Sunday, 15 April 2018

X-37B OTV-5 mission located on orbit

OTV-5, The fifth mission of the US Air Force' X-37B  robottic mini-shuttle, was launched from Cape Canaveral on 7 September 2017 on a SpaceX Falcon 9 rocket. Until last week, OTV-5 had not been located by amateur satellite trackers, and that was somewhat curious, as we did locate and track the previous four missions.

But now OTV-5 has been finally found. In the early morning of April 11, 2018, Dutch satellite tracker Cees Bassa imaged a bright unidentified satellite in a ~54 degree inclined orbit. It was seen again by Cees two days later, on April 13. Ted Molczan managed to link it to a lone sighthing of an unidentified object done by Russell Eberst in Scotland back in early October 2017 that was already suspected to perhaps be OTV-5 at that time (several of us, including me,  had tried to recover the object Russell observed in the next few nights that October, but failed).

OTV-5 immediately was suspected as the identity for this object. It was in a very low, ~355 km circular orbit, which is lower than usual for satellites, but which fits with the characteristics of previous OTV missions.

The orbital plane the object is moving in passed over Cape Canaveral at the moment OTV-5 was launched (see below, which shows the location of the orbital plane for the moment of OTV-5 orbit insertion on 7 September 2017). So that fits nicely, and as a result we are quite confident that this is OTV-5.

click to enlarge

There is a difference with previous OTV missions: OTV-5 is in a 54.5 degree inclined orbit, which is a substantially higher orbital inclination than that of previous OTV missions which were flown at orbital inclinations between 38.0 degrees and 43.5 degrees, as can be seen in this diagram below where the current OTV-5 mission orbit is white, and previous OTV mission orbits are red:

click to enlarge

But this actually fits with information released on the OTV-5 mission by the US Air Force, which prior to the launch of OTV-5 stated that:

"The fifth OTV mission will also be launched into, and landed from, a higher inclination orbit than prior missions to further expand the X-37B’s orbital envelop." 

I am very happy that OTV-5 was launched, as it now turns out, into a 54 degree inclined orbit, as for the first time this will give me a chance to see an X-37B OTV mission from the Netherlands. OTV-5 will actually pass over my country (and even somewhat north of it), while previous OTV missions passed over southern Europe only. The previous four missions therefore were not visible from my country, due to their lower orbital inclination.

An obvious question is: why did it take so long to find OTV-5? I have some answers to this that might explain.

First, I think many amateurs subconsciously reckoned it would be in a 38-43 degree inclined orbit like its predecessors. Indeed, the initial search elements we used were for a 43-degree orbit.

Second, this was an autumn launch and the very low orbital altitude means it is not well visible in wintertime from the Northern hemisphere, where almost all currently active satellite trackers are located. Almost all wintertime passes are in Earth shadow.

Now spring has arrived, OTV-5 is emerging out of these shadows, into the light. Weather has not been cooperating for me in the coastal area of the Netherlands where I am located so far, but I hope to be able to joing tracking this object soon. It is an interesting object to track, as previous OTV missions frequently manoeuvered between different orbital altitudes. Plus, the shuttle-like character of this object makes it a special one to track as well.

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