James Webb Space Telescope (JWST)

Transcription

1 James Webb Space Telescope (JWST) Background Instruments System Description Development Integration & Testing TBD Select Image Reference Information 1 1

2 Background The James Webb Space Telescope (JWST) is a large space telescope planned to launch in October The JWST will be the successor to the Hubble Space Telescope. - JWST instruments are designed to work primarily in the infrared range of the electromagnetic spectrum with some capability in the visible range. - JWST will find the first galaxies that formed in the early Universe, connecting the Big Bang to our own Milky Way Galaxy. - JWST will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System. JWST was renamed in 2002 in honor of former NASA administrator, James Webb ( ). - He accepted leadership of NASA on February 14, 1961 and he left NASA in October 1968, just as the Apollo moon landing was nearing a successful completion. -- During his administration, he maintained a balanced program, focusing on planetary as well as manned exploration. JWST was formerly known as the "Next Generation Space Telescope" (NGST). 2 2

3 Full-Scale Model The full-scale JWST model with the Webb Telescope team on the lawn at Goddard Space Flight Center in September

4 Launch Vehicle Payload Fairing JWST Observatory (Stowed Configuration) Payload Adapter Cryogenic Upper Stage Main Cryogenic Stage Solid Booster Stage (2 Places) The JWST will be launched on an Ariane 5 from Arianespace's ELA-3 launch complex at the European Spaceport located near Kourou, French Guiana in South America. The Launch Segment has 3 primary components: - The Launch Vehicle includes the Ariane 5 ECA (Evolution Cryotechnique type A) with the cryogenic upper stage. -- It will be provided in the single launch configuration, with a long payload fairing providing a maximum 15 ft static diameter and useable length of 53.1 ft. - The Payload Adapter provides the separating mechanical and electrical interface between the JWST Observatory and the Launch Vehicle. - The Launch Preparation and Support is the mutual responsibility of NASA, European Space Agency (ESA), Northrop Grumman Space Technology, and Arianespace. ESA will provide the Launch Vehicle and the Payload Adapter to the JWST Mission. 4 4

5 Primary Mirror In addition to making the JWST 21.3 ft (6.5 m) primary mirror small enough to fit into the Ariane 5 payload fairing, the JWST team also designed it light enough to be launched. - If the Hubble Space Telescope's 7.9 ft (2.4 m) mirror was scaled to the JWST, it would have been too heavy to launch into orbit. -- The JWST team found new ways to build the mirror so that it would be light enough to launch. 5 5

6 Orbit The Sun Earth JWST JWST will observe primarily the infrared light from faint and very distant objects. - To avoid swamping the very faint astronomical signals with radiation from the telescope, the telescope and its instruments must be very cold. -- JWST has a large shield that blocks the light from the sun, Earth, and moon, which otherwise would heat up the telescope, and interfere with the observations. JWST will be placed in an orbit around the L2 point where the sun, Earth, and moon are in about the same direction. - The L2 point is 940,000 miles from the Earth. - The L2 orbit is an elliptical orbit about the semistable second Lagrange point. -- The second Lagrange point is one of the five solutions, determined by the mathematician Joseph- Louis Lagrange in the 18th century, to the threebody problem. -- Lagrange was searching for a stable configuration in which three bodies could orbit each other yet stay in the same position relative to each other. He found five such solutions, and they are called the five Lagrange points in honor of their discoverer. 6 6

7 System Description Optical Telescope Element (OTE) Primary Mirror Integrated Science Instrument Module (ISIM) Select Image for JWST Deployment Animation OTE Aft Optics Subsystem OTE Primary Mirror Backplane Assembly OTE Secondary Mirror Sunshield Spacecraft Bus Star Trackers 7 7

8 System Description (Continued) Integrated Science Instrument Module (ISIM) OTE Primary Mirror Backplane Assembly Sunshield Momentum Trim Flap 8 8

