The characteristic feature of the INTERBALL project is the realization of multi point simultaneous measurements at different altitudes provided by two main satellites together with two subsatellites, each of which is launched into orbit as the passenger of its main satellite.
The main purpose of the subsatellites in the INTERBALL Project is to perform systematic complex studies in the tail polar magnetosphere, magnetosheath and solar wind, of spatial structures of individual space plasma processes, ambient plasma parameters and cause-and-effect relationships by performing measurements synchronized with those made on the main satellite. Measurements at two different points in space for each satellite-subsatellite pair - if their relative positions are known - enable one to distinguish reliably (in one direction, at least) the locations and motions of various plasma structures and/or inhomogeneities in space from the purely time variation of the medium parameters, which is very important for the correct interpretation of experimental results.
The spacecraft of Magion type have been selected as the subsatellites of the Interball project: Magion-4 (C2-X) for the Tail Probe and Magion-5 (C2-A) for the Auroral Probe. The concept of the small subsatellite for the Prognoz-type spacecraft was realized for the first time in this project. Magion-4 was produced in the Czech Republic in collaboration with Russia, Ukraine, Hungary, Austria and has onboard scientific instruments and sensors designed and built in Czech Republic, Russia, Poland, Hungary, Romania, Bulgaria and Slovak Republic. Magion-5 spacecraft is currently being prepared for the launch in 1996 and has onboard scientific insruments from France in addition to the instruments mentioned above.
Principal Technical Characteristics
The system controlling the subsatellite"s thermal regime (SOTR) is designed to balance the thermal field of the subsatellite elements in the range acceptable for all possible operation modes:
- for the mode of the subsatellite flight as a component of the main spacecraft before separation;
- for the mode of subsatellite operation on the orbit of the Earth"s satellite;
- for the mode of passing through the Earth"s shadow (the maximum duration of the shadow passage is 5 hours for the C2-X).
The system controlling the subsatellite thermal regime includes both the active and passive devices for thermal regulation. It is based on the preflight data which determine the subsatellite design, its orientation relative to the Sun in the main operation modes (before and after separation from the main spacecraft and during its pass through the Earth"s shadow), and on the requirements to the thermal regime of the subsatellite systems.
Among the passive means of the thermal control the following are used:
- Special covers for thermal regulation;
- Multi-layer metallized film insulation (MMLI);
- Calibrated thermal resistors;
- Heat pipes to balance the subsatellite thermal field.
The active devices for thermal balance include the electric foil heaters of SOTR. Their principle objective is to provide the needed thermal field up to the moment of the subsatellite separation.
The part of the outer side of the subsatellite body has the thermo-regulating covers. Besides that the KDU is shielded by MMLI. To provide the thermal regime of chemical batteries and the subsatellite body during 5 hours of passing through the shadow the calibrated thermal resistors are used.
To smooth the subsatellite thermal fields along the Z-axis oriented toward the Sun, two heat pipes are installed. Each pipe generates the thermal power of up to 35 Watts for the temperature gradient between the zone of heating and zone of condensation with the maximum value of 4deg.C.
Thermal Control system was designed and heat pipes were produced in Kiev Polytechnical Institute, Ukraine.
Testing of the system was made in Space Research Institute, Russia.
Calculations were made in Space Research Institute and in Scientific and Production Association named after S.A.Lavochkin , Russia.
The solar array consists of 14 + 4 parallel connected solar panels with the sections of 196 x 196 mm in size made on the basis of silicon solar cells. Six single-side panels are mounted on the facets of the subsatellite at the distance of 10 mm from metallic surface, 12 panels are to be deployed in space. After deploying their axes have 100 deg angle with respect to subsatellite axis directed toward Sun. Four solar panels are reserved and switched to the system of subsatellite energy supply together with their DC/DC converter-inverter MPC after degradation of the panels initially switched on.
The current of the panel being orthogonal to the Sun direction is about 0.2 A at the operation voltage of 14 Volt. The maximum total power of the solar array at the nominal solar orientation is 36 W.
The solar array was made by NPO "Kvant", Moscow, Russia.
