Saturday, 17 November 2018

Modelling the expected orbital lifespan of Orbital Reflector [UPDATED]

Update added 18 Nov 2018, 13:15 UT:
The launch of SSO-A with Orbital Reflector has been postponed, untill after Thanksgiving.

Update added 27 Nov 2018, 12:00 UT: 
New launch date of SSO-A with Orbital Reflector is on 28 Nov 2018 at 18:31:47 UT

Artist impression of Orbital Reflector. Image: Nevada Museum of Art

In just a few days from now, on 19 November 2018 at 18:32 UT, 28 November 2018 at 18:31:47 UT Spaceflight Industry's SSO-A SmallSat Express, a cubesat rideshare mission, will launch from Vandenberg SLC 4 on a SpaceX Falcon 9. SSO-A will release as much as 64 small spacecraft into space, over a 5-hour period, from two free-flying launch dispensers.

Onboard SSO-A is Orbital Reflector, a project by my artist friend Trevor Paglen. It is an interesting object, for several reasons. It is a cubesat that will inflate a large oblong balloon of about 30 by 1.4 meter, a bit shaped like an obelisk. The balloon is made of a very lightweight, Mylar-like foil that is highly reflective. Hence the name: Orbital Reflector. When reflecting sunlight, it should be easily visible from earth.

Orbital Reflector is Art. It is a sculpture in space, one that, in theory, you can see from everywhere in the world (but about reality: see later in this blog post). Trevor teamed up with the Nevada Museum of Art for this project, and it might be the first time a Museum has created an exhibit in Space.


Artist Trevor Paglen and an early spherical precursor prototype of the balloon (now at the Nevada Museum of Art)

Orbital Reflector will be released in a circular, 575 km altitude, sun-synchronous orbit with an orbital inclination of 97.6 degrees. The anticipated moment of release from the Lower Free Flying Dispenser (LoFF) is about 2h 18m (or about 1.5 revolutions) after launch, i.e. 20:50 UT, over Antarctica. At what moment the balloon will be inflated once Orbital Reflector has been released from the LoFF, is unknown to me.

My estimated initial orbit for the object:

ORBITAL REFLECTOR
1 70000U 18999A   18323.77222222  .00000000  00000-0  00000-0 0    09
2 70000 097.6000 032.4835 0001438 157.1159 325.9970 14.97378736    01



UPDATE (27 Nov 2018):

ORBITAL REFLECTOR
1 70000U 18999A   18332.77207176  .00000000  00000-0  00000-0 0    00
2 70000 097.6000 041.3000 0001438 157.1159 325.9970 14.97378736    04
 




... but once the balloon is inflated, the orbit will rapidly change.

The Falcon 9 Upper Stage is deorbited at the end of the first revolution (see map below), near Hawaii. The deorbit-burn might be visible from eastern Europe around 19:50 UT.

click map to enlarge

Orbital Reflector should initially have been launched in the spring, but launch delays pushed the date to 19 November. Unfortunately, due to this and due to the particularities of the orbital plane it is launched into, visibility of the satellite will initially be very bad, and will remain so for weeks.

The satellite will be making late evening passes (around 21:15 local time), remaining in the Earth's shadow and hence unilluminated by the sun in the northern hemisphere. New Zealand, southern Australia and South America in the southern hemisphere may have some spotting opportunity. But for Europe and the USA, initial spotting opportunities will be zero. It is the wrong season to see a satellite in this kind of orbital plane.

So the crucial question is: will Orbital Reflector survive long enough to carry over to spring and early summer, when viewing conditions are more positive? To answer this, I have done some modelling to get an indication of what orbital lifespan to expect.


SRP and modelling lifespans

Orbital Reflector in itself will be an interesting object to follow due to its highly unusual area-to-mass-ratio. Unlike typical satellites (which do experience SRP too but to a clearly lesser degree), this object will be under significant influence of Solar Radiation Pressure (SRP). And SRP will have a clear impact on its orbital lifetime, as we know from both theory and from data on the orbital evolution of earlier inflatable balloon satellites.