9 System Description (Continued) OTE Primary Mirror Sunshield Spacecraft Bus Solar Panel Momentum Trim Flap 9 9

10 System Description (Continued) v v Credit: Northrop Grumman & STScI OTE and Interfaces to ISIM OTE ISIM v v Secondary Mirror v Aft Optics Subsystem v v Fine Steering Mirror Primary Mirror Tertiary Mirror OTE Focal Plane The Optical Telescope Element (OTE) gathers the light coming from space and provides it to the science instruments located in the Integrated Science Instrument Module (ISIM). - The Aft Optics Subsystem includes the Tertiary Mirror (TM) and Fine Steering Mirror (FSM). -- The TM directs the light from the Secondary Mirror to the FSM. -- The FSM is used for accurate optical pointing and image stabilization. - Each ISIM instrument re-images the OTE focal plane onto its focal plane array. v 10 10

11 System Description (Continued) Integrated Science Instrument Module (ISIM) Fine Guidance Sensor Instrument Purge Lines & Ground Support Equipment Panel Radiator Baffle Electrical Harness & Harness Radiator Mid Infrared Instrument ISIM Electronics Compartment Near Infrared Camera ISIM Structure Radiator Harness Near Infrared Spectrograph Kinematic Mount (3X) Thermal Straps 11

12 System Description (Continued) Spacecraft Bus Propulsion Subsystem (Thrusters) Thermal Control Subsystem (Enclosure) Attitude Control Subsystem (Star Trackers) Electrical Power Subsystem (Solar Array Panel) Command and Data Handling Subsystem (Not Shown) Communication Subsystem (Antenna) 12

13 Near Infrared Camera (NIRCam) Credit: Lockheed Martin NIRCam will detect light from the earliest stars and galaxies in the process of formation; young stars in the Milky Way; physical and chemical properties of planets orbiting other stars; and objects within our Solar System. - The flight NIRCam is seen in a cleanroom at the Lockheed Martin Advanced Technology Center in Palo Alto, CA where it was designed and built. -- Lockheed Martin, under a contract from the University of Arizona, completed assembly and testing of NIRCam and shipped the instrument to Goddard Space Flight Center in July

14 Near Infrared Spectrograph (NIRSpec) Credit: Eads Astrium Credit: Astrium NIRSpec will study astronomical objects ranging from some of the most distant galaxies, to our Solar System, or planets orbiting around other stars in our own Galaxy. - The flight NIRSpec, shown in July 2011 without its cover, was delivered by the European Space Agency (ESA) to Goddard Space Flight Center in September The instrument underwent testing in Europe before being delivered to ESA by prime contractor Astrium GmbH, located in Ottobrunn, Germany. - NIRSpec is ft in size and weighs 419 lbs

15 Mid Infrared Instrument (MIRI) Credit: Rutherford Appleton Laboratory, MIRI European Consortium and Jet Propulsion Laboratory MIRI is expected to make important contributions to: the discovery of the first light ; assembly of galaxies; how stars and planetary systems form; and evolution of planetary systems and conditions for life. - Installation of the harnesses into the flight MIRI without its cover is shown at the Rutherford Appleton Laboratory in the United Kingdom, where it was assembled. - The flight MIRI arrived at Goddard Space Flight Center in May MIRI is jointly developed by the United States and a nationally funded European Consortium under the auspices of the European Space Agency

16 Fine Guidance Sensor (FGS) Credit: John A. Brebner Communication Research Center The FGS supplies the data to the JWST for fine pointing and attitude stabilization. - The flight FGS is shown undergoing cryogenic testing in July The Near InfraRed Imager and Slitless Spectrograph (NIRISS) are packaged with the guide camera but are functionally independent. -- NIRISS is expected to contribute to all of the JWST science themes. - The flight instrument was delivered to Goddard Space Flight Center in the summer of The Canadian Space Agency provided the FGS/NIRISS to the JWST Project; the prime 16 contractor was Com Dev. 16

