Allen Telescope Array

Allen Telescope Array

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The Allen Telescope Array (ATA), formerly known as the One Hectare Telescope (1hT), was a joint effort by the SETI Institute
SETI Institute
The SETI Institute is a not-for-profit organization whose mission is to “explore, understand and explain the origin, nature and prevalence of life in the universe”. SETI stands for the "search for extraterrestrial intelligence". One program is the use of both radio and optical telescopes to search...

 and the Radio Astronomy Laboratory (RAL) at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

 to construct a radio interferometer that is dedicated to astronomical observations and a simultaneous search for extraterrestrial intelligence
SETI
The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...

.

The ATA is under construction at the Hat Creek Radio Observatory
Hat Creek Radio Observatory
The Hat Creek Radio Observatory is operated by the Radio Astronomy Laboratory in the Western United States.- Location :...

, 290 miles (466.7 km) northeast of San Francisco, California. When completed, the array is expected to consist of 350 antennas. The first phase with 42 antennas (ATA-42) is complete and became operational on 11 October 2007. However, in April 2011, the ATA was placed in operational hibernation due to funding shortfalls. In August 2011, short-term funding was found

Background


First conceived by SETI pioneer Frank Drake
Frank Drake
Frank Donald Drake PhD is an American astronomer and astrophysicist. He is most notable as one of the pioneers in the search for extraterrestrial intelligence, including the founding of SETI, mounting the first observational attempts at detecting extraterrestrial communications in 1961 in Project...

, the idea has been a dream of the SETI Institute for years. However, it was not until early 2001 that research and development commenced after a donation of $11.5 million by the Paul G. Allen Family Foundation
Paul G. Allen Family Foundation
The Paul G. Allen Family Foundation is a private foundation located at in Seattle, Washington. Their mission is to transform individual lives and strengthen communities by fostering innovation, creating knowledge, and promoting social progress.-About:...

. In March 2004, following successful completion of a three-year research and development phase, the SETI Institute unveiled a three-tier construction plan for the telescope. Construction began right after, due to the pledge of $13.5 million by Paul Allen
Paul Allen
Paul Gardner Allen is an American business magnate, investor, and philanthropist. Allen co-founded Microsoft with Bill Gates...

 (co-founder of Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

) to support the construction of the first and second phases. The SETI Institute named the telescope in his honor. Overall Paul Allen has contributed more than $30 million to the project.

Overview


The ATA will be a centimeter-wave array
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....

 that pioneers the Large-Number Small-Diameter concept of building radio telescopes. Compared to a large dish antenna, large numbers of smaller dishes are cheaper for the same collecting area. However, to get similar sensitivity, the signals from all telescopes must be combined. This requires high performance electronics, and has been prohibitively expensive until now. However, due to the declining cost of the electronic components, the required electronics are now practical, resulting in a large cost saving over telescopes of more conventional design. This is informally referred to as "replacing steel with silicon".

The ATA has four primary advantages for scientific studies over all major radio telescopes built to date: a very wide field of view (2.45° at λ = 21 cm), complete instantaneous frequency coverage from 0.5 to 11.2 GHz, multiple simultaneous backends, and active interference mitigation. The instantaneous area of sky imaged is 17 times that of the Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...

. The instantaneous frequency coverage of more than four octaves
Octave (electronics)
In electronics, an octave is a doubling or halving of a frequency. The term is derived from the musical octave which similarly describes such frequency ratios, but the prefix octa-, denoting eight, has no significance in physics...

 is unprecedented in radio astronomy and is the result of a unique feed, input amplifier, and signal path design. Active interference mitigation will make it possible to observe even at the frequencies of many terrestrial radio emitters.

Because all-sky surveys are an important part of the science program, the efficiency of the ATA will be increased by doing radio astronomy and SETI searches simultaneously. The telescope will do this by splitting the signals in the control room prior to final processing. Simultaneous observations are possible because for SETI, several target stars will lie within the large field of view afforded by the 6m dishes wherever the telescope is pointed. Thus, by agreement between the RAL and the SETI Institute, the needs of conventional radio astronomy will determine the pointing of the array.

