[5.0] 21st-Century Telescopes

v3.0.0 / chapter 5 of 5 / 01 nov 16 / greg goebel

* Thanks to advances in technology, in the 21st century telescopes are reaching heights of size and sophistication that could hardly be imagined a century earlier. The increasing use of computers in telescope design -- not merely for control, but also for data collection and analysis -- has also boosted the utility of small telescopes, with arrays of them used for surveys and specialized observations.

ESO Very Large Telescope (VLT)



* The Keck Telescopes have been a pathfinder for new telescope technologies. They are being followed by other big advanced-technology telescopes elsewhere. One of the most impressive is the European Southern Observatory's (ESO) "Very Large Telescope (VLT)" in the high, dry Atacama Desert in Chile.

The VLT actually consists of four telescopes, which can be used individually or as elements of an optical interferometer array. Each of the telescopes has a thin "wobbly" unitary mirror 8.2 meters in diameter made of ZeroDur, backed by 150 micro-actuators to maintain its figure and provide adaptive optics. The secondary mirror also has adaptive optic modification. Imagery is already excellent because of the clear "seeing" at the site, which is over 2.5 kilometers above sea level, in one of the driest places on Earth.

Each telescope weighs 427 tonnes; uses an alt-azimuth mount riding on a thin film of oil; and is contained in a boxy observatory building. The four telescopes are designated "Unit Telescope 1 (UT1)" through "Unit Telescope 4 (UT4)". The telescopes also have names in the Mapuche native tribal language used in the area: UTI is "Antu (Sun)"; UT2 is "Kueyen (Moon)"; UT3 is "Melipal (Southern Cross)"; and UT4 is "Yepun (Sirius)".

For optical interferometry, tunnels link all four telescopes to a common sensor system, with moveable mirrors on rails adjusting for variations in light path length. The interferometer system also makes use of three small auxiliary moveable telescopes on the site. The interferometer has a minimum angular resolution of 0.001 arc-second, equivalent to a single telescope with an aperture of 132 meters. A VLT official said that "we will, if we wanted to, be able to resolve and photograph Apollo debris left on the Moon."

The VLT project was initiated in 1977 by the ESO, which is a consortium of Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden, and Switzerland. All the technology was tested in a smaller telescope system, the "New Technology Telescope" at La Silla, also in the high deserts of Chile. The complete VLT is now online.

* Another major new telescope now online is the "Large Binocular Telescope (LBT)" or "Bino" at Mount Graham in Arizona, USA, built by a consortium of American, German, and Italian organizations. The LBT mounts two 8.4 meter telescopes set 14.4 meters apart on a huge common alt-azimuth mount. Their combined effective aperture is 11.8 meters.

The borosilicate mirrors were made with spincasting and are supported by 160 actuators. The secondary mirrors are a meter across, only 1.6 millimeters thick, and are made of ZeroDur glass; they are each backed with 672 actuator magnets to provide adaptive optic control. Tertiary mirrors tap off the imagery to a set of instruments, including a wide-angle prime focus camera, an interferometer, and an interferometric camera. The interferometer system gives the telescope the resolving power of a 23-meter telescope.

Large Binocular Telescope

An interesting dynamic balancing system, consisting of six tanks of water with antifreeze, helps the pointing drive system keep the telescope on track. The entire telescope sits on an alt-azimuth mount inside a boxlike enclosure that rotates on a circular track. The LBT was built as an Italian-American collaboration and is also appropriately known as the "Columbus" telescope. It was dedicated in late 2004, though it didn't see "first light" for another year, and then only with one mirror -- though even at that, it was still much more powerful than the Magnum Mirror Telescope.

The telescope went into full operation with both main mirrors in the spring of 2008 -- though with fixed-focus secondary mirrors, the adaptive-optics secondary mirrors proving very hard to get right, a couple of them being broken before they could be installed. One adaptive mirror was installed in 2010, the other installed in 2012, allowing the LBT to come up to full operational capability.



* The Kecks, VLT, and LBT are spectacular instruments, but there are many other new giant telescopes that outmatch the old Hale telescope that are now observing the skies or being built:

* Along with the monster telescopes, new wide-area survey telescopes are being introduced as well. The "Panoramic Survey Telescope And Rapid Response System (PAN-STARRS)" went online in late 2008 on Mauna Kea; it consists of a 1.8 meter wide-field telescope, with a digital imager with 1.4 billion pixels that can take a picture every 30 seconds. The imaging system is smart enough to balance out shifts in the image as it is being taken, providing a crisp image over its entire field of view. The major objective is to find near-Earth asteroids that could possibly hit our planet.

