Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity.The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visiblewavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.
The need for JWST's metering structure to be stable over time while at cryogenic temperatures is derived from its scientific objectives. The operational scenario planned for JWST provides for the optical system to be adjusted on regular intervals based upon image quality measurements. There can only be a limited amount of optical degradation between the optical system adjustments in order to meet the scientific objectives. As the JWST primary mirror is segmented, the structure supporting the mirror segments must be very stable to preclude degradation of the optical quality. The design, development and, ultimately, the verification of that supporting structure's stability rely on the availability of analysis tools that are credibly capable of accurately estimating the response of a large structure in cryogenic environments to the nanometer level. Validating the accuracy of the analysis tools was a significant technology demonstration accomplishment. As the culmination of a series of development efforts, a thermal stability test was performed on the Backplane Stability Test Article (BSTA), demonstrating TRL-6 status for the design, analysis, and testing of Large Precision Cryogenic Structures. This paper describes the incremental development efforts and the test results that were generated as part of the BSTA testing and the associated TRL-6 demonstration.
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