Precious cargo: transporting contamination-sensitive instruments and optics

NASA's James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element which contains four science instruments (SI), including a guider. The SIs and guider are mounted to a composite metering structure with outer envelope approximate measurements of 2.2x2.2x1.7m. These SI units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using an Optical telescope element SIMulator (OSIM). OSIM is a high-fidelity, cryogenic JWST simulator that features a ~1.5m diameter powered mirror. The SIs are aligned to the flight structure's coordinate system under ambient, clean room conditions using opto-mechanical metrology and customized interfaces. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors and metrology in six degrees of freedom. SI performance, including focus, pupil shear, pupil roll, boresight, wavefront error, and image quality, is evaluated at the operating temperature using OSIM. This work reports on the as-run ambient assembly and ambient alignment steps for the flight ISIM, including SI interface fixtures and customization and kinematic mount adjustment. The ISIM alignment plan consists of multiple steps to meet the "absolute" alignment requirements of the SIs and OSIM to the flight coordinate system. In this paper, we focus on key aspects of absolute, optical-mechanical alignment. We discuss various metrology and alignment techniques. In addition, we summarize our approach for dealing with and the results of ground-test factors, such as gravity.

The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope consisting of the following elements: (1) Optical telescope element (OTE) (2) Integrated science instrument module (ISIM) (3) Spacecraft (4) Sunshield The Integrated Science Instrument Module (ISIM) consists of the JWST science instruments (NIRCam, MIRI, NIRSpec), a fine guidance sensor (FGS), the ISIM Structure, and thermal and electrical subsystems. JWST's instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, and the instruments and telescope operate at cryogenic temperatures (approximately 35 K for the instruments). The development and validation of a thermal distortion modeling and analysis capability for the JWST ISIM Structure was successfully completed. The modeling and analysis approach was grounded in initial constituent materials testing and benchmarked to test results at the composite bonded joint, subassembly, and fullscale flight hardware levels. Comparison of analysis predictions and test results from this series of incremental cryogenic thermal distortion tests demonstrates that the model validation goals are achieved.

The derivation of contamination control (CC) requirements for the JWST Optical Telescope Element (OTE) was presented at the SPIE conference in 20081. Since then, much work has been done to allocate contamination at each phase of Integration and Test (IandT) and to plan for achieving the allocations. Because JWST is such a large and complicated observatory, plans for meeting the requirements are many and varied. There are primary mirror segments that must be cleaned early and maintained clean; there are four science instruments that each have tight contamination requirements but cannot be cleaned after they are integrated onto the Integrated Science Instrument Module (ISIM) structure; there is the composite ISIM structure that is fragile and must be minimally handled; there are numerous cryo-vacuum tests that must be controlled and monitored in order to minimize molecular contamination during return to ambient; … and more. An overview of plans developed to implement contamination control for JWST optics, instruments, and thermal vacuum testing for JWST will be presented.

This paper describes the construction and application of an integrated optomechanical raytrace model used for optical analysis support of the OTIS cryo-vacuum test of the James Webb Space Telescope (JWST) test campaign. OTIS is the Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM). Four specific applications are described – 1) simulation of ambient over-lighting conditions from clean room luminaires and photogrammetry flashes, 2) PSF image motion predictions in the presence of auto-collimating flat (ACF) actuation, 3) science instrument field illumination (“shadowgrams”) checking for unexpected vignetting, and 4) pupil alignment simulations of the Near Infrared Imager and Slitless Spectrograph (NIRISS).

In late 2015/early 2016, a major cryo-vacuum test was carried out for the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST). This test comprised the final cryo-certification and calibration test of the ISIM, after its ambient environmental test program (vibration, acoustics, EMI/EMC), and before its delivery for integration with the rest of the JWST observatory. Over the 108-day period of the round-the-clock test program, the full complement of ISIM flight instruments, structure, harness radiator, and electronics were put through a comprehensive program of thermal, optical, electrical, and operational tests. The test verified the health and excellent performance of the instruments and ISIM systems, proving the ISIM element’s readiness for integration with the telescope. We report here on the context, goals, setup, execution, and key results for this critical JWST milestone.