Earlier balloon satellites were Echo 1 (1960-009A), Echo 2 (1964-004A), and PAGEOS (1966-056A). Like Orbital Reflector, Echo 1 and PAGEOS were 30 meters wide. Echo 2 was slightly larger at 40 meters. They were spherical in shape, not oblong like Orbital Reflector. They also initially orbitted at much higher altitudes than Orbital Reflector will do: an initial altitude of 4225 km for PAGEOS, 1030 x 1315 km for Echo 2 and  1540 x 1670 km for Echo 1.


Echo 2 during development tests in 1961. Image NASA

The orbital evolution of all these three balloon satellites showed a strong influence of SRP on the evolution of apogee and perigee altitudes. SRP "pushes" and "pulls" on apogee and perigee of the orbit, with a quickly changing orbital eccentricity as a result. The effects can be well seen in the orbital history for Echo 1 and 2 and PAGEOS (source of orbital data used to make these diagrams is JSpOC):

click diagram to enlarge
click diagram to enlarge
click diagram to enlarge

A clear pattern is visible where the orbital eccentricity highly oscillates due to SRP. It initially is quickly pumped up, lowering perigee and raising apogee, then gets back to lower values again, and this cycle then repeats.

Something similar will happen to Orbital Reflector. SRP will quickly push perigee down and apogee up, pumping up the orbital eccentricity. The progressively lower perigee at the moments SRP pumps up the eccentricity, will speed up orbital decay.

I used GMAT 2018a to model the effects of SRP on the orbital evolution of Orbital Reflector. That is not something trivial to do, as there are a number of 'unknowns' involved for which I had to make educated guesses. The results below should be taken very cautiously for that reason.

For example, SRP depends on attitude of the spacecraft with regard to the direction of the sun. That attitude will change over time, and there is the question whether the oblong balloon will be (and stay) in stable attitude or start to tumble. SRP in itself creates a torque and might induce tumbling. Issues like these will strongly influence the amount of SRP, drag, and as a result the orbital lifespan. 

There are some uncertainties in the mass of Orbital Reflector as well: depending on whom you ask, it is either 2.2 or 3.2 kg. This is important, because SRP is highly dependent on the area-to-mass ratio (and so is the effect of drag on the object). If the balloon indeed settles in a least-drag orientation after deployment, as the designers expect, the drag surface is a constant 1.97 square meter.

Because Orbital Reflector is oblong, and because of the orientation of its orbital plane with respect to the sun, the SRP surface will vary between (almost) minimum and maximum values over one orbit. I have tried to accomodate this by running the model with an SRP surface that is 50% of the maximum value, i.e. 50% of 21 square meter = 10.5 square meter.

To show the non-triviality of SRP, I first ran the model without SRP, then with SRP, for comparison.

Below are the model results for Orbital Reflector (expressed as apogee and perigee altitude against date) if we ignore Solar Radiation Pressure, for two mass values: 2.2 and 3.2 kg.

model results for a mass of 2.2 kg and no SRP taken into account. Click diagram to enlarge

model results for a mass of 3.2 kg and no SRP taken into account. Click diagram to enlarge

Below are the results if we do implement modellation of Solar Radiation Pressure. The expected lifetime clearly shortens, by up to a third, and this is because of the progressively lower perigee as SRP pumps-up the eccentricity of the orbit. The grey lines in the diagrams are the data without SRP from the previous diagrams, as a reference:


model results for a mass of 2.2 kg with SRP taken into account. Click diagram to enlarge

model results for a mass of 3.2 kg with SRP taken into account. Click diagram to enlarge

These outcomes should be viewed with caution, as the modelling includes educated guesses and, to quote Monty Python, "it is only a model". It will be very interesting to see how the real orbital evolution compares to these model outputs.

