Terrestrial Planet Finder Coronagraph, one of two potential architectures, is described. The telescope is designed to make a visible wavelength survey of the habitable zones of at least thirty stars in search of earth-like planets. The preliminary system requirements, optical parameters, mechanical and thermal design, operations scenario and predicted performance is presented. The 6-meter aperture telescope has a monolithic primary mirror, which along with the secondary tower, are being designed to meet the stringent optical tolerances of the planet-finding mission. Performance predictions include dynamic and thermal finite element analysis of the telescope optics and structure, which are used to make predictions of the optical performance of the system
This paper and oral presentation will describe the technology studies, the testbeds, and the architecture studies that will enhance the understanding and viability of a Terrestrial Planet Finder Coronagraph.
Topics to be described fall in two categories: technology development and coronagraph mission design. The focus of the paper will be explanation of the tasks, their organization and current status.
The Multi-Angle Imaging Spectro-Radiometer is a push-broom instrument using nine cameras to collect data at nine different angles through the atmosphere. The science goals are to monitor global atmospheric particulates, cloud movements, and vegetative changes. The camera optomechanical requirements were: to operate within specification over a temperature range of 0C to 10C; to survive a temperature range of -40 degrees C to 80 degrees C; to survive launch loads and on-orbit radiation; to be non-contaminating both to itself and to other instruments; and to remain aligned through the mission. Each camera has its own lens, detector, and thermal control. The lenses are refractive; thus passive thermal focus compensation and maintaining lens positioning and centering were dominant issues. Because of the number of cameras, modularity was stressed in the design.
A unique, highly automated thermal-vacuum facility for optical testing of lenses and cameras is described. In particular, measurements of MTF, boresight, and geometric image distortion over a large parameter space including wavelength, field of view and temperature will be discussed. Unique aspects of the facility include a 'virtual nodal bench' opto-mechanical metrology system and fiber-optic illumination of mechanical reference features.
The multi-angle imaging spectroradiometer (MISR) instrument is currently under development for flight on the first earth observing system platform, EOS-AM1, to be launched in 1998. The instrument will obtain global multi-angle imagery at nine separate view angles, using a separate charge-coupled-device pushbroom camera at each angle. Images will be obtained at 443, 555, 670, and 865 nm with spatial sampling, selectable in-flight, ranging from 275 m to 2.2 km. Data from the instrument will be used to retrieve the optical properties of tropospheric aerosols over land and ocean, to study the bidirectional reflectance properties of the Earth's surface and clouds, and to measure terrain topography and cloud heights. This paper reviews the MISR science objectives, presents an update to some of the instrument design parameters, and discusses the status of the instrument design and development. Test results from a recently built `brassboard' prototype camera are discussed.
The design of an Earth remote sensing sensor, such as the multi-angle imaging spectroradiometer (MISR), begins with a set of science requirements that determine a set of instrument specifications. It is required that the sensor meet these specifications across the image field, over a range of sensor operating temperatures, and throughout mission life. In addition, data quality must be maintained irrespective of bright objects, such as clouds, within the scene, or out-of-field glint sources. During the design phase of MISR, many refinements to the conceptual design have been made to insure that these performance criteria are met. These design considerations are the focus of this paper. Spectral stability with field angle, scene polarization insensitivity, and UV exposure hardness have, for example, been enabled through a telecentric optical design, a Gaussian shaped filter spectral profile used in conjunction with a Lyot depolarizer, and contamination prevention through consideration of material choices and handling procedures. Spectral, radiometric, and MTF stability of the instrument assures the scientific community that MISR imagery can be used for highly accurate aerosol, bi-directional reflectance distribution function (BRDF), and cloud studies.
A lidar facility has been established at the Jet Propulsion Laboratory- Table Mountain Facility located at an altitude of 2300 m in the San Gabriel Mountains in Southern California. This facility is using the technique of differential absorption lidar to measure atmospheric ozone concentration profiles. Two separate systems are needed to obtain the profile from the ground up to an altitude of 45 to 50 km. A Nd:YAG-based system is described for measurements from the ground up to 1 5 to 20 km altitude, and an excimer-laser-based system for measurements from 15 km
to 45 to 50 km altitude. The systems were designed to make high-precision, long-term measurements to aid in the detection of changes in the atmospheric ozone abundance through participation in the Network of Detection of Stratospheric Change.