The planning and scheduling of XMM-Newton observations is a work-intensive and complex process. The goal of this process is to maximize simultaneously the scientific return and the observation efficiency.
The planning and scheduling has to take into account the visibility of the targets, scientific constraints, times with expected high radiation background, handover between ground-stations and on-board antennas, and feasibility of slews. Observations with XMM-Newton must comply with a number of celestial constraints, such as solar, Earth limb, Moon or Jupiter avoidance angles. Examples of additional scientific constraints are specific spacecraft position angles, ``Fixed-Time'' observations, ``Anticipated Target of Opportunity'', or requests for simultaneous observations. Depending on the solar activity, a part of the science window at the start and at the end of an XMM-Newton orbit can be affected by a high radiation background, which forbids opening of the filters of the EPIC camera. During the handovers between the different ground-stations used in each XMM-Newton revolution, observations can be continued but commanding is not possible and slewing has some restrictions. Even if a target is well visible according to the visibility constraints, it may not be reachable from the perigee position at the start of a revolution, because the slew would violate some of the constraints mentioned above. Other targets may not be scheduled because the slew back to the perigee position is forbidden.
Whenever possible, the priority of an observation as allocated by the OTAC is considered for the mission planning and scheduling. However, for operational reasons, no guarantees can be given that any particular observation will, in fact, be executed, regardless of its grade. XMM-Newton reserves the right to reject any approved observation that is in conflict with safety or mission assurance priorities or schedule constraints, or is otherwise deemed to be non-feasible.
The SOC prepares the final detailed timeline about 3-4 weeks in advance. Given the various constraints, listed above, the mission planning and scheduling team can not avoid that some observations are split in multiple parts. Additionally, the actual performance of the instruments and the corresponding observing modes are taken into account, i.e. requested observing modes may be replaced by a similar but better one based on the performance reports from the instrument teams.
The PIs are automatically informed via e-mail when their observation is scheduled. It is the responsibility of the PI to check carefully the scheduling details within three days and report about any observation which is not in agreement with the enhancement or the rules and procedures in force. After three working days, the SOC assumes that the PI agrees with the implementation of the observation. It is the PI's responsibility to communicate the SOC any change of her/his e-mail address, by e-mail to firstname.lastname@example.org with the proposal number in the subject line.