Saturday, December 18, 2010

The really big spacecraft that could

The Voyager spacecraft in the previous post mass less than a metric ton, but to get each of them them on their way from the surface of the Earth required a Titan-Centaur rocket weighing around 630 tons. In contrast the Saturn V (V said as 'five') rockets used to get the heavier Apollo hardware off the ground for the moon missions in the 1960's and 70's massed around 3000 tons each at launch, most of the weight being fuel. There is an excellent wiki page on the Saturns here.

At lift off, the first stage (of three, the Saturn being essentially three rockets put together sequentially) generated more than 7 and a half million pounds of thrust. Even the most powerful jet engines have thrusts measured in thousands of pounds only. I came across this video the other day which shows and describes what happens when all that thrust hits the launch pad, filmed during the Apollo 11 launch in 1969:

As filmed the sequence is only 30 seconds long, but when you are shooting at 500 frames per second you get a lot of room for slow motion, hence the 8 minute clip length. The narration is a bit dry, but full of cool info about what is happening on screen. The first stage seen here would fire for nearly three minutes before being jettisoned with nearly empty fuel tanks (that held nearly 2,000,000 litres of propellants). By that time the Saturn V would be nearly 70 km high and travelling at nearly 2.5 km per second, at which point the second stage would take over. Ultimately only the third stage carrying the actual payload and astronauts would reach orbit.

Couple of points for perspective: There is another 360+ feet/110 metres of rocket assembly above what is visible in frame. For Wellingtonians a comparable reference is the TV mast on Mount Kaukau, which is about the same size. Each of the rocket exhaust nozzles visible from about the 2:00 minute mark is 12 feet/3.8 metres across. The Saturns were epic vehicles on a scale not seen before or since.

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