Jose et al,

 

The root cause is the Nav.EpochOffset G&C parameter which contains the leap second offset of 33 seconds. We did not load this for Mission Sim 3 and so the compiled in default was used which does not have this offset. Therefore, the ephemeris was not valid for 33 seconds after we loaded it.

 

John

 

 

John,

Did you guys find a root cause?

I checked the SPICE files just in case. They do not seem to have any issues

I loaded them into Astrogator and asked for the state at 2006:308:22:59:50

I get the same answer from both SPICE files...

Satellite-Satellite1: J2000 ECI Position & Velocity

 

Time (UTCG) x (km) y (km) z (km) vx (km/sec) vy (km/sec) vz (km/sec)

----------------------- -------------- ------------- ------------- ----------- ----------- -----------

4 Nov 2006 22:59:50.000 4835922.864355 977699.988017 439551.506575 1.142567 0.637343 0.275824

 

Satellite-Satellite2: J2000 ECI Position & Velocity

 

Time (UTCG) x (km) y (km) z (km) vx (km/sec) vy (km/sec) vz (km/sec)

----------------------- -------------- ------------- ------------- ----------- ----------- -----------

4 Nov 2006 22:59:50.000 4835922.864355 977699.988017 439551.506575 1.142567 0.637343 0.275824

 

Jose

 

---

From: Eichstedt, John
Sent: Wednesday, March 15, 2006 4:28 PM
To: Hunt, Jack; Ray, Courtney
Cc: Ossing, Daniel; Chiu, George; Coulter, Timothy A.; Guzman, Jose J.
Subject: Mission Sim 3 Ephemeris Problem

Jack and Courtney,

 

We encountered a problem with an ephemeris that was loaded to the spacecrafts during Mission Sim 3. The exact same thing occurred on both spacecraft and the ephemeris loading occurred at the same time on both spacecraft.

 

Here is the scenario, which applies to both spacecraft:

 

During setup for Mission Sim 3 we initialized the spacecraft with an ephemeris which had a span ranging from before the start of the test day (2006:303) until 2006:309:01:00:00. As a part of the test, another ephemeris was generated from a SPICE file delivered from the FDF and which had a span from 2006:308:22:59:50 until after the end of the test. This ephemeris was loaded to a macro and was executed via time tag command at 2006:308:22:59:50. The testbed ephemeris was not loaded until about 30 minutes after the spacecraft ephemeris, which should not have had much effect since the ephemeris being used should have been good for another 2 hours after the spacecraft ephemeris executed.

 

In any case, when the ephemeris was executed at 2006:308:22:59:50, G&C indicated that Inertial attitude went to “bad orbit” and the calculated sun vector went way out from the measured sun vector. About 10 seconds later autonomy executed rule 19 which loaded the “coarse” ephemeris from eeprom and everything went back to normal. The coarse ephemeris was a longer span of the initial ephemeris which we loaded as part of the test setup.

 

Today, to see what would happen and to hopefully give us a better idea of the problem, we ran the same thing through on the Hardware-in-the-Loop Simulator without autonomy enabled. What we saw was the same thing I described above, except that about 35 seconds after the new ephemeris was loaded, everything went back to “normal”.

 

We do not have a way to examine the ephemeris data ourselves, but I was hoping that you might be able to look at the data and help us determine what had happened. The HIL run was on harry and it went from a ground time of about 2006:074:19:40:00 to 2006:074:20:20:00. The time of the new ephemeris execution was at a ground time of 2006:074:20:07:38 and a spacecraft time of 2006:308:22:59:50.

 

Both of the ephemeris that were used for this test on spacecraft B are available to you in the epoch log in the following directory on davis: \\Davis\project\Stereo\Ground_Systems\Ephemeris_Files\behind_sim_3_ephemeris\epoch_behind_sim3_ephemeris.log

 

Thank you for the assistance,

 

John

 

John E. Eichstedt

STEREO Mission Operations Manager

Integration and Operations Group

Space Department

 

The Johns Hopkins University Applied Physics Laboratory

11100 Johns Hopkins Road

Laurel, MD 20723-6099

240-228-8738 / Washington

443-778-8738 / Baltimore

FAX 240-228-5583 / 443-778-5583

john.eichstedt@jhuapl.edu