Rocket science question .

en.wikipedia.org...
Earths escape velocity = 25,000 ( apx )

Theory is you need to reach this speed to escape earths gravity .
BUT here is my kicker Lets start with this a space elevator ( no humans haven't built one nore likely to Because nothing we can make that long that would hold up .)
But if we did then we could send you to space using it .-----NO escape velocity nessery just louse elevator music for two hours .
So here is my question
Take a type of plane - rocket combo say its going 500 mph UP and has enough fuel to do this for weeks .
Now it WILL keep going up ! So it WILL get into space . But then why all the hubub about escape Vol?
Theory is it has not escaped earths gravity ok ??/ so it keeps flying say to the moon then the moons gravity is stronger so wile it hasn't acutely escaped earths Gravity is is still at the moon and now in the moons gravity It never needed to escape earths gravity just get closer to another body in space with Gravity .
So tell me why this isnt possible because its the one thing i never understood about space travel .
And good luck lol better be a link btw . Not that i have ever found anything to explane this .

ps lets leave orbiting earth out for taht yes cant get around it but this is a straight UP to teh moon mars or some other body thing .
thanks

Lord i cant believe this 35 years and now i think i know the answer .Must ahve needed to see it in letetrs .
ok hows this for answer my own post question .
It ONLY matter because we ( HUMANS First put ANY ship Apollo or other wise into Orbit .Then send it to its destination .
That is the Answer is must be We COULD do it the way I think But need a better ship no orbit required .
now can you show me i am wrong lol .

a reply to: midnightstar

First, "escape velocity" is an unfortunate term. You never "escape" a gravitational pull. The force just gets smaller by a factor of the square of the distance. So, if you double the distance, the force is reduced by a factor of 4, and so on, asymptotically toward zero. Keep in mind that an object in orbit isn't just hovering there. It is constantly falling toward the earth. It's just that it's moving so fast that the earth's surface, because it is curved, is falling away from the object at the same rate as the object is falling toward the surface. So what they mean by escape velocity is the velocity needed to get to a stable orbit where the object falls at the same rate as the earth's surface bends away. There is a formula you can use to determine that velocity. It is: escape velocity equals the square root of (2 times the gravitational constant times the mass of the object to escape, divided by the radius of the object to be escaped.) The gravitational constant is 5.673X10^-11 N m^2/kg^2. I hope this helps. If not, find a class in orbital mechanics at your local university.

a reply to: midnightstar
The moon is orbiting earth so when the ship reaches the moon if it lands on the moon it hasn't escaped Earth's gravity.

The moon and the ship that landed on it will orbit the Earth together. If the ship had escape velocity you could avoid the moon and it would keep going past the moon.

Take a type of plane - rocket combo say its going 500 mph UP and has enough fuel to do this for weeks .

If you try to calculate how much fuel this will take you will likely run into problems getting enough fuel on the rocket to do this. The more fuel you add, the more extra fuel you have to add to lift the extra fuel, which is a big problem with typical rocket technology.

a reply to: midnightstar

You're not expressing yourself very clearly, but orbit isn't part of the calculation for escape velocity in your link so I'm not understanding why you think orbit matters. No orbit is necessary.

originally posted by: F4guy
a reply to: midnightstar

First, "escape velocity" is an unfortunate term. You never "escape" a gravitational pull.

It's not intended to mean you escape the gravitational pull, it's intended to mean the object is moving away fast enough so it won't fall back down when you send it up.

a reply to: midnightstar

escape velocity is the speed needed to get into "orbit". If you could go up continuously at ANY speed you would eventually get into space but you would fall back down when you stopped going up. "orbit" is when you fall in an arc that is larger than the earth and just go all the way around. You need to be going forward (not up) to fall "around" the earth.

a reply to: F4guy

You've confused "escape velocity" with "orbital velocity".

Orbital velocity is the speed needed to establish a stable orbit at a given altitude. Minimum orbital velocity is approximately 17,000MPH.

Escape velocity is the minimum speed needed to escape Earth's gravity (actually, Earth's gravity well).

In the OP's scenario, a vehicle traveling "straight up" (with sufficient fuel to continue at that speed indefinitely), per the OP, "should" be capable of reaching the Moon.

Except that it can't because the force of gravity will pull the craft into a ballistic trajectory resulting in an orbit appropriate to the vehicle's velocity.

And no, you can't just "keep steering the rocket straight up", because as your rocket rises "straight up", the Earth turns under you; that's called an "orbit", or, at least the start of one!

originally posted by: 00018GE
a reply to: midnightstar

escape velocity is the speed needed to get into "orbit".

No, it's not. If you're in a closed orbit you're not still moving away. If you've reached escape velocity you would still be moving away. The OP's link says this if you read it:

an object which has achieved escape velocity is neither on the surface, nor in a closed orbit (of any radius).

a reply to: midnightstar

Here you go.

Escape velocity is only a comparison number in reality. It is theoretically the minimum speed necessary for an object to escape the gravitational field of a planet, and thus depends on (is a function of) the mass of the planet and the distance from the planet. If a ship were travelling straight up with continual thrust, the escape velocity becomes a meaningless term, as the distance from the planet is continually increasing.

