Pinpointing the OTV 5 orbital manoeuvre on 19 April 2018

click map to enlarge

As related in a previous post, the X-37B robottic space plane OTV 5 made an orbital manoeuvre on the 19th, lowering its orbital altitude from ~355 km to ~315 km.

It has been observed in its new orbit enough by now (pass predictions for yesterday evening were spot on), to allow an analysis to reconstruct the time and location of the manoeuvre. This can be done by looking for a moment where the positions in the old orbit and the new orbit were close.

Using Mike's pre-manoeuvre OTV 5 orbit of epoch 18104.41928168 and my own post-manoeuvre orbit solution of epoch 18112.84880111, and feeding these into the COLA program written a long time ago by Rob Matson, the resulting time of coincidence is 19 April 2018 at 5:20 UT.

OTV 5 was near perigee and in its descending node at the time, over west Africa, as can be seen on the map above. Manoeuvres typically happen near the nodes and near either perigee or apogee, so that fits well with this reconstructed moment of manoeuvre.

Since the manoeuvre entailed both a lowering of the perigee and a lowering of the apogee, the time and location listed above is likely the second of two manoeuvre moments.

The first manoeuvre burn probably happened near 4:35 UT, near apogee and the ascending node of the original orbit, south of Hawaii. This burn lowered the perigee altitude of the orbit to 310 km. Next, a second burn lowering the apogee altitude to 323 km was conducted half an orbital revolution later at 5:20 UT, near perigee and the ascending node of the orbit over west Africa. The two points are depicted by red circles in the map above.

Past OTV missions frequently made such manoeuvres between different orbital altitudes. They probably are meant to be able to test experimental technology in the payload bay under various thermospheric density and irradiation regimes.

Meanwhile, we continue to track OTV 5 in its new orbit. My observations yesterday were hampered a bit by an untimely field of clouds, but I did get some astrometry. Here is some imagery from yesterday, showing OTV 5 ascending amidst a thin cloud cover (bright star in clouds at right is Capella):

click photograph to enlarge

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.