13 July 2019: Lightsail 2 Mission Manager's Log

07/13/2019 Image

During last night’s passes, the updated ADCS gains file was uplinked and activated. Following activation of the new gains, the attitude rates dropped as expected in detumble mode, as shown below. In particular, the Z-axis angulr rate dropped from over 7 deg/s to 1.25 deg/s. Torque-rod based attitude control is now behaving as expected in detumble mode.

An increase in torque rod current was not verified in telemetry. This could be due to a telemetry reporting error, or it could be that the torque rods were not active when the beacon packets were generated. The flight team will download stored telemetry to see if there are torque rod current evident, and they will also send a payload_status command to the spacecraft to get higher resolution torque rod current data.

The team continues to investigate the sun sensor voting scheme. This algorithm is part of the attitude determination process, and is used to exclude sun sensor measurements that are out of family with the other sun sensors. Using BenchSat, the team constructed a test with three sun sensors and light sources that should have resulted in agreement between the sensors, once the unit vectors to the light sources were converted to the body-fixed frame. The voting process did not return a positive vote on BenchSat. Code review has not uncovered any problems, so this issue remains unresolved. All five sun sensors are now operating in “passive” mode on the spacecraft. In the passive operating mode, the sensors report data, but the sensor measurements are not used in the ADCS process.

During tonight’s tracking passes, the higher-fidelity gyros on the payload interface board (PIB) will be activated, to provide additional insight into the spacecraft attitude dynamics.

On Sunday, an ADCS software patch will be uploaded to update the transformation of sun sensor measurements (angles in the sensor x-z and y-z planes) to unit vectors in the sensor frame, fixing a discrepancy found during testing. The team plans to transition the spacecraft ADCS to Mode 1 (Z-axis alignment) and assess performance. A hard reboot of the spacecraft will be performed to reset the long-duration watchdog timer.