SPACE TECHNOLOGY Test System Pumps Up The Volume
Jonathan Newell discusses the latest technology for acoustic testing in the space industry with Siemens PLM.
controlling costs whilst meeting the highest quality standards and complying with the requirements of certification bodies. One hotly contested area of space technology is the manufacture, launch and operation of earth satellites, all of which have to survive the traumatic rigours of launch before settling down to a lifespan enduring the harsh conditions of space.
V With such destructive launch and operating environments,
it’s little wonder that satellites have to go through stringent qualification testing at the end of their development cycle before being certified for launch.
NEW APPROACHES With the acquisition of LMS International five years ago, Siemens PLM Software built on its long experience in dynamic environmental testing and, through its partnerships with major companies in the space industry, has developed new methods of performing cost effective qualification testing for satellites based on its Simcenter Testlab software and Simcenter SCADAS hardware. To understand more about these methods, I spoke to Siemens’ Bruno Massa, Vice President of Testing Solutions, and Dr Alex Carrella, the company’s Space and Defence specialist. According to Massa, the partnerships Siemens forms with the space industry represent a crucial element of the way the products develop. “We actively engage in technology advancement in the industry as a partner and not purely as a supplier,” he says. One important partner is Thales Alenia Space, a European space satellite and payload manufacturer, with whom Siemens developed a new approach to acoustic testing of satellites.
A DEPARTURE FROM REVERBERATION Acoustic testing subjects the device under test to intense noise levels while measuring its vibration response. This test is performed on both components, such as reflectors and solar panels as well as full systems. Satellite acoustic testing is traditionally performed in
acoustic reverberant rooms. In most cases, these large facilities (sometimes over 1,000 cubic meters to accommodate large spacecraft) are filled with gaseous nitrogen which has a lower sound absorption coefficient than air. The noise is generated by modulators connected to horns placed in the chamber; the result is a noise level that can reach over 150 decibels (dB). In such a test, the item is subjected to an acoustic excitation with a frequency spectrum that changes according to the launch vehicle. The required uniformity is then guaranteed by the design of the reverberant chamber. Because of this, there is
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❱ ❱ Simcenter Testlab software provides detailed analysis capabilities for understanding the vibration or acoustic responses from devices under test
very high capital expense in setting up such facilities. They are safe, reliable and accurate but at high cost and in short supply. The challenge to the industry was to produce an alternative
test environment that is repeatable and more flexible in terms of where it can be set up.
THE ARRIVAL OF DFAN Now, an alternative means of acoustic testing which uses commercial loudspeakers is in partial use in the industry for the qualification of North American satellites. This method is referred to in the industry by the type of acoustic field that the large set of loudspeakers produces, which is a direct field as opposed to the reverberant field produced in the standard chambers. For this reason, this new alternative is known as Direct Field Acoustic Noise or DFAN (this is the acronym being adopted in one of the latest standards being produced and should replace the other different abbreviations used such as DFAT or DFAX). Modern loudspeakers and amplifiers deliver the required high decibels to obtain the target overall sound pressure level (OASPL). The vibration levels measured on the specimen during the DFAN test are comparable with those measured with reverberant field acoustic excitation. However, apart from the NASA Handbook 7010 which provides some initial guidelines to the test engineers who wants to adopt this technology, there is not yet a commonly accepted standard to perform this type of test. Therefore the space industry, where every test is regulated by standard practices, is now coming together to develop such a standard. Thales Alenia Space has been conducting experiments using Siemens PLM’s hardware and software to explore and validate new methods for satellite acoustic testing. With relatively simple equipment when compared to a
reverberant room, DFAN lowers overall test expenses, can be performed in more locations and brings more flexibility with shorter test sequences. However, the nature of the sound field in a DFAN test differs from that of a reverberant room
enturing into space has long since established itself in the domain of commercial enterprise rather than the Government run money- no-object behemoths of the past. With commercialisation comes the necessity for
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