Radiation Effects and other features in the Laser Ranging Interferometer Data

The GRACE-FO mission (2018-now) hosts the novel Laser Ranging Interferometer (LRI) that measures the inter-satellite distance with a previously unprecedented precision of better than 200 pm/sqrt(Hz) at Fourier frequencies above 1 Hz. Gravity information of the underlying Earth is retrieved by combining this ranging measurement with orbit information and accelerometer data.

In this talk, we will explore sporadic signals in the measured phase data that might be caused by radiation interfering with electronics and resulting in so-called Single-Event Upsets (SEUs). Radiation effects are known to, e.g., cause reboots of computers in space and affect data stored in memory cells. In the ranging data of the LRI, SEUs manifest as short-lived peaks that can be simulated, modeled, and removed in post-processing. Over four years mission lifetime, we identified 29 such events.

Further, we will also address other events that we call Momentum Transfer Events (MTEs), where the satellites experience short-lived accelerations measured by both, LRI and Accelerometer. The majority of these events are likely caused by tiny particles, micrometeorites, or space-debris, that hit the spacecraft and cause a change in velocity. As these velocity changes are actually physical effects, they might influence the gravity field recovery process on short arcs if they remain unmodeled.

The analysis shown here may help future missions, which will likely base on an improved LRI instrument, to understand and eventually mitigate these kinds of disturbances already in the instrument design phase. For the current mission, the proper removal of unintended features might become beneficial in future gravity field processing with reduced background and modeling noises.