Our annual international SKA meeting, this year titled "The SKA: Defining the Future", was hosted at the University of California, Berkely and jointly sponsered by the US SKA Consortium, UC Berkeley and the SETI Institute. The meeting was very successful. The meeting presentations can be found at http://www.skatelescope.org/skaberkeley/ .
The twice-yearly ISSC meeting
occured in the US this year, on 5 January at the Massachusetts Institute of
Technology and on 27 July in association with the Berkeley meeting.
The
minutes of the MIT meeting
are located on the SKA secretariat web site. At Berkeley we were joined
by observers from South Africa and Japan. The next meeting of the ISSC
will occur at Bologna on 17/18 of January. It will be preceded by a
science workshop, "New Frontiers
in Astrophysics: Square Kilometre Array
", aimed at refining the scientific drivers and technical specifications
for the SKA.
The Australian Government's announcement that it will fund an SKA demonstrator program has stimulated much activity within SKA groups. The funding will come via the Major National Research Facilities (MNRF) scheme and is about 85% of what the astronomy community requested in a joint Gemini/SKA proposal. Negotiations between bid proponents are continuing but the most likely outcome is an across-the-board scaling, implying that SKA programs totalling $US10M will be undertaken over the next five years.
At the recent Berkeley gathering the Australian team outlined programs focussing on construction of two SKA demonstrators, both of which will be integrated with existing radio telescopes. The Narrabri ATCA demonstrator will use either Luneburg Lenses or phased array receptors, while the Molonglo instrument will be based on the MOST east-west cylindrical reflector. Design studies for both instruments will be finished by the end of 2003 and the target is to have construction completed by 2005. The demonstrator work, together with SKA astronomy and engineering simulations to be undertaken by Swinburne University, will be co-ordinated by the recently-formed Australian SKA consortium. We plan to avoid R&D duplication and to collaborate with international colleagues in areas where productive research is already underway. More details of initial demonstrator proposals can be found in the Berkeley conference proceedings at http://www.skatelescope.org/skaberkeley/
The Berkeley proceedings also contain summaries of work in antenna, interference mitigation, site and outreach projects. Recent highlights include the delivery of initial artificial dielectric samples by our material science colleagues; the samples are currently being evaluated in RF tests. Characterization of the 0.9 m diameter Luneburg Lens obtained in collaboration with Russian radio astronomers is continuing, with near-field tests at 12 and 2 GHz being complete and outdoor tests about to begin. Indications are that the lens has excellent beam-forming properties and we expect to make accurate gain (and di-electric loss) measurements during the outdoor testing.
Analysis of the first Western Australian site test data is almost complete and summary reports are being compiled. Further site characterization at various inland Australain sites will begin next year and, to improve the sensitivity of the RFI measurement system, CSIRO has constructed an auto-correlator backend. This is currently being tested (Figure 1) and should be fully operational in early 2002. In related outreach work, we have obtained corporate and other sponsorship for a spectrum monitoring project designed for high school students. If a bid for associated Government funding is successful, city and country students at five or six locations will learn the value of the e.m. spectrum as a natural and commercial resource, and the value of radio quietness to astronomy and the SKA. Measurements will be made using scanning communications receivers interfaced to PCs. Data presentation and communication between participants will be via the internet. The success or otherwise of the outreach bid should be known by late October this year.
Figure 1 - ATNF engineer Mal Smith with part of the high-sensitivity RFI measurement system he has constructed for use in SKA site tests and observatory monitoring roles. The auto-correlator (centre unit in rack) has a maximum bandwidth of 64 MHz (at 62.5 kHz resolution). With typical integration times, the correlator backend improves the measurement sensitivity by 20 dB or so relative to a sweeping spectrum analyser and signals around the -150 dBm level are easily detected.
