Are they ski jumps or what?

Posted: Tuesday, August 20, 2013 - 3:35pm

Tourists often ask about what appear to be the ski jumps located at set intervals across the Talyawalka flood plain on the Cobar side of town. Former resident and Telstra employee Peter Clark who worked on the installation of the cable, gave us the following information. In the 1970’s the American space exploration program was in full swing.

Satellites launched by National Aeronautics and Space Administration (NASA) were having trouble communicating with each other and earth based stations due to the curvature of the earth. To overcome this they built an earth station at Moree NSW and another at Ceduna, South Australia. Telecom, as Telstra was known then, installed the links between the two stations. It was also used for international and local traffic, though its most important and prime function was for NASA. The link between Cobar and MacDonalds Hill, near Olary, S.A. is a co-axial cable. The project cost $35 million in 1975 dollars ($221,685,000 in todays $).

Laying the cable across the floodplain involved the use of three Caterpillar D9’s and one D7. One D9 would rip a trench 1.5 metres deep. A second D9 would give extra grunt by using its blade to push the one in front. Another D9 ripped a further 1.5 metre down and the cable was then laid, a total of 3 metres underground. The D7 was used to tidy the trench up. The trench went from Wilcannia to the 10 Mile Hill, straight across the floodplain.

The cable drums held 750 metres of cable, so there is a join every 750 metres and a manhole every 1500 metres.

Because the cable had to be accessed whether there was a flood or not the manholes were constructed in the shape of a ski ramp. The first effort was almost totally washed away in the 1976 flood because red sand from the 5 Mile sand hill was used in the concrete. This was despite local advice that said it was not suitable. After another failed attempt to use local sand, dimple fabraform was installed, which then had concrete pumped into it. This method worked. The original idea was for a hovercraft to be used by Telstra staff to access the manholes.

Two hovercraft were sent to Wilcannia however they proved almost worse than useless. They had no reverse thrust and once the bag was punctured they could not be used. So staff went back to using a boat.

The installation crew was well organised, with one specialist team following straight on from the other. They camped near town and the Golf Club lent them a poker machine. The line was commissioned in 1975.

The cable was one of the most important links in interstellar communications. When a space launch was immanent all work anywhere near the cable ceased so there would be no chance of accidental damage causing an outage.

The cable line had power running through it that was rated at 90 milliamps. 60 milliamps is considered deadly. When repairs or maintenance was needed a quiet time was chosen.

Traffic was diverted through the Riverina and the power turned off. This was usually timed between 12 midnight and 6.00am, which made work just that bit harder.

Another structure that can be seen from the highway are ½ tin huts. These are major repeaters, with a cylinder bank alongside which keeps the cable under constant pressure. They work on the theory that while air is coming out, water cannot get in. Any drop in pressure caused an alarm to sound in Broken Hill and service technicians were sent out immediately, no matter what the time of day.

The other communications structure seen along the highway are brick buildings. These house the equipment for the fibre optic cable, which took over from the co-ax. Installed in the late 1990’s they reflect how far technology had moved. Cable arrived in 15 km lengths, so less joins were needed.