The ATA is planned to comprise 350 six-meter dishes and will make possible large, deep radio surveys that were not previously feasible. The telescope design incorporates many new features, including hydroformed
Hydroforming
Hydroforming is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce...

 antenna surfaces, a log-periodic
Log-periodic antenna
In telecommunication, a log-periodic antenna is a broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency...

 feed covering the entire range of frequencies from 500 MHz to 11.2 GHz, and low-noise, wide-band amplifiers with a flat response over the entire band making it possible to amplify the sky signal directly. This amplified signal, containing the entire received bandwidth, is brought from each antenna to the processing room on optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

 cables. This means that as electronics improve and wider bandwidths are feasible, only the central processor needs to change, and not the antennas or feeds.

The instrument will be operated and maintained by the Radio Astronomy Laboratory. The RAL has worked hand in hand with the SETI Institute during design and prototyping and is the primary designer of the feed, antenna surfaces, beam forming, correlator and imaging system for radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...

 observations.

The astronomy decadal panel, Astronomy and Astrophysics in the New Millennium, endorsed SETI and recognized the ATA (then called the 1-Hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...

 Telescope) as an important stepping stone to the Square Kilometer Array (SKA).

The ATA aspires to be among the world's largest and fastest observing instruments. It will also permit astronomers to search for many different target stars simultaneously. When completed as originally envisioned, it will be one of the largest and most powerful telescopes in the world.

Although cost estimates of unbuilt projects are always dubious, and the specs are not identical (the conventional telescopes have lower noise temperature, but the ATA has a larger field of view, for example), the ATA has potential promise as a much cheaper radio telescope technology for a given effective aperture. For example, the amount spent on the first ATA-42 phase, including technology development, is roughly 1/3 of the cost of a new copy of a Deep Space Network
Deep Space Network
The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...

 34 meter antenna of similar collecting area. Similarly, the estimated total cost of building the remaining 308 dishes is estimated (as of October 2007) at about $41 million. This is about a factor of 2 cheaper than the $85 million cost of the last large radio astronomy antenna built in the USA, the Green Bank Telescope
Green Bank Telescope
The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...

, of similar collecting area. The contractor filed for a $29 million overrun, but only $4 million of this was allowed.

Status


Since its inception, the ATA has been a development tool for array technology (specifically, for the Square Kilometer Array). Future progress depends on the technical performance of the sub-array already under construction, and the procurement of additional funding.

The ATA was originally planned to be constructed in four stages, the ATA-42, ATA-98, ATA-206, and ATA-350; each number representing the number of dishes in the array at a given time (See Table 1).

Regular operations with 42 dishes started on 11 October 2007. Funding for building additional antennas is currently being sought by the RAL from various sources, including the US Navy, DARPA, NSF and private donors.

Astronomical data has been acquired since May 2005, utilizing a four-input correlator (four antennas, dual polarization) and then updated in January 2007 with two eight-input (16 antennas, dual polarization). Scientifically useful data has been acquired and is helping commission the array.

Correlator development continues, with deployment of one 32-input correlator in June 2007 and utilized as eight individual correlators with eight dual-polarization inputs each.

Beam-forming electronics utilizing the BEE2 were deployed in June 2007 and are currently (08 Nov 2007) being integrated into the system to allow for simultaneous astronomical and SETI observations. As of April 2008, the first pulsar observations have been conducted using the beamformer and a purpose-built pulsar spectrometer.

In May 2009, UC Berkeley announced it was performing all-sky surveys using the Allen Telescope Array.

The ATA Team reported initial results from their survey of the Galactic Center Region at the June 2009 meeting of the American Astronomical Society (AAS Meeting #214).

As of April 2011, the ATA has been placed in hibernation mode due to funding shortfalls, meaning that it is no longer available for use.

