A prototype of the GMT FSM has been developed to acquire and to enhance the key technology – mirror fabrication and tiptilt actuation. The ellipsoidal off-axis mirror has been designed, analyzed, and fabricated from light-weighting to grinding, polishing, and figuring of the mirror surface. The mirror was tested by using an interferometer together with CGHs, which revealed the surface error of 13.7 nm rms in the diameter of 1030 mm. The SCOTS test was employed to independently validate the test results. It measured the surface error to be 17.4 nm rms in the diameter of 1010 mm. Both tests show the optical surface of the FSMP mirror within the required value of 20 nm rms surface error.

1. INTRODUCTION
 2. GMT FSM SECONDARY
 3. FABRICATION OF AN OFF-AXIS MIRROR
 4. CONCLUSION AND DISCUSSIONS
 ACKNOWLEDGEMENTS
 REFERENCES

• Won Hyun Park(The University of Arizona)
• Hyo-Sung Ahn(Gwangju Institute of Science and Technology)
• Kyoung-Don Lee(Institute for Advanced Engineering)
• Ho-Sang Kim(Institute for Advanced Engineering)
• Joohyung Lee(Korea Research Institute of Standards and Science)
• Ho-Soon Yang(Korea Research Institute of Standards and Science)
• Myung Cho(National Optical Astronomy Observatory)
• Je Heon Song(Korea Astronomy & Space Science Institute)
• Jihun Kim(Korea Astronomy & Space Science Institute)
• Young-Soo Kim(Korea Astronomy & Space Science Institute) Corresponding Author