MISSION PLAN - PDS Small Bodies Node

4.2.4 Mission Operations Considerations
Current mission operations plan to issue a minimum of weekly updates to the spacecraft
attitude and aerogel grid collector angle during ISP collection, and spacecraft attitude
during the CIDA experiment. An intentional lead-lag strategy should be established for
most efficient tracking of the ISP stream. However, the final spacecraft attitude and
collector angle update schedules can be established only after the post launch final uplink
schedule is known. JPL will provide a list of daily spacecraft attitudes and collector
angles (see section 12) from which LMA will build the required lead-lag update
schedule.
4.3 Mission Operations
Mission operations during the Cruise phases are summarized in Tables 4.3-1.a-c. The
operations during these phases drop to the lowest level of the mission. Activities
required are essentially to maintain the spacecraft attitude profile to ensure adequate
reception of solar power, communication with Earth at the scheduled times and tracking
of ISP’s during the collection and CIDA periods. In addition, the spacecraft gathers and
transmits information on spacecraft health as well as the sporadic science data. Imaging
plans during cruise are limited to calibrations and standard camera maintenance. These
plans are described in Table 4.3-2.
Primary activities on the ground are spacecraft subsystem analysis and maintenance, and
the generation of uplink commands. DSN tracking continues using the 34-m HEF
network. Medium Gain Antenna (MGA) tracking is performed to obtain radiometric data
for orbit determination and DSM/TCM formulation. This radiometric data is comprised
of both ranging data and two-way Doppler data (See the Navigation Plan for more
details). Spacecraft mode tracking is performed for telemetry and command. An uplink
frequency of once per month is anticipated, however, commanding will increase during
ISP collection and CIDA periods to allow tracking of the reference particle.
The current request for DSN tracking in support of DSM-1 and its cleanup maneuver,
TCM-3, is reduced from the baseline for TCMs. The power constraint to avoid casting
shadows on the solar arrays with the whipple shields, and sun-Earth geometry during this
phase of the mission would drive a need for large yaw slews (rotation about the z-axis),
160° over 4 hrs, between the ISP collection attitude and the MGA communications
attitude. Given this slew scenario, the daily communication requirement surrounding
TCMs reduces the amount of time available for ISP collection. Two action are taken to
reduce the impact of NAV tracking on spacecraft slewing and on ISP collection time.
The first is to schedule use of the HGA instead of the MGA. The HGA’s tighter
deadband, together with small SPE angles (also coincident with this phase of the
mission), allows the spacecraft to communicate with the Earth without performing a large
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