Sunday, 31 May 2020

Imaging a pass of the Crew Dragon Demo-2, and a close fly-by of the Crew Dragon by USA 245!

click photograph to enlarge

Yesterday May 30 at 19:22 UT finally saw the launch of the SpaceX Crew Dragon Demo-2 with astronauts Hurley and Behnken on board, returning a human spaceflight capability to the USA after nine years of having to hitch rides on a Russian Soyuz.

When the Crew Dragon first passed over the Netherlands some 23 minutes after launch (see map with the launch trajectory in  a previous post), the sun was still just above the horizon for my Leiden location. I nevertheless tried with binoculars, using the moon as a guide, but saw nothing.

But two hours after launch on the second revolution, near 21:18 UT, we did have a visible pass, albeit in late twilight and very low above the horizon: at a maximum elevation of only 9 degrees over the horizon and a range of almost 1200 km!

To observe this pass I went by bicycle to Cronesteyn Polder at the edge of Leiden, where I have an uninterupted view to the horizon, and set up my photo camera. First, at 23:14 local time (21:14 UT), I saw the ISS pass with the naked eye low on the southwest horizon. I then took to binoculars and waited for the Crew Dragon, which should pass somewhat lower in the sky some 4 minutes after the ISS.

I picked the Crew Dragon up in my 10 x 50 binoculars starting around 21:17:30 UT, while it was passing through Crater and Corvus. I watched it untill it entered Earth shadow at about 21:19:00 UT. It was not particularly bright, due to the low elevation and still bright sky background. By comparison to stars in Corvus I estimate it to have been magnitude +3 to +3.5, too faint at this elevation and with this sky brightness to be seen naked eye. It was at a range of almost 1200 km at that time, over Northern Spain!

Click photograph to enlarge

The image above shows the Crew Dragon during this pass. It is a stack of 45 exposures of 0.5 seconds each, with a Canon EOS 80D and SamYang 1.4/85 mm lens at F2.0, 500 ISO, 21:17:40 - 21:18:09 UT (May 30). Stars in the image belong to the constellations Crater and Corvus. The small breaks in the trail are the brief moments between the successive photographs that make up the stack.

The image below is another stack, this time of 52 photographs with the same camera setup, made between 21:18:25 - 21:18:59 UT. You see the Crew Dragon disappear in Earth shadow at the left end of the image. The image is slightly wobbly - my tripod was on a soft grassy surface. I like this image best though:

Click photograph to enlarge

It was pretty cool seeing the Crew Dragon, while knowing it was carrying two astronauts!

But it becomes even more interesting: in two images around 21:18:19 UT, I have another brighter satellite moving under a slant upwards in the opposite direction. You can see it in the upper right corner of this image (several lay observers saw this brighter satellite too and mistook it for the Crew Dragon):


Click photograph to enlarge


This object is the classified US KH-11 spy satellite USA 245 (2013-043A).

And as it turns out, it was really close to the Crew Dragon, and my image truely captures, within a few seconds, the actual moment of closest approach! This was serendipity, as I had not planned this and the presence of USA 245 took me by surprise.




Nominally, the minimum distance between USA 245 and the Crew Dragon during this fly-by was only 125 km with closest approach happening at 21:18:17 UT. USA 245 was flying this distance 'above' the Crew Dragon. Both objects were over northern Spain around the time of the flyby, with the point of closest approach over 43.40 N, 2.50 W, on the Basque coast.

There is some uncertainty in the actual fly-by distance (see below), but not much.

This is the output from a COLA analysis for this fly-by:

DATE      UT          SSC   NAME    TARGET      KM  
5/30/2020 21:18:16.99 39232 USA 245 CREW DRAGON 125.3

My analysis is based on CSpOC elset epoch 20151.85044152 for the Crew Dragon, and amateur elset 20146.86101776 for USA 245. There is some leeway in the exact time and distance of the flyby, for two reasons:

1)  from my observations, the Crew Dragon was some 3 seconds late on the used elset;

2)  the USA 245 elset epoch, based on amateur observations that include my own, was 5 days old. However, the sky position of USA 245 in the image is very close to the ephemeris, so the 5-day-old orbit nevertheless seems a good fit to reality.

