from the are-the-questions-about-woodchucks? dept.
Located at the Las Campanas Observatory high in the Andes mountains of northern Chile, GMT [Giant Magellan Telescope] will be the world's largest astronomical telescope. The project is being developed by an international consortium of universities and research institutions in the U.S., Australia, Brazil, and South Korea.
GMT was designed to be a segmented mirror telescope that employs seven of today's largest stiff monolith mirrors as segments. Its six off-axis 8.4-meter segments will surround a central on-axis segment, forming a single optical surface 24.5 meters in diameter with a total collecting area of 368 square meters.
GMT is expected to be operational for many decades, enabling breakthrough science ranging from studies of the first stars and galaxies in the universe to the exploration of extrasolar alien worlds. Shelton believes that GMT has the potential to even revolutionize our understanding of astronomy.
"The GMT is poised to answer some of humanity's biggest questions about the nature of exoplanets and whether we are alone in the universe, about the beginning of the universe to understand the formation and evolution of the galaxies, about the origin of the chemical elements, and how black holes grow. The biggest discoveries that will be made by the GMT, however, will be the unexpected results that revolutionize our understanding of astronomy," Shelton told Astrowatch.net.
They may or may not put Jodie Foster in charge.
(Score: 3, Interesting) by tizan on Tuesday March 14 2017, @05:17PM (3 children)
People should define largest...(size, collecting area, power of photons usefully collected ?)
This is definitely not the largest earth bound astronomical telescope...In shear size lots of the radio astronomy instruments beat it. In collecting area too. Optical interferometers like the VLT etc have a larger physical size in optical . May be it is physically the largest instrument in the optical band single piece instrument....oh wait it has 6 seperate mirrors..darn...its hard to be the largets something these days.
(Score: 2) by c0lo on Tuesday March 14 2017, @09:31PM
Also in the pipeline European Extremely Large Telescope [wikipedia.org] - segmented, primary mirror of 39.3m (vs 24.5m Magellan - the collecting area is roughly 2.6 bigger), with a secondary monolithic mirror 4.2m diameter and a curved [wikipedia.org] tertiary mirror 3.8m in diameter; to provide images 16 times sharper than those from Hubble, will allow the study of the atmospheres [wikipedia.org] of extrasolar planets.
The Comparison [wikipedia.org] section lists the provisional first-light date as 2024 for the E-ETL and 2025 for the Magellan.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 0) by Anonymous Coward on Tuesday March 14 2017, @10:24PM
They mean optical telescope. There are lots of ways to measure a telescope's size - resolving power, field of view, etendue (https://en.wikipedia.org/wiki/Etendue), collecting area, etc.
(Score: 1) by khallow on Wednesday March 15 2017, @06:48AM
People should define largest...
It's collection area of a single optical wavelength telescope.
(Score: 2) by Runaway1956 on Tuesday March 14 2017, @05:35PM (6 children)
They spend all that time, energy, and money building a better telescope - on earth.
How 'bout they design the biggest, bestest, state of the art telescope, and send it into space?
Yeah, it would be damned expensive. The necessity of launching the components into space would require that they be pretty tough, and that they be properly protected from the stress of takeoff. But - the world's biggest and bestest, in space. No light pollution to worry about. No deterioration from the elements. Moisture will never be a problem. No passers-by, on the ground or in the ari. No tourists begging for the opportunity to come inside to admire the equipment. Just a huge telescope, hanging on nothing, at least a few thousand miles from earth. The earth itself will obstruct only a small portion of the sky at any time, compared to most of the sky all the time here on earth. And, it can run 24/7 since there's no sunrise and no sunset.
Then, a meteorite wipes out my dream, right?
(Score: -1, Offtopic) by Anonymous Coward on Tuesday March 14 2017, @05:45PM
Can't. Those thieving Mexicans and towel heads, who certainly aren't migrants (nor is Mexican or towel head a race!), are stealing our space stuff.
(Score: 2) by fishybell on Tuesday March 14 2017, @05:54PM
It's not an either-or situation. They do both, typically (I'm looking at you Hawaii) only time and money restricting.
