The world’s blackest material makes its debut in space on board a micro satellite’s star tracker, but what are the benefits?

It’s the material that has spurred the Spinal Tap inspired headline the world over, ‘None more black’. Officially the world’s blackest material, VantaBlack from Brighton based Surrey Nano Systems is moving well beyond development following the materials unveiling some two years ago.

Absorbing an incredible 99.965% of radiation in the visible spectrum, the material has been dubbed the closest anyone will get to looking in to a black hole.

The material stands out as an early adopter and application of nano material science and is made of vertically aligned nanotubes, applied directly to a substrate using proprietary photo thermal chemical vapour deposition (PTCVD). But as impressive as the science might be, what is it useful for?

Applications include being used as a functional coating within an infrared system such as thermal cameras, night vision sights and the calibration of sensors. It’s a technology the space industry, particularly those involved in instrumentation have been very keen to work with and develop, as its performance far outstrips that of the traditionally-used black paints.

This saw Surrey Nano Systems team up with Berlin Space Technology (BST) to use the ultra-black Vantablack surface coating on an optical instrument. When BST first heard about Vantablack, the development process of its Kent Ridge 1 low earth orbit (LEO) microsatellite was already at a late stage, and there were only a few weeks left before the equipment design was scheduled to be frozen.

Here, the material’s ability to absorb virtually all incident light means that it is able to improve the performance of the satellite’s star tracker-based positioning control system, as the coating minimises interference from stray-light inside the star trackers.

The star tracker is a key element of BST’s microsatellite design. On previous satellite missions, BST has used a super-black paint on the baffles inside the optical positioning system to minimise internal reflections and provide an accurate position reference based on a map of the stars.

To meet this challenging timescale, Surrey NanoSystems coated baffles for BST within a time window of around five weeks - a process that included the provision of specifications and many detailed technical discussions.

The speed of the production cycle was aided by the use of the S-VIS version of Vantablack, which is applied in a process that is similar to spray painting. The versatility of applying this material made it easy to coat the thin aluminium sections and sharp-edges. BST decided to apply Vantablack to an existing baffle design, allowing its performance to be compared with the previous generation instruments through measurement of the best ‘sun exclusion angle’.

“A star tracker’s performance relies on achieving high sensitivity,” says Tom Segert, director of business development for Berlin Space Technology. “We believe that Vantablack will reduce the effects of many common sources of error that affect the performance of star tracker systems - allowing the star identification algorithm to function over a considerably wider range than before.”

Kent Ridge 1 was successfully launched in December 2015, and the ultra-black Vantablack S-VIS material has outstripped any other conventionally applied coating, typically achieving a reflectance of less than 0.2%. Unlike other black absorbers, it offers this exceptional performance across a wide-range of viewing angles and wavelengths, which is critical for optical instruments.

The Vantablack decreased the amount of reflected light by an order of magnitude compared with the conventional coatings, and at the same time extended the angular range over which the star tracker is able to operate in the presence of bright light sources such as the Sun and Moon. This has improved the robustness of the Earth observation instruments on the satellite, and has reduced the need for gyroscope-aided position control that can introduce drift errors over time.

BST also anticipates that it will be able to further reduce the size and weight of its star tracker systems in future, enabling the design of shorter and lighter baffles offering the same high performance.

“The Vantablack coating was originally developed to improve the efficiency of optical systems in space, and this BST satellite project gives us a very early opportunity to prove its performance,” says Ben Jensen, chief technology officer of Surrey NanoSystems. “The material can be used to improve the performance of satellites, but also to dramatically reduce weight and size of optical systems - which could be crucial for future space missions.”

Tech Spec: Vantablack

The active element of Vantablack S-VIS is a carbon nanotube matrix. The coating is applied using a proprietary process that includes a number of pre- and post-application steps to achieve its ultra-low reflectance. Vantablack S-VIS can be applied to most stable surfaces, making Vantablack S-VIS suitable for many types of engineering-grade polymers and composite materials. The process is scalable and suitable for high-volume production on a range of substrate sizes.

Vantablack has the highest thermal conductivity and lowest mass-volume of any material that can be used in high-emissivity applications. It has virtually undetectable levels of outgassing and particle fallout, thus eliminating a key source of contamination in sensitive imaging systems. It withstands launch shock, staging and long-term vibration, and is suitable for coating internal components, such as apertures, baffles, cold shields and micro electro mechanical systems or MEMS-type optical sensors.

* THR (total hemispherical reflectance) 0.2% at 700 nm and 0.17% at 1064nm (near-infrared spectrum)

* Performs across a wide spectrum from ultraviolet (UV) to near infrared (NIR)

* Shock and vibration resistance to MIL-810G

* Thermal shock and cycling from -196 to +200 degrees C

* Super-hydrophobic

* High performance at extreme viewing angles (TIS - 0.6% at 70° VIS)


Author
Justin Cunningham

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