Optimization Design of Large-Aperture Primary Mirror for a Space Remote Camera

Area of Science:

• Optical Engineering
• Materials Science
• Aerospace Engineering

Background:

• Designing primary mirrors for micro/nano satellite remote sensing cameras requires lightweight, high stability, and high-temperature adaptable materials.
• Traditional back plate support systems can be susceptible to shock, vibration, and temperature fluctuations, impacting mirror surface accuracy.
• Advancements in silicon carbide (SiC) material casting enable complex reflector structures.

Purpose of the Study:

• To optimize the design and experimentally verify a large-aperture (Φ610 mm) primary mirror for a space camera.
• To improve the primary mirror's long-term surface shape accuracy under dynamic and thermal loads.
• To ensure the primary mirror assembly meets the demanding performance requirements for space-based remote sensing.

Main Methods:

• Determined design performance index based on a coaxial tri-reflective optical imaging system.
• Selected silicon carbide (SiC) as the primary mirror material due to its excellent comprehensive properties.
• Improved initial design by integrating the flange with the mirror body for direct support force transmission.
• Employed a parametric optimization algorithm (compromise programming) for initial structural parameters and flexible hinge.
• Conducted finite element simulation to analyze performance under gravity, temperature rise, and assembly errors.
• Precision manufactured and assembled the primary mirror, followed by ZYGO interferometry and vibration testing.

Main Results:

• Optimized SiC primary mirror assembly achieved a mass of 8.66 kg.
• Finite element simulation showed RMS surface error < λ/50, maximum displacement < 10 μm, and maximum inclination < 5″.
• Fundamental frequency was simulated at 203.74 Hz and experimentally verified at 208.25 Hz.
• ZYGO interferometer testing confirmed a surface shape accuracy of 0.02 λ.

Conclusions:

• The optimized primary mirror design, utilizing an integrated flange and SiC material, successfully maintains high surface accuracy under various environmental conditions.
• The achieved performance metrics meet and exceed the design requirements for the space camera's primary mirror.
• This study demonstrates a viable approach for developing high-performance, lightweight primary mirrors for satellite remote sensing applications.