Herschel Science/Instrument Planning and Scheduling

Jon Brumfitt, Herschel Science Centre, ESAC

Herschel is a far-infrared and sub-millimetre space observatory with cryogenically
cooled instruments. A single software system was designed to meet the needs of all
mission phases from early instrument development to post-operations. This 'smooth
transition' approach allowed the instruments to be developed with the real software,
and vice versa. It allowed early detection of problems and avoided the need to build
instrument simulators. A key component of this concept was the Herschel Common Uplink
System (CUS) which commands the instruments. Instrument commanding is defined in a
special scripting language, which supports both routine observing modes and one-off
scripts for test/engineering purposes. This flexibility was particularly valuable
during on-ground instrument tests and in-flight commissioning.

The Herschel Scientific Mission Planning System is used to schedule scientific,
calibration and engineering activities. Daily schedules are expanded into sequences
of low-level instrument and spacecraft commands using the CUS. The software emphasises
visualisation of the observations and their associated constraints, in both the
spatial and temporal domains, so that the mission planner can visualise the planning
task and produce efficient schedules. The system needed the flexibility to cope with
operational contingencies, iteration with users, instrument commissioning and special
scheduling constraints. The software enforces the constraints, slew times, etc. 
A long-term view (past and future) is provided by the Herschel Inspector and Long
Term Scheduler. This assists long-term optimisation, provide statistics and helps to
avoid duplicate science.

The uplink system makes use of a Java flight dynamics and mission planning library.
This was developed for Herschel but with reuse in mind. It was used for Planck and
has subsequently found applications with other missions including Euclid.