Uncoated Zerodur Precision Optical Substrate Witness Flat – LOT OF 8

n exceptional uncoated Zerodur precision plano substrate witness piece from the fabrication process of the primary mirror (M1) for the Space Surveillance Telescope (SST) – the advanced Wide Field of View (WFOV) Telescope Assembly developed by US Defense Laboratory, a key U.S. Space Force asset.

This small optical flat served as a test coupon during polishing and figuring of the massive 3.5-meter Zerodur primary mirror (fabricated by L3Harris Brashear). It was processed alongside the actual telescope mirror to verify surface quality, flatness, homogeneity, and low-expansion properties before final reflective coating was applied to the large primary optic.

Key Specifications:

• Material: Schott Zerodur (ultra-low thermal expansion glass-ceramic – the gold standard for large astronomical/defense mirrors requiring extreme dimensional stability)

• Dimensions: ~1.000″ diameter × ~0.375″ (9.5–10 mm) thick plano-parallel disk

• Coating: None

• Surface Quality: 20/10 scratch-dig (astronomy-grade)

• Surface Figure/Flatness: 20/10 with ≤0.5 RMS irregularity (actual measurements far better than spec)

• Clear Aperture: 80/50 scratch-dig outside edge

• Chamfer: 0.015″ × 45° (precise edge treatment)

• Condition: Pristine – fully in-spec, includes quality control inspection sheet for provenance

Application and Use in the SST Program: The Space Surveillance Telescope (SST) is a critical ground-based sensor for space domain awareness and orbital surveillance. Primary applications include:

• High-cadence detection and tracking of satellites, space debris, and near-Earth objects across wide sky areas

• Supporting national security through space traffic management, collision avoidance, and monitoring of geosynchronous/low-Earth orbits

• Leveraging its fast f/1.0 Mersenne-Schmidt design and enormous light-gathering power for 24/7 operational reliability in harsh environments

This uncoated Zerodur witness verified the mirror substrate’s polishing and metrology prior to the application of the final protected silver reflective coating – a vital quality assurance step in producing one of the world’s most capable optical surveillance systems (currently operational in Western Australia).

Potential Buyer Uses:

• Interferometry/metrology reference: Ideal high-quality optical flat for testing mirrors/lenses in interferometers (e.g., Zygo systems) due to its superb flatness and ultra-low thermal expansion

• Custom coating substrate: Perfect blank for re-coating with protected silver, enhanced aluminum, or dielectric stacks to create a premium small telescope mirror, laser optic, or instrument component

• Educational/demonstration tool: Excellent for optics courses, labs, or outreach to illustrate telescope-grade polishing and thermal stability

• Collectible artifact: Rare documented piece from a major U.S. Space Force program – highly valued by space/defense optics collectors and museums

• Research/prototyping: Useful in precision instrumentation, astronomy projects, or laser systems requiring a stable reference optic

A rare companion piece to coated SST primary/secondary mirror witnesses – own a tangible part of telescope engineering history from the pre-coating phase!