Allen Telescope Array

For other uses, see ATA.
Allen Telescope Array
ATA
The Allen Telescope Array (ATA-42), October 11, 2007
Organization SETI Institute
Coordinates 40°49′01″N 121°28′12″W﻿ / ﻿40.817°N 121.470°W
Website seti.org Info Service

The Allen Telescope Array (ATA), formerly known as the One Hectare Telescope (1hT), was a joint effort by the SETI Institute and the Radio Astronomy Laboratory (RAL) at the University of California, Berkeley to construct a radio interferometer that is dedicated to astronomical observations and a simultaneous search for extraterrestrial intelligence.[1][2] UC Berkeley completed divestment from the project in April 2012 [3] and the facility is now managed by SRI International, an independent, nonprofit research institute.

The ATA is under construction at the Hat Creek Radio Observatory, 290 miles (470 km) northeast of San Francisco, California. When completed, the array is expected to consist of 350 antennas.[4][needs update] The first phase with 42 antennas (ATA-42) is complete and became operational on 11 October 2007.[5][6] However, in April 2011, the ATA was placed in operational hibernation due to funding shortfalls.[7][8] In August 2011, short-term funding was found,[9] and operation of the ATA was resumed on December 5, 2011.[10]

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 four 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 content of galaxies out to z ∼ 0.2 over 3π steradians, to measure how much intergalactic gas external galaxies are accreting; to search for dark, starless galaxies; to lay the foundation for SKA dark energy detection
• Classify 250,000 extragalactic radio sources as active galactic nuclei 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 and dark energy detection
• Explore the transient sky, to probe accretion onto black holes; to find orphan gamma ray burst afterglows; to discover new and unknown transient phenomena
• Survey 1,000,000 stars for SETI emission with enough sensitivity to detect an Arecibo radar out to 300 pc within the range of 1 and 10 GHz
• Survey the 4×1010 stars of the inner galactic plane from 1.42 to 1.72 GHz for very powerful transmitters
• Measure the magnetic fields in the Milky Way and other Local Group galaxies, to probe the role of magnetic fields in star formation and galaxy formation and evolution
• Detect the gravitational wave background from massive black holes through pulsar timing
• Measure molecular cloud and star formation 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
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 0.2 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 mooncast data downlink for any contestants in the Google Lunar X Prize.[22] 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.[23] 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.[24]

Instrument details

The ATA Offset Gregorian Design

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 surveys, the ATA-42 is comparable in speed with Arecibo and the Green Bank Telescope (GBT), but slower by a factor of 3 than the Very Large Array (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 offset Gregorian telescopes, 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. Many concepts and designs originated from a SETI affiliated company in Antioch, California, Minex Engineering Corp. (Matt Fleming and others), including the compact mount and drive train.

Data Management

As with other arrays the huge amount of incoming sensory information requires real time array processing capability to reduce data volume for storage. For ATA-256 the average data rates and total data volume for the correlator are estimated to be 100 MByte/s and 15 PByte for the 5-year survey period.[25] Experiments such as transient surveys will exceed the rate significantly. The beamformers produce data at a much higher rate (8 GByte/s) but only a very small fraction of this data is archived. In 2009, the signal detection hardware and software was called Prelude, composed of rack mounted PCs augmented by two custom accelerator cards based on DSP and FPGA chips. Each Programmable Detection Module (one of 28 PCs) can analyze 2 MHz of dual-polarization input data to generate spectra with spectral resolution of 0.7 Hz and time samples of 1.4 seconds.[25]

In 2009, the site had a 40 Mb/s internet connection, adequate for remote access and transferring of data products for ATA-256. An upgrade to 40 Gb/s was planned, which would enable direct distribution of raw data for offsite computing.[25]

Computational complexity and requirement

Like other array system the ATA has a computational complexity and cross-connect which scales as O(N2) with the number of antennas $N$. The computation requirement, for example, for correlating the full ATA bandwidth ($B$ = 11 GHz) for the proposed $N$ = 350 dual-polarization antenna build-out, using an efficient frequency-multiply (FX) architecture, and a modest 500 kHz channel width (with number of channels $F$ = 2200) is given by:[26]

$2B \langle N \log_2(F)(10 OPs)+(N \frac{N +1}{2})\times 4(8 OPs) \rangle$ = 44 PetaOPs per second

where $Ops$ is an operation. Note that since each dish has a dual polarization antenna each signal sample is actually a two data set, hence $2B$.

