The attitude model lies at the foundation of the this approach. Since it is spacecraft specific, a new model must be developed and implemented for each mission. Precise attitude modeling is essential for computing the correct spacecraft pointing in altimeter measurements and antenna offset corrections [ Marshall and Luthcke, 1994a; Bar-Sever et al., 1994]. Attitude information can be obtained in various forms. Telemetered attitude can be incorporated directly if available or, on the other extreme, detailed codes replicating the on-board attitude command sequences can be developed.
Many spacecraft will require the development and implementation of attitude and temperature models. Model tuning can benefit from parameter sensitivity and correlation studies which enable effective solution design [ Marshall and Luthcke, 1994b]; these will be performed as required on new missions, especially those attempting to solve for other orbit-sensitive parameters like gravity models.
Approaches other than ``macro-model'' development are employed and are important for certain present and future missions. Approximating functions, such as the GPS ROCK4 and ROCK42 models, have been used to precisely model the effects of solar radiation pressure, thermal emission, and additional accelerations detected while on orbit [ Fliegel et al., 1992]. These approximating functions are compact, easy to implement, do not require complex attitude models, and are computer efficient. However, they require detailed finite element analyses to derive the surface characteristics, and they assume strict adherence to nominal mission profiles when employed.