Propagation issue ?

Spacecraft, Thruster, Tank, Propagator, CoordinateSystem, etc.

Propagation issue ?

Postby MaxJ » Fri Oct 10, 2014 12:20 am

Hi!

I'm trying to write my own orbit propagator in C++/Matlab.
I was searching for a tool on the web that could help me validate my computations.
I found GMAT and I find this is a great software!
While trying to validate my own program I happened to find something weird I really don't understand.
Using a very simple propagator (only force = central + J2) I had a slight disconnection between my ephemeris and GMAT ephemeris that starts after around 100s of simulation and seems to be reduced after 300s.
From the way it looks I have the feeling that it comes from the GMAT ephemeris because my plot is smooth and regular while GMAT plot isn't.
I tried to compare the data using the central gravitational potential alone and I found the same disconnection.
Is it a normal behavior of the propagator ? Did I do something wrong in my setup ?
Attached you will find the script file and two plots from Matlab: position and velocity over 500s.
The left parts of the plots are comparisons between my propagator ("ORBIT", blue) and GMAT (red).
The right parts are the differences between the 2 ephemeris files ("ORBIT" - GMAT).
For my software I use a fixed-step (1s) RK4 integrator and a Cartesian propagator.
Thanks a lot!

Max

PS: Sorry for my english...
Attachments
Velocity_Comparison.png
Position_Comparison.png
Test_Intervalidation.script
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MaxJ
 
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