Technology

The problem

The technology needed to build enormous telescopes requires innovation to:
1) decrease the mirror weight per square meter,
2) provide dynamic mirror "phasing" to allow a large telescope structure that can be much less stiff (and less massive) than conventional structures.

The solution

The Colossus consortium innovates large telescope technology by creating an imaging instrument that can be as large as 80m across while combining elements of "telescope" optics with "interferometer" design.

Several design strategies of such a interferometric telescope systems are proposed and described below:

The Colossus

The Colossus consists of 60 independent off-axis 8m telescopes which effectively merge telescope-interferometry concepts, yielding 74m diameter effective resolution. The primary consists of 60x8m off-axis parabolic primaries (Fig. 1a). The secondary structure is less than 5m in diameter with 60 independent 0.5m optics (Fig. 1b). Thus, every primary is served by its own secondary which bring light into one Gregorian focus (Fig. 1c). Each secondary mirror is illuminated by one primary mirror segment and becomes its steering and phasing element. In this way each beam is combined coherently at the Gregorian focus of the larger, two-axis tracking, primary parent optics without interferometer delay-lines. This optical system achieves the full angular resolution of the parent while efficiently matching the "softness" of the mechanical structure to the atmospheric piston phase fluctuations.

For more detail on the telescope technology see the following publications:

Looking Beyond 30m-class Telescopes: The Colossus Project, Kuhn, J.R., Berdyugina, S.V., Langlois, M., Moretto, G., Harlingten, C., Halliday, D., SPIE Astronomical Telescopes and Instrumentation, 9145, id. 91451G 8 pp. (2014) PDF

New strategies for an extremely large telescope dedicated to extremely high contrast: The Colossus Project, Moretto, G., Kuhn, J.R., Thiebaut, E., Langlois, M., Berdyugina, S.V., Harlingten, C., Halliday, D., SPIE Astronomical Telescopes and Instrumentation, 9145, id. 91451L 9 pp. (2014) PDF

Highly sensitive telescope designs for higher contrast observations, Moretto, G. and Kuhn, J.R., Adv. Opt. Techn. 3(3): 251-264 (2014) PDF

Figure 1. (a) The primary 8m mirrors with a total effective size of 74m. (b) The secondary mirrors within the structure of about 5m. (c) The Gregorian focus of the telescope.




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The ParFAIT

The Partially Filled Aperture Interferometric Telescope (ParFAIT) is another strategy for achieving higher angular resolution at lower construction cost. Similar to the Colossus, its optical configuration combines off-axis paraboloid segments with an ensemble of small elliptical secondary mirrors such that all optical beams share a common Gregorian focus. A 100m ParFAIT with 39 5mx5m mirror segments in a "cross" configuration (Fig. 2ab) can be constructed for about $150M. This system has excellent optical contrast properties and approaches the photometric dynamic range sensitivity of a filled-aperture 100m-class optical system.

For more detail on the telescope technology see the following manuscript:

ParFAIT: Partially Filled Aperture Interferometric Telescope, Kuhn, J.R. (2015) PDF

Figure 2. (a) The 39 ParFAIT primary 5mx5m mirrors in a cross configuration. (b) The Gregorian focus of the ParFAIT.

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(b)