Spacecraft bus (James Webb Space Telescope)

Technicians work on a mock-up of the JWST spacecraft bus in 2014[1]

The spacecraft bus is a carbon fibre box that houses systems of the telescope and so is the primary support element of the James Webb Space Telescope, launched on 25 December 2021. It hosts a multitude of computing, communication, propulsion, and structural components.[2] The other three elements of the JWST are the Optical Telescope Element (OTE), the Integrated Science Instrument Module (ISIM) and the sunshield.[3] Region 3 of ISIM is also inside the spacecraft bus. Region 3 includes the ISIM Command and Data Handling subsystem and the Mid-Infrared Instrument (MIRI) cryocooler.[4]

The spacecraft bus must structurally support the 6.5 ton space telescope, while weighing only 350 kg (770 lb).[5] It is made primarily of graphite composite material.[5] It was assembled by Northrop Grumman in Redondo Beach, California by 2015, and then it had to be integrated with the rest of the space telescope leading up to its planned 2018 launch.[6] The bus can provide pointing precision of one arcsecond (1⁄3600°) and isolates vibration down to two milliarcseconds.[7] The fine pointing is done by the JWST fine guidance mirror, obviating the need to physically move the whole mirror or bus.[8]

The spacecraft bus is on the Sun-facing "warm" side and operates at a temperature of about 300 kelvins (80 °F, 27 °C).[9] Everything on the Sun-facing side must be able to handle the thermal conditions of JWST's halo orbit, which has one side of continuous sunlight and the other shaded by the spacecraft sunshield.[5]

Another important aspect of the spacecraft bus is the central computing, memory storage, and communications equipment.[10] The processor and software direct data to and from the instruments, to the solid-state memory core, and to the radio system which can send data back to Earth and receive commands.[10] The computer also controls the pointing and movement of the spacecraft, taking in sensor data from the gyroscopes and star tracker, and sending the necessary commands to the reaction wheels or thrusters.[10]

  1. ^ Jenner, Lynn (2015-04-17). "Mock the Bus: NASA's James Webb Space Telescope". NASA. Retrieved 2021-04-06.
  2. ^ "Spacecraft Bus". jwst.nasa.gov. Retrieved 2021-04-06.
  3. ^ "Observatory - JWST/NASA". jwst.nasa.gov. Retrieved 2017-01-20.
  4. ^ "ISIM & Instruments". jwst.nasa.gov. Archived from the original on 2016-12-03. Retrieved 2017-01-24.
  5. ^ a b c "PRIME: The Untold Story Of NASA's James Webb Space Telescope". www.satmagazine.com. Feb 2012. Retrieved 2021-04-06.
  6. ^ "James Webb Space Telescope passes another milestone - SpaceFlight Insider". www.spaceflightinsider.com. 10 October 2015. Retrieved 2017-01-20.
  7. ^ Sloan, Jeff. "James Webb Space Telescope spacecraft inches towards full assembly : CompositesWorld". www.compositesworld.com. Archived from the original on 2019-10-24. Retrieved 2017-01-20.
  8. ^ "FAQ-Public JWST/NASA". jwst.nasa.gov. Retrieved 2017-01-24.
  9. ^ Ross, Ronald G. (2007-02-15). Cryocoolers 13. Springer Science & Business Media. ISBN 9780387275338.
  10. ^ a b c "The James Webb Space Telescope". jwst.nasa.gov. Retrieved 2017-01-20.