RE: X-37B OTV 4 search elements

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Thu, 21 May 2015 09:39:55 -0400
The Planetary Society issued a TLE of LightSail yesterday afternoon:

http://sail.planetary.org/tles/live.txt

                                                         355 X 702 km
1 91919U 15999A   15140.67013889  .00040047  00000-0  10233-2 0    04
2 91919  54.9991 339.9648 0250932 182.3369  74.3135 15.12540571    18

It is similar to one of the published pre-launch variants; the main difference is that the inclination is 2 deg less.

The manoeuvre to this orbit occurred near its first perigee, which also was near the first descending node of OTV 4,
2015 May 20 15:44:44 UTC, over 45.840 E. Propagating the above orbit to that time and changing inclination, eccentricity
and mean motion, yields the following OTV 4 search TLE:

OTV 4 search                                             359 X 361 km
1 74995U 74995A   15140.65606480  .00040047  00000-0  10233-2 0    03
2 74995  39.0000 340.0258 0001000 182.3031 357.6777 15.70500000    09 

The inclination is derived from the NOTAM, assuming no yaw-steering. I cannot rule out yaw-steering; therefore, the true
inclination may well be different, perhaps up to several degrees higher. This result is similar to the 74996 TLE I
posted pre-launch (the main difference is ~2 deg in RAAN).

I offer the 74995 TLE in support of the search for OTV 4. It should be used with reasonable allowance for uncertainty in
the mean motion and inclination. 

Historically, the X-37B has tended to maintain a constant altitude for long periods, achieved by means of frequent small
manoeuvres to counter the effects of drag. Large orbit manoeuvres have been infrequent; however, X-37B is highly
manoeuvrable, which has the potential to complicate the search.

Ted Molczan


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Received on Thu May 21 2015 - 08:41:39 UTC

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