The initial PAN-STARRS telescope was just a demonstrator for the ultimate "PAN-STARRS 4", which was to consist of four such 1.8-meter telescopes. They would independent optical systems, but all steered together, with each telescope slightly skewed from the common boresight to provide a field of view of 3 degrees, six times wider than the full Moon. It has not been decided yet whether the four telescopes will be on a ganged mount or on separate mounts. An intermediate "PAN-STARRS 2" was supposed to have gone into operation in 2014, with PAN-STARRS 4 to follow a few years later. However, the project seems to have run into funding problems, and its status is unclear.

An even more ambitious system, the "Large Synoptic Survey Telescope (LSST)", is also in the works. It will be by far the biggest dedicated survey telescope ever built, with a mirror 8.4 meters across, 1.7 times the diameter of the classic Hale telescope, and a field of view 3.5 degrees wide, capable of imaging a chunk of sky fifty times the area of the full Moon every 20 seconds, using an imaging system with a resolution of 3.2 billion pixels. It will feed imagery data to a data storage and analysis system at a rate of 30 terabytes of data each night. The LSST is being designed and built by a number of US universities and government research organizations. Groundbreaking for the telescope at the existing Cerro Telolo site in Chile was performed in 2009, with construction beginning in 2014 and "first light" to happen in 2019.

* Astronomers are now working on telescopes that will dwarf the VLT. Adaptive optics allows much wider apertures in principle, though as the mirror size increases, the computing requirements for the real-time adaptive optical control systems increase significantly, and will require very fast and powerful processors.

Roger Angel has been influential in the effort to build a "Giant Magellan Telescope (GMT)", which will be an array of seven 8.4-meter spincast mirrors, focused on adaptive-optic secondary mirrors, giving an effective aperture of 25 meters. The GMT is backed by a number of astronomical organizations in the US, Australia, and South Korea, and will be set up at Las Campanas in Chile. Initial funding was granted in 2015, with first light expected in 2024. Work on the GMT is paralleled with an effort to build a "Thirty Meter Telescope (TMT)", driven by Jerry Nelson and similar to a scaled-up Keck telescope, with 492 hexagonal mirror segments controlled by adaptive optics.

Although there were hopes that at least one of these telescopes would be operational before the end of the decade, given a tight funding climate the US National Science Foundation (NSF) said that no money could be provided by the NSF until the next decade, though the NSF wanted to provide modest funds to continue planning. Both the GMT and TMT groups do intend to go ahead anyway and see if enough funding will be available to get the projects off the ground in a few years. Land has been set aside on Mauna Kea for the TMT -- though local protests have posed problems for construction of the telescope. There's been consideration of moving to another site, but it is hard to find one that's even as good.

Even more powerful telescopes are being considered. European astronomers were enthusiastic for a time about building the "Over-Whelmingly Large Telescope (OWL)", with a diameter of 100 meters, featuring a primary mirror made up of 3,048 segments and using adaptive optics. OWL was to be so big that it wouldn't be protected by a dome, instead being an open-air structure that would be covered by four retractable covers when not in use.

ESO Extremely Large Telescope

US telescope makers were impressed with OWL's boldness but not with its practicality, suggesting that it might be a technological step too far that could go badly wrong unless preceded by a less ambitious telescope that could act as "risk reduction" effort. Analysis by a panel concluded that OWL was technically feasible but financially out of bounds, and the conclusion was to develop a smaller instrument -- with the old OWL acronym recast as "Originally Was Larger". Construction is now proceeding with the "European Extremely Large Telescope (E-ELT)" with an aperture of 42 meters and 984 segments. Groundbreaking took place in the spring of 2014 at Cerro Armazones in the Chilean Atacama desert, near the other Chilean ESO sites.



* Modern professional astronomical telescopes have "gone digital", using electronic instrument systems that produce digital data instead of photographic images, computer-controlled alt-azimuth mountings, and adaptive mirror control systems.

With these features, there is no need to actually have anyone on hand to control the telescope; it can operate on its own in a robotic fashion, using lists of targets and observing schedules programmed on a computer control system. The control system software may accept requests provided from remote locations over the internet, set up the schedule, and then send the resulting imagery back to the astronomer who made the request.

