The Liverpool Telescope group have been designing astronomical instruments for the LT and other 2-4m class telescopes for a number of years. This paper covers a variety of issues which need to be addressed in order to benefit from the unique advantages of 3D printing. In particular we discuss our experience of designing, building and testing a simple prototype structure that is analagous to a simple reflecting grating spectrograph.
The robotic 2m Liverpool Telescope, based on the Canary island of La Palma, has a diverse instrument suite and a strong track record in time domain science, with highlights including early time photometry and spectra of supernovae, measurements of the polarization of gamma-ray burst afterglows, and high cadence light curves of transiting extrasolar planets. In the next decade the time domain will become an increasingly prominent part of the astronomical agenda with new facilities such as LSST, SKA, CTA and Gaia, and promised detections of astrophysical gravitational wave and neutrino sources opening new windows on the transient universe. To capitalise on this exciting new era we intend to build Liverpool Telescope 2: a new robotic facility on La Palma dedicated to time domain science. The next generation of survey facilities will discover large numbers of new transient sources, but there will be a pressing need for follow-up observations for scientific exploitation, in particular spectroscopic follow-up. Liverpool Telescope 2 will have a 4-metre aperture, enabling optical/infrared spectroscopy of faint objects. Robotic telescopes are capable of rapid reaction to unpredictable phenomena, and for fast-fading transients like gamma-ray burst afterglows. This rapid reaction enables observations which would be impossible on less agile telescopes of much larger aperture. We intend Liverpool Telescope 2 to have a world-leading response time, with the aim that we will be taking data with a few tens of seconds of receipt of a trigger from a ground- or space-based transient detection facility. We outline here our scientific goals and present the results of our preliminary optical design studies.
We report on the first-ever demonstration of grinding and polishing full-size, off-axis aspheric, mirror segments as
prototypes for an extremely large telescope, processed entirely in the final hexagonal shape. We first describe the overall
strategy for controlling form and mid spatial frequencies, at levels in the vicinity of <10nm RMS surface. This relies first
on direct CNC grinding of the base-form of these 1.4m segments, using the Cranfield BoX™ machine. The segments are
then mounted on a custom designed (Optic Glyndwr Optoelectronic Engineering Group) three segment hydraulic
support, and CNC polished on a Zeeko IRP 1600 machine using a variety of custom tooling. We overview the fullaperture
and sub-aperture metrology techniques used to close the process-loop and certify quality, all of which operate
with the segment in-situ on the IRP1600. We then focus on the pristine edge-definition achieved by the combination of
tool-lift and smoothing operations; results never previously demonstrated on full-size pre-cut hexagonal segments.
Finally, the paper discusses the feasibility of scaling the process to deliver 931 segments in seven years, as required for
the E-ELT project.
We describe progress on a novel process-chain being used to produce eight 1.4m hexagonal segments as prototypes for
the European Extremely Large Telescope - a Master Spherical Segment as a reference, and seven aspheric segments. A
new pilot plant integrates a bespoke full-aperture test-tower designed and built by OpTIC Glyndwr, with a Zeeko 1.6m
polishing machine. The process chain starts with aspherising hexagonal segments on the Cranfield BoX™ grinder,
followed by smoothing, corrective-polishing and edge-rectification using the Zeeko CNC platform. The paper describes
the technology and progress, and anticipates how the process-chain is expected to evolve through the seven segments to
increase both process-speed and surface-quality.
The Liverpool Telescope is a 2.0 metre robotic telescope that is operating unattended at the Observatorio del Roque de Los Muchachos, Spain. This paper gives an overview of the design and implementation of the telescope and its instrumentation and presents a snapshot of the current performance during the commissioning process. Science observations are under way, and we give brief highlights from a number of programmes that have been enabled by the robotic nature of the telescope.
The resolution of a conventional telescope is determined by the spatial extent of the collecting surface, usually the primary mirror. Astronomical interferometers achieve increased fine detail by using unit telescopes spaced over large distances to increase the spatial extent. The required wavefront quality places very tight tolerances on the unit telescopes and they should be designed with the prime goal of meeting the wavefront specification. The unit telescope must be optimized for the role of a beam compressor rather than attempting to modify a conventional design.
Two alternative designs that minimize the number of reflections in the telescope will be considered, a crucial feature in obtaining the lowest possible wavefront error and maximizing throughput. The first, a siderostat has fixed imaging optics and a large steerable flat mirror to enable sky tracking. The second, an "Alt-Alt" system consists of two intersecting altitude axes in a "gyroscopic type" structure. A small flat lies at the intersection of the altitude axes to direct the starlight at a constant height and direction out of the telescope. The benefits and limitations of each are shown along with the key design issues that determine the most appropriate unit telescope for implementation in an interferometric telescope.
As the latest generation of large (8 - 10 meter) telescopes are taking their first observations of our expanding universe, a new age of 2.0 m class high performance telescopes is emerging to support them. Telescopes of this aperture can be used as part of an interferometric array to combine their science beams with that of a larger telescope, as with the W. M. Keck and VLT Outrigger Telescopes projects. These telescopes are also used for survey and target acquisition work.