FSM is a secondary mirror of the Giant Magellan Telescope (GMT), which is 3.2 m in diameter. It consists of seven
segments, each of which is 1m in diameter. The surrounding six segments are off-axis mirrors. FSM compensates image
degradations caused by wind turbulence and structure jitter by using a tip-tilt mechanism.
Korea Astronomy and Space Science Institute is developing a prototype of Fast Steering Mirror (FSM) together with
four other institutions. The prototype is a full-size FSM segment, and it has two features; an off-axis mirror and a testbed
for tip-tilt actuation. The off-axis mirror has the diameter of 1.06 m and fast focal ratio of 0.65. At present, lightweighting
is successfully finished, and polishing of the front surface is proceeding.
As for the tip-tilt, several test-beds have been assembled and the functions of tip-tilt have been checked. The third testbed
is being integrated with a dummy aluminum mirror, three axial supports, a lateral support, and a test-bed frame. It is
activated by a vacuum system. The test-bed will examine and verify the tip-tilt parameters. The FSM prototype is
expected to be completed by 2012. In this paper, system engineering and progress of the prototype development are to be