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Name: Bryant
Status: other
Grade: other
Location: TX 
Country: N/A
Date: 7/25/2005


Question:
How are the space shuttles able to take off at sea level, wind up in space, and not destroy the ship or the crew? I know that planes have to have expandable skin so they can deal with the pressure changes at low and high flying altitudes, and submarinal crafts have to be pressurized so they do not implode from all the pressure. If the shuttle were to be given expandable skin then as soon as it reached space they would be unable to maintain pressure, and if it had non-flexible skin it would get torn apart before they reached orbit, right, wrong, or both? How does it work?


Replies:
Let us clarify your concept of a "vacuum". A vacuum is zero pressure. It can't be negative, that is, less than '0' atmospheres. However, it can be much greater than 1 atmosphere. So a spacecraft need only withstand an internal pressure of 1 atmosphere. Even a basketball or football is strong enough to withstand that fairly modest pressure. Spacecraft must be sufficiently flexible to withstand vibrations and thermal expansions and contractions, but those are relatively small.

On the other hand, the construction of undersea craft is much more demanding. The internal pressure has to be about 1 atmosphere, for human occupancy, but the external pressure can be hundreds of atmospheres. So the walls need to be strong enough to withstand those crushing pressures. Compared to undersea crafts, space crafts are relatively flimsy.

Vince Calder


The questioner seems to be confused about many things. Airplanes, submarines, and spacecraft are rigid. It is difficult to engineer anything non-rigid that is rugged and durable.

The purpose of all of these is to provide transportation and maintain a livable atmosphere for the people inside.

In the case of airplanes, the designers attempt to maintain close-to-atmospheric pressure inside, even when they fly at high altitudes. To do this, air is pumped in from outside.

Submarines maintain atmospheric pressure inside, even though the outside pressure of water is enormous. Water must be pumped out if there is a leak. Spacecraft, like airplanes, maintain an internal pressure for the astronauts that is near atmospheric, or sub-atmospheric but enriched in oxygen. There's no air in space, so the spacecraft must carry its own air or oxygen for replenishment.

Airships gain buoyancy by using helium gas, which is less dense than air. The blimp or dirigible is not completely filled with helium. If they were, the gas would expend at higher altitudes, and the gas would need to be released or rupture the envelope. Rather, the airship contains one or more ballonets inside; big bags that contain air. As the airship ascends, the helium expands, and the ballonets are allowed to deflate to the outside. That happens inside of the airship and you cant see it happening from outside.

Bob Erck



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