sxgscrf1.gif Spectrum X-ray Gamma mission

 

This mission would never been launched according to foreign financial problems. Hungarian participation is finished, everything of the undertaken parts are made but they are laying on desks of laboratories. This article was written before the decision of rejecting the launch.

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The project, an international astrophysical project. The Russian spaceprobe will launched on a Proton rocket from Baikonour in 1998. Its scientific objective: astronomical observations beyond the atmosphere of the Earth, in particular in the until now less observed X-ray and Gamma range. The scientific objects of the project are the following:

  1. observation of known and unidentified as well as discovery of new gamma sources
  2. study of the environment of compact objects, neutron stars and gamma eruptions
  3. study of the physical circumstances in the center of the Galaxy
  4. look for remnants of Supernova outbursts, explosions
  5. study of interactions between cosmic ray and interstellar gas
  6. study of not thermal radiation of galaxy masses
  7. observation of active galaxy nucleus in gamma range
  8. study of X-ray Quasars
  9. study of the origin of cosmic X-ray background radiation

On the spacecraft there will be numerous, in various energy range functioning, scientific experiments as the contribution of numerous research centers in different countries, such as Russia, USA, Great Britain, France, Denmark, Germany, Italy, Finland, Israel.

Our activity covers the design and manufacture of the central data acquisition on-board computer (BIUS) and of its Electrical Ground Support Equipment as well as the evaluation of the gained science data. The design of BIUS is an attractive task both from technical and technological point of view. It must be an up-to-date design with extremely high reliability figures due to the expected high life time. The correct operation of the BIUS is of decisive importance, because almost all of the scientific experiments will be controlled by the BIUS and the collected science data will be passed over to the Earth through BIUS.

The total weight of the spacecraft will be over 4000 kg, and will be revolving around the Earth on a high-apogee orbit (1000-200000 km) with the expected life time of five years. The scientific payload (mass cca. 2.5 tons) will be composed of the following experiments:

  1. HEPC, LEPC X-ray telescope with the focal length of 8 m in the range of 0.2-10 keV (Russia-Denmark)
  2. JET-X grazing incidence telescope with the focal length of 4 m, high angular resolution in the range of 10-15 keV (Great Britain)
  3. MART-LIME coded mask telescope (Italy-Russia)
  4. SODART coded mask telescope in the hard X-ray range (Russia)
  5. SXRP X-ray polarimeter (USA)
  6. MOXE (USA)
  7. SIXA (Finland)
  8. TAUVEX (Israel)
  9. DIOGENE (France)

The project will provide a unique experiment complex. A tremendously large collecting area of the mirrors of X-ray telescopes, a wide energy range from 0.02 to 100 keV, an ability to make X-ray images with a resolution from 10 seconds of arc to 2 minutes of arc over a wide field of view, to make X-ray spectroscopic measurements, open up a unique possibility of employing observatories in the interest of cosmology.

The central data acquisition and control computer of the Spectrum-X-Ray-Gamma spacecraft

The on-board data acquisition and control computer (BIUS) is being developed in our institute. The BIUS will be connected to the other units of the spacecraft, such as other service systems and scientific experiments. In order to avoid malfunction due to any kind of erroneous operation of the external experiments the BIUS has modular construction in one hand, on the other hand the external units and the modules of the BIUS are connected together on reserved, galvanically isolated, serial buses. The control and change of information is taking place on these links.

Basic activities of it are the following:

  1. collecting science and technical data from the experiments and storing it onto the on-board magnetic tape
  2. preprocessing of science data and passing it to the Earth over radio link
  3. controlling scientific experiments according to a predefined cyclogram or the uplinked Earth commands

The BIUS is composed of different, self functioning modules having their own power supplies and the possibility of switching on/off independently of each other. The other advantage of modularity is that by implementing a standard protocol for data exchange it makes possible to work out various, flexible reservation methods. The need for a continuous operation, the extreme environmental circumstances (most dangerous of them is radiation) and the expected life-time (over 3 years) necessitates to triplicate every module of the BIUS.

We decided to apply cold reservation. The activation of reserved modules may be initiated from the Earth while the radio uplink is functioning. Since every single module is connected to the same link, overswitching from one module to another one does not need any extra hardware.

Since the functioning of radio link is not continuous, it is possible to operate BIUS in warm reserved mode in critical time intervals. In this case more processor modules are working at the same time, one of them as active, while the other ones as listener and as such they can take the active role over the module has just gone wrong. For this purpose the processor modules are connected to an internal serial bus in order to be able to test each other. Systematic exchange of critical parameters and regular test procedures running in the background ensure that change of active processor does not cause any loss of data and the functioning seems to be continuous looking from the external experiments.

Every single module can be connected to an external computer on the serial bus without dismounting of BIUS. During ground tests it makes the localization of errors easier. The BIUS is composed of the following modules:

  1. Processor modules
  2. Earth command and on-board time code receivers
  3. Scientific telemetry interfaces (1 Mbit/sec)
  4. Service telemetry interfaces (16 kbit/sec)
  5. Power supply and analogue telemetry units

The processor module uses 80C86 type processor, its memory is organized 16 bits wide. The memory is built up with PROM, EEPROM and RAM components. The clock generators of processor modules have component-level redundancy. The memory has error-checking and correcting circuits. This, at the price of the slightly increased memory-size requirement, stores information in Hamming-coded format, and with the help of this method is able to correct smaller errors (1 bit/word), or signalling more faulty bits.

The computer, due to the built-in component and module-level redundancy, in spite of its gradual degradation, is able to keep the system in a working condition.

The software is a real-time multitasking operation system, parts of it performing the tasks of both system functions and scientific experiments. The kernel of the operation system (supervisor) is written in assembly language in order to increase speed. We have solved the problem of application of high-level programming language C, written originally to IBM-PC, to our IBM-PC-independent architecture on-board computer, this way making the Turbo-C development-kit possible to use for developing the tasks. To support the software development for the computer missing human/machine connection, we made a solution including both hardware and software elements, by which, connected to the so called technological connector of the computer, we can control the running of programs, can stop it, and can check or change parameters. The technological model of the ground support equipment we have finalized the supervisor, the terminal task, the slow and fast telemetry task, and on-board time task.

The electrical ground support equipment is an IBM-PC based test system, in which special interface cards simulate the space probe's electrical signals. The system includes the following individually developed circuit cards:

  1. on-board bus simulator
  2. analogue telemetry and relay command simulator
  3. coded command and on-board time
  4. fast telemetry simulator
  5. slow telemetry simulator
  6. inner bus simulator ("processor bus")

The operating software of the EGSE has been written partly in Borland C++. The software is menu-driven, window oriented, quasi-real time, interactive. The control commands are unpitied through the keyboard then are sent to Coded-Command and time simulator card by programmed (polled) method, and again now by hardware method they are sent to the on-board system. Receiving of fast telemetry signals are organized as a background job (direct memory access).



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