Radiation Belt Reflections:
Peering Back
and Looking Forward to the
Radiation Belt Storm Probes Mission
Harlan E. Spence
University of New Hampshire
Institute for the Study of Earth, Oceans, and Space,
Space Science Center
Acknowledgements: Geoff Reeves, RBSP-ECT Science Team, and the RBSP SWG
NSF GEM 2012 Summer Workshop
And speaking of reflections…
GEM 2011
NSF GEM 2012 Summer Workshop
Outline
• Science motivations for a return
to Earth’s radiation belts
• An historical perspective
• RBSP – The next step
• RBSP science questions
(for more see R. Kessel’s talk)
• RBSP-ECT…
• Summary
NSF GEM 2012 Summer Workshop
Four Motivations For a Return
to the Radiation Belts
• Discover our own cosmic particle accelerator
• Differentiate between competing theories
• Determine climatology and develop physicsbased predictive capability
• Resolve space weather extremes in the harsh
ionizing radiation environment
NSF GEM 2012 Summer Workshop
Motivation #1: Discover Our Own Comic
Particle Accelerator
Cas A Supernova Remnant
(Credit:
NASA/CXC/UMass
Amherst/M.D.Stage et al.)
Pulsar magnetospheric physics (F.C. Michel, 1998)
• Ironically, we view through our own invisible radiation belts
when viewing exotic, high energy, astrophysical objects,
places where the same universal processes occur but where
key observations are highly limited
• Our own cosmic particle accelerator exists literally just above
our heads where we can witness the universal physics in situ
NSF GEM 2012 Summer Workshop
Motivation #2: Differentiate Between
Competing Mechanisms and Theories
• Many acceleration, transport, and loss mechanisms theorized,
however present observations insufficient to differentiate
uniquely between them and to establish relative importance
NSF GEM 2012 Summer Workshop
Motivation #3: Determine Climatology and
Develop Physics-based Predictive Models
• Climatology of the radiation
belt populations is not always
well constrained owing to
imperfect/incomplete
observations
• Neither variability nor spatial
structure of the radiation
belts currently well predicted
using physics-based models
(from GMDT report)
NSF GEM 2012 Summer Workshop
Motivation #4: Resolve the Extremes of
Space Weather in the Harsh Ionizing
Radiation Environment
• Radiation belt is not only a
harsh ionizing radiation
environment but also home
to a vast number of
commercial and noncommercial spacecraft
• Exploration, quantification,
and predictive capability of
typical and extreme
conditions is useful to “users”
NSF GEM 2012 Summer Workshop
(after Onsager et al.)
Earth’s Radiation Belts:
An Historical Perspective
• Van Allen’s discovery
• A static picture
• Dark(er) ages
• Enlightenment
• And yet it moves!
• Models outpace
observations
• Radiation belt redux - RBSP
NSF GEM 2012 Summer Workshop
James Van Allen’s Discovery
• Thrust space physics
into American culture
with discovery on
Explorer 1 in 1958
Artistic images of
Van Allen belts,
NASA/Langley,
circa 1961
NSF GEM 2012 Summer Workshop
Cover of TIME in ‘59 and ‘64
Building a Static Picture
• Van Allen’s Pioneer 3 result showing inner and outer belts
and “slot”; first page of first draft of discovery paper (1959)
• “Static”belts established from discovery through the 1960’s
NSF GEM 2012 Summer Workshop
The Dark(er) Ages (1970s-1980s)
• Radiation belt physics relegated to small AGU sessions within
a comparatively small community
• New missions focused on higher altitude regions and
phenomena – radiation belts left behind
• Topic developed an unfair and dogmatic stigma:
•
•
•
•
“The problem has been solved.”
“The radiation belts are unchanging.”
“We know they are there; just avoid them!”
“The textbook(s) are being written.”(*)
• Yet, a dedicated cohort of
space physicists carried on and
waited - developing theories,
analyzing earlier observations,
making new ones - for a new
set of missions yet to come…
(*) Schulz and Lanzerotti, 1974
The Aerospace Corporation
Space Particles and Fields Group
Circa 1970
NSF GEM 2012 Summer Workshop
BEHOLD! The Enlightenment
• CRRES (1990-91), a joint
NASA/USAF equatorial
mission, targets radiation
belt physics ~30 years
(Courtesy R. Hilmer)
after discovery
• CRRES confirmed basic
structure but revealed
unanticipatedly rich
dynamics and structure
• SAMPEX (1992 - present) was the first NASA Small
Explorer; sampled radiation belts at their low altitude “horns”
• SAMPEX revealed incessant creation/destruction/evolution
of radiation belts driven by impulsive and persistent factors
NSF GEM 2012 Summer Workshop
Redefining as a Moving Picture
• March 1991 shock injection
• Created new electron belt of
>13 MeV electrons in a matter
of minutes - transformational
• Rewrite the textbooks!
