The main computer system aboard the Mir space station will be replaced with a new one to be sent up on the US space shuttle Atlantis later this week. Russian officials hope it will it will stem an increasing number of breakdowns on the space station which have been compounded by a series of well-publicized problems caused by human error. Mir’s computer has been working as planned since the space station’s launch in 1986; when it breaks down it can be fixed and restarted relatively simply, either from mission control, by Mir’s occupants, or automatically. More breakdowns have occurred recently than usual according to Rocket Space Corp Energia, the Moscow-based company which maintains Mir, because the cash-strapped Russian Space Agency has fallen behind on upgrading the computer’s components, so much so that parts now tend to be replaced only when they fail. What Atlantis will deliver is a replicate system (plus spare parts) that’s expected to give Mir’s computer a new lease of life; after all it’s already been in operation twice as long as its original design plan called for. A Russian cargo ship scheduled to reach Mir next month is expected to bring up another new computer. Mir became the focus of intense media scrutiny when NASA physicist Michael Foale joined two cosmonauts aboard Mir earlier this summer, shortly after which a cargo ship carrying supplies up to the men collided with the station’s Spectre Scientific lab back, knocking out some of the support environments and disabling part of the station. Now barely a week goes by without a report that Mir’s computer has broken down for the umpteenth time, and yet the space station hasn’t fallen out of the sky, nor has it drifted off into deep space.
Mir’s main computer system was developed between 1978 and 1984 by the Zenlograd, Russia computer firm Aelas using components that would today be regarded as relatively unsophisticated, if not relics. According to Dr Vladimir Branets, head of RSC Energia’s scientific and technical division, which since 1992 has operated and maintained Mir’s computer, the system was designed so that failure is accepted as a normal part of general operation. The computer first shutdown just three days into Mir’s mission in 1986. As well as being controlled from the ground, components were designed so they could be easily replaced by non-technical operators aboard Mir and while the computers are still in full operation. Indeed most parts have been replaced many times over in Mir’s eleven years in space. The online replacement technique, called hot-swapping, is being now becoming popular with companies building commercial computer systems. The Mir computer is administered primarily by mission control in Korolyov which can upload programs, download data and reboot system components. All of the system’s components were designed during the Soviet era and are manufactured in Russia. The replacement computers being sent to Mir later this week were flown to the NASA’s Kennedy space center from RSC in Moscow over the weekend.
Somewhat resembling a collection of PCs networked to sensor and control instruments, Mir’s main computers are embedded systems running a low level assembler languages. They operate Mir’s Gyro dynes, gyroscopic devices which keep the spacecraft pointing in the right direction, its solar panels aligned with the sun and its antennas pointing to mission control. They also regulate on- board electrical power, communications and control the rocket motors. When the computer does fail, as happened on Monday, the 12 gyroscopic devices are turned off and Mir loses its orientation towards the sun until the system is brought back to life. Data is sent back and forth via a proprietary data bus and also downloaded to mission control which uploads new programs to run on the systems. In raw performance terms the systems have less computing power than a modern laptop PC. In addition to remote control from earth, there are onboard terminals for data input/output, a control panel for running programs control and command indicators. RSC describes the system as comprising a basic Argon-16B computer similar to that used on unmanned transport spacecraft; a newer Salyut-5 computer system; a rendezvous and docking system including the 1970s era Igla system and a new 1990s Kurs system. Branets says the system incorporates triple redundancy of information circuits and the sensors. It has three modes of operation; direct from ground control or crew control; by automated programs; and using information analysis of current conditions and backup procedures to determine action. It’s performed 129 rendezvous and docking operations in its lifetime. More modern systems, including laptops brought aboard by the newest crew members, are used for inventory purposes and recording data from the various scientific tests being performed in the weightless conditions aboard Mir. But even those, which may only be taken up for a few months’ use at a time, aren’t immune from the conditions which Mir’s computers have endured for eleven years. PC peripherals which plug into in PCMCIA slots in laptops have been subject to frequent failure in space, RSC observes. On the ground, mission control uses a mix of different computers, including Hewlett-Packard Co 9000 Series Unix systems (you may have seen HP’s advertising banner during television news reports banner from the operations room at mission control). What’s important are that lessons learnt from the operation of Mir’s computers can be used in the design of systems which will run the proposed $100bn international Alpha station being co- designed by Russia and the US which is to be built in stages by 2003. Russia is to manufacture the first Alpha module, the launch of which has already been delayed from November this year until June 1998.