SKA Progress in China: Modeling FAST
There are two major achievements
on FAST project since last issue of the newsletter. First, the actuated
main reflector was tested successfully in Feb. 2001 in Shanghai by making
a 1:3 scaled model. Four elementary panels can move up and down along the
radius of a sphere to approach a parabolic surface. These feasibility studies
were made by Tongji university in Shanghai, Nanjing astronomical instrument
research institute under the contracts with the Beijing Astronomical Observatory
(BAO, now the National Astronomical Observatories of China), with contributions
by the NAOC. Some suggestions for modification were proposed by the experience
from the Evaluating Committee and under serious consideration by our FAST
Group. According to those suggestions, we started a new type design
of the reflector element – pre-stressed back structure experiments
on the reliability and life time of the main reflector.
Secondly, the cable-car focus driven system, one of the two key approaches
for FAST feed supporting designs, reached its major goal by testing a scaled
model of 1:25 in Tsinghua university. The trolly which carries the focus
cabin is supported and driven by two cross sets of upward cables, and four
down tied cables are applied to increase the stiffness of the structure.
Positional accuracy of 3 mm was achieved on this model. Meanwhile a model
of 1:10 for the secondary adjustable system - Stewart stabilizer was manufactured
to meet the final pointing and tracking requirement. The new combined model,
including the two adjustable systems, starts to be built up according to
the similarity law, one year contract is made between Tsinghua university
and the NAOC.
Another approach on feed support design is in progress in Xidian university
in Xian to finalize a whole system (cable support designed by Xidian university
and a stewart platform produced by Beijing institute of science and technology).
The final check is expected to be completed late this year.
Some other aspects: the Science Case written in Chinese has been finalized
at NAOC, the site survey report is completed, therefore the feasibility
study of FAST as a key project of the Chinese Academy of Sciences will be
ended up by this year.
News from the European Consortium
Meetings and workshops
The European SKA Consortium
has now received financing for its meetings and workshops from the European
Union. In the coming months two workshops of general interest are being planned:
(i) “New Frontiers in Astrophysics: the Square Kilometer Array” on 14 and 15 January, 2002, in Bologna, Italy. A one day meeting on 16 January will present the project to the wider Italian community. LOC chairperson for both is Franco Mantovani ( fmantovani@ira.bo.cnr.it ) and workshop information is available at www.ira.bo.cnr.it/~skawork/ .
(ii) “High-resolution (including VLBI) imaging with SKA” on 10 and 11 Dec in Bonn at MPIfR. Contacts for the organizers are Michael Garrett (garrett@jive.nl ) and Richard Porcas (rporcas@mpi-bonn.mpg.de ).
As an aid in publicizing the SKA, Peter Wilkinson at Jodrell Bank has developed generic SKA presentation material that is accessible over the internet. Version 1.0 is now complete and is available at via anonymous ftp at: ftp.jb.man.ac.uk, directory /pub/pnw (one PowerPoint file and 6 movies) or via the web at: http://www.jb.man.ac.uk/~pnw/files.html . Refinement and extension of the material will continue.
Europe-wide Future Planning
In response to a request for comment on proposed guidelines for the Research Infrastructures line of the EU’s Sixth Framework Programme (2004-2007), an integrated initiative has been proposed involving (i) coupling the EVN telescopes to JIVE in Dwingeloo with high capacity fibers, (ii) participation in ALMA, (iii) developing plans for SKA in a global context, and (iv) evolving the initiative into a Council for Radio Astronomy in Europe to provide some of the functions that ESO provides in optical astronomy.
Technical R&D
Activities are currently concentrated at ASTRON in Dwingeloo, Jodrell Bank (JBO) in Manchester, IRA in Bologna, and TCfA in Torun. Very briefly, the main lines of work are given below.
Financing from the EU has recently been received jointly by these four groups for a coordinated development effort going by the name FARADAY. A main goal is to carry out R&D for producing phased array antenna systems for use at the foci of parabolic dish antennas. At the heart of the project is system integration using complex monolithic microwave integrated circuits (MMICs). The applications planned include cryogenic receivers in the 20-40 GHz band (InP technology) and phased arrays in the 2-5 GHz band (GaAs and SiGe technologies). In addition to the European partners, the ATNF is participating in the effort, which is planned to yield prototype arrays and feasibility studies for large production arrays.
