Large aperture telescope technology (LATT) is a design study for a differential lidar (DIAL) system; the main investigation being into suitable methods, technologies and materials for a 4-metre diameter active mirror that can be stowed to fit into a typical launch vehicle (e.g. ROKOT launcher with ∼ 2.1-metre diameter cargo) and can self-deploy – in terms of both leaving the space vehicle and that the mirrors unfold and self-align to the correct optical form within the tolerances specified. The primary mirror requirements are: main wavelength of 935.5 nm, RMS corrected wavefront error of λ/6, optical surface roughness better than 5 nm, areal density of less than 16 kg/m2 and 1-2 mirror shape corrections per orbit. The primary mirror consists of 7 segments - a central hexagonal mirror and 6 square mirror petals which unfold to form the 4-meter diameter aperture. The focus of the UK LATT consortium for this European Space Agency (ESA) funded project is on using lightweighted aluminium or carbon-fibre-composite materials for the mirror substrate in preference to more traditional materials such as glass and ceramics; these materials have a high strength and stiffness to weight ratio, significantly reducing risk of damage due to launch forces and subsequent deployment in orbit.
We present an overview of the design, which includes suitable actuators for wavefront correction, petal deployment mechanisms and lightweight mirror technologies. Preliminary testing results from manufactured lightweight mirror samples will also be summarised.
In the EarthCARE mission the BBR (Broad Band Radiometer) has the role of measuring the net earth radiance (i.e. total reflected-solar and thermally-emitted radiances), from the same earth scene as viewed by the other instruments (aerosol lidar, cloud radar and spectral imager). It does this measurement at 10km scene size and in 3 view angles. It is an imaging radiometer in that it uses micro-bolometer linear-array detector (pushbroom orientation), to over-sample these required scenes, with the samples being binned on-ground to produce the 10km radiance data. For the measurements of total earth radiance, the BBR is based on the heritage of Earth Radiation Budget (ERB) instruments. The ground calibration methods of this type of sensor is technically very similar to other EO instruments that measure in the thermalIR, but with added challenges: (1) The thermal-IR measurement has to have a much wider spectral range than normal thermal-IR channels to cover the whole earth-emission spectrum i.e. ~4 to >50microns; (2) The 2nd channel (reflected solar radiance) must also have a broad response to cover almost the whole solar spectrum, i.e. ~0.3 to 4microns. And this solar channel must be measured on the same radiometric calibration as the thermal channel, which in practice is best done by using the same radiometer for both channels. The radiometer is designed to be very broad-band i.e. 0.3 to 50microns (i.e. more than two decades), to cover both ranges, and a switchable spectral filter (short-pass cutoff at 4μm) is used to separate the channels. The on-ground measurements which are required to link the calibration of these channels will be described. A calibration of absolute responsivity in each of the two bands is needed; in the thermal-IR channel this is by the normal method of using a calibrated blackbody test source, and in the solar channel it is by means of a narrow-band (laser) and a reference radiometer (from NPL). A calibration of relative spectral response is also needed, across this wide range, for the purpose of linking the two channels, and for converting the narrow-band solar channel measurement to broad-band.
The OPTIMOS-EVE instrument proposed for the E-ELT aims to use the maximum field of view available to the E-ELT
in the limit of natural or ground-layer-corrected seeing for high multiplex fibre-fed multi-object spectroscopy in the
visible and near-IR. At the bare nasmyth focus of the telescope, this field corresponds to a focal plane 2.3m in diameter,
with a plate-scale of ~3mm/arcsec. The required positioning accuracy that is implied by seeing limited performance at
this plate-scale brings the system into the range of performances of commercial off-the-shelf robots that are commonly
used in industrial manufacturing processes. The cost-benefits that may be realized through such an approach must be
offset against the robot performance, and the ease with which a useful software system can be implemented. We
therefore investigate whether the use of such a system is indeed feasible for OPTIMOS-EVE, and the possibilities of
extending this approach to other instruments that are currently in the planning stage.
