OTV 5 or Zuma? A brief explanation why this object is OTV 5 and not Zuma

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The image above shows the US Air Force's "secret" X-37B space plane OTV 5 ascending in the western sky (the two bright stars above the roof are Castor and Pollux), in the evening of 21 April 2018.

I was asked the question: "how do we know this is OTV 5? Why can't it be Zuma?". I will explain here why it is definitely OTV 5 and definitely not Zuma.

The key is in the orientation of the orbital plane. Both OTV 5 and Zuma were launched from Cape Canaveral into a northwest direction, towards azimuth 40-50 degrees (see map with launch hazard zones below). That direction establishes the orbital plane the objects were launched into.

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From our tracking of the OTV 5 candidate the past 10 days, we have the orbital plane this object is moving in. We can project that orbital plane back to the launch dates of both OTV 5 and Zuma.

For the launch date and launch time, it should pass over the launch site, with a correct orientation in terms of direction. That means, in this case: it should pass over Cape Canaveral, into a northeastern direction.

Now let us first do that for OTV 5, which was launched by SpaceX from Cape Canaveral pad 39A on 7 Sept 2017 at 14:00 UT. The 3D plot below shows the orbital plane of the object we track projected backwards, for the moment of OTV 5 orbit insertion (7 Sep 2017, ~14:09 UT):

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As can be clearly seen, the orbital plane we established for the object we have been tracking the past few days, for this date and time lines up with the launch site, and it is oriented into the correct direction (southwest to northeast). This strongly indicates that the object we track is from the OTV 5 launch.

If we do the same for the Zuma launch, we do not get a good match. Zuma was launched by SpaceX on 8 Jan 2018 at 01:00 UT from Cape Canaveral pad 40. The 3D plot below shows the orbital plane of the object we track projected backwards, for the moment of Zuma's orbit insertion (8 Jan 2018, ~01:09 UT):

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As we can see, the orbital plane we established for the object we have been tracking the past few days, for this date and time does not line up with the launch site, and it is moreover oriented into the wrong direction too (northwest to southeast instead of southwest to northeast: a 90-degree angle!). This strongly indicates that the object we track is not from the Zuma launch.

(As avid readers of this blog know, Zuma presumably failed to detach from the Falcon 9 upper stage due to a faulty adapter provided by the satellite's builder Northrop Grumman, and reentered with the upper stage a few hours after its launch).

So the object's orbital plane lines up with a launch from Cape Canaveral on 7 Sept 2017 and orbit insertion at 14:09 UT, the launch date of OTV 5. Ad to this the very low orbit which was also typical for past OTV missions, and it is very clear that the object we are currently tracking is the X-37B mission OTV 5.

Below is a video of OTV 5 which I shot yesterday evening, 21 April 2018: