Optical Domes, Windows & Coatings for Spacecraft & Sensors

Last year, more objects were sent into space than ever before. According to the United Nations Office for Outer Space Affairs (UNOOSA), 4,510 objects were launched from across the world in 2025, 58% more than in 2024. As the number climbs, so too does the population of optical payloads that must survive the hostile conditions of space, and while components for sensors, cameras, and spectrometers are fundamental for delivering the information a mission depends on, it’s protective aerospace optics that keep these devices alive.

Aerospace applications broadly fall into two demanding domains. The first, orbital spacecraft, has different design needs from the second, high-speed aerospace systems. Spacecraft and satellites contend with ultraviolet (UV) and ionising radiation, micrometeoroid impacts, and vacuum and pressure differentials – especially in low-Earth orbit (LEO) missions where thermal cycling subjects optical components to temperatures ranging from -150°C all the way up to +150°C. On the other hand, hypersonic vehicles experience aerodynamic heating and particulate erosion.

Both carry optical payloads, including sensors, cameras, light detection and ranging (LiDAR) modules, and spectrometers, all of which require safeguarding. The two settings differ so sharply that the windows and domes shielding critical onboard components must be specified with the appropriate materials and coatings.

 

Material Choices for Domes & Windows

Thanks to its extreme hardness and thermal shock resistance, sapphire is one of the most common substrates for protective windows and domes in harsh environments, notably on high-speed aerospace systems. It tolerates aerodynamic heating and particulate erosion, and, with a broad transmission range of 0.17 to 5.5μm, it does so without compromising image quality.

For orbital operations that endure prolonged exposure, fused silica and UV-grade fused silica are ideally suited. As well as being more cost-effective substrates than sapphire, fused silica (particularly UV-grade) resists UV and ionising radiation while avoiding browning, holding transmission over the course of a deployment. They also both have a low coefficient of thermal expansion, keeping them dimensionally stable under temperature swings.

Acrylic windows are usually selected for their low weight, cost-effectiveness, and impact resistance. Often part of a multi-layer – or multi-pane – window stack, such as NASA’s Orion, they’re typically chosen when weight and safety outweigh peak clarity.

The geometry of optical domes also contributes. While helping to shield internal components and evenly distribute mechanical loads from micrometeoroid strikes and pressure differentials, they increase the field of view (FoV) for uses such as wide-area commercial Earth observation (EO) constellations, situational awareness and reconnaissance.

Optical Coatings for Protection & Performance 

Particularly beneficial in EO deployments, anti-reflective (AR) coatings boost light throughput and suppress ghosting and stray reflections on protective windows, helping image-quality-sensitive instruments relay clean, crisp data back to Earth.

Hard coatings, such as diamond-like carbon (DLC), can be combined with AR coatings (AR/DLC) to deliver durability alongside transmission. Typically applied to infrared (IR) materials such as germanium, silicon and zinc selenide, DLC adds a hard, wear-resistant surface that withstands abrasion, moisture and poor handling without significantly sacrificing optical performance.

Beyond protection and clarity, wavelength-specific coatings, including bandpass and dichroic types, transmit selected wavebands while rejecting others, which is essential for devices such as spectrometers that underpin scientific aerospace programmes.

Custom Optics for Aerospace

At Knight Optical, we offer custom-made window and dome materials, alongside coating optimisation and precision polishing, to meet the stringent demands of spacecraft and aerospace sensors. We also stay aligned with the evolving requirements set by industry agencies – for example, NASA, the European Space Agency (ESA) and AS9100 for aerospace quality management – and consistently pass ISO 9001:2015.

Although protective optics may be easy to overlook in the specification process, they’re imperative in ensuring your system remains reliable and, ultimately, to mission success. Whether you’re choosing between an optical dome or an optical window or specifying a complete assembly, contact a member of the team today to find out more about our custom optics for aerospace.