Spacecraft bus (James Webb Space Telescope)
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 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.
[5] Another important aspect of the spacecraft bus is the central computing, memory storage, and communications equipment.
[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] 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.
[12] Two major tasks are pointing the telescope and performing station keeping for its metastable L2 halo orbit.
The Secondary Combustion Augmented Thrusters (SCAT) use hydrazine (N2H4) and the oxidizer dinitrogen tetroxide (N2O4) as propellants.
[20] This raw power is fed to the SAR which consists of four redundant buck converters each operating with a maximum-power point tracking (MPPT) algorithm.
With every science instrument and all support circuits "on" simultaneously, approximately three of the four redundant converters could handle all of the power required.
The Telemetry Acquisition Unit (TAU) consists of electronic switches for various heaters for the "warm" sides of the telescope.
In addition, there are switches for the deployment actuators, and the bulk of the telemetry processors (e.g. measuring temperatures, electric power, fuel levels, etc.).
[citation needed] Some early configurations of the bus had two solar panel wings, one on each side.
[22] Although the bus was primarily designed to operate in the weightless environment of outer space, during launch it must survive the equivalent of 45 tons.
[23] The spacecraft structure provides state of the art capabilities to support the James Webb Space Telescope's first light mission.The spacecraft bus is connected to the Optical Telescope Element and sunshield via the Deployable Tower Assembly.
[27] The array is in front of the sunshield segments shield deployment boom, which at the end of it also has a trim tab attached.
[28] The plan was that during its first week of operation, the deployable tower would extend, which would separate the bus from the upper spacecraft by about 2 meters.
[30] In 2014, Northrop Grumman began construction of several spacecraft bus components including the gyroscopes, fuel tanks, and solar panels.
[34] In 2015, the communications subsystems, star trackers, reaction wheels, fine Sun sensors, deployment electronics Unit, command telemetry processors, and wire harnesses were delivered for construction.
[37] For launch, the spacecraft bus is attached to the Ariane 5 on a Cone 3936 plus ACU 2624 lower cylinder and clamp-band.
[19] This is not a traditional mechanical gyroscope; instead, an HRG has a quartz hemisphere that vibrates at its resonant frequency in a vacuum.
[38] JWST does not need as precise pointing because it has a Fine Steering Mirror that helps counter small motions of the telescope.
The HRG are sensors that provide information, while the reaction wheels and thrusters are devices that physically change the orientation of the spacecraft.