This paper describes six advanced cryogenic thermal management devices/subsystems developed by Swales Aerospace for ground/space‐based applications of interest to NASA, DoD, and the commercial sector. The devices/subsystems described herein include the following: (a) a differential thermal expansion cryogenic thermal switch (DTE‐CTSW) constructed with high purity aluminum end‐pieces and an Ultem support rod for the 6 K Mid‐Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST); (b) a quad‐redundant DTE‐CTSW assembly for the 35 K science instruments (NIRCam, NIRSpec, and FGS) mounted on the JWST Integrated Science Instrument Module (ISIM); (c) a cryogenic diode heat pipe (CDHP) thermal switching system using methane as the working fluid for the 100 K CRISM hyperspectral mapping instrument on the Mars Reconnaissance Orbiter (MRO); and (d) three additional devices/subsystems developed during the AFRL‐sponsored CRYOTOOL program, which include a dual DTE‐CTSW/dual cryocooler test bed, a miniaturized neon cryogenic loop heat pipe (mini‐CLHP), and an across gimbal cryogenic thermal transport system (GCTTS). For the first three devices/subsystems mentioned above, this paper describes key aspects of the development efforts including concept definition, design, fabrication, and testing. For the latter three, this paper provides brief overview descriptions as key details are provided in a related paper.This paper describes six advanced cryogenic thermal management devices/subsystems developed by Swales Aerospace for ground/space‐based applications of interest to NASA, DoD, and the commercial sector. The devices/subsystems described herein include the following: (a) a differential thermal expansion cryogenic thermal switch (DTE‐CTSW) constructed with high purity aluminum end‐pieces and an Ultem support rod for the 6 K Mid‐Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST); (b) a quad‐redundant DTE‐CTSW assembly for the 35 K science instruments (NIRCam, NIRSpec, and FGS) mounted on the JWST Integrated Science Instrument Module (ISIM); (c) a cryogenic diode heat pipe (CDHP) thermal switching system using methane as the working fluid for the 100 K CRISM hyperspectral mapping instrument on the Mars Reconnaissance Orbiter (MRO); and (d) three additional devices/subsystems developed during the AFRL‐sponsored CRYOTOOL program, which include a dual DTE‐CTSW/dual cryocooler test bed, a miniaturiz...

The Near Infrared Camera (NIRCam) for NASA's James Webb Space Telescope (JWST) is one of the four science instruments installed into the Integrated Science Instrument Module (ISIM) on JWST intended to conduct scientific observations over a five year mission lifetime. NIRCam's requirements include operation at 32 to 37 K to produce high resolution images in two wave bands encompassing the range from λ = 0.6 to 5.0 microns. In addition NIRCam is used as a metrology instrument for the JWST observatory, providing critical data for alignment of the observatory's multiple-segment 6.3 meter primary mirror. JWST is scheduled for launch and deployment in 2012. This paper is an overview of the NIRCam instrument's optical hardware and performance. Detailed discussions of specific subassemblies will be presented in other papers in the same conference.

The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) is one of the four science instruments to be installed into the Integrated Science Instrument Module (ISIM) on JWST. NIRCam's requirements include operation at 37 Kelvin to produce high-resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition, NIRCam is to be used as a metrology instrument during the JWST observatory commissioning on orbit, during the precise alignment of the observatory's multiple-segment primary mirror. This paper will present the optical analyses performed in the development of the NIRCam optical system. The Compound Reflectance concept to specify coating on optics for ghost image reduction is introduced in this paper.

The James Webb Space Telescope (JWST) is the next of the “Great Observatories”, scheduled to be launched before 2018. Three of the four science instruments are passively cooled to their operational temperature range of 36K to 40K, and the fourth instrument is actively cooled to its operational temperature of approximately 6K. The requirement for multiple thermal zones results in the instruments being thermally connected to five external radiators via individual high purity aluminum heat straps. Thermal-vacuum and thermal balance testing of the flight instruments at the Integrated Science Instrument Module (ISIM) element level will take place within a newly constructed shroud cooled by gaseous helium inside Goddard Space Flight Center’s (GSFC) Space Environment Simulator (SES). The flight external radiators are not available during ISIM-level thermal vacuum/thermal testing, so they will be replaced in test with controllable thermal boundaries with identical physical interfaces to the flight radiators. Those boundaries are provided on specially designed test hardware which measures the heat flow within each of the five heat straps to an accuracy of < 2 mW, which is less than 5% of the minimum predicted heat flow values. This is essential to ISIM thermal model correlation, since the physics of heat flow and temperature changes at these temperatures, coupled with instrumentation limitations, dictates that thermal models are more accurately correlated when temperature data is supplemented by accurate knowledge of heat flows. Devices that measure heat flow in this manner have historically been referred to as “Q-meters”. This paper lists the operational requirements, characteristics, and constraints for the special ISIM Q-meters, and presents the methodology used in their thermal design and evaluation. Factors leading to the selection of the optimal geometry, instrumentation, calibration program, and test usage are presented.

