MISSION PLAN - PDS Small Bodies Node

The ISP collection and CIDA experiment plans are currently defined to allow easier
mission operations and pre-launch mission design. These allowances, based on rigid
ground rules, result in less than optimal collection durations. If desired, these constraints
may be relaxed, but doing so may add operational and mission plan complexity.
ISP Collection #1
The geometrical conditions suitable for starting ISP 1 can be achieved as early as L+355
days, but DSM-1 would interfere with the collection period. A combination of spacecraft
and science constraints have led to the current plan that does not start ISP 1 until after
DSM 1 has been completed.
The location of DSM 1 is dictated, after all trajectory design considerations, by the need
to allow sufficient radiometric tracking to support the implementation of DSM 1.
Radiometric tracking is affected here by a period of solar conjunction that occurs a few
weeks prior to the DSM. Based on the NEAR spacecraft solar conjunction experience,
DSM 1 has been placed at 14 days after the spacecraft has reached a Sun-Earth-Probe
angle of 4 degrees (increasing). For the mission scenario resulting from a launch on the
first day of the launch period, DSM 1 could be scheduled such that ISP 1 would start on
L+395 days. However, to ease pre-launch trajectory development, DSM 1 has been
scheduled to support the latest SEP=4 degree occurrence across the launch period and
ISP 1 is set to start at L+403 days. The possible variation of ISP 1 as a function of
launch date is illustrated in Figure 4.2-8. Notice that not only does the start of the period
change, but so also does the end of the period. The end of the period is constrained by
the beta meteoriod avoidance constraint. After launch, it should be possible, if required,
to adjust the location of DSM 1 according to the actual launch date and flight trajectory
and obtain an earlier start to ISP 1.
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