The Wide Field 1 radiator was de-integrated and we measured it, 
so we'd know it's shape and where the critical mechanical 
interfaces are so we can replicate it when we put it on the Wide 
Field Camera 3. And with this laser tracker system we can 
measure to a 2 or 3 thousanths of an inch or better. 

So what we are doing now is measuring some points that we 
previously made. After extensive modifications to this radiator. 
What you see him doing now is measuring the edge of the 
radiator which is a critical parameter when the astronauts go to 
fit the radiator into the telescope because that very edge that 
he's measuring has just a fifty thousanths clearance initally on 
each side. Once they get on orbit they even have to worry about 
being at the right temperature because fifty thousanths is not a 
lot, that .050 inches. So we're measuring that to make sure  that 
at the end of all these modifications that we made, the 
structures that we've added to it don't change that  particular 
perimeter and we'll also scan the shape of it and make sure that 
it hasn't changed it's shape , completely hasn't changed its 
shape. Again those edges that we're measuring are the most 
critical perimeter.

The laser tracker takes thousands of measurements, both 
angular and distance from the central station. As he moves that 
retro-reflector ball you can see that follows it around so you can 
see it moving left and right. Here, you can see it moves. You can 
see it actually track it. It's scanning across. It's taking 
measurements every quarter inch as it goes across.