Radiation Belt Storm Probes and Space Weather D. G. Sibeck LWS Geospace Project Scientist

Outline Radiation Belts: Definitions, Space Weather, and Science –What’s the science/societal problem? The Radiation Belt Storm Probe (RBSP) Mission –What are we doing about it? RBSP Space Weather Beacon –Real-time observations Discussion: User needs –How can we help you?

Earth’s Radiation Belts Inner Belt: Protons (Energies > 10 MeV) to 10,000 km altitudes near magnetic equator. Outer Belt: Electrons (0.1 to >100 MeV) - 3 to 10 R E from center of Earth near magnetic equator - peak intensity between 3.3 and 4 R E Inner Outer Slot Flux vs. latitude and radial distance from Earth Earth Radii (R E ) (R E ) Equator Inner Belt Outer Belt

Radiation Hazards to Astronauts Societal Implications Understand, and enable prediction, real-time, and post-event analysis of radiation hazards to astronauts and technological systems Better first-principle and empirical models for the radiation belts will: Protect astronauts/spacecraft Prevent costly s/c over design Provide critical information for deployment of NASA’s Crew Exploration Vehicle and transits to the moon.

The particle populations in the radiation belts are dynamic and, so far, unpredictable MeV electrons Geomagnetic storms (measured by negative excursions of the geomagnetic index Dst) produce a variety of responses in radiation belt electron fluxes [Reeves et al., 2003]. Dst Radius Time Jan 1- Feb 25, 1997April 30- May 25, 1999 Feb Increases Decrease Little Change We don’t understand the fundamental physics, e.g. the response of acceleration and loss mechanisms to solar-induced geomagnetic storms.

Complicated Interactions of Multiple Processes Make Predictions Difficult Some of the processes that can drive changes in radiation belt particle populations. Inner Outer Radiation Belts

NASA’s Radiation Belt Storm Probes Mission Radiation Belt Storm Probes – twin spacecraft in highly elliptical orbits to understand the basic principals behind relativistic particle acceleration, transport, and loss. Implemented as the 2nd mission in the Living with a Star Program

We will fulfill this objective by: Understanding the acceleration, global distribution, and variability of energetic electrons and ions in the inner magnetosphere RBSP is a Science mission With Practical Applications Understand, ideally to the point of predictability, how populations of relativistic ions and electrons in space form or change in response to the variable inputs of energy from the sun

RBSP Mission Science Objectives Specific Objectives Shorthand Identify the processes responsible for the acceleration and transport of relativistic and near-relativistic particles, determine when and where these processes occur, and determine their relative significance; Acceleration, Transport Identify the processes responsible for the precipitation and loss of relativistic and near relativistic particles, determine when and where these processes occur, and determine their relative significance; Precipitation, Loss Quantify the processes that lead to the formation and subsequent decay of transient radiation belt structures; Transient Structures Quantify the relative contribution of adiabatic and non-adiabatic processes on the acceleration, transport, and loss of energetic particles; Fundamental Processes Determine the role of "seed" or source populations for relativistic particles;Sources Quantify the effects of the ring current and related storm phenomena on relativistic particles; Effects of Ring Current Quantify how and why the ring current and associated phenomena vary during storms; and Ring Current Variations Use the improved science understanding to improve and validate physics-based data assimilation and specification models for the Earth’s radiation belts. Models

RBSP Mission Concept: Two identical spacecraft target energetic particle populations Near radial cuts through major interaction regions at cadences much faster than the several day time scales associated with geomagnetic storms. Low inclination (10°) ensures that majority of particle populations are measured. Two identically-instrumented spacecraft in nearly-identical orbits. Sunward-pointing spin axes Lapping (4-5 laps/year) permits simultaneous observations over a range of s/c separations, needed to distinguish spatial from temporal variations. Two-year mission precesses through all local times and major interaction regions. Space weather broadcast 5.8 Earth radii (R E ) apogee ensures full sampling of the outer belt, particle source regions, and the major interaction regions, while 600 km perigee ensures full sampling of the inner edge of the inner belt. Lapping causes distances separating spacecraft to vary as orbit precesses

