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Description
In recent years, nanosatellites have enabled the testing and in-orbit validation of advanced instrumentation intended for larger space science missions. MELISA is a magnetic measurement payload designed to demonstrate the in-orbit performance of Anisotropic Magnetoresistance (AMR) sensors featuring dedicated noise reduction techniques at sub-milliHertz frequencies (0.1 mHz to 1 Hz). This bandwidth is critical for future space-borne gravitational wave (GW) observatories, where the local magnetic environment yields a significant contribution to the overall noise budget, requiring demanding noise floors down to $10\,\rm nT\,Hz^{-1/2}$.
The in-orbit characterisation in Low Earth Orbit (LEO) presents a major challenge for evaluating sensor performance at ultra-low frequencies, as environmental thermal and magnetic variations become the dominant contribution to the total noise budget, severely impeding the characterization of the intrinsic performance of the sensor. Nevertheless, the thermal noise contribution to the magnetic field measurements can be disentangled and subtracted through on-ground cross-correlation with onboard housekeeping data and post-processing.
This work presents the initial steps toward demonstrating the capabilities of a methodology for subtracting temperature-induced excess noise applied to MELISA data. The unit is integrated into a Thermal Vacuum (TVAC) chamber to first excite sine-wave thermal profiles at distinct frequencies and, finally, recreate the expected full in-orbit temperature profiles. While environmental magnetic stability is strictly maintained, any observed fluctuations in the magnetic field are expected to be solely provoked by temperature variations. The magnetic measurements are correlated with onboard temperature sensors, and the resulting thermal-magnetic effects are fitted to physically based models to quantify the exact amount of thermal noise that can be subtracted.
Furthermore, this TVAC-validated decoupling strategy is proposed as an in-flight operational tool to mitigate thermal noise in magnetically demanding space science missions with long integration times.