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Balloon Launch Part 2
In the last installment, I wrote how every few years, a bunch of scientific balloons are launched in Alice Springs. NASA supplies the balloon, the launch crew and the tracking crew - but the scientists provide the gondola and its telescope payload.
 We were lucky enough to meet a Caltech scientist, Steve Schindler, who was the Chief Scientific Officer for one of the balloon teams. Steve was such a "Scientific Hotshot", that he was one of the first to make the early significant discoveries about a nearby star that exploded in 1987. (When that star exploded and went supernova, it put out, in one second, as much energy as all the other stars in its galaxy would put out in their entire lives!)
The launch crew and the tracking crew liked Steve and his gondola, because once they got the balloon flying, his experiments always worked - so their time and effort wasn't wasted. Another thing they liked was that his gondola and its telescope always survived the landing. This was because before Steve became a physicist, he was an engineer. He used his considerable skill in Finite Element Analysis to design a gondola that was light enough to fly, and strong enough to survive the rigors of landing. This was the seventh flight of his gondola. He had designed it to survive a 10g force vertically, and a 15g force at 45° to the vertical. The launch crew referred to Steve Schindler's gondola as the "Rolls Royce Model". I saw why when he gave us the guided tour. Each single bolt had been individually numbered, X-rayed, crack-tested, and then finally certified! We were able to get the guided tour because they had an aborted launch that morning. In fact, we had to turn up at Alice Springs Airport four times, before we were lucky enough to witness the launch.
 The fourth time, we turned up at 4 AM. After first wandering around in the dark, and keeping out of everybody's way, we began to sense a feeling of optimism.
It's a real art launching a scientific balloon. The wind velocity has to be less than 16 knots. But the launch crew don't want zero wind velocity, because then they have very little control over the balloon. What they love is a wind with velocity of a few knots, with no gusts, and in a constant direction. This morning, the wind was light and constant, with no gusts.
 Once again, the launch truck went out onto the field with Steve's gondola hanging off the front end. The gondola was attached to the parachute laid out on the ground. The parachute was joined to the balloon, which came wrapped in a metre-wide blue condom, some 200 metres long. The balloon in its condom lay on a long skinny tarpaulin. This tarpaulin protected the incredibly thin membrane of the balloon from any sharp burrs or thorns. Suddenly the mood quickened. The launch team had decided that the weather was satisfactory, and they decided to launch. The enormous blue condom surrounding the balloon was split open. A truck carrying a weighted roller about 1.5 metres in diameter was rolled forward, and the balloon was passed under the roller. Then they began to inflate the balloon. From this moment on they were committed.
There was no way that they could possibly pack the balloon back into its blue condom without creasing it. Even if the wind began to gust, they'd still have to launch. Of course, if the wind got so high that it threatened to damage the gondola by dragging it along the ground, then under those circumstances they would definitely not launch. But otherwise, they were committed to launch.
 Compressed helium gas came rushing from the two semi-trailers, through two black plastic pipes that snaked on the ground, and then into two large open-mouthed metal tubes, about 30 cm in diameter and about one metre long. Tied around these metal tubes were hoses about 100 metres long, and the diameter of a man's thigh, that reached up to the balloon.
As the end of the balloon filled with gas, the truck holding the heavy roller gradually rolled closer to the parachute and the gondola on the launch truck. Tonnes of metal weights held the roller truck down. Finally, the roller was pivoted out of the way. Fairly slowly at first, but then faster and faster, the balloon began to rise in the air. All the gas was at one end, so it looked a little like a sperm cell with an inflated end at one end, and a very long skinny tail. At first, the balloon was upwind of the gondola, but the wind carried it slightly downwind. The plastic stretched and the balloon came to a halt and then gradually swung back to being directly over the gondola. It continued to swing until it was slightly upwind of the gondola.
 At that instant, the launch crew released the gondola from the launch truck. The balloon was on its way, with everybody cheering. Once the balloon is flying in the upper atmosphere, it spins one complete turn every five minutes. The desired altitude is usually around 120,000 to 130,000 ft (36 to 40 km).
When the scientific crew have gathered enough data, they go through a process which they call "Cutting It Down". They broadcast a radio signal, which simultaneously tears a section of rip-stop fabric on the balloon, and blows the explosive bolts that hold the balloon to the parachute. The gondola free falls for a while, until the parachute opens at around 70,000 to 100,000 ft (21 to 30 km).
 The balloon is torn apart by the winds. Because the fragments are so light and so large, they will usually travel far enough to fall into the Pacific Ocean. The balloon is made of plastics which are ultraviolet-degradable and bio-degradable, so it will rapidly disintegrate. Even so, I wouldn't like to have a 250-metre blob of Cling Wrap falling on top of me!
You can see an animation of the balloon launch... but it's a VERY BIG graphics file (372KB) so it will take a while to load!
Copyright © Karl S. Kruszelnicki
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