Each of the chemical batteries (XB-1 and XB-2) consists of 10 successively switched nickel-cadmium cells in pressure vessels of RSQ-4 type with the nominal capacity 4 A*hour. Batteries nominally operate in a buffer mode with the load power less than the solar array power. The batteries are being charged in this mode. They are discharging either when the load power exceeds the solar battery power, or on the shaded portion of subsatellite orbit. To control charge-discharge processes each of the accumulator batteries has temperature interval regulator.
Protection from an excess charging is realized by means of limiting the charging voltage at the level of 14.5 V. Emergency protection is realized through temperature regulators mounted inside batteries. Protection from excess discharging is provided by switching the battery off from the discharging circuit and by switching it to charging when its voltage falls below 10.8 V.
Correcting thruster device (KDU)
The correcting gas-jet engine is the executive instrument of the subsatellite control system and is designed for generating tractive force impulses:
- to correct the subsatellite motion along its longitudinal Z-axis and perpendicularly to it; - to realize the subsatellite rotation around its longitudinal Z-axis and its damping;
- to redirect the longitudinal axis (-Z) to the sunward direction.
Main technical characteristics of KDU are presented in Table.
|Jet body||Compressed air|
|Tractive force of one nozzle for all conditions of its operation||0.1 +/- 0.007N|
|Normal pressure of the balloon filling for the environment temperature 20 C||22MPa|
|Range of pressure variations at the input||0.25-0.37MPa|
|Pre-start gas pressure in the cavity in front of||0.5MPa|
|Balloon volume||1.85 liters|
Correcting thruster device was made in "Yuzhnoye" Design Bureau, Dnepropetrovsk, Ukraine.
In the INTERBALL project the ODCS version was chosen as the system of data collection (STS) since this version together with the STO telemetry on the main satellite provides acceptably high resolution in real time. The channel of digital data transmission can operate with the rate up to 40 Kbit/s and the channel of analog information makes it possible to transmit the data with the band width up to 60 KHz. In this case it is especially important that the data received from both spacecraft would match in time with high accuracy, otherwise some approaches to interpreting the measurement results would be impossible. However, for long distances from the Earth, the TM-rate (the band width) is rather limited. An important component of the TM-system is the digital onboard memory device with the capacity of 4 Mbyte designed for recording the housekeeping data out of the zone of the radio-visibility from the ground-based stations and for registering the scientific data in several operation modes depending on the measurement program. The onboard data collecting unit, STS, is installed to collect the analog and digital information from the complex of scientific payload and from the subsatellite service systems. This unit performs also the formation of the digital TM frame structure.
STS unit has the following features:
- 1. STS can operate in receiving/transmitting modes through 14 digital and 15 analog channels (or through 120 analog channels with the use of multiplexer controlled by STS 3-bit parallel codes).
- 2. STS includes the onboard computer on the basis of the NSC-800 microprocessor. The onboard computer can receive digital data directly from scientific instrument and from service systems, and after the data processing sends the resulting digital data both to the TM-frame (and, if needed, backward to the system) in the form of 8-bit words to control the operation modes and the programs of operation of the instruments and systems.
- 3. The rate of data transmission has 4 fixed values: 1.23, 5.12,20.48 and 40.96 kbit/s. The operative rate of data transmission is valid both for the telemetry and for data transmission from the onboard computer to instruments.
- 4. The system has 8 prefixed independent TM-frame structures and gives a possibility to form in flight an arbitrary additional structure. Each of the 8 versions of the TM-frame structures provide the optimum distribution of the TM information in a block depending on particular conditions of the experiment and on the program of studies.
The largest information block in the STS is the main block (512bytes) consisting of 4 subframes of 128 bytes. The signal to transmitter from the STS unit output has the form of bi-phase modulation.
The following organizations took part in design of the data collecting system:
-Microvawe Department of the Budapest Technical University, Hungary; -Geophysical Institute of the Czech Acad. Sci., Prague, Czech Republic; -BL Electronics, Hungary; -Institute of Atmospheric Physics of the Czech Acad. Sci., Prague, Czech Republic.
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.
Selection of scientific payload
As it follows from their main objectives, the measurements made aboard the subsatellites should be adequate to those made aboard the main satellite, as much as it is allowed by the smaller size and weight. Considering everything that has been said above, the following set of scientific payload for the MAGION-4 subsatellite was selected:
The electric antenna is a 1.6 m long dipole made up by two spherical carbon EDS detectors each with a preamplifier. The detectors are fixed at the ends of the folding booms of the subsatellite.
