FRONTIERS PHOTONICS


AEROSPACE/DEFENCE OPTICAL TELESCOPE IMAGING


NASA demonstrates asteroid defence system


I


n September 2022, NASA successfully redirected an asteroid in the first full-


scale demonstration of asteroid deflection technology. As a part of NASA’s overall planetary defence strategy, the impact with the asteroid Dimorphos demonstrates a viable mitigation technique for protecting the planet from an Earth-bound asteroid or comet, if one were discovered. The Double Asteroid


Redirection Test (DART) spacecraft targeted the asteroid moonlet Dimorphos, a small body just 530 feet (160m) in diameter. It orbits a larger, 2,560-foot (780m) asteroid called Didymos. Neither asteroid poses a threat to Earth. The spacecraft’s sole instrument, the Didymos Reconnaissance and Asteroid Camera for Optical Navigation (Draco), together with a sophisticated guidance, navigation and control system that works with algorithms, enabled DART to identify and distinguish between the two asteroids, targeting the smaller


DART team members install the Draco camera onto the spacecraft


body. It impacted Dimorphos at four miles per second (7km/s). Draco used an 8.2in (20.8cm)


aperture telescope and a CMOS imaging sensor. The telescope is a Ritchey-Chretien design, with hyperbolic primary and secondary mirrors and a field-flattening lens. It uses a lightweight, extremely low coefficient of thermal expansion design to maintain focus over


a large low-temperature range, using an M46J/R53 composite. The mirrors are composed of a glass ceramic substrate, Zerodur, with an enhanced silver coating mounted on iron-nickel flexures. The field flattening lens is fused silica with a VIS-NIR BBAR coating. The interior of the telescope is coated with Aeroglaze-Z-306 black paint.


Draco began to image the


Didymos system around 30 days before DART hit the asteroid. In the terminal phase, the images were processed autonomously on the spacecraft to determine course corrections to make an intercept. The final images it sent back to Earth will provide important constraints for modelling and interpreting the results of the impact. l


PHOTOGRAMMETRY


Mid-flight 3D modelling technique cuts aircraft drag


F


raunhofer has successfully measured Lufthansa’s aircraft wings during


flight so the airline can better optimise its anti-drag coatings. A technology inspired


by sharkskin, Lufthansa’s AeroShark coating significantly reduces frictional drag and thus emissions. To attach the coating optimally, however, it is necessary to conduct flow simulations which take the actual wing shape during flight into account. Aircraft aerodynamics can


be performed on the ground to measure flow and create 3D models. However, this does not


represent how wings behave during flight: aerodynamic uplift and the change in tank load can cause these parts to deflect upward by several metres. Using models that reflect the actual aircraft shape during flight, computer-aided flow simulations of the sharkskin technology can be carried out to determine its optimum position and orientation. Usually, at least two


cameras are needed to create such a 3D model, which can be challenging to set up in a passenger aeroplane. The new method developed at the Fraunhofer Institute of


Optronics, System Technologies and Image Exploitation only requires one camera – the missing distance information is obtained by additional measurements on the ground. For this purpose, the upper


surface of the wing is covered with numerous measurement marks whose positions are measured with the help of a tachymeter. A single camera permanently mounted in the aircraft cabin records and locates these marks several times an hour in different flight conditions. The positions of the


measurement marks can be


The black marks are used to help measure distances with just one camera


determined in the measurement images and converted into spatial coordinates. On a regular flight from Zurich to San Francisco and back, the team was able to obtain the 3D model of the wing of a Boeing 777-300ER and make it available to Lufthansa Technik. l


52 Photonics Frontiers 2023


Lufthansa Technik


NASA/Johns Hopkins APL/Ed Whitman


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