References

1. ^ Daniel Terdiman (12 December 2008). "SETI's large-scale telescope scans the skies". CNET News. Retrieved 2008-12-12.
2. ^ John Johnson, Jr. (1 June 2008). "Aliens get a new switchboard: a SETI radio telescope in Northern California". The Los Angeles Times. Archived from the original on 4 October 2008. Retrieved 2008-09-29.
3. ^ Robert Sanders (April 13, 2012). "UC Berkeley passes management of Allen Telescope Array to SRI". UC Berkeley NewsCenter. Retrieved 29 December 2012.
4. ^ http://archive.seti.org/pdfs/Shostak-spring2009-EnS.pdf
5. ^ a b c Dennis Overbye (11 October 2007). "Stretching the Search for Signs of Life". The New York Times. Retrieved 2009-04-14.
6. ^ Staff writers (12 October 2007). "Skies to be swept for alien life". BBC News. Archived from the original on 12 October 2007. Retrieved 2007-10-12.
7. ^ Hardy, Michael (2011-04-29). "Federal Computer Week". Fcw.com. Retrieved 2011-09-19.
8. ^ http://archive.seti.org/pdfs/ATA-hibernation.pdf
9. ^ John Cook (August 7, 2011). "Search for ET continues as Paul Allen-backed telescope hits short-term funding goal". Retrieved 29 December 2012.
10. ^ a b "SETI Search Resumes at Allen Telescope Array, Targeting New Planets" (Press release). SETI Institute. December 5, 2011. Retrieved 29 December 2012.
11. ^ Shannon McConnell (2005). "Deep Space Network Adds a 34m Beam Wave Guide Antenna in Madrid, Spain". Deep Space Network Home. JPL. Archived from the original on 16 April 2009. Retrieved 2009-04-14.
12. ^ Senior Review Committee (22 October 2006). "From the Ground UP: Balancing the NSF Astronomy Program" (PDF). National Science Foundation Division of Astronomical Sciences. p. 4.4.2.3. Archived from the original on 18 April 2009. Retrieved 2009-04-14.
13. ^ W.L. Urry, M. Wright, M. Dexter, D. MacMahon (16 February 2007). "The ATA Correlator ATA Memo 73" (PDF). University of California, Berkeley. p. 3. Retrieved 2009-04-14.
14. ^ "GRB 070612A: Allen Telescope Array Observations". Retrieved 2011-09-19.
15. ^ "BEE2: A modular, scalable FPGA-based computing platform". Bee2.eecs.berkeley.edu. Retrieved 2011-09-19.
16. ^ "Berkeley ATA Pulsar Processor (BAPP)". Center for Astronomy Signal Processing and Electronics Research (CASPER). University of California, Berkeley. 29 December 2008. Retrieved 2009-04-14.
17. ^ "Allen Telescope Array beings all-sky surveys". Physorg.com. Retrieved 2011-09-19.
18. ^ Results from the Allen Telescope Array: SETI Survey of the Galactic Center Region [1]
19. ^ John Matson (24 April 2011). "Budget crunch mothballs telescopes built to search for alien signals". Scientific American. Archived from the original on 27 April 2011. Retrieved 2011-04-25.
20. ^ "BBC - Future - Science & Environment - Jill Tarter: In search of aliens". BBC. BBC. Retrieved 27 February 2013.
21. ^
22. ^ "Google Sponsors Lunar X PRIZE to Create a Space Race for a New Generation" (Press release). X PRIZE Foundation and Google Inc. 13 September 2007. Archived from the original on 11 May 2009. Retrieved 2009-04-14.
23. ^ Phil Berardelli (27 September 2007). "Big Radio from the Stars". ScienceNOW. Retrieved 2009-04-14.
24. ^ "ATA "Fly's Eye" Pulse Finder". Center for Astronomy Signal Processing and Electronics Research (CASPER). University of California, Berkeley. 29 December 2008. Retrieved 2009-11-08.
25. ^ a b c A Radio Sky Surveys Project with the Allen Telescope Array - Response to the Request for Information Part 2 Geoffrey C. Bower, October 15, 2009
26. ^ Aaron Parsons et al. (Oct 29, 2006). "PetaOp/Second FPGA Signal Processing for SETI and Radio Astronomy". Signals, Systems and Computers: 2031–2035. doi:10.1109/ACSSC.2006.355123.