Mosaics

Mosaics that require more than ~20 orbits to construct should be designed taking the visit timing and orientation scheduling requirements into consideration. As a rule, mosaics can be constructed with images taken at orientations that differing by 90 degrees. This provides scheduling flexibility, resulting in more days per year when these observations can be taken. In Three Gyro mode, there will generally be three such orientations available per observing cycle. The scheduling aids available in APT can help you determine which orientations are available for your target, and how many days each provides to the schedulers. Dividing the orbits required for the mosaic by the available days gives a rough indication of the scheduling difficulty for the program. The fewer orbits per available day that a program requires, the less likely it is to have scheduling conflicts with other programs that need those same days. The amount of scheduling time available can depend strongly on the absolute orientation angle chosen for the mosaic. There can be scientific reasons for choosing a particular orientation for a mosaic, such as alignment with the object, or matching prior data sets. Proposers should examine whether orientations that provide more observing days are acceptable. It is particularly useful to indicate in the proposal how much flexibility there is in selection of the orientation of the mosaic. Providing even 10 or 15 degrees of flexibility can ease problems during program implementation. This is particularly helpful in avoiding scheduling conflicts between accepted programs that intrinsically compete for the same observing days.