Under the Defense Advanced Research Projects Agency (DARPA) Zenith program, a novel concept has been developed for a self-assembling ferrofluidic ionic liquid mirror (FILM) telescope utilizing a Halbach array of permanent neodymium magnets. The primary mirror will be constructed from two immiscible liquids containing reflective and magnetic nanoparticles (NPs), which will spontaneously phase separate. To maximize reflectivity, minimize wavefront error (WFE), and anchor the reflective layer, the volume of the upper liquid has been minimized. The system is scalable and self-healing and can be deployed without applied acceleration or rotation. The Halbach array overcomes the force of gravity for a ground-based liquid mirror, providing a Kelvin body force potential parallel to the surface of the array. The liquids are held in place and shaped within the mirror by use of the magnetic array, hydrophilic materials, and the high surface tension and high viscosity of the liquid. By tuning the position of the magnet assembly and application of components that tune the effective magnetic field, the liquid surface is forced to adopt the desired optical shape and allows tilting off-axis and slewing with acceptable imaging quality WFE levels.
We report here on the progress of this work in multiple areas including modeling and simulation of the magnetic fluid system optimized for a 0.5 m diameter demonstration mirror and the supporting development of laboratory 0.25 m × 0.25 m flat prototypes of the fluid and magnetic systems. Analytical and finite element models of the ferrofluid and magnetic array have been developed and these results have informed a PDR-level design for a notional build and demonstration of a 0.5 m diameter F/2 spherical mirror with overall root mean squared (RMS) WFE of λ/6 at λ= 550 nm at Zenith which can be slewed to off-zenith pointing angles of up to 10°.
The next generation of space-based mm-wave telescopes, such as JAXA’s LiteBIRD mission, require focal planes with thousands of detectors in order to achieve their science goals. Digital frequency-domain multiplexing (dfmux) techniques allow detector counts to scale without a linear growth in wire harnessing, sub-Kelvin refrigerator loads, and other scaling problems. In this paper, we introduce Technology Readiness Level 5 (TRL5) electronics suitable for biasing and readout of LiteBIRD’s Transition Edge Sensor (TES) bolometers using dfmux techniques. These electronics sit between the spacecraft’s payload computer and the cryogenic focal plane, and provide detector biasing, tuning, and readout interfaces between these detectors and the spacecraft’s on-board storage. We describe the overall architecture of the electronics, including functional decomposition into modules, the numerology and interconnection of these modules, and their internal and external interfaces. We describe performance measurements to date, including power consumption, thermal performance, and mass, volume, and reliability estimates. This paper is a companion piece to a description of the electronics’ on-board Field-Programmable Gate Array (FPGA) firmware.
The Tunable Filter Imager of the James Webb Space Telescope will be based on blocking filters and a tunable Fabry-
Perot etalon with an average resolution of about 100. It will operate in two wavelength bands from 1.6 μm to 2.5 μm and
from 3.1 μm to 4.9 μm at a cryogenic temperature of about 35K. It will respectively be used to study the First Light and
re-ionization of the universe by surveying Lyman-alpha sources and to provide an in-depth study of proto-planetary
systems as well as giant planets of nearby stars.
The Tunable Filter Imager (TFI) is designed to image a sky field of view of 2.2' by 2.2' (magnified to 4.6 deg. x 4.6 deg.
at the etalon). Its tunable etalon has an aperture of 56 mm. It operates at low orders 1 and 3 for the two wavelength bands
which reduces the number of blocking filters to a number of eight. The etalon gap tuning between 2.5 μm and 5.5 μm is
provided by piezoelectric actuators and will be servo controlled by using capacitive displacement sensors.
In this paper, we present the etalon's opto-mechanical design that allows us to achieve the stringent requirements in
terms of resolution over a wide infrared wavelength band, and operation at low gap at cryogenic temperature. Cryogenic
test results will be shared as well.
We present the prototyping results and laboratory characterization of a narrow band Fabry-Perot etalon flight model
which is one of the wavelength selecting elements of the Tunable Filter Imager. The latter is a part of the Fine Guidance
Sensor which represents the Canadian contribution to NASA's James Webb Space Telescope. The unique design of this
etalon provides the JWST observatory with the ability to image at 30 Kelvin, a 2.2'x2.2' portion of its field of view in a
narrow spectral bandwidth of R~100 at any wavelength ranging between 1.6 and 4.9 μm (with a gap in coverage
between 2.5 and 3.2 μm). Extensive testing has resulted in better understanding of the thermal properties of the
piezoelectric transducers used as an actuation system for the etalon gap tuning. Good throughput, spectral resolution and
contrast have been demonstrated for the full wavelength range.
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