17 Sunshield Pathfinder The Sunshield pathfinder folding and deployment trials verified the design concept and deployment techniques. - The pathfinder is one in a series of engineering models built by Northrop Grumman and the JWST team to reduce risk on the program. - The Sunshield membrane material successfully completed Technology Readiness Level-6 17 testing in the relevant operational environment in April

18 Instrument Detectors and Microshutters Detectors JWST needs extraordinarily sensitive detectors to record the faint signals from far-away galaxies, stars, and planets; and it needs large-area detector arrays to efficiently survey the sky. - JWST has extended the state-of-the-art for infrared detectors by producing arrays that have both lower noise and larger format than their predecessors. - It will use two types of detectors: four mega-pixel near infrared mercury-cadmium-telluride detectors for wavelengths microns, and one mega-pixel mid-ir silicon-arsenic detectors for 5-29 microns. - Testing of the mid-ir detectors was completed in July Production of both flight detectors types is underway. Microshutters Micro shutters are a new technology being used on the Near Infrared Spectrograph (NIRSpec) instrument. - NIRSpec is an instrument that will allow scientists to capture the spectra of more than 100 objects at once. -- Because the objects that NIRSpec will be looking at are so far away and so faint, the instrument needs a way to block out the light of nearer bright objects. - The microshutters are arranged in a waffle-like grid that contains over 62,000 shutters. -- The array of microshutters, shown to the right, are about the size of a postage stamp. - The instrument contains four of these waffle-looking grids

19 Optics Testbed The 6.5 meter diameter telescope has a segmented primary mirror that deploys after launch. - To perform like a single monolithic mirror, a wavefront sensing and control subsystem is required to sense and then correct any errors in the optics. Ball Aerospace has engineered a scaled telescope testbed that is traceable to the flight telescope so that wavefront sensing and control could be developed and demonstrated in a highfidelity environment. - The fully functional, 1/6th scale model of the JWST mirror in the optics testbed is shown. The nine distinct alignment processes, or algorithms, needed to align the deployed telescope into a high-performance astronomical telescope were designed and demonstrated on the testbed in

20 MIRI Cryocooler The Mid Infrared Instrument (MIRI) detectors must operate at 7 o Kelvin to detect thermal emissions at wavelengths out to 29 microns. - A high-efficiency pulse-tube cryocooler has been developed to provide this cooling capability. The JWST cryocooler is unique in that it provides cooling remotely. - The cold head is close to the MIRI detectors which are located approximately 66 ft from the cryocooler compressor and electronics. Credit: Northrop Grumman A three year technology demonstration program has proven the remote cooling capability. - Further testing on a breadboard system in 2008 showed that the cooler is capable of cooling the detectors to the required 7 o Kelvin operating temperature

21 Primary Mirror Backplane Assembly Credit: Northrop Grumman The Optical Telescope Element Primary Mirror Backplane Assembly and the Sunshield's Integrated Validation Article are shown mated together in Northrop Grumman's high bay in Space Park, CA in September The simulators were used to check that the actual telescope components will fit properly when 21 installed on the flight unit. 21

22 Spacecraft Bus Mock-Up Integration and test technicians work on a mock-up of the spacecraft bus testing the assembly of its components at Northrop Grumman Aerospace Systems facilities in Redondo Beach, CA in late The spacecraft bus provides the necessary support functions for the operation of the observatory

23 Successful Sunshield Deployment Test Full scale deployment and tensioning of the tennis court-sized five layer sunshield system and inspection of the deployed hardware is shown at Northrop Grumman in Redondo Beach, CA on July 9, The five sunshield test layers were unfolded and separated for the first time in July Northrop Grumman subcontractor NeXolve manufactured the flight sunshield layers in Huntsville, AL. - The five flight layers were delivered to Northrop Grumman in 2016 where testing continued 23 and will be integrated with the entire observatory. 23

