So, NASA has developed its own requirements and all components, including attenuators, must meet them. In accordance with the standard test method ASTM E595, which covers total mass loss (TML) and collected volatile condensable materials (CVCM) in a vacuum environment, the requirement is that the components must not exceed 1 per cent TCM and 0.1 per cent CVCM. Midwest Microwave is the only MIL-DTL-3933

qualified supplier on the market offering standard catalogue space attenuators. Its history of supplying MIL qualified parts for space programmes, including its portfolio of attenuators, makes it an ideal choice for the space industry. The space qualified parts supplied by Midwest Microwave go through much more stringent testing than, for example, extended screening. It may be the case that some COTS parts can be used in non-critical space applications but that doesn’t necessarily qualify the companies supplying those parts as a supplier of parts for space. Midwest Microwave is a qualified supplier and understands fully the intricacies of developing and supplying parts qualified for space.

UNDERSTANDING QPS The MIL-DTL-3933 specification covers the requirements for RF attenuators for use in space. The QPS attenuators developed by Cinch Connectivity Solutions Midwest Microwave are guided by MIL-DTL- 3933 Level T and are available in various standard dB values. Three screening levels are

available: A, B and C. Attenuators used

in pre-flight development and test may only need to meet screening level A, for

resistive element itself needs to be high quality. In addition to this, the attenuator needs to be designed to withstand the conditions of the operating environment.

QUALIFYING ATTENUATORS FOR SPACE One aspect of component design that needs to be fully appreciated when designing for space is “outgassing”. In the vacuum of space, some materials, such as plastics and epoxies, will naturally release gasses that would normally be suspended within the molecules that make up the substances. This outgassing can cause a build-up of gasses in an enclosed or sealed environment, such as the shell of an attenuator. If the build-up continues it can lead to failure, through condensation or secondary effects caused by the fumes produced.

❱❱ The QPS attenuator from

Midwest Microwave meets the specifications for RF components that are demanded by the space industry

example while equipment destined for space, from LEO all the way through to deep space missions, would be required to meet screening level C. Cinch Connectivity Solutions Midwest Microwave supplied the attenuators on the Emirates Mars Mission, which launched in July 2020 and entered orbit around Mars in February 2021. Its attenuators are also on NASA’s Parker Solar Probe, which is on its way towards the Sun in order to observe the outer corona. Other forthcoming NASA missions that will feature Cinch attenuators include the Europa Clipper mission, which is destined to orbit Jupiter. Cinch also supplied the attenuators that are being used by OneWeb. The attenuators developed by Cinch include gold

sputtered terminals on all of the critical interconnects. This includes the resistor card, edge spring, card spacer, centre plunger and plunger spring. The gold sputtering process was developed by Cinch to provide more robust and reliable internal connections. Other notable design features include an epoxy seal that has 0.77 per cent TML and 0.02 per cent CVCM.

With the ongoing challenges of space exploration, the industry will continue to rely just as heavily on suppliers that can deliver QPS that meet the world’s most stringent requirements. T&TH

June 2021 /// Testing & Test Houses /// 19

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