Chapter 2: 
Special Considerations
for Cycle 11

In this chapter. . .

Support of STIS Capabilities for Cycle 11 MAMA Scheduling Policies Prime and Parallel Observing with the STIS MAMA Detectors

STIS has been in orbit since 1997 and has been operating superbly, returning a multitude of new and unique scientific results. We have learned a significant amount about the instrument and its operation since installation, and all calibrations are either based on or consistent with data obtained in flight. We list below the STIS-specific policy items needing consideration for STIS Cycle 11 proposals.

On 16 May, 2001, STIS experienced a malfunction caused by a short circuit in its default "Side 1" set of electronics. Since there is no simple way of repairing the affected STIS electronics during the upcoming Servicing Mission, Side 1 can no longer be used to obtain STIS observations. Fortunately, STIS has a completely redundant set of electronics, including power supplies, mechanism controllers, etc., namely "Side 2". The Side 2 set of electronics has not been used since the instrument was installed during Servicing Mission 2; all STIS operations in orbit so far have been using Side 1. After modifying the full set of STIS commanding procedures, and after generating a new version of the STIS flight software, the STIS has been revived in early July, 2001, using Side 2 electronics. Initial verification testing indicates that all significant components of STIS are now fully functional again, and that the detectors and mechanisms perform very well.

While the analysis of an orbital verification program and the recalibration of various instrument capabilities is currently being pursued, it is anticipated that observers will notice very little difference between the new Side 2 and the old Side 1 observations. A possible exception might be programs using the STIS CCD for which success depends heavily on read noise or dark current. As to the CCD read noise, the latest measured value in its nominal Gain = 1 setting (see Chapter 7) for Side 2 operations is 5.3 e^-, somewhat higher than the nominal value for Side 1 operations (which was 4.4 e^-). As to the CCD dark current, the STIS CCD does not have an active temperature control on Side 2. Therefore the CCD dark current will show a stronger dependence on orbital parameters and spacecraft attitude than during Side 1 operations. Analysis of on-orbit data is being conducted to quantify such effects, which are however expected to be minimal for most applications.

The Cycle 11 Announcement Web Page referenced in the Call for Proposals should be consulted for any updated information on STIS performance. In the meantime, proposers should assume that this Handbook (Version 5.1, July 2001) correctly describes the STIS capabilities that may be requested for Cycle 11.