The Jodrell Bank group
is currently installing COBRA (Coherent Online Baseband Receiver for Astronomy).
COBRA consists of a 182-node Beowulf PC cluster designed to handle, in the
first instance, a dual polarisation 100 MHz signal from the Lovell Telescope.
Its primary role will be to act as a sophisticated pulsar signal processing
machine through coherently de-dispersing pulsar data. It can also operate
in a spectroscopic mode and can be configured to find and remove RFI. It
is hoped that COBRA is a prototype for future radio astronomy software receivers
such as those that will be used for SKA.
In collaboration with the University of Birmingham, JBO was recently awarded
a grant for the development of High Temperature Super-Conducting (HTSC) filters.
These filters are being developed, in the first instance, for use in the
L-band and UHF receivers on JBO and MERLIN telescopes with the aim of improving
their survivability in the presence of strong RFI.
JBO staff have continued their development of prototype receiver/transmitter systems for the ALMA fibre-optics systems. This is an offshoot of the generic fibre-optics development in which JBO is involved, primarily for the e-MERLIN project. It is envisaged that both ALMA and e-MERLIN will use similar systems based on wavelength-division-multiplexing. The current design for e-MERLIN will result in 30 Gbps/telescope being transmitted to JBO over a few hundred kilometres; ALMA will require data transmission rates of 120 Gbps/telescope but over much smaller distances. Fibre-optics will naturally play a major role in the data transmission system of any conceivable SKA system.
As reported in previous Newsletters, the group at ASTRON has a long-term program to develop the technologies required for the wide-band phased array concept for SKA. In recent months this effort has focussed on completing the Thousand Element Array, THEA (Figure 3). THEA consists of 1024 receiving antenna elements and will be used as an outdoor phased-array system to detect (known) radio sources in the frequency band ranging from 600 to 1700 MHz in the presence of several strong RF Interfering (RFI) signals. The THEA phased-array system has various new features compared with conventional radio telescope designs: multi-beam operation, adaptive nulling, interference monitoring and reconfigurability of the sub-array units. THEA will also serve as a test-bed for new and advanced technologies that should lead to a higher level of integration and cost reduction. Examples are the use of a high-speed optical link (32 Gb/s) and a new multi-beam analogue beamformer with a high level of integration including the antenna elements.
Figure 3. View of a Single THEA Tile with the radome removed.
LOFAR
The LOw Frequency ARray radio telescope project has received initial financing and is now aiming for first observations in 2006. A collaboration between ASTRON, M.I.T. and the U.S. Naval Research Laboratory, LOFAR will approach a square kilometer of collecting area at frequencies just above the ionospheric cut-off. It will test in an operational environment several of the key features of the wide-band phased array concept for SKA:
(i) multiple, independently pointed primary beams,
(ii) real-time interference suppression, and
(iii) on-line operation from geographically separated science operations centers.
The science drivers for
LOFAR cover an exceedingly broad range, from study of the epoch of re-ionisation
to space weather and the origin of cosmic rays. Participation by individuals
and groups in defining and planning the science program is open and is being
organized through a separate LOFAR Science Consortium. European groups discussing
substantial participation are the LOIS Consortium in Scandinavia and the
SkyView Consortium in Germany and the Netherlands.
It may be possible that LOFAR can provide much of the desired capability
being discussed for SKA for the lowest decade of frequencies, thereby reducing
the total specified bandwidth for SKA itself to two decades.
Individuals and groups
potentially interested in participating in one or another aspect of LOFAR
are invited to contact the Project Scientist, Namir Kassim, lofar-scientist@rsd.nrl.navy.mil,
and the Science Consortium secretary, Michiel van Haarlem, haarlem@astron.nl.
