The advent of extremely large telescopes will bring unprecedented light-collecting power and spatial resolution, but it will also lead to a significant increase in the size and complexity of focal-plane instruments. The use of freeform mirrors could drastically reduce the number of components in optical systems. Currently, manufacturing issues limit the common use of freeform mirrors at short wavelengths. This article outlines the use of freeform mirrors in astronomical instruments with a description of two efficient freeform optical systems. A new manufacturing method is presented which seeks to overcome the manufacturing issues through hydroforming of thin polished substrates. A specific design of an active array is detailed, which will compensate for residual manufacturing errors, thermoelastic deformation, and gravity-induced errors during observations. The combined hydroformed mirror and the active array comprise the Freeform Active Mirror Experiment, which will produce an accurate, compact, and stable freeform optics dedicated to visible and near-infrared observations.

Design and development of a freeform active mirror for an astronomy application

32-GHz Ka-band was first considered for deep-space use in 1976. In 1979, 1 GHz of spectrum at 32-GHz Ka-band was allocated for deep space use. Since then NASA's Jet Propulsion Laboratory (JPL) has been developing technologies and architectures necessary to support Ka-band planetary missions. This paper is a survey of JPL's effort. This survey includes a summary of early paper studies done in the 1980's and 1990's, development of the 34-m beam waveguide (BWG) antennas at the deep space network (DSN), and Ka-band experiments on Mars Observer, Mars Global Surveyor, Deep Space 1, Cassini and Mars reconnaissance orbiter spacecraft. The focus of this paper is on the technological and architectural challenges that 32-GHz Ka-band operations have presented throughout this long history. These include challenges presented by the weather and tighter pointing requirements for the spacecraft as well as the need to use multiple data rates during a pass.

The Struggle for Ka-band: NASA's Gradual Move Towards Using 32-GHz Ka-band for Deep Space Missions

Development of very large arrays of small antennas has been proposed as a way to increase the downlink capability of the NASA Deep Space Network (DSN) by tw oo rthree orders of magnitude, thereby enabling greatly increased science data from currently configured missions or enabling new mission concepts. The current concept is for an array of 400 × 12-meter antennas at each of three longitudes. The DSN array will utilize radio astronomy sources for phase calibration and will have wide bandwidth correlation processing for this purpose. JPL currently is building a 3-element interferometer composed of 6-meter antennas to prove the performance and cost of the DSN array. This article describes the radio frequency (RF) design of the 12-meter reflector that will use the same feed and electronics as the 6-meter antenna. The 6-meter antenna utilized Gregorian optics to enable tests with a low-frequency prime focus feed without removing the subreflector. However, for the 12-meter antenna, maximum gain divided by noise temperature (G/T )i s the overriding requirement, and a trade-off study demonstrated that Cassegrain optics is far superior to Gregorian optics for maximum G/T . Hence, the 12-meter antenna utilizes Cassegrain optics.

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Radio Frequency Optics Design of the 12-Meter Antenna for the Array-Based Deep Space Network

The next generation of focal-plane astronomical instruments requires technological breakthroughs to reduce their system
complexity while increasing their scientific performances. Applied to the optical systems, recent studies show that the
use of freeform reflective optics allows competitive compact systems with less optical components. In this context, our
challenge is to supply an active freeform mirror system, using a combination of different active optics techniques. The
optical shape will be provided during the fabrication using the mechanical property of metals to plasticize and will be
coupled with a specific actuator system to compensate for the residual form errors, during the instrument operation
phase. We present in this article the development of an innovative manufacturing process based on cold hydro-forming
method, with the aim to adapt it for VIS/NIR requirements in terms of optical surface quality. It can operate on thin and
flat polished initial substrates. The realization of a first prototype for a 100 mm optical diameter mirror is in progress, to
compare the mechanical behaviours obtained by tests and by Finite Element Analysis (FEA), for different materials.
Then, the formed samples will be characterized optically. The opto-mechanical results will allow a fine tuning of FEA
parameters to optimize the residual form errors obtained through this process. It concerns the microstructure
considerations, the springback effects and the work hardening evolutions of the samples, depending on the initial
substrate properties and the boundary conditions applied. Modeling and tests have started with axi-symmetric spherical
and aspherical shapes and will continue with highly aspherics and freeforms.

Extremely aspheric mirrors: prototype development of an innovative manufacturing process based on active optics

FAME is a four-year project and part of the OPTICON/FP7 program that is aimed at providing a breakthrough component for future compact, wide field, high resolution imagers or spectrographs, based on both Freeform technology, and the flexibility and versatility of active systems. Due to the opening of a new parameter space in optical design, Freeform Optics are a revolution in imaging systems for a broad range of applications from high tech cameras to astronomy, via earth observation systems, drones and defense. Freeform mirrors are defined by a non-rotational symmetry of the surface shape, and the fact that the surface shape cannot be simply described by conicoids extensions, or off-axis conicoids. An extreme freeform surface is a significantly challenging optical surface, especially for UV/VIS/NIR diffraction limited instruments. The aim of the FAME effort is to use an extreme freeform mirror with standard optics in order to propose an integrated system solution for use in future instruments. The work done so far concentrated on identification of compact, fast, widefield optical designs working in the visible, with diffraction limited performance; optimization of the number of required actuators and their layout; the design of an active array to manipulate the face sheet, as well as the actuator design. In this paper we present the status of the demonstrator development, with focus on the different building blocks: an extreme freeform thin face sheet, the active array, a highly controllable thermal actuator array, and the metrology and control system.

FAME: Freeform Active Mirrors Experiment

Development of very large arrays of small antennas has been proposed as a way to increase the downlink capability of the NASA deep space network (DSN) by two or three orders of magnitude thereby enabling greatly increased science data from currently configured missions or enabling new mission concepts. The current concept is for an array of 400/spl times/12-m antennas at each of the three longitudes. The DSN array utilizes radio astronomy sources for phase calibration and has wide bandwidth correlation processing for this purpose. A program is currently underway to develop the technology and prove the performance and cost of a very large DSN array. The program includes a 3-element interferometer to be completed by late 2004. This paper describes the design and development of the low cost 6-meter breadboard antenna to be used as part of the interferometer.

The 6-Meter Breadboard Antenna for the Deep Space Network Large Array

Development of very large arrays of small antennas has been proposed as a way to increase the downlink capability of the NASA deep space network (DSN) by two or three orders of magnitude thereby enabling greatly increased science data from currently configured missions or enabling new mission concepts The current concept is for an array of 400/spl times/12-m antennas at each of the three longitudes The DSN array utilizes radio astronomy sources for phase calibration and has wide bandwidth correlation processing for this purpose A program is currently underway to develop the technology and prove the performance and cost of a very large DSN array The program includes a 3-element interferometer to be completed by late 2004 This paper describes the design and development of the low cost 6-meter breadboard antenna to be used as part of the interferometer

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M. Britcliffe

Papers

The 6-Meter Breadboard Antenna for the Deep Space Network Large Array

The 6-meter breadboard antenna for the deep space network large array