What these model results do suggest, is that it is possible that Orbital Reflector, if it inflates and stays intact, might remain on-orbit long enough to carry it into the more favourable part of the year (late spring and/or summer of 2019) for visual sightings. So let's root that my models resemble reality, as I surely would like to see and image Orbital Reflector in the sky.

From the artist impressions, the balloon is flat-sided. This could mean that reflections might be specular, and bright only briefly in narrow zones on Earth, much like Iridium flares.



Sat for Art's sake?


Orbital Reflector is Art. It is distinctly non-utilitarian, in the common sense of that word: it just orbits. But it does have a deeper purpose than that. As Trevor recently put it himself:

"Orbital Reflector was designed as a provocation. An opportunity to think about outer space, the geopolitics of the heavens, and the militarization of earth orbits. It’s a project about public space, and a project about who gets to exercise power over our planetary commons, and on what terms"
In other words, Orbital Reflector is not just there to reflect light to people on Earth; it is also meant to make people reflect, pondering questions such as "who owns space?" and "what is happening out there?".

The question raised by Trevor is pertinent. Space is Public Space. At the same time, it is not public at all, but strongly the domain and playground of Nation States, and notably of the military of those Nation States.

Space is highly militarized. Not so surprising of course as the whole Space Age has its roots in the development of Ballistic Missiles. The role of the military in Space and Space innovation is often overlooked. While many people look at NASA as the big innovator in the US Space program, the real innovations in Space are often the product of another Space Agency, the NRO, which is NASA's shadier military cousin and generally unknown to the broader public, even though it sends billions worth of hardware per year into space. Hardware that plays a prominent role in geopolitics and modern warfare. They include highly detailed optical and radar imaging satellites, navigation satellites, communication satellites and giant listening radio "ears" in space. Long-time readers of this blog know what I am talking about.


Pondering Space and other things. Trevor Paglen (right) and the author of this blog (left), June 2018

It is very interesting that the only areas where it is internationally regulated what can and cannot be done in space, concern weapons in Space and national sovereignty in space. And this was done over 50 years ago already, as part of the 1967 “Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies” (or “Outer Space Treaty” in short).

The fact that after more than 60 years of Space exploration still only the military/national sovereignty aspect has been regulated, tells you how dominant that aspect of the use of space is. Nobody bothered to regulate other potential aspects of space (such as private enterprise).

We are however at a crossroads. Ideas for mining asteroids and for private crewed missions to Mars and the Moon (previously only in the realm of Nation States) have raised the topic of  private enterprise in space, and raised specific questions about regulating the exploitation of resources in Space and protection of historic sites in Space. We are standing at a decisive moment in the use of space too now that purely commercial, privatized space outfits have appeared on the launch market, taking over from companies closely alligned to what Eisenhower called the “Military-Industrial Complex”: new outfits like SpaceX, Rocket Lab and a number of other startups.

But this does not mean that the private sector takes over from the military. Some of these private firms (e.g. SpaceX) have been quickly drawn into the military sphere themselves, with lucrative launch contracts from the US military. Orbital ATK recently has been bough by Northrop Grumman, part of the "Military Industrial Complex" for decades. Meanwhile, three major spacefaring nations, the USA, China and Russia, have increased their military posturing in space, with ASAT tests and increased suggestions within the US military that the US should re-negotiate or even leave the Outer Space Treaty, as it is seen as restrictive to a more active, offensive use of space.

It is therefore a crucial time to bring up questions about who governs space, what is and what isn’t allowed there, who gets to put things up there, and to put to question the overarching role of the military in this all.

Paglen's Orbital Reflector encourages you to reflect upon these issues.






Note: I warmly thank Trevor Paglen, Amanda Horn, Zia Oboodiyat, Mark Caviezel and Ted Molczan for discussions and for providing viewpoints and data.

