Current Status and Restrictions

1. Although, the limbs are fitted to provide the pointing on a sub- arcsecond level, it's not checked whether the pointing accuracy complies with the 0.4 arcsecond requirements. Nevertheless, the estimated error is returned in the tag 'P_ERROR' if the aspect data is retrieved for given times.
2. Only SAS cycles with at least 2 limbs on two subsystems are taken as valid cycles. All other SAS cycles are currently ignored.
3. For the X-class flare on October 28, 2003, a customized pointing solution is read from the aspect database on SSW.
4. For the quality, only the triangle size and the solar radii from the SAS are calculated.
5. By default, the roll solution is read from the roll angle database on SSW. If no solution is available the software tries to reconstruct a PMTRAS solution. The control parameter AS_ROLL_SOLUTION can also be set to 'RAS' in order to reconstruct the roll angle from the CCD-RAS data. Although the latter isn't a robust software yet and the correct solution can depend critically from input parameters. Critical datagaps in the roll database will be filled with customized RAS solutions.
6. As default, the aspect time range has to be within the daytime portion of the orbit and the beginning and end must not fall within a big data gap of pointing measurements. By using the control parameter AS_NO_EXTRAPOL, the available data can be retrieved.

Figure 2: Flow chart of the aspect solution software. The Solar limbs and the Star events are fitted independently. Using a Star catalog and the known geometry, the position of the Sun center in a spacecraft fixed coordinate system and a list of position angle marks can be calculated. Integration of these information, interpolation and coordinate transformation provides the needed pointing and roll angle information with respect to a inertial coordinate system.