Absolute Zero and the Conquest of Cold  




Topic 10: Spaceflight

Flying into space is another technology that relies on low-temperature physics -- because rocket engines require cold liquid gases to work. At its most basic, a rocket engine is actually very simple. By throwing something backwards with extreme force, the rocket goes forward. This happens due to the principle of conservation of momentum. You can see it yourself when you sit on a twisting stool and throw your arms to the right; the rest of your body sitting on the stool will twist to the left. Or if you stand still on ice-skates and throw, say, a baseball to someone, you will start to slide on the ice in the opposite direction.

The trick for a rocket engine, though, is to get a big enough push to send the rocket moving so fast that it can rise up off the surface of the Earth. The solution lies in creating an explosive, but controlled, burn that fires gases out the back of the engine. In the case of the space shuttle the explosion is made from a fuel, liquid hydrogen, and an oxidizer -- liquid oxygen. And liquid gases, with temperatures near absolute zero are, of course, an example of cryogenics at work.

Storing hydrogen and oxygen as liquids takes up dramatically less room than it would to store them as gases -- which is important on a rocket where space is at a premium. The space shuttle, for example, holds the liquids in two huge external tanks, which are insulated with a layer of spray-on polyisocyanurate foam insulation to keep them cold. One tank holds 1,500,000 liters of liquid hydrogen and the other holds 550,000 liters of liquid oxygen. Together they weight about 1.6 million pounds (719,000 kg). The two liquids are funneled together at an amazing rate -- the equivalent of emptying a swimming pool once every 10 seconds. They are burned in the main combustion chamber to produce exhaust that shoots out of the bottom of the space shuttle at approximately 6,000 mph (10,000 km/h) -- thus sending the space shuttle into orbit.

Additional Resources

More Topics

  • Topic 1: Measuring the Cold - Thermometers
  • Topic 2: Understanding Heat and Energy
  • Topic 3: States of Matter
  • Topic 4: Refrigeration
  • Topic 5: Cryogenics
  • Topic 6: The Quest for Absolute Zero
  • Topic 7: How Animals Survive the Cold
  • Topic 8: Superconductivity
  • Topic 9: Astronomy
  • Topic 10: Spaceflight
  • Topic 11: Agriculture
  • Topic 12: Cold Medicine
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