Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 1 decade ago

# In regards to speed and momentum in space.If low thrust equals great speed what about large thrust?

If a small amount of energy is all required to pick up speed in space then double triplle and so on until resistance why cant we try extreme thrust one time. Something like 100,000 mph then simply coast. It would double infinintly until resistance-1-2-4-8-16-36- Thats seems like away to achieve great speed in space. Im probably dead wrong it would not double but i think it would change from original speed in the positive category and so on?

Relevance

Low thrust ACTING FOR A LONG TIME can gradually build up to high speed. That means the engine has to be firing for a long time at low thrust to build up speed and speed stops building up the moment the engine stops firing. The advantage of low thrust is that it does not use much fuel, so enough can be carried to fire the engine for a long time. High thrust, acting for a short time can do the same thing. After the thrust ends, which means after the engine is turned off or runs out of fuel, then the vehicle coasts. It doesn't continue speeding up, it just coasts at the same speed. The shuttle uses a very high thrust for 10 minutes, until the big orange external tank runs out of fuel, and then drops the empty tank and coasts at a constant 17,500 MPH for a couple weeks in orbit. To return to Earth they use small rockets fueled by small on board tanks to change direction slightly so the they enter the upper atmosphere and then friction with the air does 99% of the work to slow the shuttle down for landing.

You may be thinking of ion engines, which have VERY low thrust but can, over many months, reach great speeds. They can reach such speeds not because they are low thrust, but because they are very efficient. If an ion engine could be made that produced high thrust, it could reach the same high speed in a few minutes. So low thrust does not equal high speed, high efficiency equals high speed, with the low thrust being only an unfortunate consequence of the high efficiency design of the ion engine.

• Gene
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