NASA technicians evaluate the temperature effects of atmospheric reentry on electronic materials Photo courtesy of NASA wwwnasagov

Preparing RF/MW Parts For Space

Oct. 2, 2012
Space has been called “the final frontier” in both fiction and reality, and it does represent a challenging market for many RF/microwave companies. Along with high reliability, there is also the expectation that space-bound components maintain the highest levels of performance, with minimal degradation.

Space has been called “the final frontier” in both fiction and reality, and it does represent a challenging market for many RF/microwave companies. Components built for use on orbiting satellites as part of communications links (to give one example) simply cannot fail during the intended lifetime of the satellite, which is typically 10 years or longer. After all, there is no luxury of “making a house call” for maintenance. Along with high reliability, there is also the expectation that performance remains at the highest levels, with minimal degradation, for at least a decade (see figure).

Ensuring reliability is an essential step in preparing any RF/microwave component or subsystem for an application in space, but it is only one of many requirements that must be met before an electronic device can be considered a “space-qualified” part. Companies pursuing sales in space must first ensure that their manufacturing facilities meet the requirements for producing space-qualified components—typically through a set of guidelines as detailed in the MIL-PRF-38534 Class K standards for commercial and government spaceflight equipment. The MIL-PRF-38534 Class K documentation applies to military specification for microcircuits and multichip modules (MCMs) for use by the US Department of Defense (DoD) and other government agencies.

However, MIL-PRF-38534 Class K is only one such document or guideline for companies interested in pursuing space-grade components. Since it is generally true that most companies selling into space-based applications are also designing and manufacturing parts for military and aerospace applications, firms that intend to serve both markets will usually comply with a number of different specification guidelines. These include military documents MIL-STD-202, MIL-STD-883, MIL-STD-790, and MIL-STD-1344, as well as several NASA documents.

The MIL-STD-202 documentation, for example, covers guidelines for vibration, thermal shock, and mechanical shock, while MIL-STD-883 provides details on salt spray testing, temperature cycling, immersion, barometric pressure, and shock. In truth, many of these may be more appropriate for maritime applications. But because the reliability requirements for space applications are so demanding, a combination of military standards is typically needed to ensure that a component or assembly is “ready” for deep space use.

As an example, SV Microwave is a supplier of space-qualified RF/microwave connectors and components. The company has processes and systems for MIL-STD-202, MIL-STD-790, and MIL-STD-1344 requirements, and performs high-reliability (hi-rel) screening for a number of parameters that can impact reliability in space or even in critical ground-based requirements. Among these are screening for contact stresses, separating forces, solderability, and plating adhesion in components and assemblies. In addition, the company has an approved destructive physical analysis (DPA) laboratory for evaluating its space-qualified products. Prior to shipment, the firm can provide documented verification of any number of key reliability parameters, including adhesion, axial contact retention, contact engaging and separation forces, solderability, joint destruct torque, epoxy captivation, and full design review and verification.

For any company, selling into space requires a considerable investment in laboratory equipment and training to use that equipment properly. For example, satcom component and assembly supplier MITEQ relies on five Class 100,000 clean rooms and two Class 10,000 clean rooms to support manufacturing of components and assemblies for its military and hi-rel space businesses. In addition to the electrical and environmental test equipment needed for proper screening and testing, every circuit element that goes into an RF/microwave component intended for use in space must be carefully considered. Parts that are needed as part of an oscillator, for instance, must meet the requirements as set forth by the governments Qualified Products List (QPL). Alternately, when specific circuit elements are not available with the proper screened designation, they must be up-screened through the use of a specification-controlled drawing (SCD).

Military-grade parts may be adequate for some space applications. By way of example: For an oscillator, chip resistors screened to MIL-PRF-55342 military requirements and chip capacitors screened to MIL-PRF-55681 requirements are readily available for use in military circuits; they can also provide high reliability for space-based designs. But when space customers demand it, the highest-reliability parts, such as Class T for resistors and Class S for capacitors (which are also the most expensive circuit elements) must be used.

