Targets should be limited to those needed to carry out your research objectives, plus a few alternate targets to provide some degree of flexibility during your observing run. Alternate targets may be needed to work around any spacecraft-pointing constraints that may arise during the observing shift. These constraints may result from an underpowered or overheated condition in the spacecraft or if the particle radiation is unusually high (see Sections 3.3, 4.4, and 4.9). Such problems can usually be avoided by scheduling an observing program for dates when the principal targets are at desirable orientations with respect to the sun. If there are a large number of targets on your program, be sure to indicate your high priority targets to the Scheduler.