(Figure courtesy Gregory Ginet, AFRL)
(Movie courtesy Joseph Mazur, Aerospace)
NSF GEM 2012 Summer Workshop
Models Outpace Observations
• Observations from operational (GPS, LANL-GEO, HEO,
GOES) and science (Polar) spacecraft provided constellation
of measurements throughout region of interest
• Despite large number of observing points, data lack qualities
needed for comparing phase space density; appeal to models
• Empirical, data-assimilative and physics-based models
• Interpretation still ambiguous even with best models/efforts
NSF GEM 2012 Summer Workshop
RBSP – The Next Step…50+ yrs later
• NASA/LWS’s 2nd Mission
• LWS/GMDT report in ’02
• Led to new mission (RBSP) AO
NSF GEM 2012 Summer Workshop
The NASA/LWS RBSP Mission
•
•
•
•
Instrument proposals were due in fall 2005
Instrument science teams were selected in summer 2006
Launches SOON – 23 August 2012 from Cape Canaveral!
Two identical spacecraft in elliptical, near-equatorial orbits
provide crucial observations to resolve radiation belt physics
• Full particles (low to ultra-relativistic energies; composition)
and fields (magnetic and electric DC and waves) on both s/c
NSF GEM 2012 Summer Workshop
RBSP Mission Objective
• To understand, ideally to the point of predictability, how
populations of relativistic electrons and ions in space
are formed or changed in response to the variable inputs
of energy from the Sun.
• While connections to high speed streams are well established,
response to storms is presently not predictable! Why?
• Subtle but powerful tug-of-war between acceleration,
transport, and loss processes
(Figures from Reeves ; 2003, 1998)
NSF GEM 2012 Summer Workshop
RBSP Science Questions
NSF GEM 2012 Summer Workshop
Differentiate Among Competing Processes
Affecting the Acceleration and Transport of
Radiation Belt Particles
• Processed controlling
electron acceleration
and transport are:
 local resonant
interactions with
VLF waves, such
as Chorus and
magnetosonic
waves
 acceleration and
transport by
radial diffusion
and the role of
ULF wave
resonances
(Figure from Reeves, 2007)
NSF GEM 2012 Summer Workshop
Differentiate Among Competing Processes
Affecting the Precipitation and Loss of
Radiation Belt Particles
• Processes
controlling
electron and ion
precipitation and
loss are:
 Field line
curvature
scattering
 Magnetopause
shadowing
 Pitch angle
scattering by
wave-particle
interactions
Mysteries of the radiation belt continue to be discovered! Research by Baker et
(e.g., EMIC)
al. (2007, GRL) using SAMPEX shows that detrapping time at low L is
much shorter than that predicted by any theory.
NSF GEM 2012 Summer Workshop
Understand the Creation and Decay of
Transient Radiation Belt Structures
• RBSP will establish the role of interplanetary shocks in
producing sudden and intense electron and ion
acceleration events such as the March 1991 defining
shock event
(Figure after Li et al., 1993)
NSF GEM 2012 Summer Workshop
(Figure after Blake, 2005)
Quantify the Relative Contribution of
Adiabatic and Non-Adiabatic Processes on
Energetic Particles
• RBSP will establish
the role of adiabatic
(reversible, “Dsteffect”) from nonadiabatic processes
• Both are important
for determining the
final state of the
radiation belt, but
the latter is more
physically
interesting yet
requires that the
former be first wellunderstood
Processes which break the adiabatic invariants occur along with
those which do not – RBSP will differentiate between and
quantify their relative contributions
NSF GEM 2012 Summer Workshop
Understand the Role of “Seed” or Source
Populations For Relativistic Particle Events
• RBSP will quantify the role of
seed or source populations
for relativistic particle events,
including:
 Resident radiation belt
populations for local
acceleration;
 Plasmasheet populations
for those which are
convectively or diffusively
transported and
accelerated;
 Solar proton populations
which can be captured in
inner magnetosphere
trapping regions.
(Reeves, 2005)
NSF GEM 2012 Summer Workshop
(Selesnick and Blake, 2002)
Understand the Effects of the Ring Current
and Other Storm Phenomena – and –
Understand How and Why the Ring Current
And Associated Phenomena Varying
During Storms
• RBSP will quantify the role that the ring
current has on the radiation belt particle
populations, including:
 storm and substorm phenomena,
including substorm injections;
 Large-scale changes in the electric and
magnetic fields;
 build-up and decay of the ring current;
 interaction of energetic ring current
electrons and ions with ambient plasma
to produce storm-time wave fields.
NSF GEM 2012 Summer Workshop
Develop and Validate Physics-based, Data
Assimilation, and Specification Models of the
Radiation Belts for Solar Cycle Time Scales
• Next generation climatology
and specification models (e.g.,
AP-9, AE-9)
• Predictive models using both
data assimilation and physicsbased approaches
NSF GEM 2012 Summer Workshop
RBSP Science Investigations
NSF GEM 2012 Summer Workshop
(Mauk et al., 2012)
RBSP Particle Measurement Requirements
NSF GEM 2012 Summer Workshop
(Mauk et al., 2012)
Making Definitive Measurements in a Harsh
Radiation Environment
Energetic Particle,
Composition and
Thermal Plasma
Suite
NSF GEM 2012 Summer Workshop
RBSP-ECT:
Energetic Particle, Composition and Thermal Plasma Suite
University
of New
Hampshire
NASA/
GSFC
Rice
University
B. Larsen
S. Kanekal
E.
