Aerospace, Military and Defence
and unless avoided or passed into space, can cause its own set of issues.
Whatever the response of a product or device to large and rapid changes in temperature and pressure, these can be simulated and tested using specially designed thermal vacuum chambers (TVAC – see Figure 4) that can be programmed to subject the hardware under test to the thermal and vacuum conditions appropriate to the mission. In some tests, the product can even be subjected to bursts of radiation to simulate
Figure 3. SRS mechanical shock test system. Source: Smiths Interconnect
Thermal and vacuum loads Most payloads that orbit around the earth, normally pass from direct sunlight to darkness in a precise and calculable period. Depending on the orbit, this could range from once per day to every 90 minutes!
In the vacuum of space, there is no atmosphere to assist temperature management through the natural convective heating and cooling. As a result, temperature loads can be extreme, and depending on the exact part of the space craft, can cycle over a wide range, which is typically from -160° C to +120° C. This can happen quite quickly and can cause differential thermal strain and outgassing of electronic components, connectors and other materials. Outgassing can result in a local conducted “atmosphere” aboard a spacecraft
Figure 4. Thermal Vacuum Chamber (TVAC). Source: Smiths Interconnect
what would happen if a charged particle emanating from the Sun impacted on the product.
Voltage breakdown phenomena A subset of RF products that are used in satellite communication systems and space missions, including filters, multiplexers and isolators, can be subjected to high power levels. In vacuum or low-pressure environments, these high-power levels can lead to voltage breakdown phenomena that include Corona and Multipaction events.
A corona event can block or partially block RF signals or RF power transmissions and can ultimately damage critical hardware. To assess Corona susceptibility performance, products under development or manufacturing phases are subjected to atmospheric pressure test under high RF power conditions in a TVAC whilst monitoring key performance parameters. This testing typically includes cycling the product repeatedly through a critical pressure range often referred to as the Paschen Curve. A Multipaction effect can also render a device useless and degrade the satellite reliability. This event can be triggered in space by a combination of cosmic radiation, high RF power levels, high vacuum levels typical of deeper into space (e.g., International Space Station orbit height and higher), and gaps between product surfaces that are created within a critical range, that is proportional to the RF frequency used. The type of material used for the product wall constructions can also have a major influence on the susceptibility to Multipaction phenomena.
Testing for simulated Multipaction breakdown in a laboratory facility requires a sophisticated and expensive test setup, as well as considerable test expertise. It typically comprises the
18 July/August 2023 Components in Electronics
Figure 5: Typical Multipaction test setup in Dundee Test and Qualification Laboratory. Source: Smiths Interconnect
combination of a TVAC, high power amplifier and RF source (for each test frequency band required), plus very sophisticated Multipaction detection means, including harmonic content monitoring and electron charge detection.
Due to the significant and costly impact of a Multipaction event in deep space, Multipaction analysis and testing typically requires very large margins of safety, and consequently leads to laboratory testing at very high-power levels that are often 4x higher than nominal hardware operating power levels and leads to very expensive power amplification for laboratory testing, that increases significantly at the higher GHz levels (beyond K-band).
Electromagnetic environments A payload generally comprises a large number of electromagnetic (EM) sources in very close proximity. This combined with the naturally occurring electromagnetic energy from the Sun can influence or in extreme cases disrupt the operation of sensitive system devices. To mitigate these effects, some product classes are designed to incorporate electromagnetic shielding. The effectiveness of this shielding is evaluated during the design and manufacturing phases by exposing the products to artificially high levels of microwave radiation within a special electromagnetic compatibility (EMC) test chamber. Practically, electromagnetic shielding tends to be a conductive material (normally metallic) that acts as a barrier between the emitter of the EM waves and the more sensitive receiver.
Terrestrial environments Before launching into space, products will be subjected to a variety of handling, transportation and storage environments. These environments routinely include shock, vibration, temperature, humidity, moisture and potentially corrosive environments that
may be encountered during transportation, as well as assembly into higher level equipment, and may be routine or due to mishandling. To ensure these conditions do not adversely affect the performance or reliability of the products, qualification testing usually includes worst case terrestrial environments with testing performed in the same facilities used for operational (spaceflight) testing.
Smiths Interconnect Dundee test facility overview
Since 2019, Smiths Interconnect has built and commissioned a dedicated and state-of-the- art 300 square metre Qualification and Test Laboratory at its Dundee, Scotland location. This laboratory facility (Figure 1) represents a significant financial investment and today includes Multipaction (Figure 5), Corona and high-power thermal vacuum testing from UHF band through to K band, dynamic stress screening including vibration and classical mechanical shock testing to levels approaching 225 g (Figure 2), with SRS mechanical shock to levels of > 5000 g (Figure 3). The EMC test capability is the latest addition and comprises a 2-chamber reverberation test system which is calibrated to 40 GHz. Additionally, but no less important, investments in microscope imaging and RF VNA testing up to 110 GHz have expanded the site’s specialised test capabilities. This facility is normally used for Smiths Interconnect’s projects, but is also made available to development partners as well as customers who require independent third- party environmental testing and to support Smiths Interconnects process and new product development; a key capability that vastly reduces the cost and time to complete certain classes of process and product development, especially where these are refined through iteration to optimise performance and increase design margins (improved robustness and reliability).
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