The first time the deep-space subroutine is accessed is during the initialization portion of SDP4/ SDP8 and is via the entry DPINIT. Through this entry, certain constants already calculated in SDP4/ SDP8 are passed to the deep-space subroutine which in turn calculates all initialized (time independent) quantities needed for prediction in deep space. Additionally, a determination is made and flags are set concerning whether the orbit is synchronous and whether the orbit experiences resonance effects.
The next access to the deep-space subroutine occurs during the secular update portion of SDP4/ SDP8 and is via the entry DPSEC. Through this entry, the current secular values of the ``mean'' orbital elements are passed to the deep-space subroutine which in turn adds the appropriate deep-space secular and long-period resonance effects to these mean elements.
The last access to the deep-space subroutine occurs at the beginning of the osculation portion (periodics application) of SDP4/SDP8 and is via the entry DPPER. Through this entry, the current values of the orbital elements are passed to the deep-space subroutine which in turn adds the appropriate deep- space lunar and solar periodics to the orbital elements.
During initialization the deep-space subroutine calls the function subroutine THETAG to obtain the location of Greenwich at epoch and to convert epoch to minutes since 1950. All physical constants which are unique to the deep-space subroutine are set via data statements in DEEP rather than being passed through a COMMON.
A FORTRAN IV computer code listing of the subroutine DEEP is given below.
These equations contain all currently anticipated changes to the SCC
operational program. These changes are scheduled for implementation in March,
1981.