Adaptive Thirty Meter Telescope Sees Progress

Hugh Pickens writes "Caltech and the University of California have been making progress toward the development and construction of the Thirty-Meter Telescope (TMT) with the recent $200 million commitment from the Gordon and Betty Moore Foundation. The core of the TMT Observatory will be a wide-field, alt-az Ritchey-Chretien telescope with a 492 segment, 30 meter diameter primary mirror, a fully active secondary mirror and an articulated tertiary mirror. TMT will be the first ground-based astronomy telescope designed with adaptive optics as an integral system element that will sense atmospheric turbulence in real-time, correct the optical beam of the telescope to remove its effect, and enable true diffraction-limited imaging on the ground. TMT will have 144 times the collecting area of the Hubble Space Telescope and a spatial resolution at near-infrared and longer wavelengths more than ten times better, equivalent to observing above the Earth's atmosphere for many observations at a fraction of the cost of a space-based observatory. TMT will reach further and see more clearly than previous telescopes by a factor of 10 to 100 depending on the observation and will be a fundamental tool for the investigation of large-scale structure in the young universe including the era in which most of the stars and heavy elements were formed."

Re:Sure, they build 30-meter telescopes

[E-Lad]

If you're serious, then I might suggest to you a pair of Fujinon 7x50's.

Some clarification about "adaptive optics"

[pongo000]

Can someone in the know reconcile this statement:

TMT will be the first ground-based astronomy telescope designed with adaptive optics as an integral system element that will sense atmospheric turbulence in real-time, correct the optical beam of the telescope to remove its effect, and enable true diffraction-limited imaging on the ground.

with the adaptive optics capability of the quite beautiful HET [utexas.edu] at McDonald Observatory? I suppose with any number of very specific qualifiers, one could claim to be "first".

What is the difference between the TMT and the HET with regards to "adaptive optics" and being able to negate the effects of atmospheric turbulence in real time (which the HET can do)?

BTW, if you ever have the chance, the McDonald Observatory in Ft. Davis, TX is well worth the trip!

Re:Some clarification about "adaptive optics"

[tomz16]

Can someone in the know reconcile this statement:
What is the difference between the TMT and the HET with regards to "adaptive optics" and being able to negate the effects of atmospheric turbulence in real time (which the HET can do)?

It is all a question of scale. Correcting a 30m telescope is harder than correcting for a 9m telescope (larger pupil = more atmospheric aberration over it = higher resolution requirements on your wavefront sensor, and more degrees of freedom on your deformable mirrors). There is also the question of the level of correction. Neither telescope can correct all turbulence from all conjugates and angles perfectly in realtime. The scale of the residual is what ultimately determines the performance of your system. (In fact, there are a few effects dealing with the angular separation of the laser guide star and the edge of your telescope pupil that make correction for larger telescopes intrinsically more challenging). In short, the adaptive optics required to correct a 30meter telescope are quite a bit "harder" than those required for a 10m telescope, and the technologies being developed for the TMT are really pushing the envelope of current AO technology.

HET doesn't have adaptive optics

[Einer2]

It actually doesn't even have an imager, just spectrographs. The term "adaptive optics" refers specifically to systems where a mirror in the light path deforms at very high rates (50-2000 Hz) to correct atmospheric distortions in the wavefront of the incoming light. TMT will have this, as do the VLT, Keck, Gemini, MMT, and Palomar. TMT is just the first that is being designed from the ground up with AO in mind.

Hobby Eberly is basically a very low-budget version of telescopes like Keck. It has the same mirror size (and therefore the same light collecting ability), but they made several design compromises to knock the cost down from $100 million (for Keck) to about $15 million. Most of these compromises reduce the image quality, so they don't even bother trying. They just mounted a bunch of spectrographs since somebody taking a spectrum of a single object usually doesn't care about the nonplanar focal surface and correspondingly tiny effective field of view.