Ritchey-Common sparse-aperture testing of the Giant Steerable Science Mirror

Area of Science:

• Optical engineering
• Large telescope design
• Metrology

Background:

• The Giant Steerable Science Mirror (GSSM) is a critical component of the Thirty Meter Telescope.
• Testing large mirrors like the GSSM is challenging and costly due to size constraints.
• Existing testing methods may require multiple apertures, increasing expenses.

Purpose of the Study:

• To investigate the applicability of sparse-aperture testing for the GSSM.
• To develop a cost-effective method for testing the GSSM's mirror figure.
• To combine sparse-aperture testing with the Ritchey-Common method for efficient mirror testing.

Main Methods:

• Integration of sparse-aperture testing with the Ritchey-Common (R-C) testing method.
• Utilization of normalized point source sensitivity (PSSn) for mirror figure specification.
• Conducting a detailed error analysis, including shifting, irregularity, tipping, tangential/sagittal errors, and seeing.

Main Results:

• The combined sparse-aperture and R-C testing method offers a cost-effective solution for GSSM testing.
• The mirror figure can be specified accurately and simply using PSSn.
• Error analysis for the GSSM prototype indicated a total error in PSSn of 0.9701.

Conclusions:

• Sparse-aperture testing combined with the R-C method is a viable and efficient approach for testing large telescope mirrors.
• This integrated method significantly reduces testing costs compared to traditional multi-aperture techniques.
• The study provides a validated methodology for ensuring the optical quality of the GSSM.