Subject:
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Re: Transit Time to Mars
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Thu, 16 Dec 1999 00:40:41 GMT
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Viewed:
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152 times
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On Wed, 15 Dec 1999 21:44:21 GMT, Steve Bliss
<blisses@worldnet.att.net> wrote:
> Assume the distance to Mars is 36 million miles.
Assume that a mile is 1.6 km, because dammit, you don't calculate
these things in imperial (you'd need g in miles/sec. Ugh.)
>
> Show your work. ;)
All right.
x == v0 * t + 0.5 * a * t
x == 57.6e9 m
v0 == 0 (this means I'm calculating from reaching orbit, gimme a break
here)
a == g == 9.81 ms^-2
t == sqrt(2x/g) = 108366 seconds ~= 30 hours, 6 minutes, 6 seconds.
> I worked out an answer to this, but it was too low to believe.
No kidding.
The thing to remember is that maintaining an acceleration of 1g takes
a tremendous amount of fuel. The Shuttle does several g's for a few
seconds with its _entire_ solid-fuel boosters, and then several g's
for another few dozen minutes burning up its entire external fuel
droptank.
That is a _bloody_ huge amount of material gone in a very short while.
You'd need to maintain that not for half an hour, but for 30 hours.
And remember that this grows exponentially - every time you double the
acceleration time or the weight, you near-double the fuel weight,
which means you have to near-double the amount of fuel again, etc.
A doubling in payload or burn time can easily mean one or two extra
stages to your missile, and 10 times the amount of fuel.
Cost gets prohibitve _really_ soon.
Jasper
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Message has 2 Replies:
 | | Re: Transit Time to Mars
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| (...) No it doesn't. It takes a tremendous amount of CHEMICAL fuel, but you need to use something with a much higher specific impulse. The problem is that your chemical exhaust is going WAY too slow, hence you're not transferring much momentum. (...) (25 years ago, 16-Dec-99, to lugnet.off-topic.geek)
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Message is in Reply To:
| | Transit Time to Mars
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| Basic physics word problem, which I thought of because of NASA's publicity about renewed Mars exploration, and putting people on Mars: If a spaceship could accelerate at a constant rate of 1G, how long would it take to get safely to Mars? Assume the (...) (25 years ago, 15-Dec-99, to lugnet.off-topic.geek)
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