Edits of 27 Nov 2018: revised launch time, revised elset estimate, new map, and statement that the deorbit-burn might be visible from N-Europe

Tuesday, 9 October 2018

Falcon 9 reentry burn from SAOCOM 1A launch observed from Europe


image (c) Koen Miskotte. Used with permission
click image to enlarge
On 8 October 2018 (7 October local time) at 2:21 UT, SpaceX launched the Argentinian Radar surveillance satellite SAOCOM 1A (2018-076A) in a sun-synchronous ~620 km orbit. The launch took place from launch platform 4 at Vandenberg in California. It was a spectacular launch, yielding spectacular launch images.

An hour later, near 03:40 UT, a bright fuzzy blue object travelling through the sky was seen from northern Europe.

This fuzzy phenomena was the Falcon 9 rocket stage (the 2nd stage) form this launch performing its re-entry burn while passing through apogee, lowering perigee such that it would reenter into the atmosphere over the Pacific Ocean southeast of Hawaii near 04:13 UT, at the end of it's first revolution.

The image above is part of an image taken by a photographic all-sky meteor camera in Ermelo, the Netherlands, operated by Koen Miskotte. It is actually a stack of 4 separate images (hence the three short breaks in the trail), of 88 seconds exposure each, taken between 03:39:30 and 03:45:28 UT on Oct 8, 2018. The bright blue fuzzy streak above the treeline is well visible.

The map below shows the trajectory of SAOCOM 1A during the first revolution. It passed over eastern Europe around 03:40 UT (in making this map I used the orbit of the payload as a proxy, as there are no orbital elements of the rocket stage. At this stage of the launch, the rocket stage will have been close to the payload in a similar orbit).

The map also depicts the deorbit area near Hawaii. The deorbit burn initiating the de-orbit happens about half a revolution earlier (some 45 minutes before reentry) in apogee of the orbit, i.e. over Europe:

click map to enlarge

A surveillance camera from a weather station in SüderLügum in Germany, near the German-Danish border, produced this spectacular time-lapse movie of the event (note the "puffs when the rocket engine is firing):




The sky map below shows the trajectory for SAOCOM 1A for Ermelo, the location of Koen Miskotte's alls ky camera (times are in CEST = UT +2). The full all sky image is given as comparison. The two match well:

click map to enlarge
image (c) Koen Miskotte. Used with permission
click image to enlarge

Thursday, 27 September 2018

More images of Kounotori (HTV) 7

click image to enlarge


The image above is a stack (combination) of six images, taken at 10-second intervals with a 5-second exposure (Canon EOS 60D + EF 2.0/35 mm, 800 ISO). It shows Kounotori HTV 7 (2018-073A), a Japanese cargoship on its way to the ISS launched on September 22. This image was taken some 17 hours before it berthed to the ISS.

The cargoship was about 1m 38s behind the ISS at the time of observation. As no recent orbital elements were available, I did not know where to expect it relative to the ISS, so I started watching well before the ISS pass, and next noted it ascending over the roof just after the ISS had disappeared in Earth shadow.

The HTV 7 spacecraft was very bright during this pass: near magnitude +1, and a very easy naked eye object. Just like the day before (see an earlier post), it flared brightly, to at least mag -1/-2 at 19:50:18 UT (26 Sep 2018). The flare can be seen on the composite image above, and on the single image from this series below:


click image to enlarge

Also note the distinct orange colour of the trail, which is due to the fact that HTV 7 is wrapped in gold-coloured insulation foil.

The flare happened while HTV 7 was passing through the field of view of my video setup:





The image below is a composite of the images taken while the ISS passed, and the images of HTV 7 passing 1m 38s later (i.e., they didn't move this close in the sky in reality!). The orange colour of HTV 7 stands out. Also well visible is that HTV 7 was somewhat faster than the ISS, due to a difference in orbital altitude (and hence orbital period):


click image to enlarge

Wednesday, 26 September 2018

Imaging a pass of Kounotori (HTV) 7 on it's way to the ISS

click to enlarge

On 22 September 2018 (and after several launch delays, amongst others due to a typhoon), at 17:52:27 UT, Japan's Space Agency JAXA launched Kounotori (HTV) 7, a cargoship destined for the ISS. It will dock to the ISS tomorrow on September 27th.