(Score: 2) by bob_super on Tuesday March 14 2017, @06:03PM
Considering the budget and delays of both Hubble and Webb, and the short lifespan of the latter (if it doesn't blow up on the way), I can understand why the safe bet of the Atacama is the favored choice.
It would make sense to assemble a few telescope modules on the other side of the moon, which gives most of the benefits you want except super-long exposure times (under a couple weeks), though power could be an issue when it's dark for a couple weeks.
(Score: 3, Informative) by takyon on Tuesday March 14 2017, @06:38PM
How many times do we have to mention adaptive optics? It's not a new concept.
https://en.wikipedia.org/wiki/Adaptive_optics [wikipedia.org]
https://en.wikipedia.org/wiki/Giant_Magellan_Telescope [wikipedia.org]
Certain wavelengths penetrate the atmosphere better than others, and thus while a gigantic space telescope would be preferred, the cost/size advantage on the ground combined with the ideal wavelengths and corrective adaptive optics makes the ground telescope superior to the space one, for the moment.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 5, Informative) by khallow on Tuesday March 14 2017, @07:17PM (1 child)
How 'bout they design the biggest, bestest, state of the art telescope, and send it into space?
Because you multiply the cost by at least a factor of ten without getting ten times the science. Let's consider what it would take to put a telescope with a resolving power of a 24.5 meter telescope in orbit. First, just as on Earth, the mirror is too large to launch as a single unit for a couple of reasons. First, it's just too wide to fit in current rockets which typically has a cargo space 3-5 meters wide. Even the propose near future Falcon Heavy would have a maximum fairing size at or below 8 meters and the SLS perhaps 10 to 12 meters.
Second, most of the mass scales roughly as the cube of the radius of the mirror (mirror and tube size in particular). The Hubble telescope massed 11 metric tons (Mt) for a mirror just under a third the size of the GMT (the GMT had an effective light gathering power 10 times as great as the Hubble). So we're looking at roughly a factor of 30 more mass, if we build the telescope in the same manner as Hubble and scale everything up, we're looking at a 300 Mt telescope in orbit. Once again, nothing launches anywhere near that amount. In theory, the SLS will eventually be able to launch around 130 Mt which may work, if enough mass can be trimmed. But a launch of the full vehicle will be at least a decade away from now (if ever) and it'll probably cost the better part of a billion dollars just by itself (I'd wager on the wrong side of a billion dollars, but we'll see).
If we were to somehow break up this telescope and launch it on a fully reusable Falcon Heavy to low Earth orbit (LEO), the cost per kg, just for launch, might be as low as $1000 per kg, which would mean a launch cost of $300 million. For a more realistic $2-3k per kg for a rocket that isn't fully reusable, it's $600-900 million just in launch costs to LEO.
I'll note here that while I haven't discussed any technical details of the space telescope aside from rough guesses about its mass, I have observed that launch costs tend to be a reliable piece of the overall cost, between 5-20% of the overall cost of the mission. The reason I believe this would be consistent even for a completely undetermined space telescope mission is that there is a huge trade off [arxiv.org] between mass and cost at the optimization levels of space science missions. "Low cost" payloads will refer to payloads that have a high portion of their costs in launch costs, up to the 20% figure I mentioned earlier. "High cost payloads" would have far lower portion in launch costs (5-10% for purposes of this post).
If we assume that the space telescope is a low cost payload, then overall cost might be a factor of five higher than the launch costs ($1.5-4.5 billion). I believe here that like the Hubble and James Webb space telescopes, it'll be a high cost payload with cost about a factor of 10-20 more than launch costs. Then of course, overall costs could be much higher, up to $18 billion by my above calculations.
Then if we look at the technical aspects of the space telescope, we're looking at complex assembly and vibration issues. Current telescope design relies strongly on both rigid optics and almost complete elimination of alignment and vibration issues. The more pieces of telescope that you have to assemble, the more complicated that part of the process will be, and the more vibration issues you introduce. And needless to say, we don't have a lot of experience with assembling things in space, much less a telescope with hard tolerance thresholds.