The alignment philosophy of the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) is such that the cryogenic changes in the alignment of the science instruments (SIs) and telescope-related interfaces are captured in an alignment error budget. The SIs are aligned to the structure's coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. The ISIM structure is thermally cycled and temperature-induced mechanical and structural changes are concurrently measured to ensure they are within the predicted boundaries. We report on the ISIM photogrammetry system and its role in the cryogenic verification of the ISIM structure. We describe the cryogenic metrology error budget and the analysis and testing that was performed on the ISIM mockup, a full scale aluminum model of the ISIM structure, to ensure that the system design allows the metrology goals to be met, including measurement repeatability and distortion introduced from the camera canister windows.

The next generation of large space telescopes, including ATLAST, SAFIR, IXO and Generation-X will require the development of key technologies to enable their development at an affordable cost. This includes technologies for the rapid, low cost fabrication of ultra-light weight primary mirror segments, active figure control of primary mirror segments, high speed wavefront sensing and control, highly-packageable and scalable deployment techniques, and active vibration and thermal control for light weight structural elements to supply good pointing stability. In this paper we discuss the current state-of-the-art for these technologies and roadmaps for future development in these areas.

The James Webb Space Telescope (JWST) is the successor to the Hubble Space Telescope. JWST will be an infrared-optimized telescope, with an approximately 6.5 m diameter primary mirror, that is located at the Sun-Earth L2 Lagrange point. Three of JWST’s four science instruments use Teledyne HgCdTe HAWAII-2RG (H2RG) near infrared detector arrays. During 2010, the JWST Project noticed that a few of its 5 μm cutoff H2RG detectors were degrading during room temperature storage, and NASA chartered a “Detector Degradation Failure Review Board” (DD-FRB) to investigate. The DD-FRB determined that the root cause was a design flaw that allowed indium to interdiffuse with the gold contacts and migrate into the HgCdTe detector layer. Fortunately, Teledyne already had an improved design that eliminated this degradation mechanism. During early 2012, the improved H2RG design was qualified for flight and JWST began making additional H2RGs. In this article, we present the two public DD-FRB “Executive Summaries” that: (1) determined the root cause of the detector degradation and (2) defined tests to determine whether the existing detectors are qualified for flight. We supplement these with a brief introduction to H2RG detector arrays, some recent measurements showing that the performance of the improved design meets JWST requirements, and a discussion of how the JWST Project is using cryogenic storage to retard the degradation rate of the existing flight spare H2RGs.

The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Structure is a precision optical metering structure for the JWST science instruments. Optomechanical performance requirements place stringent limits on the allowable thermal distortion of the metering structure between ambient and cryogenic operating temperature (~35 K). This paper focuses on thermal distortion testing and successful verification of performance requirements for the flight ISIM Structure. The ISIM Structure Cryoset Test was completed in Spring 2010 at NASA Goddard Space Flight Center in the Space Environment Simulator Chamber. During the test, the ISIM Structure was thermal cycled twice between ambient and cryogenic (~35 K) temperatures. Photogrammetry was used to measure the Structure in the ambient and cryogenic states for each cycle to assess both cooldown thermal distortion and repeatability. This paper will provide details on the post-processing of the metrology datasets completed to compare measurements with performance requirements.

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop workbench to study aspects of wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing optomechanical testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science &amp;amp; Operations Center. We have developed an optical design that reproduces the physics of JWST’s three-mirror anastigmat using three aspheric lenses; it provides similar image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at HeNe wavelength. A segmented deformable mirror stands in for the segmented primary mirror and allows control of the 18 segments in piston, tip, and tilt, while the secondary can be controlled in tip, tilt and x, y, z position. This will be sufficient to model many commissioning activities, to investigate field dependence and multiple field point sensing &amp;amp; control, to evaluate alternate sensing algorithms, and develop contingency plans. Testbed data will also be usable for cross-checking of the WFS&amp;amp;C Software Subsystem, and for staff training and development during JWST’s five- to ten-year mission.

The James Webb Space Telescope is a large space-based astronomical telescope that will operate at cryogenic temperatures. Because of its size, the telescope must be stowed in an inoperable configuration for launch and remotely reconfigured in space to meet the operational requirements using active Wave Front Sensing and Control (WFSC). Predicting optical performance for the flight system relies on a sequence of incremental tests and analyses that has culminated with the cryogenic vacuum test of the integrated Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) referred to as OTIS. The interplay between the optical budgeting process, test verification results at incrementally increasing levels of integration, use of test validated models, and the WFSC process to produce the final optical performance predictions for final verification by analysis will be presented.