The geoCARB sensor uses a 4-channel slit-scan infrared imaging spectrometer to measure the absorption spectra of
sunlight reflected from the ground in narrow wavelength regions. The instrument, which is to be hosted on a
geostationary communication satellite, is designed to provide continual monitoring of greenhouse gas over continental
scales, several times per day, with a spatial resolution of a few kilometers. The paper discusses the image navigation and
registration (INR) of the geoCARB optical footprints on to the earth’s surface.
The instrument acquires data in a step and stare mode with 4.08 s stare time and 0.34s step time on 1016 footprints
spaced by 2.7 km at nadir in the NS direction along the slit, which is stepped in 3 km EW increments. Knowledge of the
instrument line of sight is obtained through use of a dual-head star tracker system (STS), high-precision optical encoders
for the scan mirrors, a GPS receiver, and a highly stable common optical bench to which the instrument components, the
scan mirror assembly, and the heads of the STS are kinematically mounted.
While attitude disturbances due to jitter and solar array flex affect spatial resolution, we show that the effect on INR is
negligible. GeoCARB performs a star sighting every 30 minutes to compensate for its diurnal alignment variation
relative to the STS, enabling a 1 sigma INR accuracy of 0.38 and 0.51 km at nadir in the NS and EW directions,
respectively. Coastline identification may be used to improve accuracy by 6%, while an additional 20% improvement is
achievable through identification of systematic errors via extensive post-processing. The paper quantifies all error
sources and describes how each of them affects overall INR accuracy.
The filter wheel assembly (FWA) is an integral and important sub-system of the Near Infrared Camera (NIRCam)
instrument on the James Webb Space Telescope (JWST). The optic elements in each of the four FWA mechanisms on
NIRCam are used to conduct science operations as well as calibration of the NIRCam instrument and the JWST
observatory. The FWA mechanism can position one of 12 different filters in the optical path of the camera and position
one of 12 different pupil optics in the same path. The filters and pupil optics are mounted in two separate wheel
assemblies in the FWA that can be positioned independently to provide the desired optical configuration for imaging.
Along with the rest of the instrument, the FWA operates at cryogenic temperatures and is used for both short and long
wavelength imaging. This paper reviews significant elements of the FWA mechanism design.
Our companion paper ‘Progress in development of Tropospheric Infrared Mapping Spectrometers (TIMS): geostationary greenhouse gas (GHG) application’ describes geoCARB performance and science. Here we describe a geoCARB instrument design study leading to near PDR maturity. It is based on heritage geostationary (AIA and HMI on SDO, SBIRS GEO-1 and upcoming GLM on GOES-R as examples) and other (IRIS and NIRcam) flight instrumentation. Heritage work includes experience and well developed specifications for near a-thermal carbon fiber honeycomb composite optical benches and optical element mounting design forms that utilize a “family” of mounts for nearly any type of optical element. The geoCARB approach utilizes composite optical benches and bipod flexures to kinematically mount optics. Tooling for alignment and staking of all elements is integral to the design and is “removed before flight” for mass minimization. GeoCARB requires a cryogenic region for focal planes and spectrometers but front end optics and main structure are designed to run much warmer. A star tracker is used for geoCARB posteriori geolocation including pseudo-diurnal thermal distortion characterization. It is kinematically mounted by low conductance thermal isolators directly on to the low expansion high stiffness composite bench that defines the master optical surfaces including the scanning mirrors. The thermal load from the camera heads is routed away from the bench heat pipes. Use of kinematic mounting is advantageous for low thermal conduction designs. Honeycomb composites enable the design’s low thermal mechanical distortions.
The geoCARB sensor uses a 4-channel push broom slit-scan infrared imaging grating spectrometer to measure the absorption spectra of sunlight reflected from the ground in narrow wavelength regions. The instrument is designed for flight at geostationary orbit to provide mapping of greenhouse gases over continental scales, several times per day, with a spatial resolution of a few kilometers. The sensor provides multiple daily maps of column-averaged mixing ratios of CO2, CH4, and CO over the regions of interest, which enables flux determination at unprecedented time, space, and accuracy scales. The geoCARB sensor development is based on our experience in successful implementation of advanced space deployed optical instruments for remote sensing. A few recent examples include the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on the geostationary Solar Dynamics Observatory (SDO), the Space Based Infrared System (SBIRS GEO-1) and the Interface Region Imaging Spectrograph (IRIS), along with sensors under development, the Near Infared camera (NIRCam) for James Webb (JWST), and the Global Lightning Mapper (GLM) and Solar UltraViolet Imager (SUVI) for the GOES-R series. The Tropospheric Infrared Mapping Spectrometer (TIMS), developed in part through the NASA Instrument Incubator Program (IIP), provides an important part of the strong technological foundation for geoCARB. The paper discusses subsystem heritage and technology readiness levels for these subsystems. The system level flight technology readiness and methods used to determine this level are presented along with plans to enhance the level.
