Forces presentation

Objects implementing the force model interface are intended to be added to a numerical propagator before the propagation is started.

The propagator will call at each step the force model contribution computation method, to be added to its time derivative equations. The force model instance will extract all the state data it needs (date,position, velocity, frame, attitude, mass) from the first parameter. From these state data, it will compute the perturbing acceleration. It will then add this acceleration to the second parameter which will take thins contribution into account and will use the Gauss equations to evaluate its impact on the global state derivative.

Force models which create discontinuous acceleration patterns (typically for maneuvers start/stop or solar eclipses entry/exit) must provide one or more events detectors to the propagator thanks to their getEventsDetectors() method. This method is called once just before propagation starts. The events states will be checked by the propagator to ensure accurate propagation and proper events handling.

Available force models

The force models implemented are the following ones:

• atmospheric drag forces,
• central gravity forces. Several attraction model are available for representing the gravitational field of a celestial body:
  • Andrzej Droziner model (Institute of Mathematical Machines, Warsaw) in his 1976 paper: An algorithm for recurrent calculation of gravitational acceleration (artificial satellites, Vol. 12, No 2, June 1977),
  • Leland E. Cunningham model (Lockheed Missiles and Space Company, Sunnyvale and Astronomy Department University of California, Berkeley) in his 1969 paper: On the computation of the spherical harmonic terms needed during the numerical integration of the orbital motion of an artificial satellite (Celestial Mechanics 2, 1970),
• third body gravity force. Data for all solar system bodies is available, based on JPL DE 405 or DE 406 ephemerides,
• solar radiation pressure force, taking into account force reduction in penumbra and no force at all during complete eclipse,
• forces induced by maneuvers. At present, only constant thrust maneuvers are implemented, with the possibility to define an impulse maneuver, thanks to the event detector mechanism.

Authors

• Luc Maisonobe
• Mathieu Roméro
• Edouard Delente