In newer astronomical observatories, the mirrors used in reflecting telescopes are not single mirrors cast in one piece like in the older telescopes, but in fact they use small mirror segments that are computer-aligned for the purpose of exactly locating them in the contour of the mirror. Invariably they use LVDTs to maintaining that position. LVDTs have become the favorite technology to use in these applications because the mirrors require the high resolution of LVDTs. In some cases, they tried other types of position sensors in the past but in the end they keep coming back to LVDTs. LVDTs are not only extremely repeatable, but also robust. Even though these mirrors may be located on a mountain top, or on mobile carriers in desert locations, there has been no problem at all regarding environment. It is not even an issue with most of the telesccope builders.

So given the reliability, the good resolution, and the extraordinary repeatability with LVDTs, these multiple mirror systems are an excellent place to use LVDTs. And they are getting bigger and bigger. Astronomers are not only making one telescope, they are making several servoed mirror telescopes and arranging them so that the visual outputs are transmitted to and combined in a computer. There is a lot of interest in applications like this. There is one where we quoted 400 LVDTs. That application used two small and relatively short range LVDTs per mirror segment, each of which is driven by a little stepper motor mechanical drive system. It sounds like it's really a science project, but it's not quite as simple as that. Usage can run into hundreds and hundreds of LVDTs.