Artist's impression of the Square Kilometre Array dishes.
Credit: SPDO/TDP/DRAO/Swinburne Astronomy Productions
It is expected to unlock some of the universe's best-kept secrets, providing clues to the origin of dark energy and detecting gravitational waves. But powering the Square Kilometre Array and processing the vast quantities of information this mega-telescope will yield presents a seriously daunting challenge.
"The science is awesome, but so is the engineering in prospect," says Richard Schilizzi, director of the international SKA project, citing an influx of data larger than the world's total Internet traffic.
The A$2.5 billion radio telescope will be operational by 2024, and could herald spin-off technologies in communications, information technology and renewable energy. Schilizzi hopes it will also inspire a whole new generation of mathematicians, scientists and engineers. "The SKA is the future of radio astronomy," he says.
Giant eye
Working in unison, thousands of receptors will simulate a single telescope with a diameter of more than 3,000 km. Each of the different receptor-types - dishes, arrays and sparse arrays - will be the most cost-effective technology for detecting different portions of the radio frequency spectrum, from 70 megahertz to 10 gigahertz.
Radio dishes
An iconic symbol of radio astronomy, the dish - or parabolic reflector - is an important part of the SKA design. Incoming radio waves are reflected and focussed onto a receiver, which captures and then converts the signals into electronic data so it can be read and measured by a computer. The SKA will have 3,000 radio dishes, each with an optimum diameter between 15 and 25 m, which can swivel to train their sights on different areas of the sky. While they can be designed to operate across a range of frequencies, "dishes are the most cost-effective method to gather the radio waves for short wavelengths", explains Robert Braun, chief scientist for astronomy and space science at Australia's national science organisation, CSIRO.
Phased Array Feed
The SKA will need to be able to survey the sky with unprecedented speed to cope with the wide-field view. "Traditionally, radio telescopes have been equipped with only a single receiver at their focus. This is like using a digital camera with only one pixel," Braun says. One of the SKA 'test bed' projects, the Australian SKA Pathfinder near Perth, is equipped with a technology that could help: a phased array feed that uses about 100 radio pixels. "When used as the receiver in an array of telescopes, the field-of- view of the array is larger by about a factor of 30, allowing surveys to be completed 30 times faster," says Braun.
Dense aperture arrays
To realise the goal of a collecting area of one square kilometre, radio dishes will be complemented with smaller receptors on the ground called aperture arrays. Dense aperture arrays will observe medium frequencies and will be packed at a spacing distance of about half the minimum- observing wavelength of each antenna. "The biggest challenge with this approach is that it requires a very large number of antennas, each of which needs its own receiver electronics," says Braun.
Sparse Aperture Arrays
Unlike radio dishes, which can rotate on their mechanical platforms, aperture arrays are motionless. Parked on the ground, staring straight up, each small antenna can essentially observe the whole sky as Earth revolves. The sparse aperture arrays will be most effective in detecting the lowest radio frequencies, offering incredible sensitivity, sky coverage and survey speed for the cost, says Braun. The spacing between the antennas will allow them to capture a wide range of wavelengths, from one to four metres in length, without sacrificing sensitivity.
Why arrays?
Size matters. Despite being remotely situated, the receptors will all be linked electronically and combine their radio signals. Multiple antennas also means astronomers will be able to look at more of the sky at once and do so more quickly. Furthermore, having multiple dishes provides a safety net: if one antenna breaks down, there are thousands of others that can still be used in the meantime. It also means the SKA can continue to grow, as more antennas could be integrated into the system in the future.
Final destination
Either Australia-New Zealand or South Africa will host the SKA telescope. The final decision, expected in February 2012, will come down to criteria such as radio frequency interference levels, degree of Internet connectivity between receptor locations for data sharing, and building and operation costs.