24 Integrated Science Instrument Module (ISIM) The flight ISIM structure is shown in the Goddard Space Flight Center, Greenbelt, MD Space Environment Simulator where it was tested for 26 days in The car-sized composite material structure survived temperatures that plunged from room 24 temperature to as low as -411 o F contracting and distorting it as predicted. 24

25 Primary Mirror Segments A NASA engineer looks on as the first six flight ready primary mirror segments are prepared to begin final cryogenic testing at Marshall Space Flight Center, AL in April Engineers are about to began the final cryogenic testing to confirm that the mirrors will respond as expected to the extreme temperatures of space prior to integration into the telescope's support structure. - This represents the first six of 18 segments that forms the primary mirror for space observations

26 Mid Infrared Instrument integrated with ISIM Credit: ESA ISIM MIRI MIRI Pickoff Mirror Location In July 2013, the Mid Infrared Instrument (MIRI) was maneuvered to the Integrated Science Instrument Module (ISIM) where it was attached and integrated. - The event took place in the Space Systems Development and Integration facility cleanroom at Goddard Space Flight Center. - MIRI is wrapped in an aluminized thermal shield to keep it cold and prevent the instrument from picking up false readings when in space due to thermal emissions from the other instruments or from the spacecraft. - The MIRI periscope-like appendage is a pickoff mirror that re-directs the light from the telescope focus onto the MIRI focal plane. -- The MIRI pickoff mirror will fit through the black rectangle in the center of the lower shield

27 PMBS Thermal Vacuum Test Backplane Center Structure Backplane Wing (2X) The Primary Mirror Backplane Support Structure (PMBS) completed testing inside the X-Ray and Cryogenic Test Facility at Marshall Space Flight Center, AL in November The PMBS went through several cycles from room temperature to -400 o F. -- During the testing, 130 diodes attached to the PMBS measured the relative motion of the structure key mounting points. - The PMBS consists of the backplane center structure and two deployable backplane wings to allow the primary mirror to fit within the launch vehicle s payload fairing. -- The structure is composed of advanced graphite composite materials mated to titanium 27 and invar fittings and interfaces. 27

28 Installation of ISIM Science Instruments Complete Credit: ESA NIRSpec Installation of the science instruments into the Integrated Science Instrument Module (ISIM) was completed on March 25, 2014 in the cleanroom at Goddard Space Flight Center and it was readied for the next series of tests. - The last instrument installed, the Near Infrared Spectrometer (NIRSpec), is shown being maneuvered into position on the ISIM. - The Near Infrared Camera, Mid Infrared Instrument and Fine Guidance Sensor were installed 28 in

29 Spacecraft Bus Structure Complete Credit: NG & NASA Manufacturing and assembly of the flight spacecraft bus structure was completed on July 1, 2015 at the Northrop Grumman (NG) facility in Redondo Beach, CA. - The bus structure integrates the system's optical telescope, sunshield, and instrument electronics, and it mounts the observatory to the Ariane 5 rocket. -- The bus must withstand a force equivalent to 45 tons while supporting the observatory during launch. -- In orbit, the bus structure provides pointing and structural stability for the telescope down to one arcsecond. -- The bus structure is made of carbon fiber composites and encloses the spacecraft propulsion, electrical power and the communication systems

30 Optical Telescope Primary Mirror Structure Deploys The Optical Telescope flight structure is shown (left) on a platform in the cleanroom at Goddard Space Flight Center (GSFC) in Greenbelt, MD on August 30, The telescope structure includes the primary mirror backplane assembly; the main backplane support fixture; the deployable tripod secondary mirror support structure and the deployable tower structure that lifts the telescope off the spacecraft. - The two backplane structure side portions or wings are shown in the launch configuration. On November 16, 2015, the two backplane wings successfully completed two deployments (right) inside the GSFC clean room. - The foldable wings are necessary so the observatory can fit into the launch vehicle. - The two wings of the telescope structure will eventually hold six of the eighteen primary mirror segment assemblies. - The wings deploy one at a time and each individual deployment can take up to 16 hours or more to complete

