phobcrf1.gif Phobos mission

In 1988 two spaceprobes (Phobos-1 and Phobos-2) were launched towards Mars planet. As a planetary mission, the Phobos Soviet spaceprobe is devoted to studying the planet Mars and its vicinity, along with its natural satellite Phobos that gave the expedition its name, but also the Sun and the interplanetary environment. At the time of the Phobos encounter, should had separate a small lander.

Phobos Lander Central Data Acquisition and Control System (CDACS)

The CDACS was planned to control all of the small spacecraft (lander) scientific experiments and the service system. The system has a fault tolerant architecture: a single error does not cause degradation in operation, in the case of multiple errors some degradation could arise, certain experiments would be ended but the functionality of the lander would be kept on. The central processor unit contains two 8-bit microprocessors, the three independent memory data flows are united in the majority logic. The circuit works even if one of the memories is not functional, on the other hand the majority logic circuits can be switched over to multiplexers by commands and data can be read from the selected memory unit. Another protection method is the use of two alternately write protected areas in the memory, in which the basic system status information is saved periodically. This protected system information can be used in case of failure, when the processor overswitch happens. In this system the clock unit is four times active (warm) reserved, and the other units of the system (interfaces) have passive (cold) redundancy.

The lander was due to soft touch down on the surface of Phobos but unfortunately the carrying spacecraft itself failed just before the initiation of landing.


Phobos ESTER plasmaphysical experiment

In the ESTER Charged Particle Complex three slightly different experiments were grouped together, simultaneous data processing and operation mode control for all three experiments were carried out by a specialized 8-bit onboard computer (so-called DPU-B).

Due to safety, weight and power restrictions, it had a simple, basic structure, pursuing reliability through massive engineering overhead rather than extensive redundancy. Still, redundant solutions were applied at all the sensitive points: triple redundant system clock, system ROM and RAM (controlled by majority logic) and switchable three mass memory banks for scientific data. Hardware watchdog helped to supervise software deviations, and a battery operated RAM containing basic operation mode data eliminated the need for uplinking long, time consuming commands in case of re-initialization during flight. The DPU communicated with the scientific experiments through galvanically isolated serial lines (optocoupled), thus allowing for switching off the experiments independently in case of a fatal error.

The data obtained have provided many important scientific results: new regions of the magnetosphere have been discovered in the environment of Mars and an intensive ion-outflow of planetary origin in the tailward direction was detected. Evidence for turbulence and heating and small- structure was seen in the planetosheath. Perhaps the most important results are related to the tail region, were a strong outflow of planetary ions and hot component of the electrons was detected. No previous Mars probe with such a good plasma physical and magnetic field instrumentation penetrated the shadow cone of Mars before. The comparison of these results with those obtained by NASA's Pioneer Venus Orbiter enabled us to reveal simulates and differences between the magnetosphere of Mars and Venus.



Go to Home Page of Space Activities

 Comments to Pál VIZI  p.vizi@rmki.kfki.hu  

 Contact to Sándor SZALAI szalai@rmki.kfki.hu

Copyright 1996 KFKI RMKI. All rights reserved.