The magnetic component is measured in two ranges: ULF (1 Hz - 2kHz) and VLF (1 - 50 kHz). The MSU detector of the ULF range is located on the folding arm of the subsatellite. Its antennas a research-coil detectors with low-noise preamplifiers. The same detector is also used for the VLF device. The one-component MSV detector of the VLF range is a search-coil detector with a preamplifier and is located on another folding boom.
The output signal of the detectors either is processed by the device electronics for transmitting the wave form by means of analog telemetry, or the amplitude of spectral lines is transmitted by means of digital telemetry. The amplitude obtained either in the VLS filter unit or in the step spectrum analyzer SAS.
The frequency range and sensitivity are the following:
- 1. component Ex: 0.1 Hz - 400 kHz; 5*10E(-8)HzE(-1/2) (2 kHz).
- 2. component Bx: 1.0 kHz - 50 kHz; 10E(-5) nT*HzE(-1/2) (2 kHz).
- 3. components Bx,y,z: 1.0 Hz - 2 kHz; 3*10E(-5) nT*HzE(-1/2) (100 Hz).
The SAS instrument consists of two SFA analyzers, time transformer and analog telemetry unit. The instrument is designed as the well-known step-frequency analyzer with two intermediate frequences: 465 kHz and 5 kHz.
Signal under analysis:
- electric component: 1-400 kHz (32-2000 Hz);
- magnetic component: 400 Hz - 20 kHz;
- magnetic component: 32-2000 Hz (Bx, By, Bz selected through the multiplexer);
- current density XZ: 0.4-20 kHz;
- current density YZ: 0.4-20 kHz;
- analog frequency range: 1-480 Hz divided into 8 subranges;
- analog output to TM is wide-band of 60 kHz.
Three-component magnetic sensor is a component of the instrument KEM (Czech Republic).
- dynamical range: -76dB - +30dB (106 dB)
- number of analyzed components: 4.
- 1. Transmission of all 4 components with the rate of 20 kbits/s or 40 kbit/s with the digitizer frequency of 280 Hz.
- 2. Transmission of one selected component for the telemetry rates 5 or 1.25 kbit/s with the digitizer frequency 70 Hz.
SG-R8 is a triaxial flux-gate magnetometer with automatic switching of sensitivity. Its characteristics are:
- Range +/- 65536 nT, resolution 8 nT
- Range +/- 8192 nT, resolution 1 nT
- Range +/- 1024 nT, resolution 0.125 nT
- Range +/- 128 nT, resolution 15,6 pT
The data from the magnetometer pass through a digital converter, which has 13 bits and the sign. Its operation is synchronized with the STS telemetry system.
The detector of the magnetometer is fixed at the top of a rigid short boom, which enables one to determine precisely the attitude oft he magnetometer axes with respect to the construction axes of the subsatellite.
DOK-S spectrometer is designed to measure the energetic spectrum and angular distribution of electrons in the energy range 20-180 keV and of ions in the range 20-1300 keV.
In the main operational mode the range of measurements includes 8 energy channels. The instrument consists of two units: detector unit and electronics unit. Two pairs of silicon detectors are used,before one of them in each pair a magnetic filter is placed. The filter deflects from the field of view the electrons with energies lower than 600 keV. The mylar foil is placed before the other detector in each pair to capture the protons with energies up to 400 keV.
The electronics unit is based on the M80C85 processor, the amplified signals are accumulated in 8 energy channels during 150 ms and then are transformed to the digital and analog form for the instrument data analysis.
The main objective of measurements of charged particles and plasma flux characteristics in the INTERBALL project is to study the spatial structure of the terrestrial magnetosphere as a global system in various scales and for varying external conditions.
The subsatellites are equipped with the ion/electron spectrometers similar to those installed aboard the main spacecraft.The MPS spectrometer aboard the Auroral Probe (AP) is designed for measuring the anisotropy of the ion fluxes along the magnetic field and the EPS spectrometer is used to study the ion and electron pitch angle distribution.
