Scheduler

The NCCS must provide at least the same scheduling capabilities as the present system.

A description of the present scheduler is as follows :

• The present system makes a distinction between the master observing program (MOP) and routine observing programs (ROP). The philosophy of the present system (as implemented by SHPRM/SCHDL on the HP 1000s) is that the telescope is managed as a global resource. The current program has control of the telescope until such time as it decides to release it. At this time if the scheduler has work to do (this has been calculated previously by looking at the input parameters) it wakes up and schedules the program which is supposed to run. The program which is supposed to run is calculated based on the present sidereal time, the requested source's coordinates and the mode of routine observation requested. The following modes are supported:

  $\surd$

  calculated hour angle (maximum of 13 observations per day),

  $\surd$

  at a given hour angle (maximum of 7 observations per day),

  $\surd$

  immediate scheduling (after 1 minute).

  Every program has to specify the observing frequency, radiometer mode (if continuum) and source name/coordinates. 5 optional parameters can be specified to the scheduler to specify anything else the observing program wants to use the optional parameters for.

  Once a ROP has gained control of the telescope it keeps it until such time as it decides to release the telescope back to the scheduler.

  The list of ROPs to be scheduled and their parameters are kept in a file which is read by the scheduler each time it starts up. This ensures that the list of scheduled programs is maintained over system crashes and that it can be modified during runs and the scheduler will take the modifications into account.

The NCCS must offer all the above options.

Additional options which are desirable are :

$\heartsuit$

The ability for the NCCS scheduler to interrupt an observing program and if necessary suspend it and schedule a new program. The notion of priorities of observing programs will have to be introduced in order to do this. Programs with a higher priority will have precedence over programs with a lower priority. Programs should only be interrupted at the end of an observation. The definition of what is an observation will depend on the kind of observation i.e. continuum, spectral lines, mapping, pulsars. Priorities will be distributed by the operations manager but it should be possible for a program to modify its priority dynamically if necessary.

$\heartsuit$

Support the notion of Background Observing Programs (BOPs). These are low priority programs which sit in the background and are only scheduled when neither a MOP or ROP are running. The BOPs are there to soak up any idle time of the telescope and ensure maximum utilisation of the telescope. Typical example of BOPs are pointing programs.