4.6.1.1 OV Phase Constraints

There are a few constraints imposed on the activities, some of which have schedule impact. The observatory will be operated only in the expected on-orbit configuration: this means for example that systems will be powered from only the primary side, systems will not be intentionally driven to operational temperature extremes, and we expect the telemetry to be in a ``science'' format a majority of the time. Many of the planned activities require the telescope sunshade door to be open which limits activities prior to this event to verifying FPSI operation. Most significant among these limitations is that the science instrument module must not be translated prior to opening the sunshade door and the objective transmission grating (OTG) insert and retract mechanism must not be operated until the time of OTG verification.

The sequence of science instrument tests at the focus of the telescope is:

• ACIS-S
• ACIS-I
• ACIS-S/HETG
• HRC-I
• HRC-S
• HRC-S/LETG

In addition to operating the instruments other aspects of AXAF operations will be tested during OV. The observatory must achieve thermal stability, have its celestial location determined, be able to acquire aspect stars, and establish pointing control. We must be able to reconstruct images based on data from the science instruments and from the PCAD system. In order to operate independently, the observatory must demonstrate the ability to execute stored command loads autonomously. We must also be able to retrieve on-board recorded telemetry.