Lightweight Garage #29 James Webb Telescope @ NASA, ESA, CSA

27.10.2022 Luca Wilhelmy

The Vehicle

Behind this gate is the latest scientific instrument for observing space. The James Webb Telescope was sent on its journey from the Guiana Space Centre on 25 December 2021, with a launch weight of 6.2 tons. After several days and at a maximum speed of 9.90 km/s (35640 km/h), the James Webb Telescope reached its destination. The Lagrange point L2 about 1.5 million km from the Earth. The telescope is now moving in unison with the Earth and the Sun. After calibration, the James Webb Telescope is now able to observe a ring-shaped section of about 39% of the sky.

©NASA, model of the unfolded James Webb Telescope.

The Technology

The telescope consists of different assemblies. The first assembly relevant to lightweight construction is the 21.2 m x 14.2 m sun shield. The shield consists of 5 layers of Kapton, a polyamide film with a 100 nm thin aluminium layer. Apart from the first foil facing the sun, these are just 25 μm thick. The first foil is also covered with a 50 nm thick silicon layer. The energy required for observation is supplied by a 2000 W solar module located in front of the sun shield. The telescope's optics are on the side facing away from the sun in order to reduce infrared radiation from the sun and moon. The main mirror has a diameter of 6.5 m, with 18 hexagonal segments forming the mirror surface. Due to its low density, high strength and low coefficient of thermal expansion at temperatures below 100 K, beryllium was chosen as the material for the segments. The segment plates were designed to reduce infrared radiation from the sun and moon. The segment plates were constructed in such a way that they can be aligned and at the same time withstand micrometeorites. The segments are additionally vapour-deposited with a gold layer and a silicon dioxide layer.

©NASA, illustration of the folding mechanism

The Lightweighting Effect

The entire telescope offers an impressive impression of lightweight construction. By combining different materials, the different properties of each material are used here. The arrangement of the components allows the material properties to be used optimally. Everything is connected by complex mechanics and sensors for calibration, position determination and thermal regulation. Due to transport and the limited packing space in the rocket, the components must also be able to be deployed, which represents a considerable risk. 

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