The 9.8 x 4.4 meter HTV (HTV stands for "H-II Transfer Vehicle". The name Kounotori stands for "white stork") are easily visible, bright objects with a distinct orange colour due to the use of gold-coloured insulation foils.  See the image below of HTV 7 being assembled at the Test and Assembly Building at Tanegashima Space Center before launch:

image: JAXA

After days with bad weather, the sky cleared yesterday. I had a low pass in the southwest near 19:18 UT (Sep 25) and went to the nearby city moat with my camera, as I have a better view lower at the horizon there. Some whisps of thin clouds still lingered in the sky.

First, at 19:04 UT, I watched HTV 7's destination, the International Space Station (ISS), sail past as a very bright object. The image below is a stitch of two image stacks (!): one stack of two images, and a stack of 4 images with the camera FOV shifted horizontally. Camera: Canon EOS 60D with an EF 2.0/35 mm lens. I used exposures of 4 seconds at ISO 800.

click to enlarge

Then  I waited for HTV 7. As the latest orbital elements at that point were almost a day old, I was not sure about the exact time it would show up.

Some 14 minutes after the ISS it emerged, clearing the trees and houses low at the southwest horizon, and to my surprise and joy featured a bright flare to at least magnitude -1. My first image just captured the end of this brief flare (first of the two images below):

click to enlarge

click to enlarge

The object was easily visible with the naked eye and had an orange hue. The image stack below was made of 5 images taken at 10-second intervals, with each image a 4-second exposure (camera details the same as for the ISS image). It shows HTV 7 from the bright flare to the moment it disappeared in the Earth's shadow:

click to enlarge


Tuesday, 4 September 2018

Capturing a flaring NOSS duo (NOSS 3-6)

click to enlarge

On 30 August 2018 near 20:59 UT I was imaging the NOSS 3-6 duo (2012-048A & 2012-048P) during a near-zenith pass, when they briefly flared. They were at a sky elevation of 77.5 degrees at that time.

The image above is a stack of the video frames showing the flaring spacecraft: the flare of the leading P component was captured just before it peaked (I was adjusting the camera FOV during the seconds before it), the flare of the A component was captured in its entirety. Below is the video itself from which these frames were extracted (video shot with a WATEC 902H + Canon FD 1.8/50 mm lens):





I next used LiMovie to analyse the video and extract brightness curves from the video frames, with the following results. The data points shown are 3-point averages of the raw data. small discontinuities visible in the curves are where the satellite passed a star:

click diagram to enlarge

click diagram to enlarge

The leading P component seems to exibit only one flare peak. The traling A component shows an interesting  double or tripple peak. The centroids of the peaks of the P and A component were some 6.5 seconds apart.

In the diagram below, I have transposed both curves on each other by shifting the curve for the A component along both axes untill it matches that of the P component:

click diagram to enlarge

What can be seen is that the curve for the A component pre- and post-peak follows the pattern of that of the P component, but unlike the P component it shows a pronounced valley at the peak, with a small secondary peak in the valley bottom. The shape of the valley is the inverse of the peak shape of the P component. Intriguing!

The rather sudden change in steepness some seconds before and after the peaks as shown by both components is interesting too. The main peak shape is slightly asymmetric.

One option for the difference in the shape of the curve for the A component (i.e. for the "valley"at the top) might be the presence of a rotating component interfering with the flare pattern caused by the satellite body, perhaps.

NOSS (Naval Ocean Surveillance System) satellites are SIGINT satellites operated by the US Navy to locate shipping, based on geolocation of the ship's radio emissions. They are also known by the code name INTRUDER. They always operate in close pairs, such as can be seen on the video.