Taking these points into account, I estimate that the uncertainty in the minimum distance between both objects is no more than 30 km, and only a few seconds in time.

In the map below, I have plotted the trajectories of both objects (I have accounted for the fact that the Crew Dragon was ~3 seconds behind on the elset in this map). USA 245 was moving nortwest-wards, the Crew Dragon southeast-wards.

Note that the USA 245 trajectory was situated some 125 km above that of the Crew Dragon. So to be clear, there was no danger of a collision. This is a safe distance.

click map to enlarge

In fact, it could very well be that this close flyby was intentional, and that USA 245 was actually imaging the Crew Dragon at that moment.

USA 245 is a KH-11 electro-optical reconnaissance satellite: a satellite that resembles the Hubble Space Telescope and makes high resolution images of the earth surface (similar to this infamous one) with resolutions of 10 cm or better.

There have long been rumors, reported by amongst others NBC News, that KH-11 satellites were used to inspect the outside of Space Shuttles post-launch (e.g. that of the inaugural STS-1 flight) for tile damage. We also suspect that KH-11 satellites inspect X-37B's after launch, based on the odd jumps in launch times of the latter (see this analysis by Bob Christy).

So there is a real possibility that this close flyby of the Crew Dragon by USA 245 was intentional, and used to image the spacecraft to see if it was not damaged and everything deployed as it should.

Saturday, 30 May 2020

New attempt to launch the Crew Dragon on May 30: trajectory

screenshot from the May 27 live webcast


In an earlier post I discussed the SpaceX Crew Dragon Demo-2 launch. Originally slated for 27 May, it was postponed (with the astronauts already seated on board) because of bad weather: Tropical Storm Bertha more north on the US coast was the main culprit.

The new launch attempt will be on May 30 at about 19:22:45 UT (the subminute time comes from Spaceflight Now, not from an official SpaceX or NASA source, so is apocryphal). If that launch is scrapped to, the third backup date is May 31 near 18:59 UT.

As things currently (29 May 21:00 UT) stand, weather prospects are not that good for both these dates either, with currently a 50% chance of a weather violation on the 30th and 40% on the 31st: so perhaps we will see a scrub again.


Click map to enlarge

But in case the launch does happen on 30 May, the map above is the trajectory the Crew Dragon will fly on its first revolution (times on the map are in UT).

Some 23 minutes after launch, the Crew Dragon will pass over Europe, along this trajectory (times are inUT: add one hour to get BST and 2 hours to get CEST):

Click map to enlarge
Note the location of the day/night terminator...only eastern and southeastern Europe has sufficiently dark skies at that moment.

The launch time has shifted considerably forward compared to the May 27 original launch date, by about 1h 10m. As a result, the pass is no longer favourable for NW Europa, as the pass will be before sunset for the UK, and around sunset for coastal Europe.

Only longitudes east of say longitude 13 deg E will have a sufficiently dark sky to see it on the first revolution, so eastern and southeast Europe will have a prime seat this time.

Coastal western Europe and the UK might have, depending on your locality, a theoretical chance to see the second pass 1.5 hours later, near 21:18 UT. For most localities, that will however be a very low elevation pass though, often at a maximum elevation of les sthan 10 degrees.

At the end of this blogpost, I will provide some sky charts for several European localities for both those localities with a chance to see something of the first pass, and those who might theoretically catch the second pass.

The reason that the launch time is 1h 10m earlier on May 30 than on May 27, is that the launch time is instantanious as it is determined by the moment that the orbital plane of the ISS passes over the launch site. This time shifts back by 23m 22s each day, as is clear from this tabel in which I calculated orbital plane crossings over LC-39A (and is visualized in the illustrations below it):

ISS plane crossing over LC-39A:
-------------------------------
Date           UT   
27 May         20:36:52
28 May         20:13:30
29 May         19:50:09
30 May         19:26:47
31 May         19:03:26

-------------------------------



You can also see in the table that the actual launch time is a few minutes before the plane crossing. This has two main reasons.

One is that what is actually of relevance is the position of the orbital plane once the rocket reaches orbital height (a few minutes after launch).

