Rocket escaping Earth's atmosphere..


by Indy
Tags: atmosphere, earth, escaping, rocket
Indy
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Jul29-07, 09:55 AM
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Hey guys, I didn't really know where to put this and this seemed like the most logical place. Also sorry if there's already been a post like this, I tried searching and couldn't find anything.

Anyway, onto the question. I'm sorta confused about some things to do with rockets and such.

First of all, how fast would something have to be going when it left the ground to escape earth's gravitational pull and ride off into space?

Secondly, why do people say that space is 62 miles above the ground when parts of our atmosphere reach up to 400km away?

Thirdly(?), does anybody here know if NASA give scholarships to Universities in the UK? I've searched on their website and things but can't seem to find anything other than for schools in the US.

Thanks in advance,

Indy

[edit] Also, one more question. Do singularities have infinite mass? Because if they do wouldn't everything in the universe be pulled toward them at an infinite velocity?
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Janus
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Jul29-07, 11:22 AM
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Quote Quote by Indy View Post
Hey guys, I didn't really know where to put this and this seemed like the most logical place. Also sorry if there's already been a post like this, I tried searching and couldn't find anything.

Anyway, onto the question. I'm sorta confused about some things to do with rockets and such.

First of all, how fast would something have to be going when it left the ground to escape earth's gravitational pull and ride off into space?
Right around 11 km/sec to totally escape, about 8 km/sec to attain orbit. Though rockets wouldn't "leave the ground" at this speed. If they tried, they would burn up from air friction. What they do is accelerate through the atmosphere, and by the time they reach these types of speeds they're high enough for air resistance to longer be a problem.

Secondly, why do people say that space is 62 miles above the ground when parts of our atmosphere reach up to 400km away?
This should help answer your question:
http://www.aerospaceweb.org/question...re/q0090.shtml

Thirdly(?), does anybody here know if NASA give scholarships to Universities in the UK? I've searched on their website and things but can't seem to find anything other than for schools in the US.

I don't know, but being a US government agency, my quess would be no.
Thanks in advance,

Indy

[edit] Also, one more question. Do singularities have infinite mass? Because if they do wouldn't everything in the universe be pulled toward them at an infinite velocity?
No, they would not have infinite mass, they would have a finite mass compressed to zero volume.
Astronuc
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Jul29-07, 11:36 AM
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Thirdly(?), does anybody here know if NASA give scholarships to Universities in the UK? I've searched on their website and things but can't seem to find anything other than for schools in the US.
NASA might support US students abroad - but that seems unlikely.

If one is a citizen of UK or other European nation, one should look to ESA, or perhaps contact a particular university or aerospace department about where one might obtain a scholarship.

Indy
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Jul29-07, 12:51 PM
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Smile

Rocket escaping Earth's atmosphere..


Cool thanks guys, you've answered all my questions.

Thanks again,

Indy.
DaveC426913
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Jul29-07, 08:35 PM
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Quote Quote by Janus View Post
Right around 11 km/sec to totally escape, about 8 km/sec to attain orbit.
One thing that is often taken for granted is that escape velocity is an artificial hurdle set by technology.

You need to achieve that velocity before you run out of fuel and your engines shut down. You will need that velocity to be able to coast out of Earth's gravity well.

On the other hand, if you have a (futuristic) fuel supply that is unlimited, then there is no such thing as escape velocity. You could lift off and gain altitude at a rate of one mile per hour all the way to the Moon if you wanted to.
Astronuc
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Jul30-07, 07:16 AM
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Quote Quote by DaveC426913 View Post
One thing that is often taken for granted is that escape velocity is an artificial hurdle set by technology.

You need to achieve that velocity before you run out of fuel and your engines shut down. You will need that velocity to be able to coast out of Earth's gravity well.
The constraints on rocket performance are not artificial, but real constraints imposed by the nature of materials, e.g. pressure which is contrained by strength of materials, which decreases with increasing temperature. The challenge to us is to understand those constraints and expand the envelope while preventing failure. There is only so much energy one can obtain from a material/physical system.

On the other hand, if you have a (futuristic) fuel supply that is unlimited, then there is no such thing as escape velocity. You could lift off and gain altitude at a rate of one mile per hour all the way to the Moon if you wanted to.[/QUOTE]
1 mph? Seems a bit slow. At 1 mph, it would take about ~240,000 hrs (~10,000 days or 27.4 yrs) to get to the moon.

Perhaps one meant an acceleration of 1 mph/s or 1 mph/min?

We don't have access to an infinite supply of propellant, with the exception of the solar wind and GCR which don't provide a lot of thrust.
DaveC426913
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Jul30-07, 10:10 PM
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Quote Quote by Astronuc View Post
The constraints on rocket performance are not artificial, but real constraints imposed by the nature of materials, e.g. pressure which is contrained by strength of materials, which decreases with increasing temperature. The challenge to us is to understand those constraints and expand the envelope while preventing failure. There is only so much energy one can obtain from a material/physical system.

Quote Quote by DaveC426913
On the other hand, if you have a (futuristic) fuel supply that is unlimited, then there is no such thing as escape velocity. You could lift off and gain altitude at a rate of one mile per hour all the way to the Moon if you wanted to.
1 mph? Seems a bit slow. At 1 mph, it would take about ~240,000 hrs (~10,000 days or 27.4 yrs) to get to the moon.

Perhaps one meant an acceleration of 1 mph/s or 1 mph/min?

We don't have access to an infinite supply of propellant, with the exception of the solar wind and GCR which don't provide a lot of thrust.
I'm not sure if you're refuting my statements or not.

Perhaps I should clarify that my comments are really academic in nature. They are about the principle of space travel from Earth, not much use in practice for the forseeable future.

What I"m trying to say is that escape velocity is only a critical target because, in practice, we must shut our rockets down and coast since we can only carry so much fuel. If we run out of fuel at any velocity less than escape velocity, our rocket will fall back to Earth (or into an elliptical orbit).

But in principle if we did not run out of fuel, we do not have to reach any specific velocity. Yes, if we chose to, we could travel at 1mph all the way to the Moon.

I'm not suggesting we'd want to; I just wanted to dispel the possible myth that it is impossible to escape a planetary gravity well without acheiving escape velocity.
Janus
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Jul30-07, 11:36 PM
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Quote Quote by DaveC426913 View Post
I'm not sure if you're refuting my statements or not.

Perhaps I should clarify that my comments are really academic in nature. They are about the principle of space travel from Earth, not much use in practice for the forseeable future.

What I"m trying to say is that escape velocity is only a critical target because, in practice, we must shut our rockets down and coast since we can only carry so much fuel. If we run out of fuel at any velocity less than escape velocity, our rocket will fall back to Earth (or into an elliptical orbit).

But in principle if we did not run out of fuel, we do not have to reach any specific velocity. Yes, if we chose to, we could travel at 1mph all the way to the Moon.

I'm not suggesting we'd want to; I just wanted to dispel the possible myth that it is impossible to escape a planetary gravity well without acheiving escape velocity.
But even traveling at 1 mph away from the Earth, you will reach escape velocity if you travel far enough, since you will eventually reach a distance where the escape velocity is 1 mph.


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