RBSP orbit provides time resolution appropriate to acceleration/loss timescales Dual-spacecraft missions with apogee ~5.8 R E and perigee ~600 km provide revisit times on the order of hours (9 hour orbital period) –Corresponds to the time scales appropriate to many acceleration and loss mechanisms –Offers many revisits per several day storm –Many storms expected during mission (~1/month) 4 Days Dst Vertical bars indicate cadence of inbound and outbound radial cuts through the radiation belts during storm measured by geomagnetic Dst index Storm

Low-inclination orbits essential to observe important particle populations Accurate inter-spacecraft comparisons require complete observations of particle distributions Since most particles and some waves lurk near the equator, orbits must have low inclinations Wave-particle interactions result in abrupt gradients in particle fluxes versus pitch angle. Higher- inclination spacecraft miss the gradient and miss the physics! A 10° inclination orbit captures 60° P.A. 80% of time Simulated Equatorial Particle Pitch Angle Distributions differ at 60 ° (Pitch Angle (P.A.) is angle between particle velocity and magnetic field) 90° P.A. means V perpendicular to B

Two lapping spacecraft are crucial to distinguish between proposed models Convection Radial Diffusion Local Acceleration Two spacecraft with a variable separation are essential to: Separate spatial and temporal effects Determine spatial extent of phenomena Simultaneously observe source and energized particle populations Quantify instantaneous radial gradients in particle phase space density * * * Two identical spacecraft

Sunward Pointing Spin Axes Nearly sunward-pointing spin axes: Enable particle instruments to capture the full range of look directions relative to the magnetic field once each spin and Enable the spin plane booms of the electric field instrument to capture the dominant dawn-dusk component of the electric field once each spin. Slight off-pointing from the Sun prevents shadowing of rear boom. Spin axis No Shadowing Spinning (5 rpm) FOV captures all angles relative to magnetic field B Dusk degree offset

Two years Required for Apogee to Precess 24 Hours in Local Time Different mechanisms operate at different local times. - Three crucial phenomena can be studied in the first year: –chorus waves at dawn –substorm injection at midnight, and –EMIC waves at dusk With 5.8 R E apogee, RBSP precesses from dawn to dusk in ~1 year, through all local times in ~2 years. Spacecraft will carry 4 years of expendables Initial Apogee Apogee After 1 Year

Mission Schedule Phase A, preliminary design:6/2006 – 1/2008 Phase B, detailed design: 2/2008 – 1/2009 Phase C/D, development: 2/2009 – 7/2012 Launch:4/2012 Phase E, flight phase: 8/2012 – 8/2014 Expendables until 8/2016

RBSP Measurements Full success requires the following measurements on one spacecraft for two years, and concurrent observations by the second spacecraft for at least the first year, : Particles –Plasma electrons and H, He +, and O + ions (20 eV < E < 50 keV) –H, He + and O + ions (50 to 400 keV) –H and O ions (1 to 50 MeV/nucleon) –Energetic electrons (45 keV to 4 MeV) –Energetic protons (20 keV to 10 MeV) –Relativistic electrons (4 < E < 10 MeV) and protons (5 < E < 75 MeV) –Very energetic protons (100 MeV to 1 GeV) Fields –3-D DC magnetic field –3-D electric field (including axial booms) –3-D VLF magnetic field (10 Hz to 12 kHz) –3-D VLF electric field (10 Hz to 12 kHz, to 400 kHz on one axis)

Science Investigations: Who’s Who? Mission Implementation: JHU/APL

RBSP Particle Measurements electrons He+ protons O+ HOPE RBSPICE MagEIS REPT RPS Particle Sensors PSBR/RPS ECT/REPT ECT/MagEIS RB-SPICE ECT/HOPE 1eV1keV1MeV1GeV MagEIS REPT ions Energy/nucleon Requirement Capability total ions discriminated ions

