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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 Huntsville 2000 A New View of Geospace (October 31, 2000)

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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

Huntsville 2000

A New View of Geospace

(October 31, 2000)

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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


John C. Foster

MIT/Haystack Observ.

Michele M. Gates


Robert S. Jankovsky

NASA/Lewis Res. Ctr.

Tim L. Killeen


* STDT Chairs

Craig Kletzing

Univ. of Iowa

Larry J. Paxton


William K. Peterson

Lockheed Martin

Robert F. Pfaff, Jr.


Art D. Richmond


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?

Key Features

Joule HeatingGravity Waves Auroral Arcs Sub-auroral DriftsField FluctuationsConvection BoundariesStorms and Substorms

  • The ionosphere-thermosphere interface is highly dynamic and structured

Temporal Scales

Few seconds to > hour

Spatial Scales

< 1 km to > 1000 km

Single satellite measurements cannot resolve space and time variations.

GEC’s 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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300 km

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 must:Discover 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 must:Discover 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

R=Required ; E=Enhances Science Objective ; N=Not 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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Since 4th s/c follows 1st we have effectively:

5 10

Pearls-on-a-string configuration with uneven spacing obtains information on many time/spatial scales

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E Field

Booms (6)



In Situ Neutral/Plasma Detectors

Energetic Particle


Langmuir Probe


Spacecraft Designed to Deep Dip and Minimize E&M 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

E&M 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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October 2000 Status

GEC SCHEDULE (9/08) Launch)