Air spring system on board of the flying observatory An air spring system provides for vibration-free working conditions on board of the Boeing 747 SP converted into the flying observatory SOFIA, conducting research on the genesis of stars and planetary systems at an altitude 14km. The SOFIA (Stratospheric Observatory for Infrared Astronomy) project aims at answering fundamental questions in galactic and extragalactic astronomy, such as, for example, the formation of stars and planetary systems and the origin of the solar system. One might ask why an airplane has to climb to a height of 14km to do that. The reason is that SOFIA enables scientists to view ranges of the infrared spectrum that earth-based observatories cannot provide. In point of fact, it is only in the stratosphere that a clear picture of the many celestial bodies giving off infrared radiation is possible. Observation of these orbs from the earth is obscured by the water vapour in the earth's atmosphere. At the heart of SOFIA is a 17-tonne telescope assembly that peers through a hatch in the rear of the aircraft. It is the world's largest infrared telescope with an extremely high spatial resolution. Its primary mirror is 2.7m in diameter. All of this allows SOFIA to deliver readings that are many times more precise than was possible before. Air spring technology plays a key role on board. The telescope rests on a vibrationisolation system (VIS) consisting of an air spring system and silicon-oil-filled dampers. The air spring system guarantees the functionality of the telescope in many ways. It absorbs vibrational interference emanating from the aircraft itself or from the wind flow when the hatch is open. Assisted by control electronics and sensors, the air spring system holds the telescope exactly in position relative to the plane's fuselage. This ensures that the highly-sensitive instrument remains directed at the observation target at all times so that it can supply perfect images. The air spring system operates with a high degree of precision under extreme conditions. In the telescope chamber, which is sectioned off from the lab, the prevailing temperature is minus 60°C when the hatch is open and air pressure just one fifth of what is normal. The air pressure varies with fluctuations in the aircraft's altitude. The air spring system makes sure that the telescope remains fixed in its original position nonetheless. Manufacturer of the system, which is composed of 24 single- and double-convolution air spring, is Hanover-based ContiTech Air Spring Systems. ContiTech sales partner CFM Schiller is completely responsible for engineering matters, from the design calculations through to final assembly at the American NASA base. The SOFIA air spring system is based on a complex design. 12 air springs are arranged in axial direction to equalize the variance in pressure between the cabin area of the aircraft and the telescope chamber and to isolate X-axis vibrations. Another twelve radially directed air springs have the job of raising the telescope and of isolating it from y- and z-axis vibrations. Three dampers, located at a 120° angle between the radially arranged air springs, are at work in all six degrees of freedom. Pressure is fed into the system via height control valves that regulate specific air spring groups independent of one another. The axially arranged air springs are supplied via a redundant system of conduits. In this case, redundant means that a valve is positioned upstream of each air spring. In the event of a power shortage, the valve closes to maintain the pressure level in the air spring. The degree of isolation provided by the air spring system is sufficient for frequencies above the eigenfrequency of the vibration isolation system (approx. 2.5Hz). Regulation of the air volume holds the telescope in position In the case of slower movements caused by wind flow. The SOFIA project represents a completely new scope of application for air springs. It presented a special challenge in terms of material as well. The purposedesigned air springs bellows are made of a self-extinguishing elastomer. Eckhard Bremers, project manager at telescope developer MT Aerospace, emphasizes that: "An important criterion in our selection was the behaviour of the air spring in fire. ContiTech air springs performed very well in tests and measure up to NASA's incombustibility requirements. A second important reason for entering into the cooperation was that in addition to being supplied with the system, we were also provided with all requisite engineering services, from design calculations through to final installation at NASA's American base, by ContiTech's partner DFM Schiller." Above and beyond this, the elastomer used is likewise resistant to the effects of UV light and cosmic radiation. Its minimal surface resistance, moreover, protects the telescope from electrostatic charges. In 2007 SOFIA successfully completed initial test flights. Others are slated to follow before research operations can be launched at the end of this year. Around 160 times a year, SOFIA, the airborne observatory, will lift off from bases in California, New Zealand and Germany for observatory field trips. All told, SOFIA is expected to provide twenty years of operational service. Speed Link InfoService Request more information by e-mail Reader Service No. Reader Number Email Address 01085    Tell a friend about this article:
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