Key science goals


The science goals listed here represent the goals of the most important projects that will be conducted over the next three years with the ATA. Each of these goals is associated with one of the 4 stages of development (see Table 1). The bulleted items are the projects that will be undertaken and the subtopics are some of the science that will be produced. The ATA will:
  • Determine the HI
    Hydrogen line
    The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...

     content of galaxies
    Galaxy
    A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

     out to z ∼ 0.2 over 3π steradian
    Steradian
    The steradian is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane...

    s, to measure how much intergalactic gas external galaxies are accreting; to search for dark, starless galaxies; to lay the foundation for SKA dark energy
    Dark energy
    In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

     detection
  • Classify 250,000 extragalactic radio sources as active galactic nuclei
    Active galactic nucleus
    An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

     or starburst galaxies, to probe and quantify star formation in the local Universe; to identify high redshift objects; to probe large scale structure in the Universe; to identify gravitational lens candidates for dark matter
    Dark matter
    In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

     and dark energy
    Dark energy
    In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

     detection
  • Explore the transient sky, to probe accretion onto black hole
    Black hole
    A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

    s; to find orphan gamma ray burst
    Gamma ray burst
    Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...

     afterglows; to discover new and unknown transient phenomena
  • Survey 1,000,000 stars for SETI emission with enough sensitivity to detect an Arecibo
    Arecibo Observatory
    The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...

     radar
    Radar astronomy
    Radar astronomy is a technique of observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the echoes. This research has been conducted for six decades. Radar astronomy differs from radio astronomy in that the latter is a passive observation and the former an...

     out to 300 pc within the range of 1 and 10 GHz
  • Survey the 4×1010 stars of the inner galactic plane
    Galactic coordinate system
    The galactic coordinate system is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy. The "equator" is aligned to the galactic plane...

     from 1.42 to 1.72 GHz for very powerful transmitters
  • Measure the magnetic field
    Magnetic field
    A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

    s in the Milky Way and other Local Group
    Local Group
    The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...

     galaxies, to probe the role of magnetic fields in star formation and galaxy formation and evolution
    Galaxy formation and evolution
    The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...

  • Detect the gravitational wave
    Gravitational wave
    In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...

     background from massive black holes through pulsar
    Pulsar
    A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

     timing
  • Measure molecular cloud
    Molecular cloud
    A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen ....

     and star formation
    Star formation
    Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...

     properties using new molecular tracers, to map the star formation conditions on the scale of entire giant molecular clouds (GMCs); to determine the metallicity gradient of the Milky Way
    Milky Way
    The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...


EWLINE
Table 1: Array performance and key science projects
Array Status Beam size (arcsec) Srms (mJy) Speed (deg²s−1) Key science
ATA-42 Dish construction complete; commissioning in progress with 32 input, dual polarization (64 total inputs) correlator. 245 x 118 0.54 0.02 FiGSS: 5 GHz Continuum Survey, Galactic Plane Molecular Spectroscopy, SETI Galactic Center Survey
ATA-98 Awaiting results ATA-42 for funding 120 x 80 0.2s 0.11 ATHIXS† Trial Surveys, HI Stellar Outflows Survey, SETI Targeted Survey: 100 stars
ATA-206 TBD 75 x 65 0.11 0.44 ATHIXS, Map The Magnetized Galactic ISM, Pulsar Timing Array, Deep continuum and transient surveys, SETI Targeted Surveys
ATA-350 TBD 77 x 66 0.065 1.40 ATHIXS, Map The Magnetized Galactic ISM, Pulsar Timing Array Deep continuum and transient surveys, SETI Targeted Surveys
Note. Beam size and continuum sensitivity (Srms are estimated for a 6 minute, 100 MHz continuum snapshot observation at transit of a source at 40° declination at a wavelength of 21 cm. Speed is given for a survey at 21 cm observations with a bandwidth of 100 MHz that reaches 1 mJy rms.
ATHIXS is an all-sky deep HI extragalactic HI survey.

Opportunistic science


After array construction, a few science goals that were not explicitly designed have been mentioned.

