We have many demanding applications on Earth, and a wide range of high-reliability connectors perform quite well in those environments. But space brings additional considerations, and extra planning is needed to make sure these are factored into the connector choice.
Before we look at each of these issues in detail, we first need to define a key phrase in that first sentence. If you work in the space industry, your definition of high reliability might differ from how others use it in the connector industry. Often, the space version of high reliability means mission-critical and involves risk to human life. Devices that are not quite so critical will be labeled commercial. Any application that subjects the connector to vibration or temperature variations for the connector industry requires a high-reliability connector.
You could specify space-approved connectors everywhere on your build—but this comes with a technology and cost penalty. Typically, an electronic device’s space qualification is an incredibly lengthy process and can take several years to achieve. This has resulted in a list of qualified components that are old technology because it’s just not possible for the long process to keep up with the pace of development. It’s also an expensive qualification process, which will be reflected in the products’ final price.
Specifying from the approved list will mean older, heavier, larger, and more expensive components are your only choices. Companies in the CubeSat industry, as an example, are free to innovate and pursue the best and latest technologies available, not restricted by space-approval requirements.
Consider each of the challenges listed earlier and some aspects to factor in your connector choices.
The lack of air affects the maximum voltage rating—the moment of flashover from a conductor to the nearest metal item. Flashover will occur at a different voltage depending on the air molecules’ density, so look for connectors with a voltage rating for altitude.
Then there is outgassing or offgassing. This is not specific to electronics—it’s an effect that occurs in all materials and is the release of gas dissolved, trapped, frozen, or absorbed. Causes can be sublimation and evaporation (phase transitions of a substance into a gas), desorption, seepage from cracks or internal gaps, and gaseous products of slow chemical reactions. This introduces contaminants into the equipment, which might cause problems during the life of the product. Both NASA and the European Space Agency (ESA) specify recommended volume levels of outgassing for materials used in their space applications, so check with the manufacturer if their materials meet these levels.
Cosmic radiation is a problem as you increase altitude and our protective atmosphere thins. The levels are detectable even in normal air travel, so it is a significant issue in a partial vacuum. The effects are like electromagnetic interference (EMI) in ground-level electronics—and the solution is the same: shielding. The space vehicle’s metal case will provide some protection, but you should also consider added shielding on vulnerable printed circuit boards (PCBs) or cables.
Thermal radiation increases when a space vehicle is in direct sunlight with no atmosphere, but the temperature can also drop to very low levels in shadow or even on the vehicle’s side away from the sun. If a satellite has its own rotation, it will experience constant thermal cycling of the outermost layers. This is less of an issue if the electronics are buried deep into the vehicle’s center, as the direct thermal effects are much lower. But with a CubeSat measuring just 10cm across, all components’ thermal cycling is a concern.
Check the connector specifications for maximum and minimum temperature range during operation—not just soldering heat resistance. Look for additional testing for thermal soak (sometimes listed as high temperature, long term, or temperature life) and thermal cycling.
Every gram pushed into space from the Earth’s surface costs money. More mass equals a bigger vehicle. The bigger your vehicle, the more room you have. However, the more fuel you need to be able to carry. Both volume and weight carry penalties—and rockets and rocket fuel are not cheap. So, you need small and light. Every gram saved on a connector is a gram that can be spent on the payload.
Look for connectors in the performance bracket you need that are also the smallest and lightest possible. Don’t over-specify where you don’t need to. This is especially true in the CubeSat market. These are miniature satellites designed to be multi-stacked in a rocket, and both space and weight are at a high premium. But longevity and human life are not factors, so the cost of failure is much lower than a manned vehicle.
Launch is a high-vibration, high-acceleration environment. Your connections need to survive this period intact and still mated, so they can be ready to perform once floating in orbit. Make sure your connectors are rated for vibration, shock, and acceleration. Specify jackscrews or latching where possible.
Are you transporting astronauts and cosmonauts, space telescopes, or the next Mars rover? As disappointing as a failure of your CubeSat might be, it’s not going to cause loss of human life or a costly setback (probably). Avoid over-specification and choose your budget wisely. Set your connector requirements based solely on your performance requirements, not paranoid what-if scenarios.
Harwin can help get the best from your design by offering connectors that meet your specifications. Harwin’s high-reliability connectors are fully tested and inspected and can withstand a wide range of environmental extremes.
Gecko-SL has been a favorite for the growing CubeSat industry since its launch (Figure 1). The compact size and very lightweight are minimal for the performance achieved. The average weight of each connector is just 1gm, including robust screw-loks to overcome any vibration issues. The plastic used meets NASA and ESA expectations.
Figure 1: Harwin Gecko-SL features a robust screw-lok connection to offer simpler access, stronger fixings, and panel-mount options. (Source: Mouser Electronics)
CubeSats comprise of a dense stack of PCBs, so height above each PCB is limited. Gecko-SL now offers both horizontal connectors and mating cable assemblies to solve this challenge. By installing the horizontal connectors on the edge of the PCB, you can route the cables sideways round the stack edge, saving space above the PCB. The cables are ready-made and available, further reducing the upfront cost of your project.
The How to Choose Connectors for Space article was written by Harwin and was first published on www.harwin.com.
Harwin is a manufacturer of High Reliability Interconnects suitable for harsh environments and are able to withstand extreme vibration, shock and temperature. Datamate, Gecko and M300 product lines have a proven history in Military, Aerospace and other safety critical markets. Other board level solutions include EMC Shielding products which increase reliability, flexibility and cost savings through the process of automated placement. Industry standard connectors and PCB hardware are also available from Harwin for commercial applications.
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