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GEC
SCIENCE THRUSTS
The theme of the mission is to establish the role of the
ionosphere/thermosphere in the electrodynamic environment
of near-Earth space. Within this context the GEC science
objectives are:
- To observe the magnetospheric energy transfer to the
ionosphere and thermosphere by making space-time resolved
observations in the transfer region.
- To determine the key processes and their space-time
scales for coupling between the ionosphere-thermosphere
as magnetospheric energy is dissipated.
MISSION
SCENARIOS
The GEC Science and Technology Definition Team (STDT) chosen
by NASA Headquarters are finalizing the mission
definition. It will be a focused two-year investigation of
the most important magnetosphere-ionosphere-atmosphere coupling
regions between 130 km and 2000 km. In order to resolve space-time
ambiguities four identically instrumented spacecraft, with
approximately 10 instruments for measuring critical plasma
and neutral parameters, will be launched from the same Delta
launch vehicle. Initially the satellites will be placed in
identical high inclination elliptical parking orbits (~200
km by 2000 km). The spacing between the spacecraft in this
pearls-on-a-string configuration will be varied from ~ 10
km to 1/4 of the orbit. This novel variation of the spacecraft
separations, using onboard propulsion, will allow unique
observations of important ranges of temporal and spatial
scales. Each spacecraft, carrying more than 200 kg of propulsion
fuel will have the capability of executing more than a dozen
weeklong dipping campaigns during the baseline 2 year mission
to altitudes below 130 km where the atmosphere effects on
plasma processes and spacecraft aerodynamics are prominent.
These dipping sequences provide the opportunity for new discoveries
because no previous spacecraft have explored this low altitude
region with GEC ‘s complete complement of plasma and
neutral atmosphere measuring instruments. Later in the mission
the 4 spacecraft will be maneuvered into different orbit
configurations, a petal formation or relative changes in
local time which will allow one to resolve vertical and horizontal
structures.
GEC
MEASURMENTS
Measurements are needed of the concentrations of all relevant
IT constituents, their temperatures and velocities, the local
electric and magnetic fields and the energetic particle distributions.
The core measurements will be made by in situ measuring sensors.
To provide a global context to the in situ observations
(e.g., the flow fields and plasma effects away from the spacecraft)
would require remote-sensing detectors. The preliminary spacecraft
design includes both in-situ measuring detectors and remote
viewing sensors. The spacecraft are 3-axis spin stabilized
to avoid compromising the in situ sampling instrument observations.
This attitude configuration will allow for the positioning
of nadir looking or limb scanning optical devices. The flat,
front ram face of the spacecraft will hold the instruments
for thermal plasma and neutral gas  measurements,
which use the ram speed of the spacecraft to efficiently
sample the environment. The solar arrays are to be body mounted
and electrically conducting, in order to minimize perturbations
on the plasma measurements due to spacecraft shadowing and
spacecraft electric fields.
Photo to right: String-of-Pearls and Petal
Formations show the orbit of the GEC spacecrafts.
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