31 Optical Telescope Primary Mirror Revealed On April 27, 2016, the flight optical telescope was shown being assembled at Goddard Space Flight Center s clean room as part of the integration and testing, and the primary mirror was revealed as the mirror covers were lifted. - Once in space, the fully deployed eighteen golden primary mirror segments will work together as one large 21.3 ft (6.5 m) diameter mirror. -- The segments were individually protected with black covers when they were assembled on the telescope. -- Each mirror segment is beryllium to ensure that it is strong and lightweight. -- A very fine film of vaporized gold coats each segment to improve the mirror s reflection of infrared light. -- The mirrors were built by Ball Aerospace and Technologies Corporation from Boulder, CO. --- Ball is the principal subcontractor for the JWST optical technology and optical system design. - A robotic arm was used to install the primary mirror segments onto the telescope structure. -- The installation of the mirrors onto the telescope was performed by Harris Corporation from Rochester, NY. --- Harris leads the integration and testing for the telescope

32 Final Sunshield Layer Complete Credit: Northrop Grumman On September 29, 2016, the fifth and final sunshield layer was delivered to Northrop Grumman Corporation s Space Park facility in Redondo Beach, CA. - Designed by Northrop Grumman, the sunshield prevents the background heat from the sun from interfering with the telescope s infrared sensors. -- The layers work together to reduce the temperatures between the hot and cold sides of the observatory by approximately 570 o F. --- Each successive layer of the sunshield, made of kapton, is cooler than the one below. --- The five sunshield membrane layers, designed and manufactured by the NeXolve Corporation in Huntsville, AL, are each as thin as a human hair

33 Primary Mirror Center of Curvature Test Conducted Interferometer In November 2016, engineers conducted a Center of Curvature test on the telescope s primary mirror in the clean room at Goddard Space Flight Center, Greenbelt, MD. - The test measured the shape of the mirror by comparing light reflected off of it with light from a computer-generated hologram that represented the ideal mirror. -- By interfering the beam of light from the mirror with the beam from the hologram, the interferometer accurately compared the two by measuring the difference to incredible precision. - Making the same optical measurements both before and after simulated launch environment testing and comparing the results is fundamental to assuring that the JWST will work in space. -- These tests simulated the sound and vibration environments the telescope will experience during launch and ascent, and could alter the shape and alignment of the primary mirror, which could degrade or ruin its performance. - After undergoing the environmental tests, the telescope team at Goddard analyzed the results from the post-optical test and compared it to the pre-optical test measurements. -- The team concluded that the mirrors passed the test with the optical system unscathed

34 OTIS Cryogenic Testing Preparation On July 10, 2017, engineers continued to prepare the Optical Telescope Element and Integrated Science (OTIS) for cryogenic testing at Johnson Space Center, TX. - The OTIS cryogenic test will be performed in the largest 15 Kelvin (-433 F) chamber in the world, Chamber A at Johnson Space Center. -- OTIS will be passively cooled to 50 Kelvin (-370 F). - OTIS is shown suspended from the ceiling of Chamber A. -- This hammock is supported by six support rods attached to a platform on which the telescope is sitting. - The telescope is isolated from the vibrations Chamber A could produce once the door closes and testing begins, as well as from disturbances that might occur outside the chamber. - The cryogenic test of OTIS will be crucial in verifying the performance of the JWST

