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New Horizons flies by Pluto
Five years ago, on the 14th July 2015, the New Horizons probe flew past Pluto at a relative velocity of nearly 50,000 km/h. New Horizons had been the fastest-ever object launched from earth, but even with the assistance of Jupiter’s massive gravity it had taken 9 ½ years to reach Pluto. It didn’t stay long.
The scale of space exploration is staggering. The huge speed that New Horizons needed to get to Pluto in a reasonable time meant that scientists had just a few precious hours to conduct their mission before the probe plummeted on into empty space. The data gathered in that short flyby took 15 months to transmit back to earth, and years will be spent analyzing the data from this far-flung and mysterious world.
Imagine if something had gone wrong.
Space missions are measured in years and millions of kilometers. At the moment of launch, years of planning can be undone by the failure of even a single component, and so products that are designed for spaceflight must be supremely reliable. This includes connectors, and the design of the contacts within any connector must be robust enough to withstand the shock and vibration of launch. The g-forces imposed on every device on board during launch make them anything up to 3 times their normal weight, and any damage they sustain is unrepairable.
Even once the launch is over, connectors must carry on working during the rest of the mission. Space probes that are destined for long missions are designed with a strict power budget to ensure that no opportunity for science is missed. This reached its peak with the New Horizons probe which, due to the distances and duration of the mission, was placed into hibernation for much of its voyage.
With such a strict power budget, any component that introduces unwanted electrical resistance will risk jeopardizing the mission. That is why all contacts used in space-rated connectors will be made from the finest materials and manufactured to the closest tolerances. Contacts will be plated with gold to a thickness rarely seen in even the most demanding applications back on Earth. Gold plating ensures that the contact resistance is kept as low as possible to reduce power loss.
Contacts with low electrical resistance are important for other reasons. Despite the sophistication of the instruments mounted to space probes like New Horizons, the measurements being taken can be tiny. When scientists are looking for minute fluctuations within magnetic fields or are trying to isolate a radiation signature from the noise of interplanetary space, unwanted electrical resistance can prevent a critical signal from being collected.
This is also the reason that manufacturers go to the trouble of reducing the magnetic signature of the components themselves. If you have ever tried to use a magnetic compass inside a vehicle, you will be aware that the body of the vehicle can affect the accuracy of the reading. With a compass, it is possible to allow for the inaccuracy, but navigation rarely requires the precision that scientific experiments require.
For this reason, connectors destined for spaceflight applications use materials that provide the best possible performance. As an example, the key feature of the D-subminiature connector is the trapezoidal shell that provides protection to the contacts and ensures correct mating. Traditional D-subs use shells made of steel, but the versions destined for spaceflight use brass to minimize their magnetic signature.
The shell also provides protection against electromagnetic interference (EMI). In the vacuum of space, unprotected by a blanket of atmosphere, equipment is exposed to solar radiation which can interfere with scientific observations or even damage sensitive instruments. The shells of D-sub connectors are gold plated in the same way as the electrical contacts to provide the best possible protection against EMI.
The Right Materials
It is important to ensure that the components themselves do not place the mission at risk. We looked at the problem of outgassing recently, which describes an effect encountered in vacuum conditions. When exposed to a vacuum, some materials give off gases that are trapped within them during their manufacture. This applies particularly to some plastics that have traditionally been used as insulators within connectors. The gas that is expelled can gather on critical surfaces, such as the lenses of optical devices, which can reduce their effectiveness or even render them useless. It is therefore vital to understand the behaviour of every material that is selected for use in space.
Why is this important? Few of us will ever design a device for use aboard a deep-space probe, so it might seem irrelevant. Components used in space flight are hugely expensive and the environment in which they work is extreme. However, there are things that we can learn from their design.
The key lesson is to select products that are appropriate for your design. Even in everyday applications, it is important to know how the materials that are chosen will affect (and will be affected by) the environment. It is vital that designers balance the demands of the application with the commercial realities of the marketplace.
Connectors for Space Applications
Image: Positronic Inc
There are times when a connector needs to cost hundreds and other times when a connector costing pennies will do. Make sure you know which is which.