Initial Time condition conversion error? [resolved]

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Initial Time condition conversion error? [resolved]

Postby bdillow » Thu Jul 02, 2015 6:12 pm

I have two spacecraft with known ECI positions are the same instant in time. I enter their initial state as UTCGregorian "2 Apr 2014 11:00:00.00". My mission currently has just one backwards propagate of a set duration in ellapsed seconds (-12127.246). When I look at the reports the elapsed time (difference between start timestamp and end timestamp) is 12127.2460001288 (good enough) but the starting time is "2 Apr 2014 11:00:35.034" and the ending time is similarly shifted by 35.034 seconds.

Is there anything I can do to ensure that the starting times don't get shift by any amount? The offset I'm getting as fractions of a day is just 0.0004054861, and the Julian Date is accurate to more than that many decimal places so I wouldn't have thought the conversion from Gregorian to modified Julian would cause such a problem. Could it be something else?

Thanks for the help.

Edit:
Resolution was that I was reporting A1Gregorian and NOT UTCGregorian, causing the discrepancy between entered epoch and first epoch of the reports.
Last edited by bdillow on Wed Jul 08, 2015 4:53 pm, edited 2 times in total.
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Re: Initial Time condition conversion error?

Postby jjkparker » Thu Jul 02, 2015 6:16 pm

It looks like the number you're getting in your reports is the A1Gregorian epoch, not the UTCGregorian epoch that you're putting in.

I'd look at your ReportFile resource or Report commands, and make sure you're reporting UTCGregorian.

Hope that helps!
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
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Re: Initial Time condition conversion error?

Postby bdillow » Thu Jul 02, 2015 6:23 pm

In my reports, I output UTCGregorian and A1ModJulian timestamps. If I take the A1ModJulian time matching the 11:00:35.034, subtract 35.034/86400, and re-enter that A1ModJulian time as my starting epochs, than the reported UTCGregorian times are reported as actually being 11:00:00.00 as desired. But I'm no longer sure that the A1ModJulian time that the propagation starts at properly matches my initial orbits.

What is the time format used for integration in the propagator? Any idea in the conversion chain is the extra 35.034 seconds being introduced?
bdillow
 
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Re: Initial Time condition conversion error?

Postby jjkparker » Thu Jul 02, 2015 6:30 pm

Can you attached your script? I can take a look.
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
Posts: 617
Joined: Thu Jan 07, 2010 9:48 pm
Location: NASA Goddard Space Flight Center, Greenbelt, MD

Re: Initial Time condition conversion error?

Postby bdillow » Wed Jul 08, 2015 4:51 pm

When I posted my second reply at 2:23, my browser didn't refresh with your reply of 2:16. You were right. I overlooked that I was reporting A1Gregorian and not UTCGregorian.

Thank you for the clarification.
bdillow
 
Posts: 7
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Location: GSFC

Re: Initial Time condition conversion error? [resolved]

Postby jjkparker » Thu Jul 16, 2015 12:18 pm

Glad to hear it's working!
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
Posts: 617
Joined: Thu Jan 07, 2010 9:48 pm
Location: NASA Goddard Space Flight Center, Greenbelt, MD


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