2017 Mar 29
Wednesday, Day 88
X-37B - Return To Earth of Mission 3
2014 October 12, news began to circulate that the currently orbiting X-37B space plane (space drone?) was to return to Earth October 14 with a landing at Vandenberg Air Force Base. Clues from the two previous missions indicate a likely time of day.
When analysing on-orbit events that follow similar patterns, a good marker to lay down is the geographical longitude and the time at which a satellite crosses the equator. It can then be related to times of events on the ground. For the X-37B missions, it is necessary to use orbital data from Amateur observers because there is none forthcoming via SpaceTrack.
When the first X-37B returned from its initial mission, it landed on the runway at Vandenberg Air Force Base 2010 Dec 3 at 09:16 UTC. It approached California from the south-west.
Its final northbound equator crossing was at 08:59 UTC with longitude 158°.6 west. Although the orbital data used for calculating the time was based on four day old observations, the equator crossing and landing times are consistent with what would be expected for a space plane returning to Earth.
It lays down a marker that says landing occurs about 17 minutes after the final northbound equator crossing.
The first flight of the second X-37B landed at Vandenberg 2012 June 16 at 12:48 UTC. There is no closely-corresponding final equator crossing based on amateur observations because the orbit was last measured on May 28, more than two weeks earlier. It is plainly obvious that the X-37B lowered its orbit sometime during that period to make it arrive earlier. Using the "17 minute" rule derived from Mission 1, it is possible to adjust the longitude to account for a manoeuvre.
For an equator crossing at 12:31 UTC (12:48 less 17 minutes) the longitude would have been 161°.9 west, not far from the value for mission 1.
2014 October 11, the USAF let it be known that landing of the original X-37B at the end of its second mission was aimed for October 14. The story started to spread through news media on October 12.
The latest Amateur measurement of the orbit was dated October 6 and predicts a final equator crossing for October 14 at 17:47 UTC over longitude 168°.6 west. If this mission followed the pattern of its immediate predecessor, the X-37B would have lowered its orbit in the few days before landing and arrive a little earlier.
Missions 1 & 2 pointed to a return to Earth from an orbital path having an equator crossing near 160° west longitude. Adjusting the timing of the prediction to account for it suggests a final equator crossing at 17:12 UTC.
Adding in the 17 minutes derived from Mission 1 gave 17:29 UTC for landing.
There is some leeway because the vehicle is a glider when flying in the atmosphere and, like the Space Shuttle, has some cross track manoeuvrability. For estimating purposes, the best that could be said is that landing was likely to occur October 14 at 17:30 UTC ±20 minutes.
Update - the anticipated landing did not occur, the Vandenberg NOTAM that seemed to cater for it was cancelled late-afternoon October 14 and replaced with a similar one for October 15. The landing may have been delayed by adverse weather in the Vandenberg area. Some reports suggested fog might be the problem but others suggested high winds.
Separately, Nico Janssen - an amateur satellite observer using radio, reported that no significant orbit change had occurred up to October 12. He noted that orbital decay was a little higher than anticipated, making the X-37B run slightly 'early' against predictions from the latest amateur-produced element set. A new orbital measurement by amateurs is unlikely because the X-37B's orbit produces passes in daylight when over the populated areas of the world.
It is difficult to determine a landing time for October 15 because the location of the ground track is significantly different from the two earlier missions. It could occur on a pass near Vandenberg around 16:25 UTC, or on the next pass at around 18:00 UTC.
For October 16, a landing opportunity from a ground track with an equator crossing near 160° longitude occurred around 16:25 UTC but it was not used. Shortly before the event, the NOTAM that seemed to cover the landing was replaced by one for October 17. Weather in the are seemed fine with reports of good visibility and low wind speed so the reason for postponement was not particularly obvious.
The October 17 landing opportunity occurs around 16:20 UTC.
Page date: 2014 Oct 13
Updated: 2014 Oct 14
Updated: 2014 Oct 15
Updated: 2014 Oct 16
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