Subject:
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Re: Hypothetical design question
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Newsgroups:
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lugnet.space
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Date:
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Thu, 26 Jun 2003 15:54:27 GMT
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Viewed:
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588 times
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In lugnet.space, George Haberberger wrote:
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In lugnet.space, David Laswell wrote:
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In lugnet.space, Leonard Hoffman wrote:
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Granted, in space you don’t have to worry about air friction or
gravitational pull (relatively), but burning fuel won’t accelerate you to
just any speed you desire.
using some of newton’s theories, it takes a certain amount of energy to
move an object a certain distance. or to say it in vacuum terms, it takes
a certain amount of energy to accelerate an object to a certain speed.
NASA’s rockets will accelerate you up to a given point, allowed they have
enough fuel to burn. this is the amount of energy that the oxygen-hydrogen
engines produce.
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I hadn’t really thought about this problem before, but I can see how it
would be a problem. If your propellent has an exit velocity of 2mph, it
shouldn’t ever be able to make you go faster than 2mph. Once you’ve hit
that point, the propellent wouldn’t even be moving when it exits the
thruster, so it shouldn’t be exerting any force at all on the vessel as it
crawls along, abandoning its propellent as it goes.
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No, if you use simple conservation of momentum, at subrelatavistic speeds,
you can still get a modest boost with a propellant speed of 2 mph. Your speed
increase is
propellant weight x 2 mph / remaining vehicle weight.
since total momentem has to stay the same after using the propellant.
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Yup, but also note that a propellant exhaust speed of 2 mph is the rough
equivalant of having the crew throw things out the back hatch. :)
James
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Message is in Reply To:
 | | Re: Hypothetical design question
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| (...) No, if you use simple conservation of momentum, at subrelatavistic speeds, you can still get a modest boost with a propellant speed of 2 mph. Your speed increase is propellant weight x 2 mph / remaining vehicle weight. since total momentem has (...) (21 years ago, 26-Jun-03, to lugnet.space, FTX)
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