Small Body Insertion Using GMAT Propagator

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

Small Body Insertion Using GMAT Propagator

Postby Pulsaro » Tue Aug 07, 2018 7:00 pm

Hello GMAT team!

I am interested in propagating two bodies, called "SB1" and "SB2" (and their resulting mutual barycenter, "SBBC"), using GMATs internal propagator. As far as it looks, the only way to define a small body (be it planet, asteroid, or comet), is to provide it an initial state(s) with a sun-centric SPK bsp file. So far, it seems that you cannot propagate small bodies independently, without moving time forward using a spacecraft, called "S/C". SB1 and SB2 can only be stepped forward/backward within the bounds of the bsp you provide it with. This makes the goal of using GMATs propagator to perturb the bodies to exist within the solar system dynamics untenable.

To be clear about the above, I have only passed in a single body, SBBC, which officially recognized in the NAIF system (has official ID), and tried to propagate. I imagine there might be issues with making up two generic bodies with NAIF IDs, but I am not certain yet. A problem I have seen is that only the bodies included in the planetary ephemeris file, such as de421 or de433, can be included in any force models used to propagate a spacecraft, so Jupiter on outward cannot be solved for in moving the small bodies forward. This hinders the accuracy of even propagating the S/C.

The only workaround I can think of is to "trick" GMAT by passing these two bodies as spacecraft, and propagate them forward from there. Some potential issues I see with that, is that these spacecraft masses cannot be inserted into the force model, which becomes a problem if they are sufficiently massive and near each other. Also, B-plane reportfiles, or any useful outputs in general, might be tricky to generate if I want to understand approach conditions to these bodies with a "real" spacecraft.

Please let me know if there are better approaches, or incorrect conclusions I have made based on my efforts so far.

Thank you!
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