Sunday, 24 May 2020

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

Photo: SpaceX

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:

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.













Wednesday, 13 May 2020

[UPDATED] OTV 6 (USSF 7), the next X-37B launch, appears to go into a 44-degree inclined orbit

OTV 6.  Image: US Air Force. Click to enlarge

If weather cooperates, the next X-37B launch, mission OTV 6 ,also known as launch USSF 7, is slated for May 16, with backup dates on May 17 and 18 in case launch is postponed. The small uncrewed space plane will be launched for the US Air Force by the United Launch Alliance, with an Atlas 5 rocket, from Cape Canaveral SLC-41.

Navigational Warnings have now appeared for this launch, which shed light on the launch window and the orbit aimed for:

   161224Z TO 161453Z MAY, ALTERNATE
   171314Z TO 171532Z AND 181354Z TO 181434Z MAY
   A. 28-36-51N 080-35-57W, 28-41-00N 080-26-00W,
      28-36-00N 080-23-00W, 28-31-36N 080-33-34W.
   B. 32-28-00N 075-12-00W, 33-50-00N 072-51-00W,
      33-08-00N 072-17-00W, 31-45-00N 074-41-00W.
   C. 38-43-00N 062-38-00W, 40-23-00N 058-26-00W,
      39-18-00N 057-47-00W, 37-34-00N 061-56-00W.
2. CANCEL THIS MSG 181534Z MAY 20.//

HYDROPAC 1415/20(74,75).
DNC 03, DNC 04.
   161319Z TO 161528Z MAY, ALTERNATE
   171409Z TO 171607Z AND 181449Z TO 181509Z MAY
   36-03S 096-54E, 33-40S 098-30E,
   37-32S 108-22E, 40-03S 107-00E.
2. CANCEL THIS MSG 181609Z MAY 20.//

The launch azimuth defined by the three launch hazard areas A, B and C in the Atlantic Ocean and the location of the Centaur upper stage deorbit zone in the Indian Ocean, point to a launch into a ~44-degree inclined orbit, give or take half a degree. The Centaur upper stage will be deorbitted about half a revolution (55 minutes) after launch.

The following map depicts the hazard areas and the trajectory of the first orbit, for a 44-degree inclined orbit and an orbital altitude of ~350 km. The latter orbit fits the locations of the hazard zones well, and the ~55 minutes time difference between the start of the launch windows and the start of the Centaur upper stage deorbit windows in the Navigational Warnings combined with the position of the deorbit zone, fits a ~350 km altitude orbit:

Click map to enlarge

Launch into a 44-degree inclined orbit unfortunately means I do not get to track it from the Netherlands, as my observing location is too high north in latitude to see it in such an orbit. Following the previous OTV 5 launch, that went into a 54.5 degree inclined orbit and could be well observed from the Netherlands, I had some hopes for OTV 6, but alas no, it is not to be apparently...

A 44-degree orbital inclination would be similar to mission OTV 3 from 2012-2014. These are the orbital inclinations of all past OTV missions:

Mission     inclination    operational period        flight duration
OTV 1       40.0o          22/04/2010 - 30/11/2010   224 days
OTV 2       42.8o          05/03/2011 - 16/06/2012   468 days
OTV 3       43.5o          25/10/2012 - 17/10/2014   675 days
OTV 4       38.0o          20/05/2015 - 07/05/2017   718 days
OTV 5       54.5o          07/09/2017 - 27/10/2019   780 days
OTV 6       44.0o ?        16/05/2020 - ?

With regard to the upcoming launch, the given launch windows for May 16 and the two backup dates are curious. These launch windows are not the same duration (May 16 is 2h 29m in duration; May 17 is 2h 18m in duration; and May 18 only 40 minutes in duration).  They shift oddly from date to date too. The start of the given windows shifts 50 minutes between May 16 and 17; and shifts 40 minutes between May 17 and 18. It moreover shift to a later time between consecutive dates: while a given targetted orbital plane would make the launch shift to an earlier time, not a later time

Perhaps this is done to obfuscate the launch time and RAAN aimed for (or maybe it is just simply Range availability at play). If we look at the common ground: all three launch windows have a potential 10-degree wide RAAN window between 331o.14 and 341o.17 in common, so perhaps that is what is aimed for. If that interpretation is correct, this would lead to the following potential 40-minute launch windows, shifting back by 4 minutes each day:

16 May     13:58 - 14:38 UT
17 May     13:54 - 14:34 UT
18 May     13:50 - 14:30 UT

But of course, it is always possible that they launch straight away at the 12:24 UT opening of the May 16 window...we will see!

[Edit 15 May 2020 23:20 UT: but see note at end of post!]

A lot has been written about the X-37B and its purpose, and there are a lot of persistent misconceptions regarding the fact that it is a "space plane" (see my blogpost "X-37B fact and fiction" from July 2019).

Far from being a nefarious device, the X-37B appears to be a testbed for experimental space technology. According to the US Space Force, one of the things that will be tested during the next OTV 6 mission is an experiment to transmit solar power by microwave. It will also contain two NASA experiments that study the effects of radiation on materials and seeds, and it will deploy at least one military cubesat, FalconSat 8 (the previous OTV mission, OTV 5, released three cubesats).

The US Space Force Press Release also indicates that, as a first, OTV 6 will be fitted with a "service module" to the aft of the vehicle, that will house experiments (previous OTV missions housed experiments in the cargo bay). It will be interesting to see what happens to this service module at the end of the mission.

Addendum 13 May 22:05 UT:
More on the microwave experiment in this article (HT to Brian Weeden). It seems it is not so much transmission by microwave, but the generation of microwaves from solar power, which is then send through a cable, if I get it correctly. Anyway: something with microwaves...

Addendum 15 May 23:20 UT:

Bob Christy wrote a very interesting analysis on his Zarya blog, in which he links similar odd jumps in past OTV launch windows to times of close KH-11 passes, the idea being that these KH-11 satellites image the OTV after launch to see whether everything is allright. If that is correct, then this leads to four possible launch times on May 16: 12:24, 13:15, 14:06 and 14:53 UT.
My estimated elsets for these four launch times can be found here.

Addendum 18 May 13:55 UT:

OTV 6 launched on 17 May 2020 at 14:13 UT. A pre-launch estimated elset can be found here;  a preliminary radio-observation based orbit here.

Based on the preliminary radio elset, OTV 6 appears to have been inserted into a 45-degree inclined orbit at ~390 km altitude. The ground track repeats every 3 days:

click to enlarge

Here is how the launch track based on the radio orbit (red dashed line) compares to my pre-launch estimated launch track based on the locations of the hazard areas from the Navigational Warnings (blue dashed line):

click map to enlarge

Saturday, 9 May 2020

The Kosmos 482 Descent Craft: imaging an old Soviet Venera probe stuck in Earth orbit

click to enlarge


On May 7 I imaged a pass of the Kosmos 482 Descent Craft (1972-023E), using the WATEC 902H camera and a SamYang 1.4/85 mm lens. This is a very interesting object on which I have blogged earlier.

It is the ascend module of a 1972 failed Soviet Venera probe, meant to land on Venus but stuck in Earth orbit after its apogee kick engine failed to push it into Heliocentric orbit towards Venus in 1972. This is the video from (a part of) the May 7 pass of this object:

The object on the video, at that time at an altitude of about 1640 km and range of 1845 km, is about 1 meter large and weighs 495 kg. It should look like this:

photo: NASA. Click to enlarge

The photo above is not Kosmos 482 itself, but an exhibit replica of a sister ship, the Venera 8 landing module in its protective shell. Venera 8 was launched four days before Kosmos 482, and unlike the latter it was successful and did reach Venus.

The failed Kosmos 482 probe still in Earth orbit was launched from Baikonur on 31 March 1972, and put in a highly elliptical 220 x 9200 km parking orbit around Earth. It's apogee kick engine next failed to push it into a heliocentric orbit towards Venus, and the spacecraft then broke up into four pieces.

Three of these four pieces have already reentered, the fourth, that is believed to be the landing module in its protective shell, is still on-orbit and is the object I imaged. It's apogee altitude has been lowering significantly since 1972.  The object will probably reenter somewhere around late 2025 or early 2026: I wrote an extensive blog post about it including a lifetime simulation a year ago.

The diagram below is from that post and shows the observed orbital decay up to March 2019, and the future decay (light blue) that I modelled with GMAT:

click diagram to enlarge

The interesting thing is that the Kosmos 482 Descent Craft might survive reentry largely intact! It is, after all, a lander that was meant to survive ascend through the thick atmosphere of Venus. It's parachute system will probably no longer function (so it will impact rather than land), but we can expect the hardware to reach Earth surface largely intact.

From a Space Heritage point of view, both this and its history makes this 48-year-old piece of Soviet Space hardware a highly interesting object. This is material culture that represents humanities' babysteps in the exploration of other planets.

Which makes this an interesting object to image, from a "Space Archaeology" viewpoint, and an interesting object to keep an eye on the coming years, until it reenters about six years from now.

Added Note9 May 2020 13:30 UT:

In response to my statement that the object likely is the lander in its enclosing protective shell, several people have pointed me to telescopic imagery that purportedly would show that a part of the main bus is still attached.

I (and many others in the amateur satellite community - we had a heated discussion on it on the Satobs list a few years ago) distrust imagery of this kind. This is imaging at the edge of resolution, in this case also notably from a non-stable imaging platform (handtracking a moving object at the limit of resolution!). It unfortunately includes cherrypicking frames. It is very difficult to objectively determine what is real detail and what is artefact of the imaging procedure. It is easy to overinterpret.

I also want to note that taking the mass and dimension of the lander only, actually give a very good fit to the observed orbital decay.

Wednesday, 6 May 2020

Imaging the new Iranian satellite NOUR 1 (2020-024A) [UPDATED triple]

click to enlarge

On 22 April 2020 around 4:00 UT, Iran's Islamic Revolutionary Guard surprised the world by launching a military satellite. The satellite is named NOOR 1. The name 'NOOR' means 'Light' in Pharsi.

The object is designated NOUR 01 by CSpOC, with catalogue number 45529  and Cospar designation 2020-024A.

NOUR 1 was launched using a new 3-stage Qased rocket from Shahroud (36.200 N, 55.334 E), the first Space Launch from this facility.

Little is known about NOUR 1, but the fairing of the Qased rocket depicted what looks like a 6U cubesat, i.e. a small satellite with a bus of roughly 10 x 20 x 30 cm in dimension (not counting any deployed solar panels):

The satellite deployed in a 427 x 435 km, 59.8 degree inclined orbit. The orbit is not sun-synchronous, but does have a repeating ground-track about every 4 days.

Three days after the launch, on 25 April, I managed to image the Upper Stage of the Qased rocket that launched the satellite, with a WATEC 902H camera and Samyang 1.4/85 mm lens:

Attempts to image the payload itself (NOOR 1) initially failed, because the late April/early May passes for my location were not the most favourable concerning illumination angles and sky elevation (these passes were low north for me).

But last night, May 6 around 1:52:11 UT, I had a more favourable pass and clear skies, and successfully managed to image the payload NOOR 1 with the WATEC 902H camera and a SamYang 2.0/135 mm lens. As this camera/lens combo has a small field of view (FOV), the observed arc is short: about 4 seconds. Here is the video:

The satellite was at a range of 595 km and a sky elevation of 46 degrees in the south-southwest at the time of the observation. I estimate it to be around magnitude +7.5 in the imagery.

The satellite shows no clear brightness variation during the captured 4 seconds, as is also visible from this 100-frame stack of the video frames:

click to enlarge

It should be noted that there is footage from May 3rd obtained by Paul Maley in the US which does seem to show some variability. But Paul's footage is very noisy, making interpretation difficult [edit: but see below!]:

(footage by Paul Maley)

At any rate, my own observation from last night does not show clear signs of tumbling, but I'll be monitioring the payload further the coming nights to look for any variability.

UPDATE 7 May 2020

New observations from the night of 6 on 7 May do show brightness variation. The satellite was filmed during a near-zenith pass with the WATEC 902H and a Samyang 1.4/85 mm lens.

Below image is a stack of 126 video frames (representing 5 seconds of footage) shwoing a brightness variability with a peak-to-peak period of about 3.2 seconds:

click to enlarge

Here is video footage from alst night: the framestack above is from the first of the 3 shown sequences:

So the satellite is rotating, at the least (note that rotation can be intentional, e.g. spin stabilisation). So far it does not seem to be wildly tumbling, but I will continue monitoring and adding more data.

[end of update: continuation of original post below]

Why this interest in potential tumbling behaviour? There has been speculation about the state of the satellite, following derogatory remarks shortly after the launch by the US Chief of Space Operations, General Jay Raymond, who called it "a tumbling webcam in space" (and says its a 3U cubesat):

US military sources are clearly trying to imply that the satellite is a failure, but that seems a politically inspired stance. My own optical imagery from last night, as presented here, has no indication for tumbling: if it tumbles at all, then it is at a very slow rate. neverthless, the new data from May 7 do show that the satellite is at least rotating.

Moreover, during the three weeks after the launch, several amateurs including myself have received strong telemetry signals from the satellite at 401.5 MHz, consisting of regularly spaced data packets with one data packet sent each 10 seconds.

The signals were first detected and identified as coming from NOUR 1 by Scott Chapman, and the story of this identification can be read in this highly informative blogpost by Scott Tilley which also points to some interesting aspects of the signal, which can be partly decoded (!).

Below is a spectrogram of the telemetry signals as received by me from Leiden, the Netherlands, during a pass in the evening of  30 April 2020: note how strong and regular the signal is:

click to enlarge

The Doppler curve of the signal matches that for NOUR 1 well, so there is little doubt this signal comes from the Iranian satellite.

(note: the spectrogram also shows the signal of a second satellite at 401.5475 MHz, 'Object F', which is an unidentified cubesat from a Chinese launch in December 2019)

Radio amateurs closer to Iran have reported data dumps when the satellite is in reach of Iranian ground stations. So clearly, the satellite is alive and relaying data of an unspecified nature.

At the end of the first week of May, reports have been coming in that detected signals were weakening or absent. This could indicate that after 3 weeks of functioning, the satellite has developed battery problems. On the other hand it could also mean that after a check-out phase the satellite has been shifted to operational mode, and might only be sending while over Iranian groundstations. Further monitoring should shed light on this.

UPDATE  6 May 2020, 18:50 UT:

 I monitored the NOUR 1 pass of 18:42 UT (May 6) and can confirm that the telemetry signal at 401.5 MHz is no longer present.

Perhaps the satellite has completed checkout and is now in operational phase, which could mean it only sends when in range of Iranian groundstations.

UPDATE 9 May 2020, 20:55 UT:

After Iranian sources indicated the 401.5 MHz frequency would be used again for a few hours on the night of May 9/10, I indeed had positive observations of the telemetry signal again on 9 May during the 18:09 and 19:45 UT passes. Here are a screenshot, full spectrogram, and Doppler-curve fit (blue line: theoretical Doppler curve for NOUR 1. Black dots: observations).

This means the satellite is still alive and the absence of the 401.5 MHz signal for a week was because it was in another operational mode, switching to another frequency.

click to enlarge
click to enlarge
click to enlarge

Monday, 4 May 2020

Guest Post: Modelling of Starlink trail brightness and comparison to observations

(The following post is a Guest Post written by Richard Cole)

Observers have been reporting ‘missing passes’ of Starlink trains since the Starlink L1.1 launch, the first of the operational spacecraft. A missing pass is where an examination of the NORAD or SpaceX orbital elements, or a prediction from one of the Starlink websites, would indicate that multiple spacecraft should be expected to be visible but none appear on time.

An observer in Argentina noted missing passes to their south in late February, local summer. Initially, I thought that perhaps the spacecraft had been temporarily placed into the operational low brightness mode (that brightness having been seen on the prototypes after deployment in mid-2019) but this did not match other observers seeing the same spacecraft at normal brightness at similar times. This phenomenon affected spacecraft in the holding orbit at 350-380km, not the operational spacecraft at 550km.

Recently, the images of the spacecraft on-orbit by Ralf Vandebergh and Szabolc Nagy showed its large solar panel of the solar array was facing the Earth when the spacecraft were overhead and explained the normally high brightness of the spacecraft as seen from the ground. The longer dimension of the panel was observed to be parallel to the velocity vector of the orbit, i.e. the orbit path.

SpaceX had referred in communications to a low-drag mode which was consistent with the observed appearance. This raised the question of how this mode of operation would deal with acquiring enough solar power. Would the panel always face upwards to the zenith, or would the spacecraft be rolled around the velocity vector to get more sunlight onto the panel?

During April 2020 more observers saw missing passes. I had personally tweeted a prediction for a late evening pass of the Starlink L1.5 train to the north of my site in southern UK on April 20th, but the spacecraft were only magnitude 6, needing binoculars to be seen at all. Observers in northern UK reported they had visually seen spacecraft on that pass. It was clear that the spacecraft were indeed being rolled around the velocity vector and by such an angle they were nearly directly facing the Sun, now towards the north in Spring, and observers to the south were just seeing the shadowed back of the panel.

Since it was clear that further analysis was needed to accurately predict visible passes, early on April 21st I created a simple model of the spacecraft panel pointing axis assuming the panel long axis was the velocity vector and the spacecraft was being rolled so that the Sun was in a plane normal to the panel and through the long axis (figure 1). Usually the panel cannot directly face the Sun, but is at some offset angle, in azimuth and elevation.

Figure 1: Spacecraft Roll-Angle concept.  Click diagram to enlarge

This concept allows calculation of the angle between the direction the panel is pointing and the observed Starlink direction for a particular observer on the ground, for the same time. This ‘panel view angle’ will be different for each possible observer of the same spacecraft at the same time, some will see a large part of the sunlit side of the panel, some will see only a little of the same side and some will see only the back of the panel away from Sun, which is dark.

The model gave panel view angles consistent with recorded occasions of observed train non-appearances.

Marco Langbroek’s excellent observation and images of the L1.5 train from Leiden on 2020 April 21 (the same day as the first version of the model was written, as it turned out) provided a useful test of the model. Further, more recent information from SpaceX has confirmed this behaviour and suggested that the actual roll-angle used on-board many not be exactly as calculated above.

In the image below (figure 2) I plot the calculated glancing angles to the sunlit side of the solar panel (so a glancing angle of zero means the view angle of the panel is to the edge of the panel, an angle of 90 would be face on). I have done this for two altitudes (elevations) in Marco's image, 50° and 70°. The roll-angle was as calculated above.

Figure 2: Marco Langbroek's image of Starlink 5 passes, with the calculated panel glancing angles overlaid. Click to enlarge

The trend of a reducing glancing angle with Starlink brightness is correct, so as the Starlinks passed further north (to the right of the image) of Marco at Leiden, less and less of the panel sunlit surface was visible until nothing could be seen. There was one predicted Starlink that passed on the right of the image (further north) but is only detectable by image analysis, it can’t be seen in the original camera image because very little of the sunlit side was facing the camera:

Figure 3: the extra and faint track of a predicted Starlink satellite in the image. Click to enlarge

I was observing the same pass from southern UK a few minutes earlier than Marco and saw the same behaviour of reducing Starlink brightness as each Starlink passed further to the north. I was very pleased to see he had recorded it in his image.

However, the fit is not perfect so I tried changing the roll-angle by a small amount from that calculated. The fit was best for a deviation of nine degrees from the model, that is the actual roll-angle was nine degrees less that the simple model predicts and the panel is pointing slightly higher in the sky. This gave a better fit:

Figure 4: the same image with the changed panel glancing angles overlaid, using an offset of nine degrees in the solar panel pointing direction. Click to enlarge

SpaceX is now promising to change the roll-angle model used on-board to minimise the Starlink brightness as seen from the ground. The panel will be rotated, at periods when the Starlink can be seen from the ground, so the sun falls on the edge of the panel, not on its face as in figure 1. This is a small portion of each orbit and as Starlinks at low altitude are not using their communication equipment, they will need less power to keep functioning.

Richard Cole
Twitter: @richard_e_cole