More X-37B spaceplane OTV 7 observations

OTV 7 imaged on August 11. Click image to enlarge

In a previous blogpost I wrote about recovering the X-37B Spaceplane OTV 7 (2023-210A) on July 30. I have now observed it a couple of times, at intervals of a few days due to a combion of weather conditions and favourable or less-favourable pass times. Above is an image from August 11. The diagram below shows where it was in its orbital position at that time, coming down from apogee:

click image to enlarge

 

Between mid-March and end-of-July, OTV 7 had brought down its apogee by a few thousand kilometers. Since recovery on July 30, it is continuously making smaller manoeuvers as well (currently, it seems to make small orbit raising manoeuvers adjusting both apogee and perigee). As a result, it is invariably off predictions (usually being a bit 'late') and a small plane scan is necessary to recover it. Having a wide-field instrument (the FOV of the instrument I currently use, an ASI 6200 MM PRO with 1.2/85 mm lens, is 24 x 16 degrees) is useful in this aspect.

The brightness of OTV 7 strongly depends on where it is located in its orbit during observation (as well as, of course, phase angle and condition of the local sky). When it is in or near apogee, it is fainter and the trail is short.

When following the object over (a part of) a pass, the brightness and apparent angular rate of movement (trail length) notably changes. How clearly it can be seen in the imagery is complex interaction of actual brightness, apparent angular movement (when it moves faster, each image pixel is illuminated less), range to the observer and phase angle.

Below are two images from the night of August 14-15, some 3 hours after OTV 7 passed apogee. The second of these images shows OTV 7 not far from M31, the Andromeda galaxy. Even though the two images are not at the same image scale (the one with M31 is reduced in size, to show a wider FOV), the difference in trail length after a mere half an hour can already be seen (both images are 10-second exposures with a ZWO ASI 6200 MM PRO and Samyang 1.2/85 mm lens).

Recovery of the X-37B spaceplane OTV 7

click to enlarge

 

The classified US Space Force X-37B spaceplane OTV 7 (2023-210A) was launched on 29 December 2023, in an unusual Highly Elliptical Orbit. Five weeks after launch, in the first week of February 2024, it was found on-orbit by Tomi Simola from Finland in a 38600 x 300 km, 59.15 degree inclined orbit (see this earlier blogpost). We followed it for a month and then lost it: the last observation was on March 15.

But now it has been recovered! On the night of July 30-31, I was imaging geosynchronous objects when I noted a short trail made by an unidentified interlooper.  Mike McCants identified the UNID as OTV 7.

The image in top of this post (one out of four images spanning half an hour) shows the short faint trail created by OTV 7. The ~9 by 4.5 meters large X-37B spaceplane was near apogee of its orbit at that time, at about 35535 km altitude (and a range of some 38775 km to my observing location). The image is a 10-second exposure with a ZWO ASI 6200 MM PRO and Samyang 1.2/85 mm lens, and shows only a small part of the original image. It was taken from Leiden, the Netherlands.

Weather next initially conspired against me, but last night, August 3-4, I again observed it, some 25 minutes late on the initial elset estimate. This is a small part of one of the images, shsowing the faint trail created by OTV 7:

click image to enlarge

The observing conditions were very dynamic this time: after rainshowers, small but bright, stamp-sized clearings were sometimes present in the clpud cover. I managed to image the object through such gaps in the cloud cover a few times over an half-an-hour-period, 25 minutes late on the preliminary orbit. 

Below is an example of what I am talking about when I say "stamp-sized clearings": this is the last image (reduced in size as the true image is 9576 x 6388 pixels) on which I could find it. All the white is clouds....:

click to enlarge

The new observations constrain the orbit a little bit better: 314 x 35552 km, 59.15 degree inclined. A provisional elset:

OTV 7
1 58666U 23210A   24216.90625742 0.00000000  00000-0  00000+0 0    01
2 58666  59.1511 329.1636 7247171 178.5736 186.3429  2.29027449    03

rms 0.004 deg   from 9 obs, arc July 30.96 - Aug 3.96 UTC

Below is a comparison between the (forward propagated) orbit from March (red), and the current orbit (white). Apogee is some 2300 km lower than it was in March (and this is not due to natural orbital decay, but due to manoeuvering). The orbital plane itself is still similar.

click image to enlarge