Radiation Belt Storm Probes Spacecraft Research Articles

A Comparison of the Location of the Mid‐Latitude Trough and Plasmapause Boundary

AbstractWe have compared the location of the mid‐latitude trough observed in two dimensional vertical total electron content (vTEC) maps with four plasmapause boundary models, Radiation Belt Storm Probes (RBSP) observations, and IMAGE extreme ultraviolet (EUV) observations all mapped to the ionosphere pierce point using the Tsyganenko (1996) magnetic field line model. For this study, we examine four events over North America: one just after the October 13, 2012 storm, one during the April 20, 2002 double storm, another during a large substorm on January 26, 2013, and one quiet event on May 19, 2001. We have found that in general, the equatorward edge of the mid‐latitude trough is within several degrees in geographic latitude of the mapped model plasmapause boundary location, the plasmapause boundary identified with IMAGE EUV, and the location identified by the RBSP spacecraft. When the mid‐latitude trough is mapped to the inner magnetosphere, the observed boundary agrees with the plasmapause boundary models within two Earth Radii at nearly all local times in the nightside and the observed mid‐latitude boundary is within the uncertainty of the observations at most local times in the nightside. Furthermore, during dynamic solar wind conditions of April 20, 2002, the mid‐latitude trough observed in the vTEC maps propagates equatorward as the plasmapause boundary identified with IMAGE EUV moves earthward. Our results indicate that the mid‐latitude trough observed within the vTEC maps represents an additional means of identifying the plasmapause boundary location, which could result in improved plasmapause boundary models.

Simulation of Van Allen Probes plasmapause encounters

AbstractWe use an E × B‐driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes (RBSP)) during 15–20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15–19 January. For 26 of 28 (92%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean model‐data difference in radial location is 0.40 ± 0.05 RE. The model‐data agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the model‐provided global information is adequate to correctly interpret the RBSP density observations.

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.

The Engineering Radiation Monitor for the Radiation Belt Storm Probes Mission

An Engineering Radiation Monitor (ERM) has been developed as a supplementary spacecraft subsystem for NASA’s Radiation Belt Storm Probes (RBSP) mission. The ERM will monitor total dose and deep dielectric charging at each RBSP spacecraft in real time. Configured to take the place of spacecraft balance mass, the ERM contains an array of eight dosimeters and two buried conductive plates. The dosimeters are mounted under covers of varying shielding thickness to obtain a dose-depth curve and characterize the electron and proton contributions to total dose. A 3-min readout cadence coupled with an initial sensitivity of ∼0.01 krad should enable dynamic measurements of dose rate throughout the 9-hr RBSP orbit. The dosimeters are Radiation-sensing Field Effect Transistors (RadFETs) and operate at zero bias to preserve their response even when powered off. The range of the RadFETs extends above 1000 krad to avoid saturation over the expected duration of the mission. Two large-area (∼10 cm2) charge monitor plates set behind different thickness covers will measure the dynamic currents of weakly-penetrating electrons that can be potentially hazardous to sensitive electronic components within the spacecraft. The charge monitors can handle large events without saturating (∼3000 fA/cm2) and provide sufficient sensitivity (∼0.1 fA/cm2) to gauge quiescent conditions. High time-resolution (5 s) monitoring allows detection of rapid changes in flux and enables correlation of spacecraft anomalies with local space weather conditions. Although primarily intended as an engineering subsystem to monitor spacecraft radiation levels, real-time data from the ERM may also prove useful or interesting to a larger community.

The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission

The Relativistic Proton Spectrometer (RPS) on the Radiation Belt Storm Probes spacecraft is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from ∼60 MeV to ∼2000 MeV. RPS will investigate decades-old questions about the inner Van Allen belt proton environment: a nearby region of space that is relatively unexplored because of the hazards of spacecraft operation there and the difficulties in obtaining accurate proton measurements in an intense penetrating background. RPS is designed to provide the accuracy needed to answer questions about the sources and losses of the inner belt protons and to obtain the measurements required for the next-generation models of trapped protons in the magnetosphere. In addition to detailed information for individual protons, RPS features count rates at a 1-second timescale, internal radiation dosimetry, and information about electrostatic discharge events on the RBSP spacecraft that together will provide new information about space environmental hazards in the Earth’s magnetosphere.

Spin-axis estimation of the Radiation Belt Storm Probes spacecraft using RF Doppler data

A methodology for using RF Doppler data for spin-axis estimation is presented. The NASA Radiation Belt Storm Probes (RBSP) mission, a dual-spacecraft mission planned for a 2012 launch, will yield valuable insights into the physical dynamics and processes of the Earth's radiation belts, particularly those that produce hazardous space weather effects and those that can affect solar system exploration. Both spacecraft have on-board Sun sensors that, in conjunction with magnetometer data, provide the required data to determine the attitude. However, the quality of the magnetometer measurements is compromised at higher altitudes because of a weaker magnetic field and also during solar storms because of variations in the Earth's magnetic field. Each spacecraft's on-board S-band radio frequency (RF) system includes a JHU/APL Frontier Radio transceiver, which provides a coherent downlink signal used for Doppler navigation. The RF system also includes two low-gain antennas offset from the spin axis with boresights parallel to the spin and anti-spin axes. Due to the spin of the spacecraft, a Doppler-induced modulation is present on the downlink carrier. Once the orbit determination is performed and the Doppler signal is analyzed, this modulation, or spin signature, is apparent. This spin signature can be used to accurately determine the spin rate, spin phase, and, in conjunction with Sun sensor data, the spin axis orientation. This provides a level of system redundancy with the magnetometer for attitude determination. The Sun sensor provides the angle from the spin axis to the Sun vector; the amplitude of spin signature on the Doppler data provides the instantaneous aspect angle from the spin axis to the ground station. These two measurements establish the spin axis direction. This paper describes the established theory and a method for processing the spin signature and determining the spin axis as applicable to the RBSP spacecraft. Further, RF-related errors on the Doppler carrier frequency measurement are characterized and related to the error in the spin axis orientation determination. Finally, this paper introduces the concept of attitude determination by processing the Doppler spin signature data alone over a period of time that encompasses a sufficient change to the spin axis/ground station aspect angle. This provides a further level of redundancy in the event of a failed Sun sensor. Results from processing actual data from a current mission are given.

Radiation Belt Storm Probes: A New Mission for Space Weather Forecasting

Radiation Belt Storm Probes: A New Mission for Space Weather Forecasting