The P component peaked at 20:59:11.85 UT (Aug 30, 2018), at position RA 313.222 DEC +45.628. The A component has a first major peak at 20:59:17.33 UT at RA  313.331 DEC +45.077; the small secondary peak at 20:59:18.37 UT at RA 313.765 DEC +45.307; and a third major peak at 20:59:19.33 UT at RA 314.170  DEC +45.518. The two major peaks are 2.0 seconds apart.

Wednesday, 29 August 2018

The X-37B OTV 5 is manoeuvering to a higher orbit

click to enlarge

The image above shows the classified robottic X-37B space-plane OTV 5 of the US Air Force, a kind of unmanned mini Space Shuttle, in the sky above my home on August 20. It had manoeuvered in the previous days (probably on August 17 or 18), from an approximately 316 km orbital altitude to 325 km orbital altitude, an orbit raise of ~9-10 km. The video below shows it the next night, passing through Delphinus:





Just two days later, on August 22, OTV 5 was a no-show, indicating another, and major manoeuvre. Three days later, Leo Barhorst found it again, and subsequent observations showed it to had moved into a 387 x 395 km orbit. A total orbital raise of some 75 km in series of manoeuvers spanning a few days.

As can be seen in the diagram below, which is based on amateur tracking data, the orbit of OTV 5 had been rather steady from when Cees Bassa first located it in late April 2018 up to mid August, at an orbital altitude of ~316 km. The orbital raises mid and late August to ~325 km and next to ~391 km could point to a new test regime for the experimental equipment onboard.

click diagram to enlarge


click to enlarge
The X-37B (image: US Air Force). Click to enlarge

Wednesday, 4 July 2018

OT: the bright fireball of 29 June 2018, 21:30:14 UT

image (c) Felix Bettonvil, Utrecht. Click to enlarge

Barely two weeks after an earlier brilliant twilight fireball discussed in a previous post appeared over the Netherlands, another bright fireball was observed, again in bright evening twilight. This fireball of about magnitude -6 occurred on 29 June 2018 at  21:30:14 UT (23:30:14 local time). It had a duration of over 3.6 seconds.

The fireball was photographically well covered this time, as it was captured by six all-sky meteor cameras (Borne, Bussloo, Dwingeloo, Ermelo, Utrecht and Wilderen) plus by an amateur astronomer from Kerkrade who was making a time lapse of the night sky. The image above (courtesy of Felix Bettonvil)  shows the fireball as it appeared over the camera station in Utrecht. Almost literally right over it: the lateral distance between the camera position and the nominal ground projected meteor trajectory is only 185 meters!

As several stations were equipped with an electronic or rotating shutter in front of the lens (see the interuptions in the trail in the image above, at 10 breaks/second), there is speed information for this fireball as well. In fact, it delivered a very fine deceleration curve (data from stations Borne, Utrecht and Dwingeloo), showing how the meteoroid rapidly slowed down upon entry into the atmosphere due to friction with the atmosphere:

click diagram to enlarge

click to enlarge
The fireball entered from the south-southeast with a  speed of 21.5 km/s and under a low 27 degree entry angle. It first became visible at 80 km altitude over the Betuwe area near 5.416 E, 51.822 N. It ended at 43 km altitude over the western suburbs of Amsterdam, near 4.837 E, 52.360 N, with an end speed of 9 km/s. End altitude and end speed point out that nothing was left at that point: there are no meteorites on the ground.



click to enlarge
The radiant of the fireball is located in Scutum: the geocentric radiant is at RA 276.4, DEC -11.4, with a  geocentric velocity of 18.2 km/s. The resulting orbit is an Apollo orbit with an orbital inclination of 7 degrees, an orbital period of 2.15 years and aphelion at 2.7 AU. The object was hence of asteroidal origin: a very small piece of asteroid.


click to enlarge
Acknowledgement: I thank Mark-Jaap ten Hove, Johan Pieper, Koen Miskotte, Jean-Marie Biets, Felix Bettonvil and Peter van Leuteren for making their imagery available for analysis.

