![]() To detect changes in direction JWST uses hemispherical resonator gyroscopes (HRG). įinally, there are two titanium helium tanks to provide unregulated pressurant for all propellants. JWST has six reaction wheels for attitude control, spinning wheels that allow the orientation to be changed without using propellant to change momentum. They are used for attitude control and momentum unloading of the reaction wheels. There are also eight Monopropellant Rocket Engines (MRE-1), so called because they use only hydrazine as fuel. One pair is used to propel the JWST into orbit, and the other performs station keeping in orbit. The Secondary Combustion Augmented Thrusters (SCAT) use hydrazine ( N 2H 4) and the oxidizer dinitrogen tetroxide ( N 2O 4) as propellants. The main Science and Operations Center is the Space Telescope Science Institute in the U.S. The system is designed to communicate with NASA's Deep Space Communication Network. The Common Command and Telemetry System is based on Raytheon ECLIPSE system. : Fig 1 There is Ka-band and S-band radio communication. The communications dish which can point at Earth is attached to the bus. The Command and Data Handling system includes a computer, the Command Telemetry Processor (CTP), and a data storage unit, the Solid State Recorder (SSR), with a capacity of 58.9 GB. Two major tasks are pointing the telescope and performing station keeping for its metastable L2 halo orbit. The spacecraft bus has two star trackers, six reaction wheels, and the propulsion systems ( fuel tank and thrusters). Command and Data Handling Subsystem (C&DH).There are six major subsystems in the spacecraft bus: It also contains the MIRI cooler and some ISIM electronics. The bus is a carbon fibre box that houses a large number of major systems that keep the telescope functioning, such as the solar panels and computers. The solar panel is in green and the light purple flats are radiators shades. The computer also controls the pointing and moment of the spacecraft, taking in sensor data from the gyroscopes and star tracker, and sending the necessary commands to the reaction wheels or thrusters. 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. Īnother important aspect of the spacecraft bus is the central computing, memory storage, and communications equipment. 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. The spacecraft bus is on the Sun-facing "warm" side and operates at a temperature of about 300 kelvins (80 ☏, 27 ☌). The fine pointing is done by the JWST fine guidance mirror, obviating the need to physically move the whole mirror or bus. The bus can provide pointing precision of one arcsecond ( 1⁄ 3600°) and isolates vibration down to two milliarcseconds. ![]() state of California by 2015, and then it had to be integrated with the rest of the space telescope leading up to its planned 2018 launch. ![]() It is made primarily of graphite composite material. The spacecraft bus must structurally support the 6.5 ton space telescope, while weighing only 350 kg (770 lb). Region 3 includes the ISIM Command and Data Handling subsystem and the Mid-Infrared Instrument (MIRI) cryocooler. Region 3 of ISIM is also inside the spacecraft bus. The other three elements of the JWST are the Optical Telescope Element (OTE), the Integrated Science Instrument Module (ISIM) and the sunshield. It hosts a multitude of computing, communication, propulsion, and structural components. The spacecraft bus is the primary support element of the James Webb Space Telescope, launched on 25 December 2021. Technicians work on a mock-up of the JWST spacecraft bus in 2014
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