Regularized propagators

[MiguelAvillez]

Implementation of regularized propagators: stabilized Cowell and Dromo(P).
Branch: https://github.com/MiguelAvillez/tudat/tree/feature/regularized_propagators

Relevant literature:

• "REGULARISED METHODS FOR HIGH-EFFICIENCY PROPAGATION", Geul et al. (2016)
• "DROMO propagator revisited", Urrutxua et al. (2016)
• "ACCURATE COMPUTATION OF HIGHLY ECCENTRIC SATELLITE ORBITS", Janin (1974)
• "Regularization in Orbital Mechanics", Roa (2016)

Stabilized cowell implemented according to Janin (1974). Dromo(P) implemented according to Urrutxua et al. (2016); same propagator used by Geul et al. (2016).

Current overall status:

• Setup of propagation using independent variable other than time implemented, though not really working. See stabilized cowell.

Stabilized cowell:

• Implemented, but not working, even without perturbations. No idea why.
• Implementation of the term dU/dr of the EOM is wrong (which doesn't explain why it isn't working without perturbations)

Dromo(P):

• Unit conversions and EOM implemented
• Conversion from Cartesian to Dromo(P) unit tested
• Conversion from Keplerian to Dromo(P) unit tested
• Conversion from Dromo(P) to Cartesian partially tested: Parabolic case (case 3) not finished. Recheck remaining cases.
• Conversion from Dromo(P) to Keplerian not yet tested

[DominicDirkx]

Thanks for posting this! It looks like it's already pretty well advanced. The next time I have a couple of hours to spend on debugging something, I'll see if I can look into the stabilized Cowell