The times quoted in all planning files (SDMOP,
refer to the reference orbit as listed in the Reference
Orbit Event (ROE) file. Since the actual orbit differs from the
reference orbit (e.g. orbit drift), the times given w.r.t. the reference orbit
also do not reflect exactly the actual absolute times of events along the
orbit (e.g. ANX, sunrise, sub-solar, moonrise, eclipse). The requirements
for orbit maintenance may result in time differences of usually < ±10 sec.
In same cases this value may even reach ±1 min, however.
FOCC provides the associated time difference via the auxiliary state vector files
While the restituted file is only available after sensing, the file with
the actual predicted state vector can be used prior to operations to derive
the difference D = predicted - reference
time with high accuracy. If the predicted times are delayed w.r.t. the
reference orbit, then D >0 sec; in
the other case D <0 sec.
SOST monitors predicted versus reference time on a weekly basis. The resulting difference - spanning a complete year - is updated with the same frequency. It can be accessed below, both as graph and text. The plot shows the time difference in sec as derived from the ANX UTC times. Orbit maintenance manoeuvres appear as distinct discontinuities. In the text file also the ANX times in UTC as given for the reference orbit (ROE_ANX) and as predicted (FPO_ANX), i.e. close to the actually flown orbit, are given.
Note that the parameter elapsed time, which denotes the time elapsed since ANX and which is also listed in the planning files, remains generally unaffected by the time difference as the D value applies to all events along the orbit in almost the same way.
|ANX - Start||ANX - Stop||
Time Difference D
Time Difference D
|09-May-2012: ESA declares ENVISAT mission ended!|
SCIAMACHY operations suspended due to major ENVISAT anomaly
(loss of communication links) in orbit 52868 (08-APR-2012, 12:28:00 UTC)
|*ABS_ORB Stop and ANX Stop refer to modified ENVISAT orbit (implemented since orbit 45222 - 24 October 2010)|