Slashdot Mirror
A Ground-Based Scope That Flexes For Better Focus
Steve0987 writes "EE Times Online has an interesting article on a deformable telescope mirror that the University of Arizona has built. It uses 336 magnetic coils to deform the 2 foot secondary mirror and change its shape to compensate for everything from wind blowing against the telescope to atmospheric aberations. It is purported to provide 3 times the resolution of the Hubble telescope. (And you don't have to go into space to fix it."
b4 u think hst is obsolete, note that the adaptive optics can only compensate the waveform deformation in a very narrow field. this is good to study binary stars, quasars, galactic neclei etc which are essentially tiny dots in the sky. hst has no waveform deformation at all, so it can use wide field imaging with full resolution; something which is not yet possible with adaptive optics. also adaptive optics requires that either the object is very bright itself or it has some bright objects very close by. hst has no such limitations.
...same/similar mirror flexing tech they are using for the AirBorneLaser weapon, if I recall correctly.
Wow!
As a person who's spent about 15 years working with closed-loop controls in computer systems, my mind boggles at the thought of the quantity and variety of feedback devices required to pull this off.
Accelerometers and strain transducers for wind forces, ground vibration and thermal effects on structures at the very least (and multitudes of them, all calibrated with respect to their location, etc). What I'm really having trouble with is how they are managing the thermal and atmospheric compensations.
OTOH, this is an acedemic project and the statement "we have the *potential* to get images that are three times sharper than the Hubble" (my emphesis added) from the article doesn't inspire great confidence in what they may *really* have.
Anyway, I'm off to look for answers at this link to the Center for Astronomical Adaptive Optics at the University of Arizona, the folks doing this work.
And that's not sarcasm. I couldn't figure out from the article what's really new and great about this particular telescope. Comparing it to one I've read about, the Starfire:
...winds of up to 30 mph had no effect on the final image. "Closing the feedback loop is something that nobody else in the world has -- feedback enables us to make our adjustments very, very precisely, because of our constant stream of position feedback," said Lloyd-Hart. Wind buffeting is reduced by the telescope's very stiff structure and high-torque motors and by angular acceleration sensors which control fast-steering mirrors designed to optically cancel out wind induced jitter.
this vs. Starfire:
The 40-kHz closed-loop adaptive optics (AO) system adjusted the position of 336 points 941 actuator adaptive optics system on its 640-mm (2.1-foot) 3.5 Meter deformable mirror 550 times per second
"This is the first time that anybody has done adaptive optics with a mirror that is an integral part of the telescope itself" said Lloyd-Hart. Primary mirror has actuators
I'm just a layman who likes reading about telescope technology, but it sure looks like they're making claims of being first when they aren't. Still, the Air Force is funding this, and they have a telescope that can image a basketball at a thousand miles, so there's obviously something good here.
Is it the 550Hz sampling rate? Maybe it's the first one available to civilian astronomers? Does anybody know?
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
Heh, a /. article that covers something I worked on!
> but it sure looks like they're making claims of being first when they aren't.
This *is* a first because the deformable mirror *is* the secondary mirror, which all modern reflecting telescopes have nowadays.
The Starfire Optical Range (SOR) telescope and all other adaptive optic (AO) systems use about 10 to 20 additional reflections between the sky and the detector to do the AO correction - it may be a 3.5 meter telescope, but it's more like a 1 meter telescope in light-gathering power after 20 bounces for light loss are taken into account. The SOR telescope was also optimised for taking high resolution picutres of fast moving objects in low earth orbit *think spy satellites*
The other bonus is that the new system is *excellent* for taking near infra-red pictures of the night sky, and a lot of recent astronomy is driven by a need for a good AO system in this regime (about 1 to 10 microns).
Dr Fish
> Note: I'm a UofA Alum, but their screwup on that mirror deserves mention whenever they do something right...
I'm trying to check my history, but wasn't the Hubble mirror made and tested at Perkin Elmer? I don't remember the U of A being involved with Hubble's mirror. It was an error in the test equipment at Elmer that led to the spherical aberration being put into the mirror...
You may be thinking of the NICMOS camera, which the U of A was involved with, and that had a problem with cryogens boiling off too rapidly, but that was corrected a while ago...
Dr Fish
> on its 640-mm (2.1-foot) 3.5 Meter deformable mirror
You're comparing the wrong things together.
It's not clear in the article, but the Starfire telescope has a PRIMARY mirror diameter of 3.5m, but the Steward telescope has a diameter of 6.5m.
The flexible secondary mirror of the Steward is the 640mm number you've compared with the primary mirror of the starfire telescope.
Hope that clears it up for you!
Dr Fish
"Introduction to Adaptive Optics", ISBN 0-8194-3511-2
"Principles of Adaptive Optics", ISBN 0-12-705902-4
However, better resolution doesn't have to be for imaging. There are a handful of optical interferometer projects (ground and proposed space) that have amazing resolution and are used for very narrow field of view imaging as well as astrometry. In this case, more resolution == better telescope (at least for its intended application). This is why, for instance, NASA has the JWST as well as SIM. Different scopes for different folks.