 |
| The James Webb Space Telescope (JWST) |
 |
| JWST Mirror Production/ Transport/ Testing/ Deployment |
 |
| Hubble Space Telescope vs JWST |
 |
| JWST Mirror Production/ Transport/ Testing/ Deployment |
Cleaned up from Wikipedia (https://en.wikipedia.org/wiki/James_Webb_Space_Telescope)
The James Webb Space Telescope (JWST) enables a broad range of investigations across the fields of astronom & cosmology. JWST main mirror of 18 hexagonal mirror segments for a combined mirror size of 6.5-meter-diameter (21 ft 4 in). JWST's primary mirror is a 6.5-meter-diameter gold-coated beryllium reflector with a collecting area of 25 m2. This is too large for existing launch vehicles, so the mirror is composed of 18 hexagonal segments, which will unfold after the telescope is launched in 2019. Its nominal mission time is five years, with a goal of ten years.
A large sunshield will keep JWST's mirror and four science instruments below 50 K (−220 °C; −370 °F). Observations in the infrared spectrum require very cold (under 50 K (−220 °C; −370 °F)), otherwise infrared radiation from the telescope itself would overwhelm its instruments with heat noise. The sunshield blocks light and heat from the Sun, Earth, and Moon. The position near the Earth–Sun L2 point keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around L2 avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield & solar arrays. The sunshield is made of polyimide film, and has membranes coated with aluminum on one side and silicon on the other, folded 12 times so it will fit within the Ariane 5 rocket's 4.57 m × 16.19 m shroud. At the L2 point unfolds to 21.197 m × 14.162 m.
The telescope has an expected mass about half of Hubble Space Telescope's, JWST will operate near the Earth-Sun L2 (Lagrange) point, approximately 930,000 mi (1,500,000 km) beyond Earth's orbit, allowing the telescope to remain at a roughly constant distance using a single sunshield to block heat and light from the Sun & Earth. Keep the temperature of the spacecraft below 50 K (−220 °C; −370 °F) JWST needs to use propellant to maintain its halo orbit around L2, which provides an upper limit to its designed lifetime, and it is being designed to carry enough for ten years. The planned five year science mission begins after a 6-month commissioning phase. An L2 orbit is meta-stable so it requires orbital station-keeping or an object will drift away from this orbital configuration.
JWST's optical design is a three-mirror anastigmat, which makes use of curved secondary and tertiary mirrors to deliver images that are free of optical aberrations over a wide field. In addition, there is a fast steering mirror, which can adjust its position many times per second to provide image stabilization.
Scientific Instruments
Integrated Science Instrument Module (ISIM)
Framework that provides electrical power, computing resources, cooling capability as well as structural stability to the Webb telescope. It is made with bonded graphite-epoxy composite attached to the underside of Webb's telescope structure. The ISIM holds the four science instruments and a guide camera.
Near InfraRed Camera (NIRCam)
infrared imager which will have a spectral coverage ranging from the edge of the visible (0.6 micrometers) through the near infrared (5 micrometers).[26][27] NIRCam will also serve as the observatory's wavefront sensor, which is required for wavefront sensing and control activities. NIRCam was built by a team led by the University of Arizona, with Principal Investigator Marcia Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center located in Palo Alto, California.
Near InfraRed Spectrograph (NIRSpec)
Performs spectroscopy over the same wavelength range. Built by the European Space Agency at ESTEC in Noordwijk, Netherlands. Leading development team people from Airbus Defence and Space, Ottobrunn & Friedrichshafen, Germany, and the Goddard Space Flight Center; with Pierre Ferruit (École normale supérieure de Lyon) as NIRSpec project scientist.
The NIRSpec design provides three observing modes: a low-resolution mode using a prism, an R~1000 multi-object mode and an R~2700 integral field unit or long-slit spectroscopy mode. Switching of the modes is done by operating a wavelength preselection mechanism called the Filter Wheel Assembly, and selecting a corresponding dispersive element (prism or grating) using the Grating Wheel Assembly mechanism. Both mechanisms are based on the successful ISOPHOT wheel mechanisms of the Infrared Space Observatory.
The multi-object mode relies on a complex micro-shutter mechanism to allow for simultaneous observations of hundreds of individual objects anywhere in NIRSpec's field of view. The mechanisms and their optical elements were designed, integrated and tested by Carl Zeiss Optronics GmbH of Oberkochen, Germany, under contract from Astrium.
Mid-InfraRed Instrument (MIRI)
Measures the mid-infrared wavelength range from 5 to 27 micrometers. It contains both a mid-infrared camera and an imaging spectrometer.[2] MIRI was developed as a collaboration between NASA and a consortium of European countries, and is led by George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre, Edinburgh, part of the Science and Technology Facilities Council (STFC)).
MIRI features similar wheel mechanisms as NIRSpec which are also developed and built by Carl Zeiss Optronics GmbH under contract from the Max Planck Institute for Astronomy, Heidelberg. The completed Optical Bench Assembly of MIRI was delivered to Goddard in mid-2012 for eventual integration into the ISIM. The temperature of the MIRI must not exceed 6 Kelvin (K): a helium gas mechanical cooler sited on the warm side of the environmental shield provides this cooling.
The telescope has an expected mass about half of Hubble Space Telescope's, JWST will operate near the Earth-Sun L2 (Lagrange) point, approximately 930,000 mi (1,500,000 km) beyond Earth's orbit, allowing the telescope to remain at a roughly constant distance using a single sunshield to block heat and light from the Sun & Earth. Keep the temperature of the spacecraft below 50 K (−220 °C; −370 °F) JWST needs to use propellant to maintain its halo orbit around L2, which provides an upper limit to its designed lifetime, and it is being designed to carry enough for ten years. The planned five year science mission begins after a 6-month commissioning phase. An L2 orbit is meta-stable so it requires orbital station-keeping or an object will drift away from this orbital configuration.
