Brian M. Sutin

The Orbiting Carbon Observatory instrument optical design

The Orbiting Carbon Observatory (OCO) will measure the distribution of total column carbon dioxide in the Earths atmosphere from an Earth-orbiting satellite. Three high-resolution grating spectrometers measure two CO2 bands centered at 1.61 and 2.06 μm and the oxygen A-band centered at 0.76 μm in the near infrared region of the spectrum. This paper presents the optical design and highlights the critical optical requirements flowed down from the scientific requirements. These requirements necessitate a focal ratio of f/1.9, a spectral resolution of 20,000, and precedence-setting requirements for polarization stability and the instrument line shape function. The solution encompasses three grating spectrometers that are patterned after a simple refractive spectrometer approach consisting of an entrance slit, a two-element collimator, a planar reflection grating, and a two-element camera lens. Each spectrometer shares a common field of view through a single all-reflective telescope. The light is then re-collimated and passed through a relay system, separating the three bands before re-imaging the scene onto each of the spectrometer entrance slits using an all-reflective inverse Newtonian re-imager.

The Orbiting Carbon Observatory instrument: performance of the OCO instrument and plans for the OCO-2 instrument

NASAs Orbiting Carbon Observatory (OCO) was designed to make measurements of carbon dioxide concentrations from space with the precision and accuracy required to identify sources and sinks on regions scales (~1,000 km). Unfortunately, OCO was lost due to a failure of the launch vehicle. Since then, work has started on OCO-2, planned for launch in early 2013. This paper will document the OCO instrument performance and discuss the changes planned for the OCO-2 instrument.

Current development status of the Orbiting Carbon Observatory instrument optical design

The Orbiting Carbon Observatory, OCO, is a NASA Earth System Science Pathfinder (ESSP) mission to measure the distribution of total column carbon dioxide in the earths atmosphere from an earth orbiting satellite. NASA Headquarters confirmed this mission on May 12, 2005. The California Institute of Technologys Jet Propulsion Laboratory is leading the mission. Hamilton Sundstrand is responsible for providing the OCO instrument. Orbital Sciences Corporation is supplying the spacecraft and the launch vehicle. The optical design of the OCO is now in the detail design phase and efforts are focused on the Critical Design Review (CDR) of the instrument to be held in the 4th quarter of this year. OCO will be launched in September of 2008. It will orbit at the head of what is known as the Afternoon Constellation or A-Train (OCO, EOS-Aqua, CloudSat, CALIPSO, PARASOL and EOS-Aura). From a near polar sun synchronous (~1:18 PM equator crossing) orbit, OCO will provide the first space-based measurements of carbon dioxide on a scale and with the accuracy and precision to quantify terrestrial sources and sinks of CO2. The status of the OCO instrument optical design is presented in this paper. The optical bench assembly comprises three cooled grating spectrometers coupled to an all-reflective telescope/relay system. Dichroic beam splitters are used to separate the light from a common telescope into three spectral bands. The three bore-sighted spectrometers allow the total column CO2 absorption path to be corrected for optical path and surface pressure uncertainties, aerosols, and water vapor. The design of the instrument is based on classic flight proven technologies.

Fabrication and assembly integration of the orbiting carbon observatory instrument

Final assembly and integration of the Orbiting Carbon Observatory instrument at the Jet Propulsion Laboratory in Pasadena, California is now complete. The instrument was shipped to Orbital Sciences Corporation in March of this year for integration with the spacecraft. This observatory will measure carbon dioxide and molecular oxygen absorption to retrieve the total column carbon dioxide from a low Earth orbit. An overview of the design-driving science requirements is presented. This paper then reviews some of the key challenges encountered in the development of the sensor. Diffraction grating technology, lens assembly performance assessment, optical bench design for manufacture, optical alignment and other issues specific to scene-coupled high-resolution grating spectrometers for this difficult science retrieval are discussed.

VAMOS: a SmallSat mission concept for remote sensing of Venusian seismic activity from orbit

The apparent youthfulness of Venus’ surface features, given a lack of plate tectonics, is very intriguing; however, longduration seismic observations are essentially impossible given the inhospitable surface of Venus. The Venus Airglow Measurements and Orbiter for Seismicity (VAMOS) mission concept uses the fact that the dense Venusian atmosphere conducts seismic vibrations from the surface to the airglow layer of the ionosphere, as observed on Earth. Similarly, atmospheric gravity waves have been observed by the European Venus Express’s Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument. Such observations would enable VAMOS to determine the crustal structure and ionospheric variability of Venus without approaching the surface or atmosphere. Equipped with an instrument of modest size and mass, the baseline VAMOS spacecraft is designed to fit within an ESPA Grande form factor and travel to Venus predominantly under its own power. Trade studies have been conducted to determine mission architecture robustness to launch and rideshare opportunities. The VAMOS mission concept was studied at JPL as part of the NASA Planetary Science Deep Space SmallSat Studies (PSDS3) program, which has not only produced a viable and exciting mission concept for a Venus SmallSat, but has also examined many issues facing the development of SmallSats for planetary exploration, such as SmallSat solar electric propulsion, autonomy, telecommunications, and resource management that can be applied to various inner solar system mission architectures.

An optical toolbox for astronomical instrumentation

The author has open-sourced a program for optical modeling of astronomical instrumentation. The code allows for optical systems to be described in a programming language. An optical prescription may contain coordinate systems and transformations, arbitrary polynomial aspheric surfaces and complex volumes. Rather than using a plethora of rays to evaluate performance, all the derivatives along a ray are computed by automatic differentiation. By adaptively controlling the patches around each ray, the system can be modeled to a guaranteed known precision. The code currently consists of less than 10,000 lines of C++/stdlib code.

Generalized atmospheric dispersion correctors for Thirty Meter Telescope

The Thirty Meter Telescope (TMT) is unbaffled and has stability requirements tighter than the previous generation of 10- m class telescopes, leading to tougher requirements on atmospheric dispersion correctors (ADCs). Since instruments are internally baffled, ADCs may no longer shift the position of the telescope exit pupil. Designs that control pupil position are explored.

Smoke Detection for the Orion Crew Exploration Vehicle

The Orion Crew Exploration Vehicle (CEV) requires a smoke detector for the detection of particulate smoke products as part of the Fire Detection and Suppression (FDS) system. The smoke detector described in this paper is an adaptation of a mature commercial aircraft design for manned spaceflight. Changes made to the original design include upgrading the materials and electronic to space-qualified parts, and modifying the mechanical design to withstand launch and landing loads. The results of laboratory characterization of the response of the new design to test particles are presented.

Field testing the wide-field-of-view imaging spectrometer(WFIS)

The Wide Field-of-view Imaging Spectrometer (WFIS), a high-performance pushbroom hyperspectral imager designed for atmospheric chemistry and aerosols measurement from an aircraft or satellite, underwent initial field testing in 2004. The results of initial field tests demonstrate the all-reflective instruments imaging performance and the capabilities of data processing algorithms to render hyperspectral image cubes from the field scans. Further processing results in spectral and photographic imagery suitable for identification, analysis, and discrimination of subjects in the images. The field tests also reveal that the WFIS instrument is suited for other applications, including in situ imaging and geological remote sensing.