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How Spitzer Scheduling Works

The scheduling process starts with a database full of AORs, a spacecraft engineering plan, and a set of instrument calibration plans. There are three major stages: Long Range Planning (LRP), Scheduling, and Sequencing. LRP goes on more or less continuously in the background. The scheduling process itself begins 5 weeks prior to the observing sequence execution, and produces a week-long sequence of Spitzer science observations, calibrations and necessary maintenance activities. There are a number of scheduling challenges which influence the way in which and when AORs are scheduled.

Long Range Planning
After each proposal call, a major adjustment to the long range planning is made. Highly constrained activities and conflicts are identified at this point in the process. Incremental changes may be made to it as scheduling proceeds, in order to deal with such issues as DSN station allocations and constraints imposed by the previous week's schedule.

Plan windows for Spitzer consist of the intersection between visibility constraints and any timing constraints which have been placed. They allow OPST to identify which observations are available to schedule in a given time period, but do not represent a commitment to schedule the observation in any particular window.

Scheduling begins about 5 weeks prior to when a sequence begins execution on the observatory. Since the sequences run from Wednesday to Wednesday, this process usually begins on the Monday of the 5th week in advance, but can be slightly earlier on any given week.

The scheduling process consists of laying down spacecraft and science instrument calibrations, selecting a "pool" of available science observations, laying these out on the timeline, accounting for all the constraints and periodicities on the calibrations while trying to minimize slew times (this is facilitated by the scheduling tool SIRPASS), planning the downlinks, etc. The provisional schedule is then reviewed by the SSC Director, Science User Support and instrument scientists. Adjustments are made, and the schedule is reviewed again by those parties, in addition to the Observatory Engineering Team and the Mission Manager. After approval, the timeline is converted into command sequence products and handed over to the JPL Mission Sequencing Team (MST) for final sequence product generation and flight rule checking. The scheduling process takes the better part of 3 weeks with delivery from OPST to MST occurring on the 3rd Friday


The JPL Mission Sequence Team uses a set of software tools, called the Uplink Toolkit, to reformat, constraint check and flight rule check the products which OPST delivers. There are two passes allocated to this process, so that problems uncovered on the first attempt can be resolved. This takes a week and a half for two cycles of processing, review, and correction. A command conference is then held for final approval of the sequence and the uplink window begins on the Friday preceeding the Wednesday on which the sequence begins execution.

Parallel Development Threads

Since it takes 5 weeks of development effort and one week of execution for each sequence built, there are 7 parallel threads of effort going on at any one time, with one OPST member assigned to each:

  • Week N is executing and being monitored
  • Weeks N+1 and N+2 are in the sequencing phase
  • Weeks N+3, N+4, and N+5 are in the scheduling phase
  • Weeks N+6 and onward are affected by long-range planning updates.

We expect users to monitor the SSC website. An observer should have a good idea if their AORs could be in a pool - they simply have to be visible to Spitzer during the 1 week schedule to which the pool refers (modulo any other observer constraints). The SSC plans to publish the BIC approximately every 6 months. As noted above, once a given observation has made it into an approved schedule, the Principal Investigator and Technical Contact will be notified. We expect this to occur about 3-4 weeks before the observation is performed. Note that if an observer has more than one AOR scheduled, he or she will only receive one email; we will not send one email per AOR scheduled! Note also that once this mail goes out, it is too late to change the schedule!

Occasionally, there will be internal adjustments to the approved schedule, such that science program AORs are added or removed from the schedule. The SSC will not publish these further updates to the schedule or email observers revised schedule information. There is a maximum of just one amendment permitted per week's planned schedule of observations.

For completeness, we note here that after execution of the observation, the data will be processed through our pipelines and go through Data Quality Analysis (DQA) at the end of an entire instrument campaign. (For complete processing, most observations need calibrations taken at the start and end of a campaign.) The time between when the observations are completed and when the observer has access to the verified data is typically 2-4 weeks, depending on when within the instrument campaign the given observations are scheduled and how long the pipeline processing and quality analysis takes. Of course, when the data are available via the archive, the observer will be notified. Please see this page for more information.

From the scheduling rules above, one can see the origin of the "impact classifications" for Targets of Opportunity (ToOs) spelled out in the Spitzer Observing Rules, e.g., High-Impact is < 1 week, because it can significantly impact the schedules being created at that time. not just for that week, but also for the forthcoming 3-6 weeks.

If an observer requests a modification to an AOR that is 6+ weeks away from the start of the visibility window opening for Spitzer, there should be no effect on it making the first available pool that is appropriate for its instrument type and visibility window. This assumes 1 week instrument campaigns and a quick (1 week or less) turnaround time in processing the modification request through ingest of modified AOR(s).

Scheduling Challenges

A number of challenges exist which affect the way in which and when AORs will be scheduled. One or more of these factors may influence the scheduling of your program's AORs. The following is likely not a complete list, but these items include:

  • Scheduling highly constrained observations (both with timing windows and/or follow-on constraints)
  • Observations of bright sources or with bright sources in the field
  • Finishing up programs from the previous Cycle
  • Scheduled Exploration Science programs
  • Extrasolar transiting planet observations, some requiring non-standard observing modes
  • Handling high data volumes
  • Interruptions by anomalies ("safe modes")
  • Scheduled or interruptions by Targets of Opportunity
  • Bridging the Cycles