| SCL Enables FUSE to Autonomously Recover from SEU's with No Loss of Science Data
Columbia, MD, June 14, 2000 -- – Interface & Control Systems (ICS) announced today that the Far Ultraviolet Spectroscopic Explorer (FUSE), which uses SCL extensively for onboard fault detection, correction and other automation now has the capability to autonomously detect and correct single event upsets (SEU). This autonomous code repair is typically performed within 2 to 3 minutes with NO impact to science data collection. FUSE is using SCL to detect and correct SEU's in one of its main instrument computers that controls the ultraviolet detector. An SEU is memory corruption that occurs when a particle of radiation impacts computer memory causing a bit to change or "flip" potentially rendering the software code useless. Typically, SEU's occur when the spacecraft is traveling through areas of high radiation such as the South Atlantic Anomaly where the Earth's radiation belt dips low enough that FUSE passes through it.
FUSE was experiencing an SEU in the detector anywhere from one to three times a week. This was having a severe impact on FUSE science efficiency. SCL scripts and rules were developed to autonomously detect SEU's and take corrective action thereby minimizing the detector down time.
There are two areas in computer memory where the detector software can run called upper and lower core. Each has its own error detection software, which computes individual cyclic redundancy check (CRC) bytes. Normally, the detector code runs in the upper core with the lower core as a backup. SCL scripts and rules have been developed to monitor the CRC byte in the upper core. When an SEU is detected, SCL checks the lower core CRC byte. Should the lower core check out, the detector software is restarted in the lower core and a reload or recovery of the upper core is automatically initiated. Once the upper core has been recovered and verified, SCL switches the detector software back to the upper core and to its normal configuration.
Should both the upper and lower core experience a corruption, SCL initiates a reset of the detector, which reloads both the upper and lower core software. All of this takes place with no intervention from the ground.
There are plans to use SCL in other areas for automation. The Fine Error Sensor (FES) is a star camera used to track targets for observation by FUSE. The FES gradually accumulates contaminants, which result in "hot" pixels. These hot pixels will ultimately degrade its performance.
One way to recover some of the hot pixels is to perform an annealing operation where the pixel array is heated over a period of time to "bake out" contaminants. During initial annealing experiments, it was determined that the heater is apparently oversized for the job. Further complicating matters is the fact that there is no thermostat to control the heaters. This results in the heaters driving the temperature above the high temperature limit of the FES and triggering an automatic heater shutdown that aborts the annealing sequence. Since FUSE is out of contact with the ground most of the time, it has been difficult to maintain the annealing temperature for the required duration.
A study is underway to develop SCL scripts and rules to act as a thermostat. The temperature of the pixel array would be monitored by SCL rules. SCL would autonomously cycle the heaters on and off to maintain an appropriate temperature range for the required period of time. Again, this would be accomplished with no intervention from the ground.
ICS is a product development and engineering services company specializing in the development of real-time, embedded, and autonomous command and control software systems. Services include software systems engineering, integration and test, and project and software life cycle management. ICS is a privately held company with main offices in Columbia, MD, and Melbourne, FL.
Contact information:
 |
