To maintain a sufficient level of power supply, the Solar Paddle must be pointed close to the Sun. There is a hard operational limit of 25 deg, meaning that ASCA can observe targets 65-115 deg away from the Sun. This is because the quality of SIS data degrades due to scattered sunlight at lower Sun angles. However, consecutive observations at large Sun angles tend to warm the CCDs, which also has serious detrimental effects to the data quality. Because of the square shape of the CCD chips, particular roll angles may be required to fit an extended source onto the SIS field of view.
Many PIs are interested in coordinated observations with ground-based telescopes.
This can be achieved, to a degree, without making the ASCA observation time-critical. Source Placement Use default position for point source. In the case of observations of a single point source, the primary concern is to place the target so as to collect as many photons as possible. The grid in GIS window, which lowers the quantum efficiency. In all the above, the uncertainty in the locking attitude must be taken into account.