Science Overview

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Geospace Electrodynamic Connections (GEC)
Mission Definition Joseph M. Grebowsky,
GSFC Jan J. Sojka, USU Rod A. Heelis, UTD On
Behalf of the Entire GEC-STDT (Visit our website
at http//sec.gsfc.nasa.gov/gec.htm) Huntsville
2000 A New View of Geospace (October 31, 2000)
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Geospace Electrodynamic Connections (GEC)
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GEC Definition Team
Jan J. Sojka Utah State University Rod A.
Heelis UT Dallas William A.
Bristow Geophysical Res. Inst. James H.
Clemmons Aerospace Corporation Geoff
Crowley SwRI John C. Foster MIT/Haystack
Observ. Michele M. Gates GSFC Robert S.
Jankovsky NASA/Lewis Res. Ctr. Tim L.
Killeen NCAR STDT Chairs
Craig Kletzing Univ. of Iowa Larry J.
Paxton APL William K. Peterson Lockheed
Martin Robert F. Pfaff, Jr. GSFC Art D.
Richmond NCAR Jeff P. Thayer SRI
International Mary DiJoseph GSFC Formulation
Janette C. Gervin (GSFC Formulation) Joseph
M. Grebowsky GSFC Study Scientist James F.
Spann HQ Program Scientist
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GEC Mission Objectives

• The Solar Terrestrial Probe for
• Understanding Plasma Interactions with the
  Atmosphere

A constellation of 4 deep dipping spacecraft
Pearls-on-a-string formation
Petal formation
The Ionosphere-Thermosphere System A dynamic
element in the chain of energy transfer from the
Sun to the Earth
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Why a Multi-Satellite Mission?

• The ionosphere-thermosphere interface is highly
  dynamic and structured

Key Features Joule HeatingGravity Waves Auroral
Arcs Sub-auroral DriftsField FluctuationsConvec
tion BoundariesStorms and Substorms
Temporal Scales Few seconds to gt hour
Spatial Scales lt 1 km to gt 1000 km
Single satellite measurements cannot resolve
space and time variations.
GECs multi-point measurements will reveal the
spatial and temporal variations.
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Physics Foundations

• How is the ionosphere-thermosphere involved in
  geospace electrodynamics?

Electromagnetic Energy Transfer Rate
Pedersen conductivity
? The ionosphere provides a Hall and Pedersen
conductivity layer to enable closure of
magnetosphere currents and energy exchange
between the magnetosphere and the I-T system.
? The closure process involves collisional
interactions that change the conductivity and
thus the energy exchange between the
magnetosphere and the I-T system.
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Fundamental Physics Question 1
How Does the I-T System Respond to Magnetospheric
Forcing?
Largest Effects are below 300 km No Global
Picture below 300 km Different physics above
and below 300 km
1) How is the magnetospheric E field and
particle input into the I-T system structured in
space and time? 2) How does Joule heating affect
the I-T system? 3) How do E fields affect winds
and composition in the I-T system? 4) How do
magnetospheric influences extend to middle and
low latitudes?
Above 300 km described by DE
To answer these questions GEC mustDiscover the
spatial and temporal scales for the
magnetospheric inputs.Determine the spatial and
temporal scales for the response.Quantify the
altitude dependence of the response.
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Fundamental Physics Question 2
How is the I-T System Dynamically Coupled to the
Magnetosphere?
1) How do atmospheric dynamo processes modify
the energy flow between the magnetosphere and the
I-T system? 2) What controls the connections
between horizontal gradients in conductivity,
electric fields, currents, and neutral winds? 3)
How does the I-T system affect field-aligned
currents and Alfven waves that connect it to the
magnetosphere?
To answer these questions GEC mustDiscover The
important spatial and temporal scales that change
the energy flow between the I-T system and the
magnetosphere. Determine which altitude regions
in the I-T system contribute to coupling at
different spatial and temporal scales.
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Why Deep Dipping to 130 km or Lower?
At 130 km ? Ion Collision Frequency equals Ion
Gyrofrequency ? Pedersen conductivity peaks ?
Joule heating energy deposition peaks ? Ion
velocity vector departs from E ? B direction by
about 45?
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Science - to - Mission Requirements
RRequired EEnhances Science Objective NNot
Required for Science Objective Dips to 130 km
perigee and Petal orbits for altitude
discrimination are required to fully achieve the
science objectives.
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GECS SPACECRAFT MULTIPLE SCALE MEASUREMENTS
Since 4th s/c follows 1st we have effectively
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Pearls-on-a-string configuration with uneven
spacing obtains information on many time/spatial
scales
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Spacecraft Designed to Deep Dip and Minimize EM
Disturbances
Each Spacecraft Mass Total 673 kg Fuel 326
kg Instruments 55 kg Size 1.1 m diameter
2 m length E-Field booms 10m Orbits
2000 X185 km 830 Inclination Enough fuel for
a dozen week-long dipping campaigns to 130 km
Cylindrical Shape, Rounded Front
Face Body-mounted Solar Arrays EM Field
Instruments on Deployable Booms Large Propellant
Tanks
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Pearls-on-a-String Orbit Configuration
Near horizontal path for long distance near
perigee - allows separation of time and
horizontal structure. Different spacing between
each spacecraft - multiple scale resolution. Can
have a dozen or so weeklong deep dips to near or
below 130 km.
Plot is for 2000X130 km orbit, perigee at
65o. Traversal time plotted 14 minutes.
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Pearls-on-a-String Orbit Configuration
Changing argument of perigee for spacecraft and
adjusting phase along orbit provides capability
of measuring altitude profile.
Plot is for 2000X130 km orbits with arguments of
perigee at 65, 60 , 55 and 50 degrees.
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Possible Dipping Campaigns to 130 km
Nominal 2000 X 185 km orbit in blue. Dips to 130
km in red
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Launch Configuration
Configured for DELTA 7920H-10. Launch Vehicle
Capacity 3554 kg. Cruciform type of carrier for
launch - traditional. Ends of spacecraft are
clean - desirable for science instruments.
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