Case study: creating more sensitive and efficient space-based sensors by minimizing stray light at grazing angles – with Acktar

Case study

This case study features Acktar’s Hexa Black™ products. It is developed in collaboration with ACM Coatings GmbH (subsidiary of Acktar Ltd.), a paying participant in the satsearch membership program.


The optical space systems have been crucial for the world to explore cosmic entities in a detailed manner. From scientific study to analysis of physical forms of the planets, galaxies, and other heavenly bodies, optical space systems have provided an edge to global space sciences research. On the other hand, these optical systems face some difficulties due to stray light, in such cases the system can capture the image of its target object, but it might significantly reduce the quality of the image captured, due to light pollution, which is referred to as stray light. This further damages the end result of the image, making it difficult for the users to effectively analyze the image for their respective purposes.

The problem

Image quality degradation is one of the most immediate effects of stray light in space-based optical systems. Any unwanted light that enters the optical system and disrupts the intended signal is considered stray light. This can happen through scattering, reflection, or diffraction, and it can have a big effect on how clear these instruments’ images are.

An optical system’s resolution and contrast suffer as a result of stray light mixing with the intended signal. This can bring about pictures that come up short of the freshness and detail required for logical investigation. Therefore, our ability to comprehend the characteristics and behavior of celestial objects like galaxies, nebulae, and planet features is hampered by the obscuration or indistinctness of their fine structures.

The majority of the stray light in a star tracker or telescope occurs at grazing angles of the incident; When the beam is nearly parallel to a particular surface. The grazing angles are Angle of Incidence (AOI) angles of about 80-90 degrees.

One of the recent key examples of stray light disrupting operations in space is, Beresheet, a small robotic lunar lander and lunar probe designed by SpaceIL and Israel Aerospace Industries. During the mission, dust accumulated on its star tracker, causing navigation failures due to stray light that scattered from the dust into the sensor. The space environment in general is filled with dust, especially the solid planetary bodies like the Moon and Mars. This generally causes dust accumulation on spacecraft and other critical systems/instruments deployed in such ecosystems.

The GAIA mission by the European Space Agency (ESA) was also facing the stray light issue during its commissioning. After several investigations and analysis by ESA, it was concluded that the “Stray light is caused in every space mission due to the Sun and bright objects, it affected the image of GAIA because the light was scattered by fibers coming out of a MLI blanket.” In this mission, the starylight affected the mission’s ability to absorb faint objects. These are some of the prime examples of the starylight and how it can affect the overall operations of the spacecraft.

The solution

Eliminating stray light from the optical systems is important and at the same time crucial to ensure the smooth operation of the overall system. Acktar’s Hexa Black™ product line is an important asset is eliminating stray light at the grazing angles.

In situations where grazing angles are a problem, the Acktar Light Absorbing Panel is used to reduce stray light reflectance. From 0° to 88° AOI, Hexa Black™’s distinctive structure and coating allow for extremely low reflection. These panels include high emissivity with low reflectance and low outgassing. It is also accessible in varied shapes and sizes to meet clients’ mission demands.

The Acktar Hexa Black™ is a space-qualified light-absorbing panel designed for use in optical space systems. It is used to eliminate stray light reflectance in applications where grazing angles are an issue. The unique structure and coating of hexa black allows extremely low reflection from 0° to 88° angle of incidence (AOI). The product is available in wide range of standard sizes along with custom options to suit the needs of the customers.

The Acktar Hexa Black™ Noise Reduction Extension Tubes are space-qualified tubes primarily used as spacers to increase the image distance when using SM1-Mount, C-Mount, and CS-Mount instruments for cameras and camera lenses. It has a wavelength range between 200nm – 5µm and can be used in between a lens and a camera to extend the focal length and increase the effective aperture of the lens.

Similarly, Acktar‘s Hexa Black™ Light Absorbing sheet allows extremely low reflection from 40° to 88° AOI. Though its properties are similar to Light Absorbing Panels, it use in space applications might differ as per the mission demands.

Acktar Hexa Black™ Light Trap Sheets are space-qualified, light-absorbing sheets designed for space applications. It is used to eliminate stray light reflectance in applications where grazing angles are an issue. Its unique structure and coating of Hexa Black™ allows extremely low reflection from 40° to 88° angle of incidence (AOI). The product is available in a wide range of standard sizes along with customizing options.

The results

According to the scientific studies and proven methodologies by Acktar, the Honeycomb structure is effective in trapping stray light.

Honeycomb structure in light absorbing sheets (image credits: Acktar)

To extend on this issue, three TracePro simulations in 2D were carried out at 512 nm and AOI 80 to verify the effectiveness of the new coating at grazing angles: Acktar coating, honeycomb-structured Acktar coating, and standard black. Following are the test results in the image below:

Fig 1: Specular reflectance simulation at AOI 80. Top to bottom: Standart black, Acktar coating, Acktar coating with honeycomb structure – Hexa Black™ (image credits: Acktar)

Utilizing a standard dark, the relative flux was 46%, with a most extreme brilliant power of 0.95. The maximum radiant intensity was 0.8 and the total integrated relative flux decreased to 21% when the Acktar black coating without the honeycomb structure was simulated. The maximum radiant intensity was 0.021 and the flux was reduced to 1.4% when the Acktar coating and honeycomb structure were combined.

Similarly, using the optical design software ZEMAX and Synopsys, a 3D simulation of the AOI 30 and 60 in VIS (white light) and IR (1.55 micron) was carried out. The results are as follows:

Fig 2: Hexa Black™ 3D simulation at AOI 30 (image credits: Acktar)
Fig 3: Hexa Black™ 3D simulation at AOI 60 (image credits: Acktar)

According to this 3D simulation results, the relative flux observed at AOI 30 was 0.56% in VIS and 0.79% in IR. While at AOI 60, it was 0.72% in VIS and 0.99% in IR.


Hexa Black™ stands out as a unique material to eliminate stray light at grazing angles. Given the fact that the space technology and the instruments used onboard spacecraft are sensitive to even the minute interference of cosmic rays and dust, Hexa Black™ proves to be the most effective material for space applications, as mentioned above in the test results.

Acktar‘s product lines of Black Coatings provide edge to modern space systems both in protecting as well as help ensure the smooth running of the system. Its products vary for different space applications and should be consulted with the company prior to their use to allow the effective use of its products.

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