) fails somewhere during the coming days and the drag reducing attitude is lost as a result, GOCE will come down much earlier than the current forecast suggests. That is one reason to be very cautious with GOCE re-entry predictions, certainly at this point in time.

It is currently impossible to say if, and if so when, such a loss of attitude will happen. But if it does, the current re-entry forecast will be turned completely obsolete.

Meanwhile, let us not forget that GOCE is still functioning! As it spirals down to its doom faster and faster, it continues to gather valuable data on the Earth's gravitational field.

GOCE below 200 km - now one week or less from reentry

Over the past 12 days I have been covering the demise of GOCE, ESA's Gravity Field and Steady-State Ocean Circulation Explorer. Following the cut-off of its ion engine on October 21st, it is coming down, at an increasing speed. It is heading towards an uncontrolled re-entry later this month, perhaps even within a week from now.
 

 

click diagram to enlarge

The diagram above shows the increasing rate at which the orbital altitude is dropping since October 21st. As I write this, the drop rate has increased to about 4 km/day (from initially about 1.5 km/day on October 21st) and that rate is increasing exponentially, as can be seen in the diagram.

The average orbit of GOCE, at 227.5 km altitude before the engine cut off, has now dropped to below 200 km altitude. Perigee is already below 195 km. The Mean Motion (the number of orbital revolutions per day) of the satellite is increasing fast.

While it is still too early to provide really meaningful predictions, I currently have a nominal re-entry prediction for a window of a few days centered on November 10.7. It hence now seems possible that GOCE is within a week of plunging into the atmosphere.

The diagram below shows how predictions of the re-entry window have been evolving the past days (the grey line is the nominal prediction value, i.e. the center of the uncertainty window, and the dashed lines show the window of uncertainty on the prediction. The top three panels give observed and predicted solar flux; drag terms; and the orbital drop rate trend).

These predictions were made using two satellite orbital decay programs written by Alan Pickup, called SatAna and SatEvo. The program called SatAna analyses the orbital evolution over a number of recent orbit determinations and (taking into account the average solar flux for that period) fits a decay term that should be a bit more realistic than the decay terms from one single orbit only (which vary widely, see the second subwindow with B* values in the diagram above). The SatAna result and the predicted average solar flux for the next few days is next fed into SatEvo, a program that evolves the orbit into the future, up to re-entry.

The calculated moment of re-entry becomes more accurate based on orbital elements closer to decay. Currently, some 7 days before the prognosed moment of re-entry, the uncertainty window is still very large (several days), so giving an exact time at this moment is still meaningless. It is also still completely impossible to say where it will come down.

A lot can still happen the coming few days, that can drastically alter the picture. I have written about this before: e.g., if GOCE for some reason loses its current drag-reducing attitude (flight orientation) or is starting to shed bits and pieces at some point, the drag it experiences will significantly change, and with that the re-entry predictions will significantly change. Differences between the predicted solar activity for the upcoming days and real solar activity values the coming days, likewise can change the re-entry time.

(note: I thank Alan Pickup for making available SatAna and SatEvo)