James Webb Space Telescope Integration & Test. Gregory S. Jones 1 and James M. Marsh 2. Redondo Beach, CA I. Abstract

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1 SPACE Conferences and Exposition September 2016, Long Beach, California AIAA SPACE 2016 ` AIAA James Webb Space Telescope Integration & Test Gregory S. Jones 1 and James M. Marsh 2 1 Northrop Grumman Aerospace Systems, JWST Integration & Test Director, AIAA Senior Member, Redondo Beach, CA NASA Goddard Space Flight Center, Mission Manager, Greenbelt MD I. Abstract This paper describes the element and observatory level Integration & Test () program for the James Webb Space Telescope (JWST). The test flow implemented at each level of assembly is discussed as well as the separation of thermal vacuum testing between the hot and cold zones of the observatory. The current status of JWST elementlevel is included and consists of the Integrated Science Instrument Module (ISIM), the Optical Telescope Element (OTE) and the Spacecraft Element (SCE). Key facilities, test beds, pathfinders, simulators and ground support equipment used to implement the program and reduce risk are also summarized. Keywords: James Webb Space Telescope, JWST, Integration & Test, II. JWST Overview JWST is NASA s next generation space-based observatory and will be the premier space observatory of the next decade. The James Webb mission will assist scientists observation of the formulation of the first stars and galaxies after the Big Bang. It will also study the birth and evolution of exoplanets. The observatory architecture consists of a cold zone with telescope and instruments operating at cryogenic temperatures and a hot zone with the spacecraft bus constantly exposed to the sun. Between the hot and cold zones is the tennis court sized sunshield providing a passive barrier to achieve this extreme temperature differential. Cold Zone The infrared telescope and instruments are constantly shielded from the sun by a five ISIM layer, tennis court sized sunshield while orbiting the L2 Lagrangian point, approximately one million miles from Earth. OTE Arenberg 3 and Atkinson 4 provide additional detail with respect to JWST architecture and design. Northrop Grumman Aerospace Systems (NGAS) is under contract to NASA s Goddard Space Flight Center (GSFC) and leads the James Webb industry team for design and development of the telescope, sunshield and spacecraft as well as final observatory. GSFC is responsible for the ISIM and leads for the assembled ISIM and OTE. Hot Zone Figure 1. JWST Artist Rendering. Sunshield Spacecraft Bus III. JWST Overview The major subassemblies of the fully assembled JWST observatory are defined as follows: OTE/ISIM, referred to as OTIS, consisting of the following: o OTE o ISIM SCE, consisting of the following: o Spacecraft bus 1 Copyright 2016 by the, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.

2 o Sunshield See Figure 2 for the summary level flow. Each of these phases is further detailed in subsequent sections below. Verification of Webb thermal performance by test with the observatory fully assembled is far more challenging than a typical spacecraft design due to the large size of the primary mirror (6.5m diameter) and sunshield (21.2m x 14.6m) and the wide operational temperature gradient from +85C to - 233C. As a result, Webb performs separate thermal vacuum tests of the cold and hot zones of the observatory. Protoflight level environmental tests are performed at the element level and acceptance ISIM OTE Spacecraft Bus Sunshield Figure 2. JWST Summary Flow. level dynamics tests are performed at the observatory level. Simulation of missing interfaces during tests of the lower levels of assembly and testing of various non-flight models provide the data for final analysis and verification of the overall observatory performance. Commonality of test personnel and products across each level of assembly, including test sets, command and telemetry system / database, procedures and automated test scripts provides test consistency across levels of assembly, enables test product reuse and reduces cost and schedule risk. Similarly, mechanical ground support equipment for flight hardware lifting, rotations and deployments provide the same benefit for mechanical operations and testing. Contamination control is another key driver of JWST processes. Typically, telescope optics are installed in an internal enclosure which facilitates isolation from contamination and moisture via a nitrogen gas purge. For JWST, purges are used to protect the instruments. However, the external primary and secondary optics on JWST preclude reliance on typical purging to maintain optical cleanliness. External optic cleanliness can only be maintained through the use of ISO Class 7 facilities (class 10K) and personnel protocols throughout all phases of. At this time ISIM and OTE have successfully completed. Integration of the ISIM and OTE into the OTIS configuration is underway and will be followed by functional and environmental testing. SCE has started with spacecraft equipment panels assembled, spacecraft bus structure delivered and electrical integration in progress. IV. Testbeds & Simulators Testbeds, pathfinders, developmental test articles, mock-ups and simulators are various names applied to non-flight hardware that reduce risk, provide a venue for tests that can t be performed on the flight hardware or simulate flight interfaces that aren t available for a particular flight test. JWST utilizes many articles of this type in addition to the flight program. Key items developed for JWST are described below. OTIS SCE Observatory Ship & Launch Cryo Thermal Vacuum Tests LN2 Thermal Vacuum Test A. Sunshield Scale Model This one-third scale model of a five layer sunshield was built and successfully cryo tested at NGAS to validate thermal modeling and performance at operational temperatures. The reduced size enabled testing in an existing thermal vacuum chamber. Thermal modeling is especially important for JWST since the flight sunshield is not thermally tested in a deployed configuration. 2

