THE Chinese have been a whiz with rockets for thousands of years. Now they are successfully launching, and recovering, wooden spaceships. To be precise, only the heat shield in the nose cone of the rocket is made from wood. But it鈥檚 the part that is exposed to temperatures of some 1500 掳C, so hot that most known metals get soft and begin to flow.
On re-entry, the friction between the atmosphere and the skin of the spaceship could melt the whole thing into an expensive blob unless a heat-resistant material is used. On the space shuttle, for example, the Americans have settled for a ceramic made of silica.
The Chinese, however, have used a 15-centimetre heat shield made of oak. On re-entry into the atmosphere, air friction causes the wood to burn and the nose cone chars into charcoal. As the craft descends, the outer layer of this charcoal is stripped off by the wind, molecule by molecule. At the same time, the new outer layer of wood turns into charcoal. So the nose cone is always coated with charcoal, even though its total thickness is decreasing. Very little heat gets through to the metal underneath because charcoal and wood are great insulators.
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The first artificial object launched into space on 4 October 1957 was the Sputnik satellite. Right? No 鈥� in fact the first object dispatched into space by the human was actually a manhole cover 鈥� and it was all a nuclear accident! This amazing piece of space age trivia comes courtesy of Air & Space, (vol 6, p 19) published by the Smithsonian Institution.
Back in the 1950s, the Americans were becoming increasingly worried about radioactive fallout from nuclear test so they decided to go underground. In the summer of 1957, a team working on Project Thunderwell drilled a hole about 160 metres deep in the Nevada desert. They then lowered a small nuclear weapon equivalent to only a few hundred tonnes of TNT 鈥� to the bottom. It was sealed with a manhole cover measuring about 10 centimetres thick and weighing a few hundred kilograms. High-speed cameras were positioned to record the blast and the weapon was detonated. The cameras recorded a brief glimpse of the manhole cover as the blast of energy hurled it upwards.
Later analysis of the film showed that the cover had moved at a speed about six times faster than escape velocity. It was fast enough to escape, not just the Earth鈥檚 gravitational field, but the Sun鈥檚 as well.
If the air friction didn鈥檛 vaporise it and if it actually survived, the manhole cover went past the outermost planet of Pluto many years ago, and is, in a sense, our first interstellar ambassador.
SEISMIC data sent back from the Moon seems to support one of childhood鈥檚 most treasured beliefs 鈥� that the Moon is made of cheese!
According to an article in the journal Australian Physicist, the speed that sound travels in Moon rocks is between 1.2 and 1.8 kilometres per second, depending on the type of rock. This is much lower than rocks on Earth 鈥� where the speed of sound is around 5 to 6 kilometres per second. As it happens, the speed of sound in cheeses such as Romano and Cheddar is also around 1.5 to 1.8 kilometres per second.
Convinced? Remember, there鈥檚 no water in Moon rocks, and the rocks are very porous with lots of holes. These two factors make sound travel very slowly in Moon rocks, compared with those on Earth. Science, alas, has spoiled a good story.
WHEN Skylab, the US space station, fell to Earth in 1979, bits of debris landed near Esperance in Western Australia. NASA officials who came to inspect the damage were presented with a A$400 fine for littering by the town council. Kerrie Dougherty, a space historian from the Powerhouse Museum in Sydney, says that the money would have been used for a musuem in the town. But NASA didn鈥檛 pay. 鈥淭hey never saw the joke,鈥� she says.
BACK in the 1970s, the European Launcher Development Organisation had grand plans to use a British rocket, Blue Streak, as the first stage of a satellite launcher from a site at Kourou in French Guiana. After spending almost A$700 million and nine years of effort, not one satellite had made it into orbit. The last of the rockets was sold to a farmer outside Kourou who has finally found a use for Blue Streak 鈥� as a chicken coop.