35 JWST Integration and Testing Status (as of July 2017) Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM): - After the ISIM environmental test was completed in February 2016 at Goddard Space Flight Center (GSFC), Greenbelt, MD, the ISIM was installed onto the OTE finishing in March The Optical Telescope Element and Integrated Science (OTIS) environmental tests started in November The GSFC OTIS tests began with functional tests, and then the mechanical test (vibration and acoustic). -- A center of curvature test was successfully conducted on the primary mirror before and after the mechanical test to verify that its shape and alignment did not change. - After the completion of the environmental tests, OTIS was shipped to Johnson Space Flight Center (JSC) in Houston, TX and arrived on May 7, The OTIS cryogenic vacuum test in Chamber A at JSC started on July 13, 2017 to demonstrate the optical performance of the telescope and instruments together. Spacecraft Element (SE): - The last flight Sunshield layer was delivered in September 2016 to Northrop Grumman (NG) in Redondo Beach, CA. -- The Sunshield flight layers were delivered to the to Observatory Integration and Testing in December SE assembly has been delayed to enable the technicians to re-weld transducers into the propulsion system to replace units damaged during testing. - The Sunshield and Spacecraft Integration and Testing is planned to be completed in 2017 at NG. James Webb Space Telescope (JWST) Full Observatory: - Integration of the OTIS and SE into the JWST full observatory is scheduled in 2018 at NG Testing of the JWST full observatory is planned in 2018 at NG. 35

36 Reference Information - Sheet 1 of 2 Images: NASA, John A. Brebner Communication Research Center, Northrop Grumman, Space Telescope Science Institute, Lockheed Martin, Astrium, Rutherford Appleton Laboratory, Mid Infrared Instrument European Consortium, Jet Propulsion Laboratory, European Space Agency Text: Status of the James Webb Space Telescope Integrated Science Instrument Module, Ray Lundquist, NASA GSFC, April 6, JWST status as of April MIRI Cooler System Design Update, M. Petach, Northrop Grumman Aerospace Systems Redondo Beach, CA, Status of MIRI cryocooler Successfully-Completes-Manufacturing-of-Optical-Class-Spacecraft-Structure-for-NASA-s-James-Webb- Space-Telescope.html

37 Reference Information - Sheet 1 of 2 Text (Continued): Lessons Plan, Frank Morring, Jr; Aviation Week and Space Technology; January 18, 2010; Volume 172, Number 3, page 27 - NASA engineers seek servicing tools for future space missions Video: JWST Deployment Animation: End 37 37

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40 Background The 13,700 lb JWST will be launched by an Ariane 5 expendable launch vehicle provided by the European Space Agency into an orbit at the L2 Lagrange point some 940,000 miles from Earth. On orbit, JWST will look far beyond the reach of current telescopes observing objects in the near and mid IR region of the electromagnetic spectrum (radiation with wavelength of microns). NASA s Goddard Space Flight Center, Greenbelt, MD. Goddard is managing JWST with contributions from a number of academic, international and industrial partners. - Northrop Grumman is the prime contractor and is leading the overall system design and integration effort; Ball is developing the JWST telescope, with a special emphasis on the optical elements; ITT is the integration and test lead for the optical telescope. -- The contract was awarded to Northrop Grumman Space Technology in September The Space Telescope Science Institute (STScI) in Baltimore, MD has been selected as the Science and Operations Center for JWST. STScl is responsible for the scientific operation of the telescope and delivery of data products to the astronomical community. Several innovative technologies have been developed for JWST. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals; microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid IR detectors to 7 o Kelvin

41 System Description The JWST is composed of an Optical Telescope Element (OTE), an Integrated Science Instrument Module (ISIM), and a Spacecraft Element (SE). The OTE gathers the light coming from space and supplies it to the science instruments located in the ISIM. - Light is reflected from the primary mirror to the secondary mirror to the science instruments. -- The segmented primary mirror will deploy on orbit, unfolding to approximately 21.3 ft (6.5 m) in diameter. -- The primary mirror will have about six times the light-gathering capabilities of the Hubble Space Telescope. -- The primary mirror is composed of 18 hexagonal segments, each individually controllable to align the primary mirror on orbit and will be sensitive to light from micrometers. - The OTE tertiary mirror and the fine steering mirror are both contained within an OTE subsystem known as the Aft Optics Subsystem. - The Primary Mirror Backplane Assembly (PMBA) and the deployable tripod secondary mirror support structure provides the structural pieces to hold the OTE together. -- The PMBA holds the telescope perfectly stable at cryogenic temperatures during long periods of light collection. --- The carbon composite structure s thermal stability is within 38 nanometer (1.49x10-6 in), where a nanometer is one billionth of a meter or one millionth the diameter of a human hair

