Spacecraft InstrumentsOverview

The Johns Hopkins University Applied Physics Laboratory built and operates the twin Van Allen Probes spacecraft for NASA's Living With a Star program.

The Van Allen Probes operate entirely within the radiation belts throughout their mission. When intense space weather occurs and the density and energy of particles within the belts increases, the probes do have the luxury of going into a safe mode, as many other spacecraft must do during storms. The spacecraft engineers designed probes and instruments that are "hardened" to continue working even in the harshest conditions.

The twin probes carry a number of instruments and instrument suites to support five experiments that will address the mission's science objectives. Because it is vital that the two craft make identical measurements to observe changes in the radiation belts through both space and time, each probe carries the following instruments.

Spacecraft InstrumentsECT

Energetic Particle, Composition, and Thermal Plasma Suite (ECT)

ECT will directly measure near-Earth space radiation particles to understand the physical processes that control the acceleration, global distribution, and variability of radiation belt electrons and ions.

ECT Science Investigation Objectives:

  • Determine the physical processes that produce radiation belt enhancements
  • Determine the dominant mechanisms for relativistic electron loss
  • Determine how the inner magnetospheric plasma environment controls radiation belt acceleration and loss
  • Develop empirical and physical models for understanding and predicting radiation belt space weather effects

ECT Instrument Suite:

ECT's three highly-coordinated instruments (MagEIS, HOPE, and REPT) cover comprehensively the full electron and ion spectra from one eV to 10's of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts, optimized to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments.

RBSP-ECT MagEIS instrument figure

Magnetic Electron Ion Spectrometer

MagEIS uses magnetic focusing and pulse height analysis to provide the cleanest possible energetic electron measurements over the critical energy range of 30 keV to 4 MeV for electrons and 20 keV to 1 MeV for ions.

RBSP-ECT HOPE instrument figure

Helium Oxygen Proton Electron

HOPE uses an electrostatic top-hat analyzer and time-gated coincidence detectors to measure electrons, protons, and helium and oxygen ions with energies from less than or equal to 20 eV or spacecraft potential (whichever is greater) to greater than or equal to 45 keV while rejecting penetrating backgrounds.

RBSP-ECT REPT instrument figure

Relativistic Electron Proton Telescope

REPT covers the challenging electron range of 4-10 MeV and proton energy range of 20-75 MeV to capture most intense events.

For more information, go to the ECT web site.

Spacecraft InstrumentsEMFISIS

Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS)

The EMFISIS investigation will focus on the important role played by magnetic fields and plasma waves in the processes of radiation belt particle acceleration and loss. EMFISIS offers the opportunity to understand the origin of important magnetospheric plasma waves as well as the evolution of the magnetic field that defines the basic coordinate system controlling the structure of the radiation belts and the storm-time ring current.

EMFISIS Science Investigation Objectives:

  • Differentiate among competing processes affecting the acceleration and transport of radiation particles
  • Differentiate among competing processes affecting the precipitation and loss of radiation belt particles
  • Quantify the relative contribution of adiabatic and non-adiabatic processes on energetic particles
  • Understand the effects of the ring current and other storm phenomena on radiation electrons and ions
  • Understand how and why the ring current and associated phenomena vary during storms

EMFISIS Instrument Suite:

Central Data Processing Unit (CDPU): Instrument control, spacecraft interface, on-board analysis, 50 Mbyte mass memory.

Tri-axial Magnetometer (MAG): MAG is a tri-axial fluxgate magnetometer: Vector B, DC-15 Hz, 0.1 nT accuracy, three sensors on rigid boom.

WAVES, a tri-axial search coil magnetometer and sweep frequency receiver.

EMFISIS accommodation diagram

Waves Components:

  • Magnetic field - vector B
    • 10 Hz - 12 kHz
    • sensitivity: 3x10-11 nT2Hz-1 @ 1 kHz
    • 3 sensors on rigid boom
  • Electric field - spin-plane E
    • 10 Hz- 12 kHz (vector)
    • 10 kHz-400 kHz (single channel)
    • sensitivity: 3x10-17 V2m-2Hz-1 @ 1 kHz
    • shares booms with Electric Fields and Waves (EFW) Instrument

Van Allen Probes-EMFISIS Data Products:


  • Rapid delivery of four vectors/second in a variety of coordinate systems (GSE, GSM, S/C, etc.)
  • Later delivery of 20 vectors/second (32 vectors/second burst) at full Level 1 quality


  • Spectral matrices for 10 Hz –12 kHz with a 6-second cadence (more often is desired and necessary for some objectives)
  • Spectrum, wave normal, and polarization summaries, based on both on-board and ground processing at 6-second cadence (or more often)
  • Electric field spectrum to 7 MHz with 6-second cadence; electron density from fUHR and continuum radiation cutoff
  • Simultaneous 6-channel waveforms

Spacecraft InstrumentsEFW

Electric Field and Waves Suite (EFW)

EFW will study the electric fields in near-Earth space that energize radiation particles and modify the structure of the inner magnetosphere.

This investigation consists of a set of four spin-plane electric field (E-field) antennae and a set of two spin-axis stacer (tubular, extendable) booms. The investigation will provide understanding of the electric fields associated with particle energization, scattering and transport, and the role of the large-scale convection electric field in modifying the structure of the inner magnetosphere.

