The backplane is made of advanced graphite composite materials jointed to fittings and interfaces made of titanium and a nickel steel alloy known as invar, which is notable for expanding very little due to temperature changes. Even at temperatures below -400 degrees Fahrenheit, the backplane is steady down to 32 nanometers, or less than a thousandth the diameter of a human hair. It must essentially hold the mirror motionless as it peers into deep space, just as a camera sometimes needs a tripod to hold it steady--any shaking makes it much harder to focus on an object.