Orbit requirements

To achieve its task within the INTERBALL project, the subsatellite must have an orbit close to that of the main satellite and be at a certain distance away from the latter.
The specific way of separating from the main satellite depends, first of all, on the properties of the separating mechanism and on the time instant of the separation. The separation itself is controlled by a separating momentum directed perpendicularly to the satellite velocity vector; under the action of the momentum the subsatellite acquires a small relative velocity of the order of several tens of cm/sec.

For correcting their orbit, the subsatellites are equipped with the gas-jet orbital maneuvering and attitude control device (KDU) and corresponding controlling system.

For example, in case of the Tail Probe, to study the fine structure of boundaries between the formations in the interplanetary space (shock waves, magnetopause, magnetic clouds, plasma pistons, etc.) the distance between the subsatellite and the main spacecraft should be in the range of 100-300 km. For examining the processes in the magnetospheric tail, where the scale of inhomogeneities (plasma layer boundaries, fireballs, neutral sheet, etc.) can be comparable, or much greater, the distance between the subsatellite and main satellite could be increased to 1 to 3 thousand km.

In the case of the Auroral Probe, whose orbit is much lower and whose velocity at the apogee is significantly higher, so that it rapidly passes through sufficiently narrow geophysical zones (polar cap, auroral oval, cusp, etc.), with their characteristic small-scale plasma structures, it is desirable to have the distance between satellites within narrower limits: from several tens to several hundred km.

The radiomethods are the main means of controlling the subsatellite orbit parameters and of determining the satellite-subsatellite distance. Radio-distancemeter system is used which allows to measure the Doppler shift of the satellite's telemetry frequencies simultaneously both of the satellite and subsatellite, from which the orbit characteristics can be deduced.Besides that, the radio-interferometric method will be applied which will allow to obtain a better precision in orbital tracking.

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