The Near Infrared Camera (NIRCam) for the James Webb Space Telescope (JWST) has been developed over the last
several years and during the course of development, the team of engineers has overcome several technical difficulties
and discovered many things that could be improved about the design. The instrument employs a Beryllium optical
bench, mounted transmissive and reflective optics, several mechanisms and the electronics to control them. This paper
will discuss some of the technical issues encountered and the lessons learned as a result of them. These issues involve
tapping of threads in and anodic coating of Beryllium, material interfaces within mechanisms, paints and coatings of
metals, mounting of optics and general engineering practice. The issues, root causes and resolutions for problems will
be presented in addition to suggestions and recommendations for future designs.
The near infrared camera (NIRCam) instrument for NASA is one of four science instruments installed into
the integrated science instrument module (ISIM) of the James Webb space telescope (JWST) intended to
conduct scientific observations over a five year mission lifetime. The NIRCam instrument will have a pupil
imaging lens actuator assembly (PIL) to provide a means of imaging the primary mirror for ground testing,
instrument commissioning, and diagnostics which must operate from 293 - 37 Kelvin and be in support of
the usual launch environments.
More refined optic prescriptions and initial PIL vibration test data led to the redesign of the PIL. This paper
discusses the redesign of the lens mounts to accommodate a new optic prescription. This paper also details
the analysis of vibration test data that led to the redesign of a stiffer bearing mount for the PIL flight
mechanism that would ultimately be tested to show appropriate margins for meeting program vibration test
The near infrared camera (NIRCam) is one of four science instruments installed on the integrated science instrument
module (ISIM) of NASA's James Webb Space Telescope (JWST) which is intended to conduct scientific observations
over a five-year mission lifetime. NIRCam's requirements include operation at 37 Kelvin to produce high-resolution
images in two-wave bands encompassing the range from 0.6 to 5 microns. The NIRCam instrument is also required to
provide a means of imaging the primary mirror for ground testing, instrument commissioning, and diagnostics which
have resulted in the development of the pupil imaging lens actuator assembly.
This paper discusses the development of the pupil imaging lens (PIL) assembly, including the driving requirements for
the PIL assembly, and how the design supports these conditions. Some of the design features included in the PIL
assembly are the titanium isothermal optical flexure mounts with multi-axis alignment flexures, a counterbalanced direct
drive rotary actuator, and a fail-safe retraction system with magnetic stowage stop. The paper also discusses how the
PIL assembly was successfully tested to the demanding requirements typical for cryogenic instruments.
More optical engineers are choosing to use Risley prism devices to accomplish alignment and steering of optical
systems. A Risley prism device consists of a pair of rotating wedged optic elements that redirect rays of light by
refraction. By rotating each wedge independently, the originating ray can be steered to a new angle or translated within a
cone respective of the wedge angle and separation of the prism pair. The automated miniature Risley mechanism
(MRM) was designed and tested for space flight where the physical envelope was significantly constrained, only very
low power was available, and a unique power-off hold function was required. The MRM incorporates a prism pair with
a 19 mm clear aperture and 0.75° wedge angle; it performs at 6 rpm (maximum speed) with a beam deflection accuracy
of 25 μrad, and a power-off holding accuracy of 8 μrad within a 64 mm (optic axis) by 58 mm (height & width)
envelope. This paper describes the driving requirements for the MRM and how the MRM assembly was successfully
tested to verify its space flight performance requirements. Some design features included in the MRM assembly are: the
radial titanium isothermal optical flexure mounts, a direct-drive zero-cog motor, a 37 Hz bandwidth closed-loop control
system; a unique inductive position sensing system; and a fail-safe flexure-type brake assembly.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space telescope (JWST) is one of four science instruments to be installed into the integrated science instrument module (ISIM) on JWST for the purpose of conducting scientific observations over a five year mission lifetime. NIRCam is required to operate at 37 Kelvin to produce high resolution images in two-wave bands ranging from 0.6 to5 microns. A relatively recent requirement for the NIRCam instrument is to provide a means of imaging the primary mirror for ground testing, instrument commissioning, and diagnostics throughout the mission. This paper discusses the development of the pupil imaging lens (PIL) assembly. In addition to detailing the driving requirements, this paper briefly covers the mechanism design and delves more deeply into the engineering of the optical design.