COMPOSITES PLAY STARRING ROLE IN LARGEST SPACE TELESCOPE EVER BUILT?

‘Built by our world to discover new worlds,’ the James Webb Space Telescope (Webb) is the largest space telescope ever made and it’s discovering new star systems and gathering scientific evidence about cosmic history from its observatory position 1.6 million km away from Earth.??

Webb was launched Christmas Day 2021 by NASA and its partners the European Space Agency (ESA) and the Canadian Space Agency (CSA). Northrop Grumman was the prime contractor, and suppliers and experts from 14 countries and 29 US states were involved in the project.??

Webb is seven times larger than the Hubble Space Telescope but weighs almost half as much at about 6,486 kg. The three-story tall telescope and its tennis-court-sized sunshield had to retract and fold intricately to fit within an Ariane 5 rocket’s 5.4 m diameter fairing. After launch, the sunshield’s five layers of thin Kapton material had to unfurl and spread out on its support structures to the proper tension. The Deployment Tower Assembly lifted the observatory from the spacecraft bus, the primary mirror unfolded to its full 6.5 m diameter, and other mirrors took their positions.??

Composite materials play a major role in this incredible feat of engineering.??

Composites innovations??

Webb has two primary sections, the Integrated Science Instrument Module (ISIM)/Optical Telescope Element (OTE), or OTIS, and the Spacecraft Bus.?

OTIS contains the telescope’s 6.5 m diameter primary mirror, secondary mirror and mission-critical telescope optical equipment and scientific instruments. Made primarily of M55J carbon fibre composite material, the Primary Mirror Backplane Support Structure (PMBSS), or Backplane, is approximately 7.3 m tall and 6.1 m wide. Also known as Webb’s spine, the PMBSS composite structure supports about 3,311 kg of mirrors, optical instruments and other OTIS components. The weight supported by the Backplane is more than three times its own weight. A major design challenge was the requirement for OTIS to remain stable at ultra-cold temperatures to enable the optical equipment to function optimally. To accomplish this, the Backplane materials could not expand or contract more than 38 nm root mean square (RMS), which is about 1/1000 the diameter of a human hair over the range of operational temperatures. A new composite laminate was designed to meet this demanding coefficient of thermal expansion (CTE) specification from room temperature to the 50 K to 30 K operating temperature range (about -223°C to -243°C). The material must be stable to 38 nm RMS over this operating temperature range within a tolerance of +/-0.15 K.??

The Spacecraft Bus also makes good use of composites. This includes the Sunshield, which is crucial for keeping light and heat from the sun, Earth and moon from the telescope’s science instruments so they can operate in darkness at approximately 50 K. It also contains guidance, navigation and communications systems. For this Webb section, composite materials were chosen primarily for their light weight rather than for their performance at cryogenic temperatures.?

Read more about the composites applications on Webb in the article Composites play starring role in humankind’s largest space telescope in JEC Composites Magazine 151.?

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