Spitzer warm mission transition and operations

Abstract

Following the successful dynamic planning and implementation of IRAC Warm Instrument Characterization activities, transition to Spitzer Warm Mission operations has gone smoothly. Operation teams procedures and processes required minimal adaptation and the overall composition of the Mission Operation System retained the same functionality it had during the Cryogenic Mission. While the warm mission scheduling has been simplified because all observations are now being made with a single instrument, several other differences have increased the complexity. The bulk of the observations executed to date have been from ten large Exploration Science programs that, combined, have more complex constraints, more observing requests, and more exo-planet observations with durations of up to 145 hours. Communication with the observatory is also becoming more challenging as the Spitzer DSN antenna allocations have been reduced from two tracking passes per day to a single pass impacting both uplink and downlink activities. While IRAC is now operating with only two channels, the data collection rate is roughly 60% of the four-channel rate leaving a somewhat higher average volume collected between the less frequent passes. Also, the maximum downlink data rate is decreasing as the distance to Spitzer increases requiring longer passes. Nevertheless, with well over 90% of the time spent on science observations, efficiency has equaled or exceeded that achieved during the cryogenic mission.

Development of sensitive long-wave infrared detector arrays for passively cooled space missions

“…The Spitzer space telescope's focal planes [6][7][8] have equilibrated to ∼27 K now that its liquid helium cryogen supply has been exhausted, demonstrating the efficacy of passive cooling for a thermally well-designed space telescope. Throughout this warm mission Spitzer's two midwave InSb channels at 3.6 and 4.5 μm have performed with undiminished sensitivity, but require focal plane temperatures not much higher than 30 K. The WISE mission's 5.4 μm cutoff HgCdTe arrays, manufactured by Teledyne Imaging Systems (TIS), operated at 32 K with dark currents <5 e − ∕s∕pixel.…”

Spitzer operations: scheduling the out years

“…The responsibility for scheduling observatory activities has been assigned to the SSC and is carried out by OPST. The team's primary responsibilities involve long range planning during which provisional slots are defined for the more difficult and highly constrained observations and short term scheduling when the detailed weekly sequences are designed, reviewed, and prepared for execution on the observatory [8] . OPST consists of one long-range planner and four schedulers with each spending approximately half-time building every fourth week of operational activities.…”

“…The general outline of activities determined by long range planning is used to build the detailed sequences of spacecraft activities which typically span about one week of operations (see Mahoney et al [8] ). The primary tool used by OPST members to build the weekly sequences remains SIRPASS (Spitzer Integrated Resource Planning and Scheduling System), a user interactive application that provides the scheduler a platform for developing the schedule, assessing numerous scheduling options and requirements, and providing a number of reports, many of which flag scheduling errors.…”

Spitzer warm mission: maximizing the science return in the extended mission phase

“…The nominal five-six week scheduling process in shown here. The observatory scheduling is described in detail in the references [5] and [6].…”

“…Additional time was added to the early part of the scheduling process on the ground for warm operations. See [5] and [6] for more details on the scheduling process. A schematic of the process is shown in Figure 2.…”