Tuesday, 26 June 2018

Capturing a pass of the X-37B OTV-5, and imaging an ISS transit over the Sun

click to enlarge

Yesterday evening was very clear, and the moon low in the south no real hindrance. I observed a very fine pass of the X-37B secret space plane OTV-5. It was an easy naked eye object. The photograph above (10-second exposure with an EF 2.0/35 mm lens) shows it ascending in the southwest, through Bootes (Arcturus is just above the open window).

The next morning (26 June) at 10:17:21 local time (8:17:21 UT), the International Space Station ISS was predicted to make a transit over the solar disc as seen from my house in Leiden.

I set up the Celestron C6 telescope in the courtyard, put a Baader Solar Foil filter in front of it, and hooked up the Canon EOS 60D to the prime focus. Instead of photographing at rapid burst, the technique I used for imaging with previous transits, I this time put the camera in HD movie mode. While this yields a lower resolution image than photography, the upside is that it yields more images showing the ISS silhouetted in front of the sun. And the ISS is big enough that the reduced resolution is not a real problem, the solar panels of the ISS are still well visible.

The image below is a composite of 21 frames from the resulting movie:

click to enlarge

Here is the movie itself, showing you how rapid such an ISS transit over the sun is (the total duration was only 0.8 seconds - it is over in a blink of the eye). The ISS had an apparent size of 45.8" during the transit, with the sun at 41 degrees elevation in the east:


The movie was made in the prime focus of a Celestron C6 (15-cm, F1500 mm Schmidt-Cassegrain, equiped with a Baader Foil solar filter) with a Canon EOS 60D DSLR in HD movie mode at 25 frames/second, with each frame having an exposure time of 1/4000th of  a second to avoid blurring the ISS. The track and time of the transit had been checked before the observation by loading the latest orbital elements for the ISS into Guide.

The biggest challenge with this kind of imagery is always to focus properly, certainly when the sun is spotless as it was this day. I always find focussing on the sun cumbersome. The focus this time turned out to be reasonably good though.

Thursday, 21 June 2018

OT: The brilliant "Pinkpop" fireball of 16 June 2018 (UPDATED)



In early evening twilight of 16 June 2018, around 21:11 UT (23:11 local time), a brilliant fireball at least as bright as the full moon and fragmenting into multiple pieces, appeared over NW Europe. It was widely seen and reported by the public in the Netherlands, Belgium, France and Germany. It garnered a lot of press attention, especially in the Netherlands.

The fireball notably rose to fame because it appeared over the stage of a concert by the Foo Fighters at Pinkpop, the large annual music festival at Landgraaf in the Netherlands. Here is footage of the event over the stage:



From this video, we can determine that the fireball duration was at least 1.65 seconds, and probably longer as the video clearly did not record the start of the fireball but only part of the apparition.

At first it seemed there were no records of the fireball by our dedicated meteor camera network, as it was still very early in twilight. But as it turned out the All-Sky meteor camera of Jean-Marie Biets in Wilderen in Belgium, where it is slightly darker than more north like in the Netherlands at this time of the year, had captured it in a still bright blue sky with only a few stars (and bright planet Jupiter) visible. Here is the image:


The fireball as seen from Wilderen, Belgium. Image (c) Jean-Marie Biets.
click image to enlarge

Another image, that popped up through Twitter, was made by a German amateur astronomer, Uwe Reichert from Schwetzingen, who was photographing the conjunction between the moon and Venus low in the west when the fireball shot through the field of view of his camera. That yielded this very nice picture, which also clearly shows the fragmentation into at least two fragments:

image (c) Uwe Reichert
Detail of previous image showing fragmentation. Image (c) Uwe Reichert.

(Note: while it appears as if the fireball pierces a cloud, it in reality appeared behind the cloud, being bright enough to shine through the thinner edges of the cloud. It ended well above cloud levels.)

 The Landgraaf video shows at least 5 separate fragments near the end of the fireball apparition:

Fragmentation into 5 pieces on the Landgraaf video. Click to enlarge.

