THE last of 66 massive satellite antennae was delivered last week
to the Atacama Large Millimetre/sub-millimetre Array (Alma) observatory in
Chile.
This observatory studies signals with tiny wavelengths of only 0,3
to 9,6 mm from deep space, but to zoom in its antennae, uses two 28-wheeled
colossal transporters to precisely position the 100-plus ton satellite dishes on
any of 200 foundations.
“I can tell you, it feels cool to move 250 tons the same way as a
toy car,” Max Kraus, project engineer at Eso Garching, told Witness
Wheels.
The transporters were built by Scheuerle to have a technical top
speed of 30 km/h, but are only driven at 20 km/h when unloaded and at 12 km/h
when carrying an antenna along a 28 km road from the Operations Support Facility
at an altitude of 2 900 metres up to the Chajnantor plateau at an altitude of
5 000 metres.
“It takes almost six hours of driving full power at walking speed,”
said Kraus.
For the operators, their biggest challenge is not the size or
speed, but the thin air. Apart from the reduced engine power and icy winds, the
reduced oxygen level causes physical fatigue and reduces mental capacity, which
means people tend to make mistakes and forget things.
Depending on the type of observation, the antennas have to be
arranged in different patterns, which is where the transporters come in.
Alma used two of the enormous transporters, which have been named
Otto and Lore, both measuring 20 metres long, 10 metres wide and six metres
high, each riding on 28 tyres. Empty, the vehicles weigh 130 tons.
“It takes a lot of power to move that much weight, so each vehicle
comes equipped with two approximately 500 kW diesel engines and two 1 500-litre
fuel tanks,” said Kraus.
It is not just the driver who feels the effect of the altitude:
each of Otto and Lore’s 500 kW engines actually generate about 320 kW in the
rarefied air of the Atacama desert.
“Despite their bulk and power, these bright yellow behemoths can
position the antennas to within a few millimetres, ensuring accurate placement
on the antenna foundation pads,” he said.
Many unique design challenges were met in constructing Otto and
Lore. A custom braking system and special safety devices were installed to
protect against accidents and damage to the valuable Alma antennas. The backrest
of the driver’s seat is shaped to allow him or her to wear the oxygen tank
needed for high-altitude driving in Chile. Steering is computerised and the
system is certified for use on public roads, with several steering modes
available: “normal” with front axle steering, “forklift” with rear axle
steering, “max turn” for minimum turning radius and “crab” for lateral
movement.
Kraus said two operators usually ran the machine, but one operator
could safely do all tasks. Other specialists connect the antennas to and from
the ground. During loading and unloading of an antenna, or other critical
manoeuvres, the transporters can be operated by a radio remote control, allowing
the driver to stand outside the vehicle and keep a close eye on the
machinery.
“Without these impressive machines to carry its antennas, Alma
would be impossible,” said Kraus.
