Emergent Engineers Provide Critical Support to ATLAS on ICESat-2
Emergent engineers support the Advanced Topographic Laser Altimeter System (ATLAS), the sole instrument onboard NASA’s $2 billion ICESat2 observatory. Our instrument support facility (ISF) team performs mission planning, instrument data trend analysis, health and safety monitoring, and instrument commanding via remote and onsite operations at NASA GSFC. We have been part of the larger ATLAS development effort from the early days of preliminary design reviews through component and instrument integration and test (I&T), culminating in launch and on orbit operations.
ISF ATLAS operations planning take place daily, culminating in a weekly upload of instrument activities to the ICESat2 spacecraft. These activities include frequent calibrations of key components, targets of opportunity, off-points over vegetated land to sample tree canopy density at the mid-latitudes, and a series of orbit and attitude calibration activities. One example of this process is the scheduling of frequent collections of ATLAS transmit echo pulse data from the Photon Counting Electronics (PCE) detectors at randomized geographic grid locations. The ISF processes this data to calculate time dependent millimeter scale corrections to the ICESat2 zero range bias of the ATLAS measurements. The ISF and precision orbit determination team worked together to identify a sizable discrepancy in the computation of the original zero range bias supplied to ATLAS. Removing that source of error and applying the time dependent zero range bias corrections greatly reduce errors in ICESat2’s primary science products.
The ATLAS performance analysis tools ISF uses on orbit originated as the Instrument Science Analysis Workstation (ISAW), a set of real-time I&T GUIs that gave instant feedback to the test engineers and created processed ATLAS data for post-test analysis. ISAW functionality provides the core of the ATLAS performance trending and monitoring (PMT) system. PMT creates pages of trends plots for every instrument mnemonic on hourly to yearly timescales for assessments of, and adjustments to, ATLAS settings to accommodate changes to component temperatures due to the slowly changing angle of the sun with respect to ATLAS, keeping the instrument functioning at peak efficiency.
Recently the PMT generated automated email notifications of yellow limit violations indicating that the ATLAS flight software (FSW) was in a non-nominal mode. The PMT ‘Daily Checks’ page showed the most recent two hour ‘Quick Look’ plots of laser energy and wavelength showed our laser was firing nominally. However, the temperature of the PCE FPGA cards inside ATLAS had dropped precipitously in the last hour, much lower and faster than the temperatures changed during a yaw flip maneuver clearly seen in the 30 day plot on the same page. A switch to the automatic screen capture from the most recent contact with ICESat2 showed values of zero milliseconds for the PCE range window start and width, the PCEs were not actively processing returns, and thus generating less heat. The same parameters were nominal in the contact prior to the onboard test. The onset of the errors was coincident with a scheduled onboard test of new FSW parameter settings earlier that morning.
Within minutes ISF was able to notify FSW of the error flags and anomalous telemetry, and coordinate loading corrective commands at the next ground station contact. ATLAS producing science within hours of detecting the error flags. This rapid response was possible due to insight and foresight. When an anomaly occurs, the diagnostic data the ISF most likely need are already plotted at meaningful intervals on our Daily Checks page. Instead of scrambling to process data, we can immediately assess the behavior of any component during the past two hours, or past two years and transition to resolving the issue.