Although the reliability required of space-based components is easily associated with the performance needed in military electronic systems, many space-based applications are actually commercial. Think of the many satellite-communications (satcom) systems used for commercial broadcast television services, telephone services, computer networking, and other high-speed digital services (including Direct TV, EchoStar, and Globalstar), not to mention the Global Positioning System (GPS) satellites so often used for position information. To give an idea of the many thousands of satellites currently in orbit around the Earth, either active or decaying, EchoStar XVII was launched this past summer. The orbits for these vehicles are at different altitudes, defined by a number of different designations [including low-earth-orbit (LEO) and medium-earth-orbit (MEO) satellites].

Manufacturing a component such as an oscillator for space requires using the proper materials and following the proper guidelines. Using standardized circuit elements and parts—from such lists as the QPL, the NASA Parts Selection List, and the NASA Goddard Space Flight Center (GSFC) Preferred Parts Lists (which are screened for the effects of radiation in space)—can help the overall process of documenting reliability, but it will also add to manufacturing costs. And the costs of components for space far outweigh the costs of components for commercial or military applications on Earth.

Of course, an RF/microwave component that has been readied for space use does not look any different that a commercial component; however, it has been through extensive testing and inspections. It must be made with space-approved materials, and even the circuit elements within the component must be qualified for use in space. As an example of a space-qualified oven-controlled crystal oscillator (OCXO), model OSC029 from TRAK Microwave Corp. has been space qualified for at least 10 years of in-orbit operating life, and its performance has been characterized over a 10-year period. The S-level OCXO, which operates at 10.3 GHz, exhibits long-term stability of ±1.2 ppm over 10 years, with outstanding spurious performance of typically -95 dBc. The phase noise is a mere -95 dBc/Hz offset 2 kHz from the carrier. Designed for a space environment, it is rated for baseplate operating temperatures from -15 to +65°C.

Many suppliers of space-grade components and assemblies refer to their track record of success in space as an assurance that its products will be 100% reliable when put to work. Dow-Key Microwave, for example, refers to its heritage and its use of a dedicated group for its space products, with zero failures in its past. Supplying space-qualified coaxial and waveguide switches since 1970, the firm has placed over 150 different product designs in more than 100 different space programs, with no failures. Similarly, Teledyne Cougar points to its 22-year legacy of supplying components for space missions—as well as its MIL-PRF-38534 Class K cerification—as assurances that its products are reliable. Suppliers of miniature passive components and waveguide assemblies, respectively, Anaren Microwave and ARRA, Inc. have also built strong reputations as space-level component manufacturers. Both companies lay claim to more than 40 years of supplying products for space use without any failures.

W.L. Gore & Associates has provided its cable assemblies to more than 70 satellite programs since 1976, with a 100% failure-free flight record. The firm designs and manufactures its coaxial cable assemblies specifically for the harsh environment of space, using spaceflight-approved materials with high radiation resistance. EMC Technology has even gone as far as creating a space-level product working reference sheet, available for free download on their website, by which space customers can review three different options for screening their component orders for space-level requirements.

Finally, given the high price of space-grade components and assemblies, some companies have considered ways to cut costs for their space-level customers without sacrificing reliability. Merrimac Industries, which has supplied everything from power dividers to complete beam-forming networks for space platforms, has developed a program called Merrimac Space Qualified Products (MSQP). The MSQP program was created to reduce the complexity of procuring RF/microwave components for space. It builds on Merrimac’s heritage of designing and shipping hi-rel military and space-qualified components for a large number of systems and already having documentation and screening levels set for those components; in effect, the company has created a list of “standard” components that are already qualified for use in space. Customers can select a part from the MSQP list, or have Merrimac create a specification for the component they need based on the MSQP design, process, qualification, and screening guidelines.

About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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