KEYWORDS: Space telescopes, Design and modelling, Telescopes, Observatories, Mirrors, James Webb Space Telescope, Space mirrors, Equipment, Astronomy, Coronagraphy
New development approaches, including launch vehicles and advances in sensors, computing, and software, have lowered the cost of entry into space, and have enabled a revolution in low-cost, high-risk Small Satellite (SmallSat) missions. To bring about a similar transformation in larger space telescopes, it is necessary to reconsider the full paradigm of space observatories. Here we will review the history of space telescope development and cost drivers, and describe an example conceptual design for a low cost 6.5 m optical telescope to enable new science when operated in space at room temperature. It uses a monolithic primary mirror of borosilicate glass, drawing on lessons and tools from decades of experience with ground-based observatories and instruments, as well as flagship space missions. It takes advantage, as do large launch vehicles, of increased computing power and space-worthy commercial electronics in low-cost active predictive control systems to maintain stability. We will describe an approach that incorporates science and trade study results that address driving requirements such as integration and testing costs, reliability, spacecraft jitter, and wavefront stability in this new risk-tolerant “LargeSat” context.
We present a plan to address the calibration needs of the Wide Field Instrument (WFI) on the Wide Field Infrared Space Telescope (WFIRST), for on on-orbit observations and ground testing. The science mission of WFI is based on a combination of large surveys, a Guest Observer program, and a strong archival research program.
The WFIRST Science Requirements Document delineates several data quality and calibration requirements for the Mission. The Calibration Plan aims to be prescriptive and predictive, discussing which observations will be needed and estimating the total time required to carry out such observations. We discuss these requirements from an instrumental perspective, and identify the measurements, observations, and analysis steps needed to achieve the desired calibration and data quality levels, especially in terms of on-orbit observations..
The SCALA system provides a physical flux calibration for the SuperNova Integral Field Spectrograph (SNIFS) mounted to the University of Hawaii 2.2m telescope on Mauna Kea by transferring the flux scale from a NIST- traceable photodiode to SNIFS. This calibration is then applied to CALSPEC standard stars. We thereby remove stellar atmospheric models from the calibration chain. Measurement results for supernova cosmology are directly improved, as systematic uncertainties in the flux calibration limit them. Using the existing SCALA setup we achieved a calibration that agrees with the CALSPEC and Hayes6 systems to within ~4 mmag / 1000 A over a wavelength range from 4500 A to 9000 A. We are now upgrading the SCALA system to reach measurement uncertainties below 0.5 %. To provide the flux references for the new system and to perform tests of the improved components, we have built a laboratory light source enabling measurements with sub-percent uncertainties. The light source provides monochromatic light (FWHM 1.8/3.6 nm) spanning UV to IR, with wavelength accuracy and reproducibility of ≤ 1A. Neutral density filters enable fluxes that induce photodiode currents between fA and µA. A subsystem allows linearity testing for detectors with their readout system. Using a gantry robot, we can measure our detectors’ spatial response and angular acceptance with active areas up to 0.5 m2.
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