by JackCrenshaw » Thu Aug 22, 2013 3:33 am
I, too, have been having a lot of crashes on my XP machine. As a total newbie, I'm perfectly prepared to accept that the problem is pilot error, but I sure wish I could make it stop.
As near as I can tell, my problems all have to do with the DC solver. If I guess right on the parameters in the Vary block, I get good results. If not  if the solver hits some conflict between trial values and the trial value parameters (min, max, step, etc.) I'm seeing one of two problems: Either GMAT seems to stick (as in an endless loop), or it simply stops working (program is not responding). I'm working the problems as best I can, but it's slow going.
Can you tell me the DC algorithm being used? I know that in one case, the solver was approaching the desired Achieve goal, just adding thruster burn time in max step quantities. But the first time it chose a value less than the max step value, it HUGELY overshot the trial value, yielding an orbit apogee 1012 times larger than the target goal. I'm attaching a graph of the solver's convergence.
One possible contributing factor: I'm simulating a lunar mission (who ain't?), and the earthbased, elliptic orbit is very close to parabolic/hyperbolic. As you know, a hyperbola doesn't have an apogee, but depending on the implementation of your code that computes osculating Keplerian parameters, they might go wonky if we cross the parabolic threshold.
Maybe I should use C3 instead of apogee?
Speaking of which: Does your calculation of Keplerian elements use universal variables, or the classic twobody formulas?
 Attachments

 GMAT Solver Results.xls
 (18 KiB) Downloaded 255 times