The other is that the Crew Dragon initially is inserted into a ~200 km altitude orbit, which is only half the orbital altitude of the ISS. As a result, the Precession rate of the RAAN is faster than that of the ISS: so launch has to be somewhat earlier or otherwise, over the 19 hour flight, its RAAN would overshoot rather than match that of the ISS upon arrrival at the orbital altitude of the ISS.

The reason May 28 and May 29 were not chosen as backup dates, is because of a second consideration: the ISS has to be within a certain distance window to the launch site in order for the two (Crew Dragon and ISS) to meet up after 19 hours of flight. As it happens, and I am not sure that is deliberate or just a happy coincidence, this also means that on the chosen dates, docking will happen on the night-time side of the Earth (with launch on May 28 or 29 it would have happened on the daytime-side).

Below are a number of sky maps for localities that have a dark enough sky (generally: sun no less than 5 degrees below the horizon) to see the first pass, some 25 minutes (for eastern Europe) after launch near 21:46 CEST. Note that there is a time uncertainty of about 1 minute or so.

TLE's are provided below the maps.

NOTE: if you are not near one of these localities, then Heavens-Above provides you with predictions for your custom location. Please note however that Heavens-Above predictions for the second revolution (the 23:19 CEST pass over Europe) seem to be based on the TLE for the first revolution, resulting in a time difference of about 1 minute with my predictions below.(but also realise there is an uncertainty of 1-2 minutes in the estuimated orbit anyway).










Maps for locations in NW Europe might theoretically be able to see the Crew Dragon on its second revolution, near 23:18 CEST (22:18 BST), some 2 hours after launch. But in most cases this will be very low above the horizon. Please note that the time uncertainty is 1-2 minutes at least!







Here is an estimated TLE for the first revolution:

CREW DRAGON                                      initial orbit
1 70000U 20999A   20151.80474535 -.00003603  11390-4  00000+0 0    04
2 70000  51.6423 075.0039 0122953  45.6251 315.4951 15.99554646    01



And here is an estimated TLE for the second revolution:

CREW DRAGON                                      second revolution
1 70001U 20999A   20151.93029831 -.18507952  12289+0 -23808-1 0    05
2 70001  51.6233 074.5097 0096856  46.3995 314.2887 15.95177824    03


Tuesday, 26 May 2020

Imaging some splendid passes of HTV-9 (Kounotori-9) and Cygnus NG-13



It are very busy times at the International Space Station. Spaceships come and go.

First, on May 11, the US cargoship Cygnus NG-13 was released from the ISS, three months after berthing to it. This cargoship had been launched on 15 February 2020 and berthed on 18 February. After its release from the ISS two weeks ago, it is currently free-flying to do experiments. It will perform a controlled reentry over the southern Pacific on 29 May.

On 20 May at 17:31 UT, the Japanese cargoship HTV-9 (Kounotori-9) was launched. It berthed to the ISS on 25 May. This provided the opportunity to see two ISS cargoships, one departing and one arriving, in the sky last week.

And it continues: we are in anticipation of the Crew Dragon Demo-2 launch, on May 27 if weather cooperates (see my previous blogpost), bringing to astronauts to the ISS.

Both Cygnus NG-13 and HTV-9 made some splendid evening passes last week. Weather was clear on most days, allowing me to observe and photograph several passes, often two on one evening. Through Twitter, I managed to get a lot of people to go out and watch the passes. HTV's are very bright and distinctly orange objects, easily visible with the naked eye even in deep twilight and from an urban environment. So they are ideal objects to get people out and watch.

HTV-9 was a spectacular sight on every pass. It reached magnitude 0 to -1, with a very distinct orange colour that is due to the orange thermal foil it is wrapped in. It was also prone to producing brief bright flares to magnitude -2 to -3. It did this on almost every pass, sometimes multiple times. here is an example, from May 21:


Click to enlarge

click to enlarge

Below are a number of photographic stacks I made during these HTV-9 passes (gaps in the trails are the brief periods between successive photographs in the stack). The first image showing another flare: the second bright satellite crossing the path of HTV-9 in the third image is Resurs P1. Note the orange colour, especially apparent in the second image. Visually, the orange colour was even more profound than in these images (where they have washed out a bit due to the brightness of the trail).