A small- or medium-sized robot telescope may be programmed to check a list of variable cosmic objects over and over again, waiting for some sign of activity. If the appearance of the object changes significantly, the computer controlling the telescope can sound an alarm, possibly sending a message to a larger robot telescope for a closer inspection. Computer networking can also be used to link together robot telescopes on different continents, forming a network that can keep a specific cosmic object under near-continuous observation, with the observations pooled in a central database.

SDSS survey telescope

Robot telescopes can also be specifically used to produce digital sky surveys, with the imagery in the survey dumped automatically to a website that astronomers can query at will. Current survey telescopes include the 1-meter "Deep Near Infrared Survey (DENIS)" telescope to scan the southern skies; the 1.3 meter "2 Micron All-Sky Survey (2MASS)" telescope; and the 2.5-meter "Sloan Digital Sky Survey (SDSS)" telescope.

These are relatively modest telescopes, but the British "Visible & Infrared Survey Telescope for Astronomy (VISTA)" telescope has an aperture of 4 meters and a field of view 1.7 degrees wide, nine times the angular size of the full Moon. It is cited at Cerro Paranal, next to the VLT, and saw first light in 2007; it was handed over to the ESO in late 2009.

VISTA telescope

VISTA was joined in 2011 by the "VLA Survey Telescope (VST)", intended to support the VLA with wide-angle imaging to scout out regions of interest. It has a field of view of 1 degree, twice the size of the full Moon, and a 268-megapixel camera named MegaCAM. While it has a mirror with a diameter of "only" 2.6 meters, it is the biggest optical survey telescope in the world.

* Many robot telescopes are small, at the high end of the amateur range, but they range up in capability to telescopes that dwarf the capabilities of, say, the Mount Wilson Telescope, and would have been regarded a century ago as wonders of the world, even without their electronic capabilities.

These powerful "small" telescopes are largely the product of "Telescope Technologies LTD (TTL)" in the UK, established in the late 1990s by astronomers at John Moore University (JMU) in Liverpool and at the Royal Greenwich Observatory (RGO). TTL produces high-quality astronomical telescopes with mirrors two meters or more wide on almost an assembly-line basis, and sells them for a few million dollars each. All the TTL instruments are essentially traditional reflectors, based on a standard design that can be scaled to mirrors of different size as per customer request.

However, although the TTL telescopes do not use adaptive mirror control systems, they are otherwise state of the art. They use an alt-azimuth mounting with an automatic feedback stabilization system, and feature electronic imagers and automated controls.

TTL Liverpool 2-meter telescope

TTL telescopes are now going into operation around the world, one example being the 2-meter "Liverpool" robotic telescope at the La Palma site in the Canary Islands. While the notion that led to TTL was the need of astronomers to have more "eyes" around the world to keep track of the sky, they have also had more interesting uses. The Faulkes Telescope Project, funded by a British astronomer turned software entrepreneur named Peter Faulkes, involves a pair of 2 meter TTL telescopes, one at Mauna Kea and the other at Siding Springs in Australia. The primary users of these two telescopes, either of which are more powerful and capable than any telescope built before the 20th century, are not astronomers, but schoolkids, who get to use them to observe targets of their selection.

Given such relatively low-priced telescopes, however, astronomers shouldn't feel they are being stiffed. There will be plenty of 2 meter instruments available for their use. In the meantime, even larger networks of smaller instruments are being implemented. A group at the University of California at Berkeley has set up a global network of 36 centimeter telescopes, primarily for educational purposes, and sees "hundreds" of telescopes in the network in a decade or two.



* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

* Sources include:

Astronomy enthusiast Bill Arnett also has a very handy little linkslist on new telescopes.

* Revision history:

   v1.0.0 / 01 apr 07 
   v1.0.1 / 01 aug 08 / Review & polish.
   v1.0.2 / 01 may 10 / Review & polish.
   v1.0.3 / 01 jun 10 / Review & polish.
   v1.1.0 / 01 feb 11 / Review & polish.
   v2.0.0 / 01 jan 13 / Split out chapters on space astronomy.
   v2.0.1 / 01 dec 14 / Review & polish.
   v3.0.0 / 01 nov 16 / Split out radio astronomy.