I have had a few questions I hope you can help clear up.
Over the past few days I have been messing around with the Batch Least Squares estimator, and I noticed for every satellite I tested when adding Relativity I was getting a worse chi squared, this occurred consistently.
From playing around with it I found that by adding the force models in a different order suddenly fixed this issue.
Looking into the source code of Orekit I found out why. When setting Relativity I was using: Constants.JPL_SSD_EARTH_GM For it’s value for GM. This seemed to be overriding my value for Mu throughout the program.
I understand GM and Mu are the same thing fundamentally, however the fact Relativity specified a parameter “GM” rather than “Mu” like elsewhere implied to me they were separate constants and thus wouldn’t override each other.
Upon further investigation I found that if you add Newtonian Attraction it’s mu is always the mu the program uses regardless of what other forces set as mu.
So my questions are this:
- Why does Relativity use GM as a parameter name rather than Mu? Does it use it’s value for GM when calculating the acceleration even if the Central Attraction Coefficient Parameter Driver is overwritten?
- Is there a recommended order to add force models?
- In General, what are the best practices for adding force models (e.g. should I always explicitly add Newtonian Attraction?)
Thank you for your time.