Hi, Apologies if this is not the correct mailing list for this however I am looking to get help with a GMAT model I am creating.
I want to perform a simple, small altitude change of 500m on a satellite with a low altitude (SMA = 6878 km). I did some hand calculations and got the ideal theoretical dV out as 0.00203 kms^-1 to make sure my model lined up. I have attached the script if anyone wants to run through this but I'll describe my issue below. I started off using JGM-2 with 10, 10 as well as other pertubations. The results I get are confusing. If I start the spacecraft at 0 DEG TA, the position magnitude (RMAG) never shows the spacecraft reaching the expected apogee radius before the burn. It also does not show a clear perigee. Once the burn is performed, the orbit is raised to the correct RMAG at apogee and the dV value to get there is 0.002243 kms^-1, close enough to my validation value. If I change the starting TA to 180 DEG, the RMAG shows a much more sensible value, with radius of apogee at the expected point and a clear perigee, where the burn was performed. The dV value however, is only 0.0001815 kms^-1, very small in comparison. Changing TA to both 90 DEG and 270 DEG shows an even more confusing picture, as well as no convergence on my solution. Reducing the JGM-2 model to 1,1 allows the orbit to behave the same regardless of starting TA, however the dV value is still the smaller one. 1. Why does starting TA have an effect? I was under the impression that as long as I propagate to perigee before performing the burn, my result should always be the same? 2. Why, when I get the orbit behaviour looking correct, is my dV value still way off? 3. Could the large variation in the SMA due to the higher order gravity model be causing the RMAG to be calculated incorrectly? Hopefully someone can help as I've been trying to find my mistake for weeks or where I've gone wrong in the set-up. Thanks, Scott
ImpulseTargetedCAM.script
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