Pretty much everything you suggest is being considered. At this point, the weight of the fuel necessary to break the Earth's gravitational field starting at sea level is so high that it needs additional fuel just to carry the fuel. The idea of orbit is that fuel could be delivered to the ISS by shuttles that need not reach such velocities, then used to refuel a ship for adventures beyond Earth orbit. By using only enough to fuel to reach orbit in an infinite time window (meaning it can take longer and be more efficient to travel to orbit), farther flights become more fuel-efficient in limited time windows.

TheRedneck

a reply to: midnightstar

If you just lift something up, even to very distant from the Earth, and release it, it will usually fall back down.

This is because the Earth's gravitational field doesn't just stop at any height threshold, but reaches out far into space.

The only ways not to free-fall back down are to orbit the Earth, or to go past orbit (which implies a velocity, orbital or greater), or to continue to resist gravity with a constant thrust or lifting force.

Exceeding escape velocity is not the only way to get into space. It just happens to be an efficient one where beyond that point, you are just free-falling away from Earth.

a reply to: midnightstar

What you are proposing reminded me of an old Andy Griffith show, Salvage 1.

If anyone in this thread hasn't played 24 hours of Kerbal space program, go get to it.

basic space physics are hard, this educational game helps.

The earth's spin is used to help achieve the velocity needed to break the force of gravity. You would not get that help with a straight shot up.
a reply to: midnightstar

originally posted by: lordcomac
If anyone in this thread hasn't played 24 hours of Kerbal space program, go get to it.

basic space physics are hard, this educational game helps.

KSP is awesome!

I recommend it to anyone curious about space and rockets.

originally posted by: moebius

originally posted by: lordcomac
If anyone in this thread hasn't played 24 hours of Kerbal space program, go get to it.

basic space physics are hard, this educational game helps.

KSP is awesome!

I recommend it to anyone curious about space and rockets.

Aye!
And I recommend it to anyone with questions about space travel. "Why don't we just..." Questions are most easily answered with a good demonstration. The ksp universe is something like a 10:1 scale, and it demonstrates pretty well what's involved with space travel.

A vast misunderstanding of physics is strong with OP, reminds me of someone saying "If my car can drive 5mph, if i am going the speed of light at the event horizon, then I can just drive away at 5mph" totally misunderstanding physics that basically mean you require infinite energy to do such a thing.

The other one is "if i go straight up at a constant speed, I will escape gravity." which sounds reasonable, but isn't really the case energetically.

a reply to: midnightstar

"no humans haven't built one nore likely to Because nothing we can make that long that would hold up ."

Want to bet, carbon nano tubes or even better diamond nanothread would be more than sufficient to do the job and take the load of the tether if and when we manage to scale up the production technique and procedures.

Fact of the matter is that a space elevator would usher in a new golden age for humanity allowing us to colonise low Earth orbit cost effectively.

Tell you one thing better to build a space elevator than nonsensical 2000 mile long border walls.

originally posted by: midnightstar
en.wikipedia.org...
Earths escape velocity = 25,000 ( apx )

An important part of that Wikipedia page says this (the important part is emphasized by me):

"...Once escape velocity is achieved, no further impulse need be applied for it to continue in its escape...."


Or, as I read in another definition (again, the important part is emphasized by me):

"Escape velocity is the speed that an object needs to be traveling to break free of a gravity well and leave it without further propulsion."

That is to say, 25000 mph is only the coasting speed for escape velocity -- NOT the speed all things need to be moving to escape Earth's gravity. There is no real minimum velocity if we are talking about things under continuous thrust.


For Example:
If a spacecraft had the ability to continuously provide engine thrust, a spacecraft could conceivably escape Earth's gravity well with a velocity of only 1 mph, as long as it was providing a constant thrust to keep it from falling back to Earth.

a reply to: andy06shake

Researchers at the Hong Kong Polytechnic Institute figured out that even a single atom out of place in the structuring of a carbon nanotube reduces the strength of the structure by dozens to factors.

And that's a serious problem, since it's very hard to create large-scale sections of carbon nanotubes without a single flaw.

Popular Science - Carbon Nanotubes Can't Handle a Space Elevator.

Trying to make multiple strands of 60+ miles of carbon nanotubes with out a flaw??

Cool sci-fi idea but we are not even close yet. Guess we're still stuck with rockets or Aerodyne Research's lifters.

Right I do understand it now .
ovesly needing rocket fuel as fuel makes the ships heaver and the size vers the fuel becomes the problem .
a billion tons of fuel could build a ship big enough it would just sit on the pad a burn never moving .
So its more of a well we got to do what we got to do thing .
But if we could produce thrust with a fuel that was 20 times less in amount or weight then Bingo .
Ram jet maybe ?
really kinda pointless even if it could be done now a sip going 500 mph isnt getting anywhere fast lol .
just getting to the moon 138000 miles would take 270 hours or so almost 2 weeks .
forget mars .
This has always just been a why not thing I always have understood the need for speed .
5 billion miles to the edge of the solar system even voyagers have just got there after 40 years at over 28000 mph
all numbers are just rounded off or more or less as i did not look it all up to be excat ty