Survivor astronomy style

Marina Joubert

The radio frequency interference measurements at the proposed SKA site took place in some of the remotest parts of South Africa.

A mobile RFI measurement hoisted up in a tree in Carnavon for on-the-spot repairs.

If South Africa wants to host the world's biggest radio telescope, the Square Kilometre Array (SKA), we have to prove that a remote part of our country is "radio quiet" enough to allow this cutting-edge mega telescope to be built here.

In the same way that light pollution from big cities impairs optical astronomy, human settlements and communication networks produce radio waves that interfere with radio astronomy. The radio signals from outer space that astronomers measure can be a million times fainter than a cell phone signal. Therefore finding the best place to build a new radio telescope means getting far, far away from where people are.

Based on measurements over the last three years, South African scientists identified potential sites for hosting the SKA in the Northern Cape.

There is probably no site on earth 100% free from radio interference. The challenge is to find the best possible site with minimal radio interference and where it is also possible to mitigate the existing interference through measures such as providing local communities with alternative television and phone services, thereby getting rid of some of the sources of radio interference. The proposed SKA sites are also shielded against radio interference from the Cape metropolitan areas by a mountain range towards the south.

Engineers at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) designed a unique RFI measuring system that could run unattended at the sites and do measurements across a wide range of radio frequencies. Components such as receiving antennas, low noise amplifiers and spectrum analyzers, as well as control and data storage systems, were all built into three robust trailers that could be parked on rugged terrain. Each unit had to be air-conditioned to protect the equipment against sub-zero winter temperatures and temperatures that soar to more than 40 degrees Celsius in summer. One of these trailers was dedicated to measurements at the core of the proposed site, while two mobile units moved between remote areas where outlying stations of the SKA could be located in other parts of South Africa, as well as Botswana, Namibia and Mozambique. The Independent Communications Authority of South Africa (ICASA) provided key people and expertise to make the RFI project possible.

The team spent months at a time in some of South Africa's harshest environments, where hours can go by without a single car passing on the narrow gravel roads. They had to cope with bad roads, and often no roads, to get to the designated coordinates. "This was as tough as any Survivor series," says Gerhard Petrick, who worked for the SKA South Africa project at the time and spent months in the field for the on the RFI project.

The team was working around the clock to complete the RFI survey in time for a deadline set by the international SKA project. So, when the core site's RFI unit broke down, HartRAO immediately dispatched a rescue mission. They hoisted the cabin up into a tree just outside Carnavon, and fixed it on the spot.

The team enjoyed the cooperation of local farmers on whose land the measurements were done and especially the hospitality of the Louw family, who provided accommodation, meals and logistical support.

South Africa is one of four countries shortlisted to host the SKA. A final decision on the host site is only expected in 2008. The RFI project has also helped to select an ideal location for the Karoo Array Telescope (KAT). The Department of Science and Technology (DST) supports both the SKA South Africa bid and the building of the KAT.