3 B. CORE Thermal Test Articles The term CORE is used as these tests are a cryogenic thermal balance test of the observatory s core area thermal control hardware. Two different full scale CORE thermal test articles have been built and tested on JWST, CORE-1 and CORE-2. The core area is the key mechanical and cryogenic interface area between all observatory elements [OTE, spacecraft, sunshield, and ISIM Electronics Compartment (IEC)]. Core area thermal control hardware allows for temperature transition of 300K to ~50 K by attenuating heat from room temperature IEC and spacecraft bus. The majority of parasitic heat reaching OTIS flows through the Core area. The CORE-1 test was performed early on in the program at NGAS. The CORE-1 test article is shown in Figure 3. This test provided successful data and insight to thermal modeling and the projected thermal performance of JWST. As changes to the design and hardware occurred through the design process, it was determined that a second test, CORE-2, was necessary. CORE-2 was performed at GSFC in the Space Simulator (SES) chamber after the final ISIM CV3 test. The successful CORE2 provided updated thermal performance date for the final observatory flight design. C. OTE Pathfinder One of test beds manufactured and used to reduce OTE assembly and optical test risk is the OTE pathfinder. The OTE pathfinder is comprised of a flight like backplane structure, two primary mirror segments and a secondary mirror as shown in Figure 4. The pathfinder provided many demonstration and training opportunities. Assembly of the structure provided the team with the opportunity to ensure all processes and procedures were validated prior to the flight build. Installation of the primary and secondary mirrors demonstrated the installation and alignment of these components in a flight like manner. During the OTE pathfinder build, the team ensured that the metrology processes and algorithms were successfully demonstrated prior to flight. Figure 4. OTE Pathfinder and JSC Chamber A. Figure 3. CORE-1 Cryo Test Article. Once the OTE pathfinder was fully assembled it was transported to Johnson Space Center (JSC) and installed in Chamber A for cryogenic vacuum testing. Chamber A was substantially modified for use on JWST including the addition of helium shrouds and an ISO Class 7 environment for preparations inside and outside the chamber. Two Optical Ground Support Equipment (OGSE) tests were performed to demonstrate optical test equipment and methodologies. The first test, OGSE-1, used the OTE pathfinder and necessary thermal, optical and mechanical Ground Support Equipment (GSE). This test verified optical and thermal performance of the ground support equipment. After OGSE-1, the flight Aft Optics Subsystem (AOS) was installed on the pathfinder along with an ISIM instrument simulator called the Beam Image Analyzer (BIA). A second test, OGSE-2, was performed with the AOS and BIA to transmit light through the OTE pathfinder and AOS, and onto the BIA in a flight-like manner. The test successfully demonstrated the ability to optically test the flight telescope at cryogenic temperatures. After OGSE-2, the flight AOS and BIA were removed for a future Pathfinder Thermal Test to validate flight thermal performance as well as the thermal influence of the GSE. For this thermal test, additional primary mirror simulators, thermal components, Multi-Layer Insulation (MLI) and other simulations of a flight-like thermal environment were 3

4 added. Insulation was not installed for OGSE-1 and -2 since it would slow the temperature transitions and add time to perform those tests. OTE pathfinder provides the opportunity to fully demonstrate and verify the optical ground support equipment, thermal ground support equipment, and the upgraded chamber and facility support equipment prior to the delivery of flight hardware. These demonstrations include not only testing, but also all the complex integration activities that occur during the assembly, transportation and handling of the OTE. D. Sunshield IVA The sunshield IVA, shown in Figure 5, is a full scale development article used to demonstrate the sunshield design. It includes structure, mechanism functionality, and flight-like membranes. This article evolved through multiple iterations of flight design maturity to demonstrate flight functionality and processes for membrane handling, folding and deployments. E. Full Scale Mock Ups Figure 4. Sunshield IVA Membrane Deployment. Full scale models of the OTE and spacecraft bus were developed and used in conjunction with the sunshield IVA to validate methodologies for assembly sequence, accessibility to critical items during all phases of and floor space requirements for various flight and GSE configurations. Lessons learned from these exercises were implemented in the form of changes to the flight design, GSE design and planning. The cleanroom outside of JSC s Chamber A, for example, was sized based on the demonstration of the space required to prepare OTIS for cryo vacuum testing. Figure 5. OTE, Sunshield and Spacecraft Mock-Ups. 4