42 System Description (Continued) The ISIM, built by Goddard Space Flight Center and international and university partners, contains four science instruments: a near infrared camera, a near infrared multi-object spectrograph, a mid infrared instrument and a tunable filter imager. - The instruments are mounted to the ISIM structure and enclosed by a thermal management system. Spacecraft Element - The SE includes the Sunshield, Spacecraft Bus, and Momentum Trim Flap. - The SE is dominated by a deployable sunshield the size of a tennis court (40 ft by 59 ft) that will allow passive cooling of the telescope and instruments to their cryogenic operating temperatures of around 45 o Kelvin (nearly -400 o F). -- The sunshield consists of five layers of inch thick polymer-based polyimide film, DuPont Kapton E, separated from each other and held in place at the center as well as tensioned by six perimeter booms and perimeter cables. - The Spacecraft Bus provides standard electrical, mechanical, communications, and control devices including the star trackers. A propulsion system provides mid-course correction in transfer trajectory, inserts JWST into its final orbit, and maintains that orbit for up to 10 years of operational lifetime. -- The electrical power required is 2079 watts. - The Momentum Trim Flap is an adjustable appendage that compensates for the JWST center of gravity (CG) uncertainty in space. This allows for more sensitive control of the observatory during pointing maneuvers. -- The flap angle will be selected prior to the last deployment test. The angle will be based upon the estimates of the deployed JWST CG made from the measurement of the stowed observatory CG

43 System Description (Continued) NASA is studying the feasibility of performing emergency servicing operations on the JWST, if the need arises, and, if future, servicing capability becomes available. - The observatory is not designed to be serviceable; astronauts will not be able to replace instruments and subsystem modules as done on the Hubble Space Telescope. -- The JWST is being designed and ground tested to ensure that it deploys and operates reliably in space. -- The distance from Earth to where the telescope will orbit is too far for existing NASA servicing capability to reach. - Hubble Space Telescope engineers at Goddard Space Flight Center are studying servicing tools for future space missions. -- The study will gauge how robotic and human servicing missions can aid several notional missions in low-earth orbit, geostationary orbits, and sun-earth Lagrange points (where JWST will deploy). -- NASA is examining the possibility of adding a lightweight grapple fixture to JWST that would provide a future manned or robotic servicing mission a provision for attachment

44 Integrated Science Instrument Module (ISIM) The ISIM provides structure, environment, control electronics and data handling for the three modular science instruments, Near Infrared Camera, Near Infrared Spectrograph, and Mid Infrared Instrument, as well as the observatory Fine Guidance Sensor. - The ISIM is provided by Goddard Space Flight Center (GSFC). -- In addition to designing the ISIM structure, GSFC provides the ISIM subsystems needed to operate the instruments including: thermal control, control and data handling, and flight software; as well as the remote services unit, electronics compartment, and harness assemblies. - The ISIM thermally stable structure is comprised of carbon fiber/cyanate-ester composite square tubes bonded together using a combination of invar fittings, clips, and specially shaped composite plates joined with a novel adhesive process. -- Invar is a nickel steel alloy notable for its uniquely low changes due to thermal expansion. - The ISIM Electronics Compartment (IEC) contains a number of high power boxes at room temperature on the cold side of the sunshield. -- The IEC has been designed to hold the room temperature electronics boxes in close proximity to the cryogenic telescope and instrument module so it does not have a negative affect on the observatory performance. --- This is made possible through multiple radiative isolators in series, conductive isolation, and directional baffles. - The ISIM is mounted to the OTE Back Plane Support behind the Primary Mirror

