page_title: Spacecraft thermal control
section_title: Sun shield
hierarchical_section_title: Spacecraft thermal control / Sun shield
caption_attribution_description: English: NASA: The Sunshield on NASA's James Webb Space Telescope is the largest part of the observatory—five layers of thin membrane that must unfurl reliably in space to precise tolerances. Last week, for the first time, engineers stacked and unfurled a full-sized test unit of the Sunshield and it worked perfectly. The Sunshield is about the length of a tennis court, and will be folded up like an umbrella around the Webb telescope’s mirrors and instruments during launch. Once it reaches its orbit, the Webb telescope will receive a command from Earth to unfold, and separate the Sunshield's five layers into their precisely stacked arrangement with its kite-like shape. The Sunshield test unit was stacked and expanded at a cleanroom in the Northrop Grumman facility in Redondo Beach, California.
context_page_description: In spacecraft design, the function of the thermal control system is to keep all the spacecraft's component systems within acceptable temperature ranges during all mission phases. It must cope with the external environment, which can vary in a wide range as the spacecraft is exposed to deep space or to solar or planetary flux, and with ejecting to space the internal heat generated by the operation of the spacecraft itself.
  Thermal control is essential to guarantee the optimum performance and success of the mission because if a component is subjected to temperatures which are too high or too low, it could be damaged or its performance could be severely affected. Thermal control is also necessary to keep specific components within a specified temperature stability requirement, to ensure that they perform as efficiently as possible.
context_section_description: In spacecraft design, a sun shield restricts or reduces heat caused by sunlight hitting a spacecraft. An example of use of a thermal shield is on the Infrared Space Observatory. The ISO sunshield helped protect the cryostat from sunlight, and it was also covered with solar panels.
  Not to be confused with concept of a  global scale sun shield in geoengineering, often called a Space sunshade or "sun shield", in that case the spacecraft itself is used to block sunlight on a planet, not as part the spacecraft's thermal design.
  An example of a sunshield in spacecraft design is the Sunshield (JWST) on the planned James Webb Space Telescope.
caption: Sunshield full-size test for the James Webb Space Telescope
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