Instrument Health and Safety
- Optical path shifting – Because of the sensitive optics in SOLSTICE, the temperature gradients across the instrument must be analyzed for any large discrepancies which could cause changes in these optics. This is done by using data from the 14 temperature monitors attached around SOLSTICE and the 4 internal temperature sensors to construct a temperature gradient display of the instrument.
- Gain Changes – Because the SOLSTICE detectors are sensitive to large temperature changes over a short time period, it is important to watch for these periods and apply a temperature dependent correction. This occurs when the instrument is turned on after being off typically due to a spacecraft anomaly.
BOS/Slit failsafe logic – The SOLSTICE microprocessor is programmed with slit failsafe logic. This logic prevents the instrument from placing itself in an unsafe configuration with the slits in stellar position while the sun is up. This could cause large scale degradation in the detectors.
Loading errors – SOLSTICE is loaded daily between 2000-2400 UT with the next days experiments. Sometimes this load information becomes corrupted during transmission. If this occurs, it would be possible for the instrument to configure itself in an unknown and undesirable state. To ensure proper configuration, SOLSTICE telemeters it’s memory contents at the rate of 254 bytes per second. These contents are verified with the expected contents to ensure proper execution of the planned experiments.
Autonomous Instrument Analysis
SOLSTICE ground software is configured to take advantage of near real time (15 minutes every orbit) and quick look (approximately 1.5 hours 3 times per day) data sets in order to automatically check the telemetry for out of limits conditions, verify memory and check for bad instrument configurations. When a bad state is detected, the software will page SOLSTICE personnel. The SOLSTICE analyst can then respond to the anomalies at any location and any time of day.
Spacecraft Operational Constraints
Power Availability – Although the spacecraft’s available power is a constraint on operations, SOLSTICE consumes less than 6 watts of power. This allows SOLSTICE to remain operational in times of low power availability and when other instruments are turned off.
In order to ensure proper execution of current as well as future experiments, the success rate of the daily instrument loads is analyzed. This is accomplished with ground software which compares the planned experiment with what was actually executed. This prevents future anomalies, and provides ways to improve the amount of data taken.
Accurate knowledge of the position of the target with respect to the SOLSTICE detectors, must be known. This allows us to correctly adjust the data to account for the target’s position on the detectors. When tracking the sun, this position knowledge is obtained from a sun sensor mounted near the SOLSTICE instrument’s bore sight. During a stellar track we rely on spacecraft attitude and pointing information to calculate the pointing error rather than measuring it directly.