However, observing grid stars adds overhead and reduces the amount of time available for observing target and reference stars. Proposers will need to choose the optimum number of grid stars needed for their observations. Assumptions back to top All numbers and parameters reflect best current knowledge of the spacecraft and instrument design. Science targets are evenly distributed over the entire sky. Performance is enhanced when a science target sits near the center of a tile, which is more likely to happen when the degree of overlap is higher.
Overhead costs are lower when the total number of tiles is smaller.
For these calculations, tile fractional overlap is assumed to be 0. Targets will be scheduled such that the average slew between successive fields of regard is 15 degrees.