EFW Science Investigation Objectives:

Measure electric fields associated with a variety of mechanisms causing particle energization, scattering and transport in the inner magnetosphere, including:

  • Energization by the large-scale convection E-field
  • Energization by substorm injection fronts propagating in from the magnetotail
  • Radial diffusion of energetic particles mediated by ultra-low frequency (ULF) magnetohydrodynamic (MHD) waves
  • Transport and energization by intense magnetosonic waves generated by interplanetary shock impacts upon the magnetosphere
  • Coherent and stochastic acceleration and scattering of particles by small-scale, large-amplitude plasma structures, turbulence and waves (electromagnetic and electrostatic ion cyclotron waves, kinetic Alfven waves, solitary waves, electron phase space holes, zero frequency turbulence).

Why Measure E on Van Allen Probes?

  • The dynamics of the Earth’s radiation belts are all about particle energization, scattering, and transport; in other words, particle acceleration.
  • In collisionless plasmas, such as the Earth’s radiation belts, the electromagnetic field is responsible for all observed particle acceleration.

Particle acceleration occurs in the radiation belts at a variety of spatial and temporal scales:

  • ...from the large-scale E-field associated with the global circulation of plasma in the magnetosphere, down to small-scale structures in plasma density,
  • ...from the slow pumping of particles by ULF waves, to the scattering and energization by high-frequency whistlers.

EFW Instrument:

Image of Spin Plane Booms
Spin Plane Booms
Image of Axial Booms
Axial Booms

EFW Data Products:

Key Measurement Quantities:

  • Spin plane component of E at DC - 12 Hz (0.05 mV/m accuracy)
  • Spin axis component of E at DC - 12 Hz (~3 mV/m accuracy)
  • E- and B-field spectra for nearly-parallel and nearly-perpendicular to B components between 1 Hz and 12 kHz at 6-second cadence
  • Spacecraft potential estimate covering cold plasma densities of 0.1 to ~100 cm-3 at 1-second cadence
  • Burst recordings of high-frequency E- and B-field waveforms, as well as individual sensor potentials for interferometric analyses

Spacecraft InstrumentsRBSPICE

Radiation Belt Storm Probes Ion Composition Experiment

RBSPICE will determine how space weather creates what is called the "storm-time ring current" around Earth and determine how that ring current supplies and supports the creation of radiation populations.

The geomagnetic field drives relativistic electron motion via time-dependent gradient-curvature drift. Thus, structural variations of the inner magnetospheric field due to storm-time ring current growth control transport and losses in the outer belt.

This investigation will accurately measure the ring current pressure distribution, which is needed to understand how the inner magnetosphere changes during geomagnetic storms and how that storm environment supplies and supports the acceleration and loss processes involved in creating and sustaining hazardous radiation particle populations.

RBSPICE Science Investigation Objectives:

  • Understand the effects of the ring current and other storm phenomena on radiation electrons and ions
  • Understand how and why the ring current and associated phenomena vary during storms
  • Support development and validation of specification models of the radiation belts for solar cycle time scales

Measurement Requirements: Hot plasma pressure must be derived to calculate the ring current contribution to storm-time magnetic fields. Thus, it is necessary to resolve the full energy spectrum of the ring current as well as its composition (H, He, O).

RBSPICE Instrument:

Image of RBSP-RBSPICE Instrument


Ring-current ion composition, pitch-angle, and energy sensor.

RBSPICE-Puck covers the full range of expected ring current intensities, from quiet to extreme events, with a factor of 10 margin against saturation.

Measurement quality is independent of the angle between the B-field and the spin axis.

  • Ion composition energy range is low enough to determine the complete Ring Current energy density.
  • High angle and energy resolution provide detailed pitch-angle and energy spectra: Δθ = 22.5°, ΔE/E = 0.1

More information about RBSPICE can be found at

Spacecraft InstrumentsRPS

Relativistic Proton Spectrometer (RPS)

The RPS will measure inner Van Allen belt protons with energies from 50 MeV to 2 GeV. Presently, the intensity of trapped protons with energies beyond about 150 MeV is not well known and thought to be underestimated in existing specification models. Such protons are known to pose a number of hazards to astronauts and spacecraft, including total ionizing dose, displacement damage, single event effects, and nuclear activation. This instrument will address a priority highly ranked by the scientific and technical community and will extend the measurement capability of this mission to a range beyond that originally planned. The project’s goal is development of a new standard radiation model for spacecraft design.

RPS Science Investigation Objectives:

  • Support development of a new AP9/AE9 standard radiation model for spacecraft design
  • AFRL to develop and test model for Van Allen Probes data in general and RPS specifically
  • AP9 (protons) and AE9 (electrons) will provide standardized worst-case specifications: dose rate; internal charging/deep dielectric charging; surface charging (most intense fluxes in keV electrons)

Answer the following science questions:

  • How do solar energetic particle (SEP) events, large magnetic storms, and shocks/sudden commencements modify the Inner Belt?
  • What, in addition to cosmic ray albedo neutron decay (CRAND), determines the steady-state inner belt?
  • How does the inner belt decay during geomagnetic quiet time

RPS Instrument:

RBSP-RPS Spectrometer instrument figure

Relativistic Proton Spectrometer

RPS measures energy spectra and angular distributions of protons from 50 MeV to 2 GeV (expect full inner-zone spatial distributions with better-than-weekly cadence)

  • Energetic protons responsible for total dose in MEO for shielding thickness over 200 mils aluminum
  • Protons responsible for displacement damage
  • Telescope consists of 8 silicon detectors and a Cherenkov detector
  • Stacked Si detectors used for 50 MeV to ~400 MeV, incident angle constrained by 8-fold coincidence
  • Chenrenkov detector used for >400 MeV
  • Absolute flux accuracy: dJ/J ~10%
  • Energy resolution: dE/E ~30% @ 50 MeV, to 100% @ 2 GeV
  • Angular resolution: 30° instantaneous, 5°deconvolved
NASA Logo Van Allen Probes Logo

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