VMEbus technology applications
SBS Technologies, Germany, has supplied ruggedized VMEbus and other equipment for use in the International Space Station (ISS). The European Space Agency (ESA) manages the European space projects. The United States’ participation in the ISS began in 1984 during the Reagan administration. President Ronald Reagan committed the USA to building a permanently manned space station. Other nations participated. In 1998, the Russian Zarya module and the American Endeavour were connected together in space. Numerous modules and scientific experiments have since been added to ISS. Europe will develop and launch the Columbus module and attach it to the ISS. ESA also manages the development of the Automated Transfer Vehicle (ATV), a logistics vehicle. Figure 1, provided by ESA, shows the ISS with VMEbus equipment onboard.
The ISS orbits at about 400 km (250 miles) above the earth, where it is exposed to temperatures between +200 °C in sunlight and -200 °C in the shade and extreme levels of radiation for an operational lifetime of more than 10 years. Despite these and other extreme environmental conditions, ESA is using Commercial Off-The-Shelf (COTS) equipment from SBS Technologies and other suppliers for cost reasons. The Data Management System (DMS-R) on the Russian service module Zvezda was awarded to ESA in 1995 with Germany funding 74 percent of the cost, and France, Belgium, and The Netherlands funding the remaining 26 percent. The DMS-R is a set of computers, avionic electronics, and software that provides the overall control of the Russian part of the ISS. Components from SBS include chassis, backplanes, power supplies, and VMEbus boards featuring Ethernet, 1553B, and serial interfaces. There are 7 sets of Fault Containment Region (FCR) hardware connected via MIL-STD-1553B buses. This system features triple redundancy, built-in fault masking, and three interconnected processing units that operate by majority voting. The FCRs are the first space application to use a Byzantine fault-tolerant computer. In order to survive F simultaneous faults, the system must meet the following requirements, as specified in 1982 by Lamport, Shostak, and Pease in the Byzantine General’s Problem:
- The system must consist of 3F+1 Fault Containment Regions (FCRs).
- FCRs must be interconnected via 2F+1 individual paths.
- Inputs must be exchanged F+1 times between the FCRs.
- FCRs must be synchronized.
Another problem is to avoid deadlock situations where one software task is waiting for an event or data coming from another software task, which is itself waiting for events or data from the first task. The integrity of the system has been verified through many millions of simulation runs by an independent team at the University of Bremen, Germany.
A rather interesting space application at a very low cost is microgravity (zero gravity is impossible) space testing on solid ground. A tower of about 150 m (500 feet) in height, close to the city of Bremen, Germany, is completely air-sealed to create a vacuum inside during experiment runs. Beginning in 1994, VMEbus equipment from PEP (now Kontron) is loaded together with experimental equipment to be examined into a capsule that falls from top to bottom inside the tower and, during its travel, provides a microgravity experimental lab for almost five seconds on each flight. Global companies line up to do microgravity experiments inside this worldwide unique space lab. Optical and electrical test results are reported in real time on storage devices inside the moving capsule, and some are radioed in-flight to receivers on the side of the tower and stored in VMEbus systems on ground level. The VMEbus equipment inside the capsule crashes into a bed of Styrofoam balls 8 m (25 feet) deep, decelerating at a rate of 50g. It is being reused again for the next experiment. This cost-effective space lab, no rocket fuel required, is occasionally augmented by experiments on real Russian rockets that may travel in a parabolic flight (microgravity) several thousand miles from one end of Siberia to the other end. This allows more time for the zero gravity experiments but at a significantly higher cost.
In 2004, the drop tower, designed and operated by the Zentrum fuer angewandte Raumfahrttechnologie und Mikrogravitation (ZARM), an institute of the University of Bremen, Germany, was significantly enhanced. A catapult was installed to shoot the experimental platform upwards to the top. It then falls back again into the bed of Styrofoam. With this improvement there is now about 10 seconds of continuous microgravity. If this experiment were done as before in a drop only tower, this tower would have to be approximately 500 m (1,650 feet) high as required by the laws of physics. The catapult is an extremely complex system of vacuum pumps, hydraulics, and electronics that accelerates the capsule in 0.3 seconds to a speed just right. As a result, it would reach the top without going through the roof and falling back in an unbroken flight at microgravity up and down. The catapult is moved out of the way within seconds before the capsule would crash into it on its way down. Up to three flights are possible in one day. Creating the vacuum takes about 2.5 hours each time using 18 pumps. Figure 2, provided by ZARM, University of Bremen, is a capsule with VMEbus system and experimental equipment ready for a drop under microgravity conditions.
One of the most important experiments done by Prof. Dreyer from the University of Bremen for ESA, ISS, and NASA is research in Capillary Channel Flow (CCF). This is important for all spacecraft because at zero or microgravity, rocket fuel does not collect at the bottom of its tank, from where it would be pumped to the combustion chamber. Capillary action between parallel plates is utilized to direct the liquid flow toward the pipe that feeds the pump. A steady flow, and thus undisturbed operation of the rocket engines, is only obtained if the flow rate is below a critical value under space conditions. If the flow rate is too fast, the liquid stream breaks and causes engines to stall.
Hermann Strass is an analyst and consultant for new technologies including industrial automation, computer bus architectures, mass storage technologies, and industrial networking. He is an active member of several national and international standardization committees and is the VITA Europe technical coordinator for European activities.