Additional information about LOFAR may currently be found at web sites
set up by the three collaborating institutes:
http://www.lofar.nl/
, http://www.haystack.mit.edu/
, and http://LOFAR.nrl.navy.mil
. Soon all project information will be consolidated at the web site
www.lofar.org
.
South Africa sends a representative to the ISSC
Justin Jonas is completing
a report on his visit to the SKA meetings in Berkeley which will be presented
to the National Research Foundation (South Africa's primary research funding
body) and the Department of Arts, Culture, Science and Technology (the responsible
government ministry). The report will contain a motivation for funding of
South African membership of the SKA consortium, and also for funding to carry
out RFI surveys in remote areas of the country. The ISSC will be kept
informed of the progress of this report.
Justin would like to thank the ISSC, the Berkeley conference orgainizers,
and all the conference delegates for their hospitality and their inclusive
attitude.
Progress Report from the US SKA Consortium
The US SKA Consortium met four times during this past year; in Washington DC in September, at MIT in January, at the Harvard/Smithsonian Center for Astrophysics in April (during this meeting we held a one day SKA symposium for local scientists), and in Berkeley in July. At the urging of the NSF, consortium members prepared "A Roadmap for the United States Development Efforts on the Square Kilometer Array" and submitted it on March 15th. The intent of this document was to give the NSF some framework against which to assess any proposals involving SKA technology development. The US Decadal Review (Astronomy and Astrophysics for the New Millennium) had recommended SKA technology development at a level of $22M through the decade, one of twelve so-called moderate initiatives. While individual proposals to the NSF are always possible, the consortium members made the strategic decision that a combined, coordinated proposal had a better chance of success. The proposal preparation was led by Jim Cordes from Cornell University serving as the PI. On August 31st a multi-institutional proposal covering 3 years of technology development effort was submitted to the NSF ATI (Advanced Technology Initiative) program. It will be spring of 2002 before the fate of this proposal is decided. Of particular interest to the international community, that proposal included a request to fund the US share of a Project Manager for the International SKA Project Office during the first year, with funds for a Project Scientist and a Project Engineer being added in later years. As the result of prior proposals to the NSF MRI (Major Research Initiative) program, funding has been provided to build a correlator for LOFAR. Another proposal to build an imager for the ATA was not funded, and will be resubmitted at a future date.
Consortium members presented a number of papers describing work in progress trying to understand the benefits and challenges of a Large-N implementation for the SKA (where N refers to the number of stations). Roger Capallo concluded that a correlator (probably FX) for N=1000 is buildable with some combination of FPGAs and DSPs, though not yet affordable. A scientifically valuable data buffer for transients also looks feasible. The decade-long timescale for doubling software functionality is almost as much of a concern as the cost. Shep Doleman summarized current approaches and severe limitations to simulating Large-N performance (for N= 100, 200, and 400), as well as the first efforts to define a set of "benchmark observations" to be used in selecting a final SKA design. The first application of these simulation tools will be for LOFAR. Tim Cornwell argued that AIP++ was now a viable tool for detailed simulation studies, including the Large-N concept, but innovation in calibration and imaging algorithms lags significantly. Colin Lonsdale discussed the frequency dependent tradeoffs that are inherent in the current strawman science goals for the SKA. He concluded that the SKA is not one single instrument, and even so, cannot be all things for all scientists. Sandy Weinreb reported on work at JPL and Caltech concerning array requirements for space communications, gravitational distortion of hydroformed reflectors, and wideband low-noise receivers over a wide range of observational frequencies. Bryan Gaensler discussed the need for extreme polarization purity in the SKA (better than -40 dB) in order to permit polarimetry studies of the magnetized interstellar medium. Such studies would probe regions of low n and B, turbulence, and diffuse emission, while providing "instant" rotation measures and position angles
Several studies on techniques for RFI excision were presented. Steve Ellingson reported on experiments done with the Argus array of 7 quarter-wave monopoles at OSU to to find angles-of-arrival (including multipath) for mobile radios, and with another array of 7 compact spirals to identify LEOs using a multibeam "patroling" technique. Rick Fisher reported on studies of pulsed radar interference with the GBT, and concluded that multipath and poor clock standards make simple blanking techniques inadequate, but that more complicated algorithms that track pulses should work well. A poster by Rob Ackermann and Gerry Harp described the current state of the Rapid Prototyping Array for the ATA (the site of dinner one evening during the meeting) and the scope of the experimental and software development programs currently ongoing at that facility. Geoff Bower briefly described several different RFI excision experiments using the RPA that had been done by Fisher, Harp, Ackermann, Ellingson, and Mitchell. He presented details of his own experiments using Wiener Filters to adaptively remove satellite interference. At NRL, low-frequency (74 and 330 MHz) VLA observations are being used to develop tchniques for RFI excision that will have broad applications to both existing and future instruments (LOFAR, EVLA, and SKA). Discussions are also underway as to the extent that LOFAR prototype stations could be used as testbeds for RFI excision techniques.