Based on the Wilderen and Schwetzingen images and some quick azimuth determinations for the fireball endpoint using Jupiter, Venus, the moon and the few bright stars visible on the Wilderen image as reference, I made this cross-bearing as a quick initial assessment, suggesting the fireball appeared over the Belgian Ardennes in the southeast Belgian province of Wallonia, close to the border with Luxemburg:
click to enlarge

Next, it turned out that there was a second meteor camera image, from the All Sky camera located at Bussloo Public Observatory (Mark-Jaap ten Hove):



The fireball as seen from Bussloo, the Netherlands. Image (c) Mark-Jaap ten Hove/Bussloo Public Observatory.
click image to enlarge

Like the Wilderen image, only a few stars are visible, not enough to do serious astrometry. I therefore used a trick to get decent astrometry on the images: I asked both photographers for images from somewhat later that night. By measuring star positions on those, I could create an astrometric grid over the camera field, yielding the positions of the start and end of the fireball on both images. This means that, with triangulation, a proper atmospheric trajectory could be reconstructed.

The result is this trajectory, with the endpoint of the fireball only a few km from where my initial crude cross-bearing analysis had placed it:

click to enlarge

The fireball started over the Luxemburg-Belgian border, at 70 km altitude. It came in from the southeast under a steep angle (48 degrees with the horizontal), and ended over the Belgian Ardennes at 30 km altitude. The endpoint is located some 30 km south of Liege.

The apparent radiant of the fireball is on the Ophiuchus-Hercules border. As alas no speed information is available (the Wilderen image has no discernable sektor breaks; the Bussloo camera is unsectored), a precise geocentric radiant cannot be given, and a precise heliocentric orbit cannot be computed either.

The Landgraaf video however puts some constraints on the maximum speed: that cannot have been above 29 km/s, and was probably much less as the Landgraaf video did not pick up the fireball from the start. This is an interesting constraint. For a range of likely speeds up to 24 km/s, the resulting orbits are  all asteroidal in character with inclinations smaller than 23 degrees and aphelion within the orbit of Jupiter.

The map below shows the observed apparent radiant (blue) and geocentric radiant positions for a range of assumed speeds (red):

click map to enlarge

The fireball penetrated deeply into the atmosphere and showed fragmentation, but the lack of speed data precludes a definite statement on the end velocity and on whether something could have survived. An end altitude of 30 km is a borderline case: most meteorite droppers end lower, at 25-15 km altitude.

Acknowledgement: I thank Mark-Jaap ten Hove and Jean-Marie Biets for making available their all-sky images for analysis.

Note: the radiant map initially had a labelling error in the declination. This has been corrected

Thursday, 24 May 2018

Orbital ATK's Cygnus AO-9 cargoship chasing the ISS

click to enlarge
click to enlarge


The two images above show Orbital ATK's Cygnus AO-9 cargoshi  chasing the International Space Station (ISS), a few hours prior to berthing. The Cygnus OA-9 cargoship, launched on May 21 from Wallops Island, brings supplies (food, equipment etc.) to the Space Station.

I could observe three passes of the two objects during the night of May 23-24: in all three cases the two objects could be seenr at the same time in the sky, with the Cygnus (the fainter trail in the images above) somewhat behind ISS.

The images above are from the first pass (21:48 UT, 23:48 local time), a high pass,  and the third pass (01:00 UT, 03:00m local time), low over the southwest horizon. The Cygnus spacecraft was about 22 seconds behind the ISS on the third pass. The sky over Leiden was somewhat hazy.

The very short third trail near the ISS on the first image is Kosmos 2392.

As usual, the Cygnus spacecraft was quite faint (mag +4.5), so not an easy naked eye target. The brightness of these Cygnus spacecraft is strongly phase-angle dependent. The Dragon spacecraft of their competitor SpaceX are much brighter and easier to see.

The video footage below is from the third pass: