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I measured a couple of Starlink satellites tonight, finally, Starlink 1130 (Darksat) arrived (March 17th 2020, 20:15 local time). I could not see the sat on the screen although I turned up to gain a lot. Has something happened to him? Wrong TLE files (would be very strange) or - is it really dimmer than the others? This would be great news. I´ll try to detect the satellite tomorrow again.

Best regards

Rudolf

Update:

I was able to make a comparative measurement between STARLINK 1130 (darksat, left) and STARLINK 1084 (right) on March 19th 2020 (both at operational height, similar altitude above horizon, ASA Astrograph and ASI1600 MM-Cool, G filter, exposure 1 s, gain 294

The coated darksat seems to be considerably dimmer than its uncoated follower. Measurements will follow.

enter image description here

Update 2:

Here is a measurement of the two satellites at similar altitudes from March 19th 2020.

Plate-solved and compared against known stars, the 1130 trail seems to be considerably dimmer. In my measurement, the difference in magnitude was Mag 1.1528 (-65% !). I will do some more comparisons.

enter image description here

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  • $\begingroup$ Oh it's you again! It's great that you're continuing this work. I've asked a different question: Astrophotographer Thierry Legault is not convinced that DarkSat is darker than the others. Have photometric measurements been reported? so one you resolve this you may be able to post an answer to that as well. $\endgroup$ – uhoh Mar 17 at 23:46
  • $\begingroup$ Are you sure the satellite was sunlit when you looked? They're pretty much invisible at optical wavelengths once they pass into Earth's shadow. You can see an example of what that looks like in What causes this arc in the night sky where the background is brighter on one side than the other? It's pretty easy to calculate from a TLE if a satellite is in eclipse or not using Skyfield. $\endgroup$ – uhoh Mar 17 at 23:47
  • $\begingroup$ (I meant "visible wavelengths") $\endgroup$ – uhoh Mar 18 at 3:44
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    $\begingroup$ Yes, I am sure it was sunlit. I am using a beta version of Skytrack in which the sunlit parts of the trails are clearly marked. I will try tonight with higher gain and report back ... $\endgroup$ – rbumm Mar 18 at 11:37
  • $\begingroup$ Since you are looking at TLEs I think it would be good if you refer to the spacecraft by an internationally recognized name. In this question I saw that "Darksat" was NORAD ID: 44972, Int'l Code: 2020-001BL but in Universe Today it says "T.S. Kelso over at Celestrak later identified DarkSat as NORAD ID 2020-001U (COSPAR ID 44932)." $\endgroup$ – uhoh Mar 18 at 11:49
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Yes.

The March 16, 2020 paper in arXiv First observations and magnitude measurement of SpaceX's Darksat found that Darksat reflects 55% less light compared to a regular Starlink satellite. It has an estimated magnitude of 6.21 compared to the estimated magnitude of 5.33 for a regular Starlink satellite.

Aims. Measure the Sloan g’ magnitudes of the SpaceX STARLINK-1130 (Darksat) and 1113 LEO communication satellites and determine the effectiveness of the Darksat darkening treatment at 475.4 nm.

Methods. Two observations of the SpaceX STARLINK Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06 using a Sloan r’ and g’ respectively. While a second satellite, STARLINK-1113 was observed on 2020/03/06 using a Sloan g’ filter. The initial observation on 2020/02/08 was a test observation when Darksat was still manoeuvring to its nominal orbit and orientation. Based on the successful test observation, the first main observation was conducted on 2020/03/06 along with an observation of a second STARLINK satellite.

Results. The calibration, image processing and analysis of the Darksat Sloan g’ image gives an estimated Sloan g’ magnitude of 7.57±0.04 at a range of 976.50 km. For STARLINK-1113 an estimated Sloan g’ magnitude of 6.69±0.05 at a range of 941.62 km was found. When scaled to a range of 550 km, a reduction of (55 % ± 4.8 %) is seen in the reflected solar flux between Darksat and STARLINK-1113.

Conclusions. The data and results presented in this work, show that the special darkening “treatment” used by SpaceX for Darksat has reduced the Sloan g’ magnitude by 0.88±0.05 mag (55 % ± 4.8 %), when the range is equal to a nominal orbital height (550 km). This result will serve members of the astronomical community modelling the satellite mega-constellations, to ascertain their true impact on both the amateur and professional astronomical communities. Concurrent and further observations are planned to cover the full optical and NIR spectrum, from an ensemble of instruments, telescopes and observatories.

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