McDonald
S.
Claudepierre
A. Chan
NSF GEM 2012 Summer Workshop
Relative Electron Flux
RBSP-ECT
consists of three
coordinated sensor
types:
• HOPE
• MagEIS
• REPT
ECT measures
electrons
(continuously) and
ions (with
composition up to 50
keV) from ~20 eV to
~10’s of MeV with
energy resolution,
and pitch angle
coverage and
resolution required
for mission success.
Relative Electron Flux
RBSP-ECT Suite Summary
HOPE
MagEIS
Medium x2
MagEIS
Low
0.02
MagEIS
High
REPT
200
HOPE
Dr. Herb Funsten
Los Alamos National Laboratory
MagEIS (4)
Dr. J. Bernard Blake
The Aerospace Corp.
NSF GEM 2012 Summer Workshop
REPT
Dr. Daniel Baker
University of Colorado
RBSP-ECT Suite Summary: HOPE
Helium Oxygen Proton Electron
• 6 ECT instruments per spacecraft: HOPE (#1)
• Helium Oxygen Proton
Electron Spectrometer
• LANL-led
• Top-hat electrostatic energy
analyzer (ESA) front end; timeof-flight (TOF) drift region;
CEM start and stop detectors
• Not synchronized to spin pulse
• Electron and ion modes during
alternate spins
• FOV: 5 pixels at +/- 72°, +/36°, 0°
• Energy sweep: every 0.75s
• 16 azimuthal sectors (normal
operations)
• Higher azimuthal resolution in
burst support mode
NSF GEM 2012 Summer Workshop
RBSP-ECT Suite Summary: MagEIS
Magnetic Electron Ion Spectrometer
• 6 ECT instruments per spacecraft :
MagEIS Low (#2), Medium 1 (#3) , and Medium 2 (#4)
• Magnetic Electron Ion Spectrometer
• Led by The Aerospace Corporation
• One low (energy) spectrometer with FOV
centered 75° to spin axis
• Two medium (energy) spectrometers with FOVs
centered at 75° and 35°
 2 medium units for optimal pitch-angle coverage
• Particles enter magnetic-field chamber through
collimator-defined field-of-view
• Magnetic field uniform, normal to plane
• Electrons focused on 9-pixel SSD focal plane;
thickness matched to e- energy (500-3000 µm)
• Momentum selection by magnetic field means
each pixel has uniquely defined differential
energy range; all events outside this defined
range are thus background and are tracked
• Positive particles deflected in opposite direction
from electron pixels for clean e- measurements
NSF GEM 2012 Summer Workshop
RBSP-ECT Suite Summary: MagEIS (cont.)
Magnetic Electron Ion Spectrometer
• 6 ECT instruments per spacecraft: MagEIS High (#5)
• Four pixels in focal plane
• Front detector 300 µm thick
• Three pairs of back-to-back 1500 µm
detectors (up to 9 mm) used as rear detector
• Outputs from co-aligned pixels summed to
silicon thickness needed (green) in common
electronics chain
• Unused detectors support background
removal
• Each of eight pixels (four front and back)
connected to a separate electronic system
• Pulse-height spectrum generated for each
pixel
• Data processing includes coincidences
between front and back pixels
• High units also include proton telescope to
cover protons in ring current energy range
p+
e-
1 2
3
4
20°
Incoming
particles
NSF GEM 2012 Summer Workshop
Magnetic field
normal to plane
of figure
RBSP-ECT Suite Summary: REPT
Relativistic Electron Proton Telescope
• 6 ECT instruments per spacecraft: REPT (#6)
• CU-LASP-led
relativistic electron
proton telescope
• Multiple solid state
detector telescope
• Onboard coincidence
logic identifies particle
species and energy
• Particle counts reported
1/spin
• FPGA-based (no
software)
• Calibration &
configuration tables
loaded at start-up
• Nominal operations:
listen and report
NSF GEM 2012 Summer Workshop
RBSP Mission: Status Report
• Twin RBSP s/c in
final preparations at
Astrotech for late
August launch
• Photo to right shows
s/c being tipped for
muon testing on
Sunday
• RBSP on schedule
and on budget
• All instruments meet
or exceed
measurement
requirements
• Commissioning lasts
60 days followed by
flight operations;
Phase E begins late
CY12 for a nominal
2-year prime mission
NSF GEM 2012 Summer Workshop
RBSP : Exploring the Extremes of Space Weather
NSF GEM 2012 Summer Workshop
Summary
• The radiation belt is an area still ripe for
discovery, despite its 50+ year history of study
• Radiation belt dynamics are scientifically
compelling, universally relevant, and important
to variety of user communities
• Transformational measurements made by RBSP
will achieve outstanding science objectives
• Modeling opportunities abound – both local and
global processes require a variety of models and
techniques - students encouraged to participate
NSF GEM 2012 Summer Workshop
RBSP : Exploring the Extremes of Space Weather
NSF GEM 2012 Summer Workshop