The MPS spectrometer aboard the Tail Probe is designed to carry out a long-period monitoring of the solar wind parameters and to register the ion fluxes in the bow-shock region when the satellite will be in the appropriate regions. The spectrometer is oriented along the Sun-Earth direction. The SPS spectrometer is designed for estimating the ion energy and angular distributions and for measurements of the electron energy distributions. The MPS and SPS spectrometers have limited angular characteristics, for this reason the system includes the VDP-S instrument which is designed for rapid determining of the ion flux direction variations. The described above instruments have the parameters listed in the Table.
|Particles under measurements||ions/electrons||ions|
|Number of channels||3 for ions,1 for electrons||2 for ions|
|Energy range||0.2-20 keV||0.2-20 keV|
|Number of energy steps (can be varied by command)||16||16|
|Angular aperture (in the plane parallel to the main axis)||3x45 for ions,135 for electrons||4|
|Angular aperture (in the plane perpendicular to the main axis)||4||4|
|Method of registration||double hemispherical analyzer with microchannel plates||Electrostatic analyzer (127 ) with channeltron|
The X-ray photometer RF is designed to measure the solar X-ray radiation in the soft spectral range. In addition to continuous monitoring of the solar radiation in the X-ray range, the instrument can be used as an indicator for automatic switching-on the scientific instrumentation for registering the processes of the active solar events, assuming a change in the solar X-ray radiation as a "precursor" of these phenomena. The photometer is oriented along the -Z-axis of the subsatellite, i.e. toward the Sun.
The photometer consists of two units: the detector unit and electronics unit. The photometer is the scintillating detector with the aluminium foil in front of it to prevent penetration of the soft particles and X-rays.
The output signal of the detector is passed to the two-channel amplitude analyzer where it is selected in two ranges: 10-15 keV and15-60 keV. The impulses from the channels with a fixed amplitude are transferred to the electronics unit where they are accumulated during 0.8 s (time of one exposure step).
The maximum capacity of the detector is 183441 imp/0.8 sec., so for higher flux intensity (which is hardly probable) the detector data are not valid.
- Detector type: Faraday cups.
- Type of registered particles: ions and electrons with energies above 170 eV.
- Number of detectors: 4.
- Angular aperture: 100deg.
- Detector orientation: +/-45deg. from the main axis.
- Frequency (max.): 1, 2, 4, 8 Hz (depending on the telemetry mode).
List of scientific measurements aboard MAGION-4 subsatellite
- Magnetic field measurements: 3 axes 0 - 10 Hz.
- ULF waves: 3 axes, search-coils; 1-10 Hz or 1-30 Hz filters; telemetry: 12 bit ADC; dynamical range 76 dB.
- ULF/ELF waves: 3 axes search-coils, filterbank (8 channels) 10 Hz - 2 kHz and subcarrier (IRIG) analog telemetry channel.
- VLF waves: 1 axis, search-coil detector, filterbank (8 channels) in the range 8 Hz - 40 kHz. Spectrum analyzer SAS with 64 frequency steps, 400 Hz - 20 kHz; broad-band analog telemetry channel.
- Electric fields and waves: 1 axis in the range 0,1 Hz - 400 kHz, set of filters (8 channels). Spectrum analyzer SAS: 64 steps, (1 step - 20 ms), 32 Hz - 2 kHz or 96 steps, 1 - 400 kHz, wide-band analog telemetry (60 kHz max), subcarrier (IRIG) analog telemetry channel.
- Ion flux fluctuations 1e-12 - 1e-10A, (4sensors, spaced at 120 deg.)
- Energetic particles - solid-state spectrometer for electrons 20-230 keV and protons 20 keV - 1,3 MeV, 2 directions: antisunward and perpendicular to it.
- Plasma particles - electrostatic analyzer MPS, electrons and protons 0,2 - 20 keV, axes in the directions of the + and - Z subsatellite axis, i.e. toward the Sun and antisunward, on 16 energy levels.
- Plasma particles - multidirectional electrostatic analyzer SPS for electrons and protons 0,2 - 20 keV, 16 energy levels.
- Solar X-ray photometer two energy bands: 10-15 keV, 15-60 keV
- Two-components current Langmuir probe: 0,3 Hz - 50 kHz