Living With a Star Radiation Belt Storm Probes and Associated Geospace Missions

1. Living With a Star Radiation Belt Storm Probes and Associated Geospace Missions D. G. Sibeck Project Scientist NASA Goddard Space Flight Center

3. Original Geospace Mission Concept

4. The Radiation Belt Storm Probes Mission is in Phase A Formulation The Radiation Belt Storm Probe (RBSP) mission will provide understanding of the dynamics of charged particles that compose the Earth’s radiation belts. This mission with two satellites in a common elliptical near-equatorial orbit will be instrumented to measure the relativistic electrons, ring current and inner belt ions, the plasmasphere, the geoelectric field, geomagnetic field perturbations and the electromagnetic waves that fill the Earth’s inner magnetosphere. RBSP will be the first mission to the inner magnetosphere able to give the dual point measurements needed to decipher the candidate particle energization, distribution and loss mechanisms that give the belts their dynamics. This understanding will enable model development for nowcasting and forecasting of the particle intensities that create the harsh radiation environment of the belts, with their societal consequences. The Radiation Belt Storm Probe (RBSP) mission will provide understanding of the dynamics of charged particles that compose the Earth’s radiation belts. This mission with two satellites in a common elliptical near-equatorial orbit will be instrumented to measure the relativistic electrons, ring current and inner belt ions, the plasmasphere, the geoelectric field, geomagnetic field perturbations and the electromagnetic waves that fill the Earth’s inner magnetosphere. RBSP will be the first mission to the inner magnetosphere able to give the dual point measurements needed to decipher the candidate particle energization, distribution and loss mechanisms that give the belts their dynamics. This understanding will enable model development for nowcasting and forecasting of the particle intensities that create the harsh radiation environment of the belts, with their societal consequences.

5. Radiation Belts:Our Window on Fundamental Physics A cut-away view of the magnetosphere, showing the dusk equatorial plane and the noon-midnight-north pole plane, illustrates in three dimensions the many physical phenomena occurring during magnetically active periods. The spacecraft will orbit approximately coincident with this equatorial plane. Particle angular distributions to be measured at the equator will also give the distributions along the magnetic field lines. Distortions of the magnetic field from the particle energy density distributions maximize at the equator, and the geoelectric field at the equator maps down magnetic field lines to the ionosphere. Over the course of the two year mission, the orbit will precess, approximately twice, through these inner magnetospheric regions and collect observations for many magnetic storms.A cut-away view of the magnetosphere, showing the dusk equatorial plane and the noon-midnight-north pole plane, illustrates in three dimensions the many physical phenomena occurring during magnetically active periods. The spacecraft will orbit approximately coincident with this equatorial plane. Particle angular distributions to be measured at the equator will also give the distributions along the magnetic field lines. Distortions of the magnetic field from the particle energy density distributions maximize at the equator, and the geoelectric field at the equator maps down magnetic field lines to the ionosphere. Over the course of the two year mission, the orbit will precess, approximately twice, through these inner magnetospheric regions and collect observations for many magnetic storms.

6. LWS Geospace RBSP Study Objectives

7. Mission Approach

8. Radial Profiles -->Distinguish Mechanisms Three classes of processes for relativistic electron enhancements can be readily differentiated from phase space density radial profiles, large-scale convection, radial diffusion and stochastic acceleration. The density profiles are particularly important for understanding wave-particle mechanisms, which produce resonant acceleration, loss, or enhance simple radial diffusion. Closely spaced spacecraft will be especially important for observing shock-induced acceleration. Three classes of processes for relativistic electron enhancements can be readily differentiated from phase space density radial profiles, large-scale convection, radial diffusion and stochastic acceleration. The density profiles are particularly important for understanding wave-particle mechanisms, which produce resonant acceleration, loss, or enhance simple radial diffusion. Closely spaced spacecraft will be especially important for observing shock-induced acceleration.

9. Spatial Extent Much of the magnetic storm-time ring current that is enhanced to produce the storm-time magnetic field is not stably trapped and escapes out of the system on the dayside, thus making the ring current highly asymmetric. The acceleration mechanism in the pre-midnight hours is apparently dependent on radial transport of existing lower energy plasma but is not understood. The spatial distribution of the ring current and its temporal variation are drivers for the selection of the orbit parameters. Local particle acceleration can be accomplished through interactions of charged particles with waves at frequencies that resonate with their Doppler-shifted cyclotron frequency. Two resonant waves known to be important are whistler-mode chorus and electromagnetic ion cyclotron (EMIC) waves. The energy densities for these have local time dependencies, the dynamics of which must still be mapped by RBSP.Much of the magnetic storm-time ring current that is enhanced to produce the storm-time magnetic field is not stably trapped and escapes out of the system on the dayside, thus making the ring current highly asymmetric. The acceleration mechanism in the pre-midnight hours is apparently dependent on radial transport of existing lower energy plasma but is not understood. The spatial distribution of the ring current and its temporal variation are drivers for the selection of the orbit parameters. Local particle acceleration can be accomplished through interactions of charged particles with waves at frequencies that resonate with their Doppler-shifted cyclotron frequency. Two resonant waves known to be important are whistler-mode chorus and electromagnetic ion cyclotron (EMIC) waves. The energy densities for these have local time dependencies, the dynamics of which must still be mapped by RBSP.

10. Identify Source Populations For transport acceleration to extreme energies, important source populations are electrons from a few keV to a few MeV, originating at high L-shells. Local acceleration provides energization for source populations typically ranging from 1-50 keV. Source populations come from outside the plasmapause. Three distinct populations targeted for attention are the plasma sheet (and its extension into the inner magnetosphere), substorm injected electrons/ions from the near-magnetospheric tail region, and pre-existing relativistic particles. These populations are strongly controlled by the ring current pressure distribution and distortions of the magnetic field due to ring current intensifications. Times in which one RBSP spacecraft lies within an acceleration region and the other spacecraft resides beyond the region of interest will allow observations of potential source or “seed” populations, and the accelerated populations simultaneously. For transport acceleration to extreme energies, important source populations are electrons from a few keV to a few MeV, originating at high L-shells. Local acceleration provides energization for source populations typically ranging from 1-50 keV. Source populations come from outside the plasmapause. Three distinct populations targeted for attention are the plasma sheet (and its extension into the inner magnetosphere), substorm injected electrons/ions from the near-magnetospheric tail region, and pre-existing relativistic particles. These populations are strongly controlled by the ring current pressure distribution and distortions of the magnetic field due to ring current intensifications. Times in which one RBSP spacecraft lies within an acceleration region and the other spacecraft resides beyond the region of interest will allow observations of potential source or “seed” populations, and the accelerated populations simultaneously.

12. The Radiation Belt Storm Probes: Particle Experiments This slide illustrates the role of THIS mission within the overall Living with a Star program … This slide illustrates the role of THIS mission within the overall Living with a Star program …

13. The Radiation Belt Storm Probes: Field and Wave Experiments This slide illustrates the role of THIS mission within the overall Living with a Star program … This slide illustrates the role of THIS mission within the overall Living with a Star program …

14. Three Missions of Opportunity in Competitive Phase A Study