|
|
|
|
Atacama Large Millimeter Array
|
| |
|
| |
The Atacama Large Millimeter/submillimeter Array (ALMA) is an international astronomy project that consists of an astronomical interferometer formed from an array of radio telescopes, located at Llano de Chajnantor Observatory in the Atacama desert in northern Chile. The telescope is expected to revolutionize modern astronomy by providing an insight on star formation in the early universe and imaging local star and planet formation in great detail. With a cost in excess of one billion US dollars, it is the most ambitious ground-based telescope currently under construction.
telescopes and their receivers are capable of detecting sub-millimeter and millimeter wavelengths.
Discussion
Ask a question about 'Atacama Large Millimeter Array' Start a new discussion about 'Atacama Large Millimeter Array' Answer questions from other users |
Encyclopedia
The Atacama Large Millimeter/submillimeter Array (ALMA) is an international astronomy project that consists of an astronomical interferometer formed from an array of radio telescopes, located at Llano de Chajnantor Observatory in the Atacama desert in northern Chile. The telescope is expected to revolutionize modern astronomy by providing an insight on star formation in the early universe and imaging local star and planet formation in great detail. With a cost in excess of one billion US dollars, it is the most ambitious ground-based telescope currently under construction.
Overview
The telescopes and their receivers are capable of detecting sub-millimeter and millimeter wavelengths. The array will have much higher sensitivity and higher resolution than existing sub-millimeter telescopes such as the single-dish James Clerk Maxwell Telescope or existing interferometer networks such as the Submillimeter Array or the IRAM Plateau de Bure facility. By moving the antennas at regular intervals, the resolution of the array and the size of object that can be imaged will be altered, producing a "zoom-lens" capability, similar to that employed at the VLA site in New Mexico. The high sensitivity is mainly achieved through the large numbers of telescopes that will make up the array. While 64 x 12 m dishes were originally envisaged, it is now possible that there will ultimately only be 50. The American and European partners have each placed orders for 25 antennas, with options for an additional seven. Japan is also contributing antennas in the form of the Atacama Compact Array (ACA) which will also be located at the ALMA site. By using smaller antennas than ALMA (12 x 7 m and 4 x 12 m dishes are planned) larger fields of view can be imaged at a given frequency. The ability to move them closer together also results in the possibility to image sources of larger angular extent. The ACA will work together with ALMA in order to enhance the latter's wide-field imaging capability.
Controversy
The original plan was for the project to employ a single antenna design. The intent of testing the three prototype antennas was to compete the designs to down-select (choose the best). Three factors conspired to alter the plan:
- The size of the antenna production contract is substantial.
- It was politically expedient (or necessary) for each of the major partners to realize some non-scientific, economic return on their investment (see realpolitik).
- No arrangement was found to break up the antenna production into parts that could be parceled to the partners.
The evaluation of the prototypes yielded each partner finding technical justification to favor their own prototype. Since there was no clear winner, the plan was changed to allow different antenna designs. Each partner is now funding production of a portion of the antennas via associated contractors. This is a workable solution which allows the project to complete without any significant descope (erosion) of the science capabilities. The disadvantages with this solution are:
- The complexity of combining the electronic signals from different antenna designs is significantly increased.
- The overall costs of funding multiple contractors with smaller contracts increases (see Economies of Scale).
- The additional overhead of integrating different antenna designs and managing multiple contractors likely results in an overall schedule delay.
A positive result of the new plan is some reduction of risks. Because some productive science can be accomplished with partial completion of the array, both technical and schedule risks are reduced.
Funding
ALMA was initially a 50-50 collaboration between ESO and the North American partners. The array has been extended with the help of the new Japanese, Taiwanese, Spanish and Chilean partners. ALMA is the largest and most expensive ground-based astronomical project currently under construction (current cost estimate is US$1.3 billion).
Partners
Assembly
The complex will be built primarily by European, U.S., Japanese and Canadian companies (including General Dynamics) and universities. Three prototype antennas have undergone evaluation at the Very Large Array site in New Mexico since 2002. General Dynamics C4 Systems signed a contract with Associated Universities, Inc. to provide 25 to 32 12m antennas Alcatel Alenia Space, a consortium of manufacturers from France, Italy, and Germany, has been signed up to provide 25 of the antennas, the largest-ever European industrial contract. The first antenna will be delivered in 2007, and the rest at about one per month, finishing in 2011.
Transporting antennas to the site
Transporting the 115 tonne antennas from the base camp at 2900 m altitude to the site at 5000 m presents enormous problems. The solution chosen is to use two custom 28-wheel self-loading heavy haulers. The vehicles are made by in Germany and each is 10 m wide, 20 m long and 6 m high, weighing 130 tonnes. They are powered by twin 500 kW diesel engines. The transporters, which feature a driver's seat designed to accommodate an oxygen tank to aid breathing the thin high-altitude air, can pick up the antennas and place them precisely at the site. The first vehicle was completed and tested in July 2007. Both transporters were delivered to the ALMA Operations Support Facility (OSF) in Chile on February 15, 2008. On July 7, 2008 an ALMA transporter for the first time moved an antenna, moving it from inside the antenna assembly building (Site Erection Facility) to a pad outside the building for testing (holographic surface measurements). The antenna was of the North American VertexRSI design.
General information
ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory (NRAO). NRAO is managed by Associated Universities, Inc (AUI). ALMA construction and operations are led on behalf of Europe by ESO and Japan by the National Astronomical Observatory of Japan (NAOJ).
Administration of the ALMA site in Chile is lead by ESO.
Project detail
- 50 to 64 antennas of 12 m diameter located at an elevation of 5,000 m at Llano de Chajnantor Observatory, enhanced by a compact array of 4 x 12 m and 12 x 7 m antennas (consortium currently considering to build 50 or 64)
- Imaging instrument in all atmospheric windows between 350 µm and 10 mm
- Array configurations from approximately 150 m to 14 km
- Spatial resolution of 10 milliarcseconds, 10 times better than the Very Large Array (VLA) and the Hubble Space Telescope
- The ability to image sources arcminutes to degrees across at one arcsecond resolution
- Velocity resolution under 50 m/s
- Faster and more flexible imaging instrument than the VLA
- Largest and most sensitive instrument in the world at millimeter and submillimeter wavelengths
- Point source detection sensitivity 20 times better than the VLA
Project timeline
style="font-size:125%;"| Timeline| Date | Activity | | May 1998 | Start of Phase 1 (Design & Development). | | June 1999 | U.S./European Memorandum of Understanding for Design & Development. | | February 2003 | Final North American / European Agreement, with 50% of funding from ESO, and 50% of funding shared between USA and Canada. | | September 2004 | North American, European & Japanese draft agreement, with Japan providing new extensions to ALMA. | | October 2004 | Opening of Joint ALMA office, Santiago, Chile. | | October 2005 | Groundbreaking at 5000 m altitude Array Operation Site of ALMA. | | September 2005 | Taiwan joins the ALMA Project through Japan. | | June 2006 | N. American, European, & Japanese sign agreement on the Enhanced ALMA. | | 2010 | Call for shared-risk early science proposals. | | 2012 | ALMA construction complete. |
See also
External links
|
| |
|
|
