Time Reference

The times quoted in all planning files (SDMOP, State_Summary, Gelocation) 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.

ABS_ORB
Start
ABS_ORB
Stop
ANX - Start ANX - Stop Time Difference D
(graph)
Time Difference D
(text)
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)
51453 56711 01-JAN-2012
00:18:04.665
31-DEC-2012
23:55:45.200
AUX_TIM_51453_56711 AUX_TIM_51453_56711
46210 51452 01-JAN-2011
01:36:28.439
31-DEC-2011
22:38:37.782
AUX_TIM_46210_51452 AUX_TIM_46210_51452
40981 46209* 01-JAN-2010
00:26:04.441
31-DEC-2010
23:56:14.418*
AUX_TIM_40981_46209 AUX_TIM_40981_46209
*ABS_ORB Stop and ANX Stop refer to modified ENVISAT orbit (implemented since orbit 45222 - 24 October 2010)
35757 40980 01-JAN-2009
01:37:55.819
31-DEC-2009
22:45:28.513
AUX_TIM_35757_40980 AUX_TIM_35757_40980
30517 35756 01-JAN-2008
00:00:12.346
31-DEC-2008
23:57:19.891
AUX_TIM_30517_35756 AUX_TIM_30517_35756
25293 30516 01-JAN-2007
01:12:03.723
31-DEC-2007
22:19:36.418
AUX_TIM_25293_30516 AUX_TIM_25293_30516
20068 25292 01-JAN-2006
00:43:19.172
31-DEC-2006
23:31:27.795
AUX_TIM_20068_25292 AUX_TIM_20068_25292
14843 20067 01-JAN-2005
00:14:34.621
31-DEC-2005
23:02:43.244
AUX_TIM_14843_20067 AUX_TIM_14843_20067
09604 14842 01-JAN-2004
00:17:27.076
31-DEC-2004
22:33:58.693
AUX_TIM_09604_14842 AUX_TIM_09604_14842
04380 09603 01-JAN-2003
01:29:18.454
31-DEC-2003
23:36:51.200
AUX_TIM_04380_09603 AUX_TIM_04380_09603
00001 04379 01-MAR-2002
02:53:55.245
31-DEC-2002
23:48:42.526
AUX_TIM_00001_04379 AUX_TIM_00001_04379



Page generated 04 February 2003; last update: 10 May 2012