5 F. Engineering Model Test Bed The Engineering Model Test Bed (EMTB) integrates engineering model electrical units together with flight-like harness and a duplication of the electrical test environment. The EMTB objective is to perform validation of flight software as well as electrical compatibility of observatory electronics. EMTB is a shared resource between systems engineering for flight design objectives as well as for test process demonstration objectives. G. Spacecraft Simulators Various configurations of spacecraft simulators were built by NGAS and delivered to lower levels of assembly to provide a flight-like command and telemetry interface for testing like-you-fly before instruments, ISIM or OTIS are ever mated with the flight spacecraft. Spacecraft simulators used in conjunction with a common command and telemetry system and database at all levels of assembly facilitate re-use of test products at each level of assembly. V. Integrated Science Instrument Module (ISIM) The ISIM structure houses four science instruments: Near-Infrared Camera (NIRCam), Fine Guidance Sensor (FGS), Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI). The structure is enclosed with blanketing and the ISIM Thermal Control System (ITCS) mounted on the Backplane Support Fixture (BSF) of the OTE. The ISIM IEC, which is a separate structure, contains the instrument electronics. The four science instruments were integrated to the ISIM structure individually. The IEC was assembled and integrated separately. In parallel to the ISIM manufacture and integration the SES chamber at GSFC was being prepped for ISIM cryo vacuum (CV) testing. Upgrades to the chamber included a large helium shroud that enabled the payload to reach the required cryogenic temperatures. An Optical telescope Simulator (OSIM) was built and tested. OSIM provided an optical interface to ISIM and allowed for optical testing of ISIM. The overall integration and testing phases of all of the ISIM components were interconnected. Three CV tests were performed and labeled CV1, CV2 and CV3. Protoflight vibration and acoustics tests were performed in addition to Electromagnetic Interference (EMI) / Electromagnetic Compatibility (EMC) testing. The first CV test, CV1 was considered a risk reduction test. The SES along with the OSIM was ready. ISIM was installed with only MIRI and FGS as the other instruments were not ready. CV1 enabled the team to conduct test run procedures to reduce any Figure 6. ISIM Cryo-Vacuum Test. unknown risks of the cryogenic testing. The test was a complete success and the team was able to incorporate lessons learned into the future ISIM test program. After CV1, the remaining instruments, NIRSpec and NIRCam, were installed. The second cryovacuum test, CV2, was performed next. After CV2, protoflight sine vibration and acoustic tests were performed along with EMI/EMC testing. Pre- and post-ambient functional testing was performed for these tests. Ambient metrology was also performed pre- and post-testing to ensure the hardware remained aligned. CV3 was the final phase of ISIM testing. ISIM was successfully performance tested with OSIM in CV3 and then delivered to OTIS for integration onto the OTE. The ISIM and SES chamber are shown in Figure 6. 5

6 VI. Optical Telescope Element (OTE) OTE starts with assembly of the structural subassemblies and deployment mechanisms at NGAS. Flight harnesses and thermal components are installed. Zero-g offloaded deployment tests are performed on the primary mirror wings, secondary mirror support assembly and deployable tower assembly. A rollover fixture is used to orient the structure as required for access for assembly and optimal orientation for deployment tests. The OTE structure is then transported to GSFC for installation of the optics. At GSFC, all 18 primary mirror assemblies are installed and aligned to the OTE structure. The secondary mirror and aft optics assembly are also installed and aligned. The completed OTE assembly, shown in Figure 7, is then ready for integration with the ISIM at the OTIS level of assembly. VII. Integrated Optical Telescope Element and Science Instrument Module (OTIS) The integration of OTIS occurs at Goddard Space Flight Center (GSFC) and is cryogenically tested at JSC. The primary objective of the integration and test program is to successfully deliver a fully tested and verified OTIS that meets all functional requirements and performs as designed when placed on the SCE at NGAS to create the full JWST observatory. The OTIS flow is shown in Figure 8. ISIM OTE Integrate ISIM and OTE Pre- Functional Tests Figure 7. OTE Mounted on Roll-Over Fixture Pre- Deployment Tests & Metrology Protoflight 3-Axis Sine Vibe Protoflight Acoustics Post- Functional Tests Post- Deployment Tests & Metrology Ship to JSC Prepare & Install in Chamber A Cryo-Vacuum Test Ship To NGAS To Observatory Figure 8. OTIS Summary Flow. 6

