The ACES-II sounding rocket mission launched two payloads from Andøya Rocket Range into a post-dusk discrete auroral arc and observed field-aligned electron dispersions near inverted-V precipitation. Five repetitive suprathermal electron bursts (STEBs) associated with low frequency (< 8 Hz) Earth-ward traveling Alfvén waves are observed at 400 km altitude. The electron bursts occur both coincident and outside inverted-V electrons, with those nearest to inverted-V precipitation displaying higher peak energy and differential flux values than events further away. We interpret the events as wave-particle acceleration via inertial Alfvén waves along near-Earth field lines and employ time-of-flight methods to gauge source altitudes. We show the differences in STEB behavior are better explained by changes in the resonant source population and not from significant variation in Alfvén wave parameters, a result that agrees with previous simulated predictions.

Fluxgate magnetometers are an important tool for measuring space plasmas. In-situ magnetic field investigations often involve measuring small perturbations of a large background field, so robust instrument calibration is critical to accurately resolving geophysical signals. Fluxgate instruments aboard recent space science missions have observed calibration anomalies that have been attributed to thermal gradients across the sensor. Here we present data from a laboratory experimental investigation of effects of thermal gradients on fluxgate calibration and performance. A purpose-built laboratory apparatus fixed two thermal reservoirs at either end of a racetrack fluxgate sensor. Varying the reservoir temperatures allowed us to vary the sensor temperature and impose thermal gradients as large as 50 °C across a racetrack fluxgate sensor. We find that changes in instrumental sensitivity, offset, and noise can be explained purely by changes in the average temperature of the sensor without a dependence on the difference in temperature across the sensor. We suggest that invoking concept of a static thermal gradient inducing thermoelectric currents within the fluxgate core or sensor may not be appropriate to explain changes in instrumental sensitivity, offset, and noise that have been observed on orbit.

Robust in-situ magnetic field measurements are critical to understanding the various mechanisms that couple mass, momentum, and energy throughout our solar system. However, the spacecraft on which magnetometers are often deployed contaminate the magnetic field measurements via onboard subsystems including reaction wheels and magnetorquers. Two magnetometers can be deployed at different distances from the spacecraft to determine an approximation of the interfering field for subsequent removal, but constant data streams from both magnetometers can be impractical due to power and telemetry limitations. Here we propose a method to identify and remove time-varying magnetic interference from sources such as reaction wheels using statistical decomposition and convolutional neural networks, providing high-fidelity magnetic field data even in cases where dual-sensor measurements are not constantly available. For example, a measurement interval from the Parker Solar Probe outboard magnetometer experienced a 95.1% reduction in reaction wheel interference following application of the proposed technique.

In-situ spacecraft observations are critical to our study and understanding of the various phenomena that couple mass, momentum, and energy throughout near-Earth space and beyond. However, on-orbit telemetry constraints can severely limit the capability of spacecraft to transmit high-cadence data, and missions are often only able to telemeter a small percentage of their captured data at full rate. This presents a programmatic need to prioritize intervals with the highest probability of enabling the mission’s science goals. Larger missions such as the Magnetospheric Multiscale mission (MMS) aim to solve this problem with a Scientist-In-The-Loop (SITL), where a domain expert flags intervals of time with potentially interesting data for high-cadence data downlink and subsequent study. Although suitable for some missions, the SITL solution is not always feasible, especially for low-cost missions such as CubeSats and NanoSats. This manuscript presents a generalizable method for the detection of anomalous data points in spacecraft observations, enabling rapid data prioritization without substantial computational overhead or the need for additional infrastructure on the ground. Specifically, Principal Components Analysis and One-Class Support Vector Machines are used to generate an alternative representation of the data and provide an indication, for each point, of the data’s potential for scientific utility. The technique’s performance and generalizability is demonstrated through application to intervals of observations, including magnetic field data and plasma moments, from the CASSIOPE e-POP/Swarm-Echo and MMS missions.

In-situ magnetic field measurements are critical to our understanding of a variety of space physics phenomena including field-aligned currents and plasma waves. Unfortunately, high-fidelity magnetometer measurements are often degraded by stray magnetic fields from the host spacecraft, its subsystems, and other instruments. One dominant source of magnetic interference on many missions are reaction wheels - spinning platters of varying rates used to control spacecraft attitude. This manuscript presents a novel approach to the mitigation of reaction wheel interference on magnetometer measurements aboard spacecraft where multiple magnetometer sensors are deployed. Specifically, multichannel singular spectrum analysis is employed to decompose multiple time series simultaneously. A technique for automatic component selection is proposed that classifies the decomposed signals into common geophysical signals and disparate locally generated signals enabling the robust estimation and removal of the local interference without requiring any assumptions about its characteristics or source. The utility of this proposed method is demonstrated empirically using in-situ data from the CASSIOPE/Swarm-Echo mission, and a data interval with near-constant background field was shown to have its local reaction wheel interference reduced from 1.90 nT RMS, for the uncorrected outboard sensor, to 0.21 nT RMS (an 89.0\% reduction). This technique can be generalized to arrays of more than two sensors, and should apply to additional types of magnetic interference.