OPTIMOS-EVE (OPTical Infrared Multi Object Spectrograph - Extreme Visual Explorer) is the fibre fed multi object
spectrograph proposed for the European Extremely Large Telescope (E-ELT), planned to be operational in 2018 at Cerro
Armazones (Chile). It is designed to provide a spectral resolution of 6000, 18000 or 30000, at wavelengths from 370 nm
to 1.7 μm, combined with a high multiplex (>200) and a large spectral coverage. Additionally medium and large IFUs
are available. The system consists of three main modules: a fibre positioning system, fibres and a spectrograph.
The recently finished OPTIMOS-EVE Phase-A study, carried out within the framework of the ESO E-ELT
instrumentation studies, has been performed by an international consortium consisting of institutes from France,
Netherlands, United Kingdom and Italy. All three main science themes of the E-ELT are covered by this instrument:
Planets and Stars; Stars and Galaxies; Galaxies and Cosmology.
This paper gives an overview of the OPTIMOS-EVE project, describing the science cases, top level requirements, the
overall technical concept and the project management approach. It includes a description of the consortium, highlights of
the science drivers and resulting science requirements, an overview of the instrument design and telescope interfaces, the
operational concept, expected performance, work breakdown and management structure for the construction of the
instrument, cost and schedule.
VISTA was designed as a survey facility, and was optimized for use with the 64Mpix VISTA IR Camera in the sense
that the optical system of the instrument and telescope was designed as a single entity. The commissioning of the IR
camera therefore formed a major part of the system integration and commissioning of the whole VISTA system. We
describe some aspects of the commissioning process for VISTA, the interplay between the camera and telescope
systems, and summarize the results of the verification phase.
We describe the integration and test phase of the construction of the VISTA Infrared Camera, a 64 Megapixel, 1.65 degree field of view 0.9-2.4 micron camera which will soon be operating at the cassegrain focus of the 4m VISTA telescope. The camera incorporates sixteen IR detectors and six CCD detectors which are used to provide autoguiding and wavefront sensing information to the VISTA telescope control system.
The VISTA IR Camera has now completed its detailed design phase and is on schedule for delivery to ESO’s Cerro Paranal Observatory in 2006. The camera consists of 16 Raytheon VIRGO 2048x2048 HgCdTe arrays in a sparse focal plane sampling a 1.65 degree field of view. A 1.4m diameter filter wheel provides slots for 7 distinct science filters, each comprising 16 individual filter panes. The camera also provides autoguiding and curvature sensing information for the VISTA telescope, and relies on tight tolerancing to meet the demanding requirements of the f/1 telescope design. The VISTA IR camera is unusual in that it contains no cold pupil-stop, but rather relies on a series of nested cold baffles to constrain the light reaching the focal plane to the science beam. In this paper we present a complete overview of the status of the final IR Camera design, its interaction with the VISTA telescope, and a summary of the predicted performance of the system.
The infrared camera for the Visible and Infrared Survey Telescope for Astronomy (VISTA) sets many technical challenges for mechanical and thermal design. The flexion between optical subsystems must be minimised to maintain alignment in various camera orientations and meet performance requirements. Thermally induced stresses, atmospheric pressure and earthquake loads place high demands on structural components, some of which must also thermally isolate the cold (~70 K) detectors and optics. The success of the design hinges on the optimisation of heat flow to minimise thermal loads on the detectors whilst holding external temperatures very close to ambient to reduce misting and convective disturbances in the field of view.
This paper describes the mechanical and thermal components of the design and discusses the analyses in detail.
As detailed instrument design progresses, judgements have to be made as to what changes to allow and when models such as thermal, stray-light and mechanical structure analysis have to be re-run. Starting from a well-founded preliminary design, and using good engineering design when incorporating changes, the design detailing and re-run of the models should bring no surprises. Nevertheless there are issues for maintaining the design and model configuration to a reasonably concurrent level. Using modern modeling software packages and foresight in setting up the models the process is made efficient, but at the same time the level of detail and number of cases now needed for instrument reviews is also large in order to minimise risks.
We describe examples from the detailed instrument design of the VISTA IR Camera to illustrate these aspects and outline the design and analysis methods used.