7 OTIS integration occurs at the Spacecraft Systems Development and Integration Facility (SSDIF) at GSFC. Integration starts with the deliveries of OTE and ISIM as shown in Figure 9. Components of the OTIS integration include the Aft Deployable ISIM Radiator (ADIR), the Fixed ISIM Radiator (FIR), IEC, Thermal Management System (TMS), ISIM, OTE and various other flight elements. To accomplish the integration of all components, specialized GSE was developed. One of the key pieces used is the Ambient OTE Assembly Stand (AOAS). The AOAS holds the flight telescope for the integration of ISIM and various parts of the TMS. A high capacity roll over fixture is used to rotate the payload and is also used for access and integration in various orientations. Specialized lifting tools are utilized for components such as the radiators and the IEC. During the integration phase the team installs non-flight accelerometers that are used for mechanical testing along with thermal diodes that are used for thermal testing. After ambient integration, OTIS is ready for mechanical testing that includes protoflight acoustics and sine vibe testing. Prior to mechanical testing pre environmental system functional testing is performed. A series of mirror and metrology measurements are made and then OTIS is ready for acoustics and sine testing. A specialized In Plant Transporter (IPT) was designed and manufactured to move the flight hardware from the cleanroom to the vibration and acoustics facility. The IPT has a portable clean tent around OTIS that provides the necessary cleanliness required. After protoflight acoustics and sine testing the hardware is returned to the cleanroom. Post Figure 9. ISIM Integration with OTE. environmental system functional tests, deployment tests, and metrology measurements are made. The hardware is then prepped for transportation and transported to JSC. JSC refurbished a large thermal vacuum chamber (Chamber A) and a new cleanroom was built specifically for JWST. Chamber A is a larger thermal vacuum chamber that was originally built and used during the Apollo era. Upgrades include a new nitrogen shroud and nitrogen cooling system. A new helium shroud and compressor were also installed. An airflow management system that provides cleanroom conditions during ambient testing was added. Outside the chamber door, a large cleanroom was built that provides integration and staging areas for all hardware prior to installation into the chamber. Installed in the chamber is specialized mechanical, optical and thermal GSE that has been operated and completely performance verified prior to the installation of the flight OTIS. Upon arrival at JSC, the flight OTIS is removed from the transporter and prepped for installation into the chamber. Preparations include deployments, sensor installation, metrology and ambient functional testing. Once installed into Chamber A, the cryogenic testing of OTIS can begin. In general, the objective of the cryogenic vacuum test is to verify OTIS level requirements in the conditions of the expected flight environment, with emphasis on optical measurements that can be performed in this test configuration. The optical tests will verify OTIS system optical workmanship, and provide optical test data to support integrated telescope modeling used to predict flight optical performance. After the testing in Chamber A, OTIS is then removed from the chamber and prepped for transportation. The hardware is transported to NGAS in Redondo Beach, CA where it will be mated to the SCE to create the JWST observatory. 7

8 VIII. Flight Hardware Transportation Transportation of the major pieces of the OTE Pathfinder, Flight OTE, OTIS and observatory are accomplished by the use of the Space Telescope Transportation Air, Road and Sea (STTARS) shipping container. This specialized container was designed and manufactured specifically for transporting the OTE, OTE pathfinder, OTIS, and observatory. First use of the container with hardware began with the transportation of the OTE pathfinder from GSFC to JSC. The first time STTARS was used with flight hardware occurred during the shipment of the bare OTE backplane structure from NGAS in Redondo Beach, CA to GSFC in Greenbelt, MD. STTARS will also be used to transport OTIS Figure 10. STTARS Unloading from the Air Force C-5C. to JSC in Houston, TX and then back to NGAS in Redondo Beach. Up to this point, all shipments have been on an Air Force C-5C aircraft as shown in Figure 10. After OTIS has been delivered to NGAS, STTARS will be modified with a larger lid to accommodate the size of the observatory. STTARS will then be used to transport the observatory from Redondo Beach to the launch site in French Guiana aboard a large specialized transport ship. The mechanical design of the STTARS transporter incorporates a vibration isolation system to help protect the payload from unexpected shock during moves. An environmental control unit (ECU) is attached to STTARS to provide temperature and humidity control. A second ECU is also brought along as backup in case the primary unit fails. A telemetry monitoring system with data recorder is used during all transportation operations to monitor vibration, temperature and humidity of the payload. SC Panel Integrate Equip on Bus Structure CST-1 EMC IX. Spacecraft Element (SCE) Integrate Sunshield Pre- Deployments Separation Shock Protoflight Acoustics Protoflight 3-Axis Sine Vibe Protoflight TV CST-2 (hot) CST-3 (cold) Post- Deployments To Observatory Figure 11. SCE Summary Flow. SCE is performed at NGAS and consists primarily of the spacecraft bus and sunshield. In addition to the typical spacecraft bus subsystems of power, attitude control, communications, command and data handling, the SCE configuration also includes the MIRI instrument cryo cooler, ISIM data handling unit and OTE / sunshield actuator and motor drive electronics. The objective of SCE is to deliver a fully verified and tested element that meets all functional requirements prior to integration with the OTIS at the start of observatory. The SCE flow is shown in Figure 11. 8