RBSP Fields & Waves Coverage DC Magnetic DC Electric AC Magnetic density EMFISIS FGM EFW Perp 2D EFW AC 3D EMFISIS Waves EMFISIS SCM Fields & Waves Sensors EMFISIS/MAG EMFISIS/Waves EFW ~DC 10Hz1kHz1MHz AC Electric EFW Par 1D EFW E-fld Spectra 2D EFW cold plasma density EMFISIS Waves EMFISIS Density Cadence sampling

Space Weather Broadcast Assumptions The RBSP Space Weather (SW) broadcast will be a transmission like those on ACE and STEREO. (mission science data will be stored and downlinked once per orbit) Only a small subset (200 of 100,000 bps) of science data observed will be broadcast. It will not be possible for ground stations to receive broadcast continually. Ground processing for SWx products will be provided by receiving organization(s): there will be little or no onboard processing. The mission will supply receiving organizations with some processing algorithms. Detailed list of SW broadcast data products will be finalized after Initial Confirmation Review in December, 2007.

Space Weather Return Broadcasts Intention is to broadcast space weather at all times. Limits include:  Availability of space weather ground stations.  Seasonal blind spots in antenna coverage  No real time broadcast during primary missions contacts (3 hours/sc/day)  Mitigations:  Supplement with TDDRS contacts  Use the other observatory when only one s/c is in primary mission contact  Pass space weather packets through the RBSP Mission Operations Center during primary mission contact periods.

Observatory Communications S-Band Transmission –8 W SSPA Transmitter Observatory pointing geometry, orbit, and spin stabilization determine communication system requirements –Earth location, as viewed from the spacecraft covers a very broad angle of space as shown in the required RBSP antenna angle coverage plot –Geometry necessitates broad coverage with low gain antennas Coverage is maximized within practical limits with two low gain antennas as shown in the antenna pattern figure –2 Antennas with 70° FOV (near hemispherical coverage) –40° null band depicted as gray patch in required antenna angle coverage plot Required RBSP Antenna Angle Coverage RBSP Antenna Pattern Null Region Mast Angle Mast Angle To Sun Spin Direction Note - Sample taken every 15 minutes throughout 2 year mission

Seasonal Variations in Communications Coverage Due to Antenna Coverage Limits Antenna coverage to Earth depends on orbit geometry that seasonally varies –Although antenna coverage is large, there are times when the antenna patterns are not aligned with the Earth –There is excellent coverage when the line of apsides (major axis of orbit ellipse) is along or near the Earth-Sun line –Coverage is reduced significantly near apogee when the line of apsides is near perpendicular to the Earth-Sun line View from North Pole of Ecliptic Plane Null Line of apsides Full antenna coverage to Earth Partial antenna coverage to Earth No antenna coverage Note – Graphic coverage transition points and times are approximate and are for illustrative purposes only. Earth

Potential Contact Time for Space Weather Showing Seasonal Variations Potential contact time maximized by using multiple stations with longitudinal diversity Peaks and valleys in potential contact periods primarily due to seasonal effects on observatory antenna coverage Space weather delivered directly to space weather ground station Accounts for line-of-sight to ground station and observatory antenna coverage only Represents coverage for a single observatory Visibility averaged over 3 day increments Two 70° half angle antennas Generic ground stations assumed at 35° N latitude Assumptions: Potential Contact Time per Day (%) Min. Angle Between Earth-Sun Line & Line of Apsides (deg)

Proposed Space Weather Products 1 minute averages of the –Electric field vector (E) –Plasma density inferred from spacecraft potential (V) –Ion and electron particle fluxes at , , 0.001, 0.03, 0.07, 0.15, 0.3, 0.6, 1, 3, 10, 50, and 400 MeV with 22.5° angular resolution 6 second time resolution magnetic field vectors (B)

Audience Participation What parameters are of greatest interest to potential users? What cadences are needed? Which regions of space are most interesting? Thank You!