The Interball Project is a multi-national effort that consists of four spacecraft: two
main spacecraft of the Prognoz series, made in Russia, each with a small subsatellite (Magion) made in Czechoslovakia. The main objective is to study the
physical mechanisms responsible for the transmission of solar wind energy to the
magnetosphere, its storage there, and subsequent dissipation in the tail and auroral
regions of the magnetosphere, ionosphere, and atmosphere during magnetospheric substorms.
A ground-based support group will provide coordinated and simultaneous ground-based data
of many types, including observations from auroral and polar cap regions. Interball is an
IACG-related mission. Key physical parameters will be generated, and will be available for
exchange with other projects. Campaigns for intercomparison with the Wind and Geotail
spacecraft are expected.
One pair of spacecraft, Tail Probe and its subsatellite S2-X (X for the first letter of
the Russian word for ``Tail''), was launched into the magnetospheric tail. The second
pair, Auroral Probe and S2-A (A for ``Auroral''), will have an orbit that crosses the
auroral oval to observe the acceleration of auroral particles and the flow of electric
currents that connect the magnetospheric tail with the conducting ionosphere. To study the
equilibrium tail structure, during about half of each year the Tail Probe pair will cross
the main parts of the magnetotail every four days. The Auroral Probe pair will support the
Tail Probe pair with auroral region measurements. Each main spacecraft has more than
twenty scientific instruments.
The spacecraft is cylindrical, with spin axis toward the sun (within 10 degrees), and
with spin period of ~120 s. The electric and magnetic field sensors are on booms connected
to the ends of the solar panels.
The subsatellites are small, each with about ten scientific instruments. The spin axis
will be directed within 10 degrees of the sun, with a spin period of ~120 s, as with the
main spacecraft. The subsatellites also carry gas-jet thrusters for limited control of the
orbit. Separation distance will range from hundreds of kilometers to several tens of
thousands of kilometers for the Tail Probe pair. Separation distance will range from
hundreds of meters to hundreds of kilometers for the Auroral Probe pair. The Tail Probe
has two telemetry systems, at up to 32 Kbps in real-time, with a memory mode capacity of
30 Mb in the RTK telemetry system and 120 Mb in the SSNI system. The Auroral Probe has
similar capability plus the additional real-time-only STO system, capable of 40 Kbps. Each
subsatellite has only the STO real-time telemetry system. For S2-X the rate can be varied
from 2--40 kbps. The Tail Probe has an adapting alert mode while in the memory mode,
allowing time resolutions that are the same as in the real-time mode. The aim is to have
the highest time resolution available at the thin borders of magnetospheric regions or the
sharp borders of some features. In the alert mode (triggered by an on-board computer
monitoring plasma and field parameters), the bit rate is increased for plasma, field, and
wave measurements. The duration of these alert periods is about 10 minutes, and there can
be 5--6 of them during one orbit.
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