9 SCE integration begins with assembly of thermal components, harness and electronics on two equipment panels. Validated flight software is delivered from EMTB and utilized throughout the remainder of. A complete electrical integration of all bus mounted electronics is performed in this flat sat configuration called Panel, shown in Figure 12. Electrical equipment that will be flight mounted to the bus primary structure is temporarily mounted to a ground support table to enable full flight electrical integration of the entire complement of bus-mounted equipment. Typical electrical system integration issues are discovered during Panel, which is performed independent of the primary structure critical path. In parallel with Panel, the spacecraft bus structure, shown in Figure 13, is delivered to with the propulsion subsystem installed. Thermal components and MIRI cryocooler are first installed. Next, the completed equipment panels are integrated with the bus structure and all bus mounted equipment and harnesses are also flight installed. The equipment panels are electrically mated with all electrical equipment but remain horizontal in a tailgated configuration for access during SCE electrical integration. Major tests during SCE include an initial ambient baseline electrical Comprehensive System Test (CST 1), alignments, ambient deployments, RF compatibility, EMC/EMI, launch vehicle separation shock, acoustics, sine Figure 13. Spacecraft Bus Structure. vibration, thermal vacuum followed by post-environmental functional and deployment testing. ISIM and OTE interfaces are electrically simulated during functional and environmental testing. All environmental tests are performed at protoflight levels and a fully tested and verified SCE is ready for mate with the OTIS in observatory. X. Observatory Figure 12. Spacecraft Panel. Observatory integrates the fully qualified OTIS with the fully qualified SCE. See Figure 14 for the observatory flow. Full electrical and software compatibility across the interface has been previously validated on the EMTB. Also, testing at OTIS and SCE levels utilized high fidelity simulators to validate those interfaces through ambient and protoflight level environmental testing. Observatory consists of ambient functional testing (CST- 4), alignments, and deployment testing to demonstrate the full end-to-end observatory functionality and compatibility both electrically and mechanically. Acceptance level acoustics and sine vibe tests are performed to verify the fully assembled structure and post-environmental functional (CST-5), deployments and mass properties are performed. Finally, the observatory is stowed in launch configuration and prepared for transport to the Ariane 5 launch site in French Guiana. 9

10 OTIS Integrate OTIS and SCE CST-4 Pre- Deployments Separation Shock SCE Acceptance Acoustics Acceptance 3-Axis Sine Vibe CST-5 Post- Deployments Ship & Launch Figure 14. Observatory Summary Flow.. XI. Conclusion JWST is a unique mission with a unique implementation. The large size of the deployed OTE and sunshield combined with extreme temperature difference from the hot to cold zones makes thermal testing of the full observatory impractical. Instead, the cold zone elements are processed through a separate protoflight test program with cryogenic thermal vacuum testing and the hot zone is processed through its own protoflight test program that is analogous to a typical spacecraft flow. Testing of thermal simulators such as the one-third scale sunshield and CORE are used to validate thermal modeling used for the ultimate verification of a deployed observatory and address aspects of the flight system that are not tested in full flight configuration. Many other testbeds and simulators have also been implemented to address cost / schedule risk and interface verification for this one-of-akind mission. References. 3 Arenberg, J., Flynn, J., Cohen, A., Lynch, R. and Cooper, J., Status of the JWST Sunshield and Spacecraft, SPIE Astronomical Telescopes and Instruments, Edinburgh, Scotland, Atkinson, C., Texter, S., Keski-Kuha, R., and Feinberg, L., Status of the JWST Optical Telescope Element, SPIE Conference on Astronomical Telescopes and Instrumentation, Edinburgh, Scotland, Approved for public release; NG dated 8/17/16. 10