In theory, a crude parabolic-shaped, vibrating sheet of mylar would suffice - as long as you know within a small fraction of a wavelength what the shape of the mirror is at any given moment (and aren't too concerned about any Doppler effects from having the mirror move like that). Then you can computationally apply a transformation filter to the optical output to reverse the effects from deviation from the perfect parabolic shape and get a near optimal image from the system.
To summarize the benefits and costs, you're observing above most of the atmosphere which does help particular with UV and infra red imaging, both which are more strongly absorbed than visual light and have a longer observation day (by about a factor of three or so, depending on weather, etc). And you don't have to deal with light scattering in atmosphere (which is responsible for a variety of headaches including light pollution and stellar scintillation or star twinkling). But you exchange that with the above higher cost problem, a lower lifetime (several working telescopes are a century or older while the Hubble telescope has been active for about 27 years only due to numerous expensive repair missions), and a lack of repair and upgrade options that Earth-side instruments have.
In practice, anything you can do in space, you can do for lower cost on the ground. The workarounds may sound clumsy (such as adaptive optics and building on top of a tall mountain in the Andes range), but it's still vastly cheaper than trying the same thing in space.
(Score: 0) by Anonymous Coward on Tuesday March 14 2017, @10:46PM
If you're willing to wait till it's ready, SpaceX's ITS (previously MCT) may be the most economical choice -- with 12m diameter stages and a maximum diameter of 17m for the intended spaceship, a cargo fairing of 20m might be feasible, and it will lift 300t to LEO in fully reusable (=cheap) mode.
Still, it's a hard sell -- I think it's better, given the state of adaptive optics, to mostly ignore LEO for telescopes, and focus on Earth-based telescopes (and the wavelengths they can observe) for now. Once we have the manufacturing and support capabilities in place, whether that's on the moon's surface, in high orbit, or at lagrange points, we'll be able to can build some truly gargantuan instruments out there.
(Score: 0) by Anonymous Coward on Tuesday March 14 2017, @09:31PM (1 child)
And when it does, you'll have something to write an article about. Of course, our poorly educated modern journalists will be unable to write intelligently about any discoveries from this telescope, so this is probably the best we'll get. At least they used meters instead of school buses to describe distances.
(Score: 2) by c0lo on Wednesday March 15 2017, @12:46AM
Yes, but it will be full of gorgeous "artist impression" images.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by stormwyrm on Wednesday March 15 2017, @02:21AM
I don’t know if such a telescope would be able to see the first stars though. Various estimates of when the first stars formed range from 177 million to 98 million to 44 million years after the Big Bang, which correspond to redshifts of 20, 30, and 50 respectively, which means that even the strong ultraviolet Lyman-α emission line at 121.567 nm we’d expect to see from the first stars would be redshifted to 2,553 nm, 3,769 nm or 6,200 nm, all well within the infrared range. Trying to do infrared astronomy from the surface of the earth is kind of like doing visual astronomy during the day as there’s plenty of other infrared coming from the planet itself at those frequencies too. The other problem is that at these times when the first stars formed the universe was still full of neutral atoms, which are very good at absorbing electromagnetic radiation, particularly visible and UV light which is much of what these stars emit. Those atoms need to be ionised again, as they are today, and that was caused by the first stars themselves, but that process would have taken some 500 to 700 million more years, though there are some places where one might expect reionisation to have occurred sooner. I think we’d need a space-based infrared-capable telescope like the James Webb Space Telescope to even have a chance of seeing them.
This is not to say that the GMT won’t provide plenty of interesting science. It definitely will. It should allow us to measure the rotation curves of very distant galaxies. This important because dark matter models of galaxies predict that the acceleration law [soylentnews.org] recently discovered that galaxies seem to obey will begin to fail the younger the galaxy is [soylentnews.org]. So to those of you who say dark matter isn’t falsifiable, there it is, although the theory already made many potentially falsifiable predictions that were borne out by further observation. It also ought to be able to image exoplanets like Proxima Centauri b, provide a look at other relatively nearby objects at incredible resolution, and who knows what other new and unexpected things it will be able to show us.
Numquam ponenda est pluralitas sine necessitate.