Testing with the Dummy Mirror
The main mirror is
the most expensive component in the Liverpool Telescope taking about
nine months to manufacture. For testing purposes this mirror is
replaced by a dummy mirror of the same size and weight as the
original glass mirror.
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The dummy mirror, seen on the right, is a steel structure filled with
concrete giving it a total weight of 1.1 tonnes. The pictures show
the dummy mirror being lifted into position onto the mirror cell which is in turn placed into a
test jig.
With the mirror being so heavy, it is very important that it is held firmly in place as the telescope moves from one part of the sky to another. For this reason the test jig places the mirror cell and dummy mirror into various positions, as if it were in the telescope itself. Special sensors, called load cells, allow TTL engineers to measure all the stresses and strains that take place with the results being fed into a computer. To compensate for these stresses a computer activates the mirror supports directly under the mirror each time the telescope moves from one position to another. In this way the mirror can be kept in perfect alignment at all times. |
 The Dummy Mirror |
 Closeup of support | |
 Across to the Mirror Cell | |
 Ready to lower | |
 In the jig |