JWST's optical design is a three-mirror anastigmat, which makes use of curved secondary and tertiary mirrors to deliver images that are free of optical aberrations over a wide field. In addition, there is a fast steering mirror, which can adjust its position many times per second to provide image stabilization.
Scientific Instruments
Integrated Science Instrument Module (ISIM)
Framework that provides electrical power, computing resources, cooling capability as well as structural stability to the Webb telescope. It is made with bonded graphite-epoxy composite attached to the underside of Webb's telescope structure. The ISIM holds the four science instruments and a guide camera.
Near InfraRed Camera (NIRCam)
infrared imager which will have a spectral coverage ranging from the edge of the visible (0.6 micrometers) through the near infrared (5 micrometers).[26][27] NIRCam will also serve as the observatory's wavefront sensor, which is required for wavefront sensing and control activities. NIRCam was built by a team led by the University of Arizona, with Principal Investigator Marcia Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center located in Palo Alto, California.
Near InfraRed Spectrograph (NIRSpec)
Performs spectroscopy over the same wavelength range. Built by the European Space Agency at ESTEC in Noordwijk, Netherlands. Leading development team people from Airbus Defence and Space, Ottobrunn & Friedrichshafen, Germany, and the Goddard Space Flight Center; with Pierre Ferruit (École normale supérieure de Lyon) as NIRSpec project scientist.
The NIRSpec design provides three observing modes: a low-resolution mode using a prism, an R~1000 multi-object mode and an R~2700 integral field unit or long-slit spectroscopy mode. Switching of the modes is done by operating a wavelength preselection mechanism called the Filter Wheel Assembly, and selecting a corresponding dispersive element (prism or grating) using the Grating Wheel Assembly mechanism. Both mechanisms are based on the successful ISOPHOT wheel mechanisms of the Infrared Space Observatory.
The multi-object mode relies on a complex micro-shutter mechanism to allow for simultaneous observations of hundreds of individual objects anywhere in NIRSpec's field of view. The mechanisms and their optical elements were designed, integrated and tested by Carl Zeiss Optronics GmbH of Oberkochen, Germany, under contract from Astrium.
Mid-InfraRed Instrument (MIRI)
Measures the mid-infrared wavelength range from 5 to 27 micrometers. It contains both a mid-infrared camera and an imaging spectrometer.[2] MIRI was developed as a collaboration between NASA and a consortium of European countries, and is led by George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre, Edinburgh, part of the Science and Technology Facilities Council (STFC)).
MIRI features similar wheel mechanisms as NIRSpec which are also developed and built by Carl Zeiss Optronics GmbH under contract from the Max Planck Institute for Astronomy, Heidelberg. The completed Optical Bench Assembly of MIRI was delivered to Goddard in mid-2012 for eventual integration into the ISIM. The temperature of the MIRI must not exceed 6 Kelvin (K): a helium gas mechanical cooler sited on the warm side of the environmental shield provides this cooling.
Fine Guidance Sensor and Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS)
Canadian Space Agency under project scientist John Hutchings (Herzberg Institute of Astrophysics, National Research Council of Canada), is used to stabilize the line-of-sight of the observatory during science observations. Measurements by the FGS are used both to control the overall orientation of the spacecraft and to drive the fine steering mirror for image stabilization. The Canadian Space Agency is also providing a Near Infrared Imager and Slitless Spectrograph (NIRISS) module for astronomical imaging and spectroscopy in the 0.8 to 5 micrometer wavelength range, led by principal investigator René Doyon at the University of Montreal.
Because the NIRISS is physically mounted together with the FGS, they are often referred to as a single unit, but they serve entirely different purposes, with one being a scientific instrument and the other being a part of the observatory's support infrastructure. NIRCam and MIRI feature starlight-blocking coronagraphs for observation of faint targets such as extrasolar planets and circumstellar disks very close to bright stars.
The infrared detectors for the NIRCam, NIRSpec, FGS, and NIRISS modules are being provided by Teledyne Imaging Sensors (formerly Rockwell Scientific Company). The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) and Command and Data Handling (ICDH) engineering team uses SpaceWireto send data between the science instruments and the data-handling equipment.
JWST Spacecraft Bus
The primary support component of the James Webb Space Telescope, that hosts a multitude of computing, communication, propulsion, and structural parts, bringing the different parts of the telescope together. Along with the Sunshield, it forms the Spacecraft Element of the space telescope.
The other two major elements of the JWST are the Integrated Science Instrument Module (ISIM) and the Optical Telescope Element (OTE). Region 3 of ISIM is also inside the Spacecraft Bus; region 3 includes ISIM Command and Data Handling subsystem and the MIRI cryocooler.
The Spacecraft Bus is connected to Optical Telescope Element via the Deployable Tower Assembly, which also connects to the sunshield.
The structure of the Spacecraft Bus must support the 6.5 ton space telescope, while it itself weighs 350 kg (about 772 lb). Made primarily of graphite composite material assembled in California by 2015. The bus can provide pointing of one-arcsecond & isolates vibration down to two (2) milliarcseconds.
The Spacecraft Bus is on the Sun-facing "warm" side and operates at a temperature of about 300 K. Everything on the Sun facing side must be able to handle the thermal conditions of JWST's halo orbit, which has one side in continuous sunlight and the other in shade by the spacecraft sunshield.
Another important aspect of the Spacecraft Bus is the central computing, memory storage, and communications equipment. 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. 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 depending.
No comments:
Post a Comment