6 July 2019: Lightsail 2 Mission Manager's Log

Based upon the Doppler shift of the received radio signal from tracking station passes, the flight team derived an orbit estimate that indicates that LightSail 2 has drifted approximately 35 seconds in its orbit relative to Prox-1. An updated two-line element (TLE) was produced based upon this orbit estimate, and the new TLE was used for tracking station pointing during the July 5 PDT passes. Tracking station performance was significantly improved at Cal Poly. The Kauai Community College tracking station came online, and received a number of telemetry beacons.

The automated momentum wheel test was successfully performed. The script-driven activity commanded the momentum wheel to wheel speeds of 500 and 2000 rpm in each direction, followed by commanded torques of +/- 0.001 Nm. The momentum wheel axis of rotation is aligned with the spacecraft Y-axis. The angular rate history about the Y-axis during the wheel test is shown below. Review of the test data indicates that the momentum wheel is performing as expected.

The flight team then proceeded with solar panel deployment. The panel deployment command was sent, and it was confirmed in telemetry that the panels had deployed. A set of three images was obtained from both cameras, and the image thumbnails were downlinked. Images from Camera 1 (left) and Camera 2 (right) are shown below. The images were taken at different times. Both images show the limb of the Earth as the spacecraft is about to enter eclipse. The Camera 1 image shows objects in the foreground that are thought to be remnants of the restraint line that was burned through to initiate panel deployment. The flight team will attempt to downlink one or both high resolution images.

Following panel deployment, the panel-mounted magnetometers returned magnetic field measurements that are much more consistent with the Earth’s magnetic field model.

Through analysis of earlier attitude control performance in Z-axis alignment mode, the flight team determined that the magnetic dipole moments commanded by the attitude control software are not being properly commanded to the torque rods. This is a subject of ongoing investigation.

Today’s commanding will prioritize the downlink of imaging and stored telemetry. Tomorrow will be focused on attitude determination and control testing.

Open Anomalies:
1. Solar panels indicate spacecraft in eclipse, ADCS algorithm flag (based on TLE) indicates illuminated. Open.
2. Norms of +X magnetometer measurements are too high compared to the Earth magnetic field model at the spacecraft orbital altitude (>250 µT compared to the known value of ~50 µT). Open. Much improved following panel deployment. Awaiting analysis prior to marking this resolved.
3. Mode 1 behavior not as expected. Angle between +Z axis and magnetic field vector is oscillating around 135 deg +/- 20 deg, based upon computed attitude quaternions. Should be oscillating around 0 deg. Open. Possible attitude determination error due to significant magnetic field bias introduced by spacecraft components in stowed configuration.
4. ADCS_Status command reports zeros for magnetometer bias regardless of what the actual biases are in the gains file (determined via BenchSat testing). The DGmag command provides the correct magnetometer biases. Open. Correcting this would require an ADCS flight software update.
5. Torque rods are not being commanded to the proper current levels to provide the magnetic dipole issued by the attitude control software algorithm. Open. This is related to anomaly 3, above.