A suite of papers and posters described other progress on the ATA. John Dreher presented the overview of the design, timeline, and current budget estimates extrapolated to the SKA. Ed Ackerman reported on the testing of three different options for the ATA wideband analog link between the antennas and the processing lab. Three types of system are under test; Mach-Zehnder Modulators (most expensive, proven track record), integrated Electro-Absorption modulators (mid cost, will work for the ATA if thermal stability is adequate), directly modulated VCSELs (cheapest, but not yet available at 1350 nm for the ATA --- these should be viable for the SKA). Douglas Bock described the tentatively selected configuration for the ATA that produces a round 78" beam at 1.4 GHz with peak, close-in sidelobes below 1%. He also discussed the GPS-aided surveying program underway at the site. Jack Welch summarize the design studies and tradeoffs that led to the selection of a 6.1 m primary (2.4 m secondary) offset Gregorian antenna design, and the current status of manufacturing by a hydroforming technique. Dave DeBoer outlined the current ATA signal path design that accommodates multiple, simultaneous backends for different science programs. Lynn Urry sketched the current plans for a radio astronomy imaging correlator, and Mike Davis provided an update on the implementation of a new generation of SETI backends for the independent ATA beams.
Rick Perley laid out the science goals and phases of the expanded VLA project (EVLA), illustrating how it will serve as one pathway and technology demonstrator for arriving at the eventual SKA. Sandy Weinreb and Larry D'Addario provided the participants with a preliminary cost equation in the form of a spreadsheet tool for estimating the eventual cost of the SKA in any implementation. This is now readily available on the web at http://www.skatelescope.org/ska_memos.shtml , and will be updated as system engineering studies progress. Dayton Jones highlighted a use of the SKA (or its DSN equivalent) for spacecraft tracking and planetary science. Putting the gain on the ground enables faster, better, cheaper missions with much higher return data rates, and greatly reduces the risk from navigational errors.
Since the July meeting,
this last item has enjoyed a significant amount of attention. Strong
support for a large array for the NASA deep space network (DSN) has
developed at JPL and will add impetus to the US SKA effort. FY02 funds
are expected from NASA for technology development (antennas and receivers),
system design, and for liaison with other array projects. A
plan for design and prototyping of a DSN array is under discussion. A small
group (Sandy Weinreb, Peter Napier, and Lee King) visited the ATA antenna
manufacturer, Andersen, in September to discuss manufacture of 6 to 12 meter
antennas for the SKA, EVLA, and the DSN. The results were highly encouraging
with regard to developing a 12m antenna with precision sufficient for 50
GHz operation and for construction of an on-site factory to circumvent the
problems of transporting large one-piece hydroformed reflectors.
And on the LOFAR front, considerable progress has been made (by NRAO and NRL
personnel) in the past year in developing methods to compensate for ionospheric
phase distortions. These phase distortions will be significant for SKA
observations in the L band. In some (but probably not all) observing
modes, multi-frequency observations will be capable of solving for the ionospheric
phase exactly.
Jill Tarter, SETI Institute