Click to enlarge
Click to enlarge
Click to enlarge


Cygnus NG-13 was much fainter than HTV-9. During a  good pass it would reach magntude +3, but often was below naked eye visibility. Here is imagery from one of the brighter passes, on May 19 when it reached magnitude +3:


click to enlarge
Click to enlarge
Click to enlarge

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Sunday, 24 May 2020

The trajectory of the upcoming Crew Dragon Demo-2 launch, returning the US to crewed spaceflight

Photo: SpaceX

UPDATE: the Crew Dragon launch has been postponed to NET 30 May, 19:22 UT
Below is the original text and maps, which are however no longer valid!
New maps in a new, separate post.

If everything goes well, SpaceX and NASA will launch the Crew Dragon Demo-2 flight with astronauts Bob Behnken and Doug Hurley to the International Space Station on 27 May 2020. The launch is slated for 20:33:33 UT (note: some sources now say 20:33:31 UT), from LC-39A.

This is a historic flight, because after a 9-year hiatus it will return NASA to a crewed flight capacity. It is the first crewed flight launching from US soil on a US rocket since the Space Shuttle program ended in 2011. Over the past 9 years, US astronauts had to hitch a ride on Russian Soyuz spacecraft in order to get to space.

The Crew Dragon Demo-2 will fly this approximate flight trajectory, bringing it over Europe some 23 minutes after launch:

click map to enlarge
click map to enlarge

The times in the map above are in UT (GMT): for CEST add +2 hours; for BST add +1 hour. I created the maps using the (uncrewed) Crew Dragon Demo-1 test flight from March 2019 as a proxy.

Based on that same Crew Dragon Demo-1 flight, I estimate these orbital elements for the first orbit:


CREW DRAGON DEMO-2   
1 70000U 20999A   20148.85443285 -.00003603  11390-4  00000+0 0    03
2 70000  51.6423 089.9835 0122953  45.6251 315.4951 15.99554646    09
 

estimated initial orbit for launch at 27 May 2020, 20:33:33 UT


You can use this so called TLE (for an explanation of these numeric lines click here) to make pass predictions and maps of the trajectory in your local sky for your own location, using prediction software like HeavenSat.

Be aware that it is approximate: so allow for a possible error of 1-2 minutes in the time it will pass in your sky, and a small cross-track error (I expect this latter to be less than 1 degree, i.e. less than two moon diameters).

Weather willing,  the Crew Dragon containing the astronauts and the Falcon 9 upper stage will be visible from much of Europe some 23 minutes after launch.

Northwest Europe has it pass in twilight, but Dragon's tend to be bright, so twilight should be no problem and the Dragon and Falcon 9 should be easily visible by the naked eye, except perhaps from the British Isles where it is still quite light.

I do advise using binoculars once you have located the spacecraft, as the Crew Dragon and the Falcon 9 upper stage will be close together, and with binoculars you will see them separately (you can see some photographs of a pass of a just launched Cargo-Dragon and its Falcon 9 upper stage from March this year in an earlier post here).

If you are lucky, you might even catch some small corrective thruster firings as small "puffs", like in this movie which I shot of a pass of the Dragon CRS-20 in March this year (look for the "puff" going upwards around 05:13:00 UT in the video):




(the two slowly varying objects astride the Dragon and Falcon 9 stage in the video above are the two ejected solar panel covers. The Crew Dragon does not have these, as far as I know).

The Falcon 9 upper stage will be deorbitted some 55 minutes after launch, over the southern Indian Ocean west of Australia.


photo: SpaceX

Below are my predicted sky tracks for a number of places in West and Central Europe, valid for launch on 27 May at 20:33:33 UT .

Times listed in the plots below are in local time (generally CEST, except for London which is BST). Please be aware that there is an uncertainty of about 1 to 2 minutes in the actual pass time!!! The track placement in the sky should generally be correct though. Bottom of the plots is either South or North, depending on the location (see the annotations on the plots).


Note added 25 May: the Heavens-Above webservice now provides you with custom predictions for the Crew Dragon for your observing site.



Amsterdam

Berlin

Brussels

London

Paris

Prague

Vienna
Hamburg

Lyon

Marseille

Munich

Reims

Strassbourg