XMM-Newton Announcement of Opportunity: Policies and Procedures

5.4 Fixed-Time Observations

A ``Fixed-Time'' observation (``Time Critical'' in RPS) is defined as an observation whose scheduling is not solely determined by its visibility and spacecraft position angle constraints. Examples of ``Fixed-Time'' observations are:

• ``Triggered Observations'', see section 5.2.4,
• Observations for which the observer can specify the calendar date, or relative date through, e.g., an orbital ephemeris,
• Observations which must be conducted more than once with a pre-determined time lag in between,
• ``Coordinated Observations'', see section 5.5.
• Observations for which non-standard instrument modes are used, see section 5.6

``Fixed-Time'' observations reduce the flexibility available to the mission planning system for scheduling of observations and can lead to larger than nominal slew overheads. Thus, all proposers are reminded that ``Fixed-Time'' observations should only be asked when there is a strong scientific requirement. This justification must be provided explicitly in the proposal justification. For operational reasons, the start time of ``Fixed Time'' observations should not be constrained below a margin of $\pm$15 ks. In addition, the scheduling constraints should be described in detail in the ``constraints'' sub-menu after entering an observation as ``Time critical''.

It is the responsibility of the PI to demonstrate that proposed ``Fixed-Time'' observations are visible, see section 5.7.