45 Spacecraft Bus The Spacecraft Bus provides the necessary support functions for the operation of the JWST observatory. - The bus consists of six major subsystems: -- The Electrical Power Subsystem converts sunlight shining on the solar array panels into the power needed to operate the other subsystems in the bus as well as the science instrument payload. -- The Attitude Control Subsystem senses the orientation of the JWST, maintains the observatory in a stable orbit, and provides the coarse pointing of the JWST to the area in the sky that the science instruments want to observe. -- The Communication Subsystem is the ears and mouth for the observatory. The system receives instructions (commands) from the Operations Control Center (OCC) and sends (transmits) the science and status data to the OCC. -- The Command and Data Handling (C&DH) System is the brain of the spacecraft bus. The system has a computer, the Command Telemetry Processor (CTP) that takes in the commands from the Communications System and directs them to the appropriate recipient. --- The C&DH also has the memory/data storage device for the JWST, the Solid State Recorder (SSR). --- The CTP will control the interaction between the science instruments, the SSR and the Communications System. -- The Propulsion System contains the fuel tanks and the rockets that, when directed by the Attitude Control System, are fired to maintain the orbit. -- The Thermal Control Subsystem maintains the operating temperature of the bus

46 Near Infrared Camera The Near Infrared Camera (NIRCam), provided by the University of Arizona, is an imager with a large field of view and high angular resolution. - The NIRCam covers a wavelength range of micrometers and has ten mercurycadmium-telluride (HgCdTe) detector arrays. -- These are analogous to CCDs found in ordinary digital cameras. - The optical assembly consists of two modules, each imaging a 2.16 x 2.16 arcminutes field of view. - The NIRCam is a science instrument but also an Optical Telescope Element wavefront sensor that provides something similar to instant LASIK vision correction

47 Near Infrared Spectrograph The Near Infrared Spectrograph (NIRSpec) enables scientists to obtain simultaneous spectra of more than 100 objects in a 9-square-arcminute field-of-view. - This instrument provides medium-resolution spectroscopy over a wavelength range of 1-5 micrometers and lower-resolution spectroscopy from micrometers. -- The NIRSpec employs a micro-electromechanical system microshutter array for aperture control, and it has two HgCdTe detector arrays

48 Mid Infrared Instrument The Mid Infrared Instrument (MIRI) is an imager/spectrograph that covers the wavelength range of 5-27 micrometers, with a possible spectrographic coverage up to 29 micrometers. - The MIRI has three Arsenic-doped Silicon (Si:As) detector arrays. - The camera module provides wide-field broadband imagery, and the spectrograph module provides medium-resolution spectroscopy over a smaller field of view compared to the imager. -- The imager field of view is 79 x 113 arcseconds. - The nominal operating temperature for the MIRI is 7 o Kelvin. -- This level of cooling cannot be attained using the passive cooling provided by the Thermal Management Subsystem. --- Instead, there is a two-step process: A Pulse Tube pre-cooler gets the instrument down to 18 o Kelvin; and a Joule-Thomson Loop heat exchanger lowers it down to 7 o Kelvin. -- The cryocooler compressor assembly and control electronics are located in the Spacecraft Bus

49 Fine Guidance Sensor The Fine Guidance Sensor (FGS) is a very broadband guide camera that is incorporated into the cryogenic instrument payload in order to meet the image motion requirements of the JWST. - This sensor is used for both guide star acquisition and fine pointing. - The sensor operates over a wavelength range of 1-5 micrometers and has two HgCdTe detector arrays. - Its field-of-view is sufficient to provide a 95% probability of acquiring a guide star for any valid pointing direction. The FGS Tunable Filter Camera is a wide-field, narrow-band camera that provides imagery over a wavelength range of micrometers, with a gap between 2.6 and 3.1 micrometers, via tunable Fabry-Perot etalons that are configured to illuminate the detector array with a single order of interference at a user-selected wavelength. - The camera has a single HgCdTe detector array