For a very different science goal, the Allen Telescope Array has offered to provide the downlink for any contestants in the Google Lunar X Prize
Google Lunar X Prize
The Google Lunar X PRIZE, abbreviated GLXP, sometimes referred to as Moon 2.0, is a space competition organized by the X Prize Foundation, and sponsored by Google. It was announced at the Wired Nextfest on 13 September 2007...

. This is practical since the array, with no modifications, covers the main space communications bands (S-band and X-band). A telemetry decoder would be the only needed addition.

Also, the ATA was mentioned as a candidate for searching for a new type of radio transient. It is an excellent choice for this because of a large field of view and wide instantaneous bandwidth. Following this suggestion, an instrument was custom-built for the ATA to search for bright radio transients, and observations were carried out between February and April 2008.

Instrument details


The ATA-42 configuration will provide a maximum baseline of 300 m (and ultimately the ATA-350, 900 m). A cooled log-periodic feed on each antenna is designed to provide a system temperature of ~45K from 1 GHz to 10 GHz, with reduced sensitivity in the range 0.5 GHz to 1.0 GHz and 10 GHz to 11.2 GHz. Four separate frequency tunings (IFs) are available to produce 4x100 MHz intermediate frequency bands. Two IFs support correlators for imaging; two will support SETI observing. All tunings can produce four dual polarization phased array beams which can be independently pointed within the primary beam and can be used with a variety of detectors. The ATA can therefore synthesize up to 32 phased array beams.

The wide field of view of the ATA gives it an unparalleled capability for large surveys (Fig. 4). The time required for mapping a large area to a given sensitivity is proportional to (ND)2, where N is the number of elements and D is the diameter of the dish. This leads to the surprising result that a large array of small dishes can outperform an array with smaller number of elements but considerably greater collecting area at the task of large surveys. As a consequence, even the ATA-42 is competitive with much larger telescopes in its capability for both brightness temperature and point-source surveys. For point source
Point source
A point source is a localised, relatively small source of something.Point source may also refer to:*Point source , a localised source of pollution**Point source water pollution, water pollution with a localized source...

 surveys, the ATA-42 is comparable in speed with Arecibo and the Green Bank Telescope
Green Bank Telescope
The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...

 (GBT), but slower by a factor of 3 than the Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...

 (VLA). The ATA-350, on the other hand, will be an order of magnitude faster than the Very Large Array for point-source surveys and is comparable to the Expanded VLA (EVLA) in survey speed. For surveys to a specified brightness temperature sensitivity, the ATA-98 will exceed the survey speed of even the VLA-D configuration. The ATA-206 should match the brightness temperature sensitivity of Arecibo and the GBT. The ATA, however, provides better resolution than either these single dish telescopes.

The antennae for the ATA are 6.1 m × 7.0 m hydroformed
Hydroforming
Hydroforming is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce...

 offset Gregorian telescope
Gregorian telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke...

s, each with a 2.4-meter subreflector with an effective f/D of 0.65. (DeBoer, 2001). The offset geometry eliminates blockage, which increases the efficiency and decreases the sidelobes. It also allows for the large subreflector, providing good low frequency performance. The hydroforming technology used to make these surfaces is the same hydroforming technique used to generate low-cost satellite reflectors by Andersen Manufacturing of Idaho Falls, Idaho. The unique, interior frame rim-supported compact mount allows excellent performance at a low cost. The drive system employs a spring-loaded passive anti-backlash azimuth drive train.

See also

  • List of radio telescopes
  • SETI Institute
    SETI Institute
    The SETI Institute is a not-for-profit organization whose mission is to “explore, understand and explain the origin, nature and prevalence of life in the universe”. SETI stands for the "search for extraterrestrial intelligence". One program is the use of both radio and optical telescopes to search...

  • SETI
    SETI
    The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...

  • setiQuest
    SetiQuest
    setiQuest is a project of the SETI Institute, whose declared aim is to "globalize the search for extra-terrestial intelligence and empower a new generation of SETI enthusiasts", by creating means for a deeper involvement from the interested public...

  • exoplanets

External links