escaping earths gravity

[justncredible]

ok, on the MIB II post BA says to escape the earths gravity you would have to go 11KM a sec. UUUUMMMM,,, WHY???? escapeing the earths gravity is not about velocity,,, getting from earth to space could be done with going faster than a crawl if you put enough power behind you. why does rentry vechicles have heat shelds???? they come into the atomshpere fast and firction heats it up,,, if you came in slow under power you would not need heat shelds...... before we put up rockets men used ballons,, they went up like 50 miles, they were on the "edge" of space, they had no great velocity, floated up,,, no i do not buy into the 11KM/s,,,, can anyone prove you have to go this fast?????

[Silas]

Think of it as a question of firing a cannonball straight up.

If you fire a cannonball straight up at too small a velocity, it will fall right back to earth. It slows down as it rises, then speeds back up until it hits the ground again.

There is a minimum velocity, such that the cannonball will keep slowing down as it rises...but will keep rising. It won't fall back to the ground, but keep edging away, slower and slower.

If you fire the cannonball upward with a velocity greater than that minimum velocity, it will not only keep on going forever, but it will maintain a residual upward speed. The Voyager probe has that residual speed.

Now, yes, we use rockets and not cannons, and so the energy is "spread out" over time instead of coming all at once. The math works out more or less the same.

That minimum velocity needed to escape the earth is 11 km/s or roughly 7 milles/s.

On another thread, I posted the "vis viva" equation, which is very useful in working with orbital velocities.

Silas

[Kaptain K]

11kps (7miles/sec) is the ballistic escape velocity. As Silas said, it is the velocity needed by a cannon shell (or Saturn V rocket) to escape Earth's pull. IF you had unlimited power, you could escape at 1kph, but it is extremely wasteful of fuel to do it that way!

[thkaufm]

escapeing the earths gravity is not about velocity

Yes it is.
Gravity doesn't go away just because you've traveled out past earths atmosphere.without velocity you will just fall back to earth. You can escape earths atmosphere as slow as you want, but you'll have to shut down your engine eventually. It's kind of like driving up a hill and then shutting off your engine.
without enough speed you'll never make it.

before we put up rockets men used ballons

A balloon is just floating on heavier air the same as a boat floats on heavier water.
A balloon works because of gravity, so it's not really escaping from it.

Tom

<font size=-1>[ This Message was edited by: thkaufm on 2002-07-07 21:02 ]</font>

[nebularain]

On 2002-07-07 20:59, thkaufm wrote:
A balloon is just floating on heavier air the same as a boat floats on heavier water.
A balloon works because of gravity, so it's not really escaping from it.

Just to add to that, I forget the exact mechanics and don't know where to look for the info [img]/phpBB/images/smiles/icon_redface.gif[/img] , but with a balloon there comes a point where the atmosphere becomes too thin for the balloon to to rise any higher; I believe the weight of the outer air because close or equal to the weight of the inner air. So that's as high as it can get.

[Gsquare]

On 2002-07-07 16:13, justncredible wrote:
ok,.....escapeing the earths gravity is not about velocity,,, getting from earth to space could be done with going faster than a crawl if you put enough power behind you...

Ha, Ha! Good point Justin; yes, it is possible to crawl into space. Usually when speaking of escape velocity there is an implied assumption that we are talking about the velocity we need to reach where no further energy is required to escape. Even though its 'not about velocity', it IS about economics, and doing it slowly requires a huge and prohibitive amount of energy (and $). Not to mention, how are you going to shuttle such a huge amount of energy to the rocket to keep it suspended against gravity while it creeps forward?

G^2





<font size=-1>[ This Message was edited by: Gsquare on 2002-07-07 22:56 ]</font>

[honestmonkey]

There was a TV show in the late 70's, maybe eairly 80's with Andy Griffin. Issac Asimov was the science advisor, I believe. In it, they built a space ship from a cement mixer. The only thing that was outrageous (ie., outside the realm of science at the time) about the show was the fuel used, Asimov said. The "brilliant scientist" had concocted a fuel that had a lot of energy, and so the space ship didn't need all the stuff to protect astronauts from G-forces (like seatbelts), they had all the power they needed to 'creep' into space.

I think there were other implications, like a trip to the moon actually being quicker at constant exceleration half way then constant deceleration. They also used the craft to try and push an iceberg down to LA for fresh water.

Anyway, yes, if you have power to burn, then you can inch your way into space, as it were.

[Hale_Bopp]

Yes, I remember the movie you are referring to. It was called Salvage I. That was a long time ago...can't remember how old I was, but I was young and impressionable [img]/phpBB/images/smiles/icon_smile.gif[/img]

There was a short lived television series based on the movie as well. It might have lasted one season, tops. Maybe I will have to do a google search and see if I can find anything more on it.

Rob

[honestmonkey]

It's just amazing what you can find on the net. Yes, "Salvage 1". They apparently did a bunch more than go to the moon. Andy Griffith starred. There were apparently 20 episodes, 16 of which actually aired during winter of 1979, and two in the fall. I was - well, never mind how old I was, old enough to remember liking the show. [img]/phpBB/images/smiles/icon_smile.gif[/img]

[Hale_Bopp]

Well, you can find a couple of web pages on anything...here are some on Salvage 1...bet we can find some BA in here [img]/phpBB/images/smiles/icon_smile.gif[/img]

http://www.snowcrest.net/fox/Salvage/

http://www.geocities.com/CapeCanaver.../salvage1.html

Rob

[Phobos]

OK so the consensus of opinion is that you cannot crawl into space, and it is a bad idea to try to think of a way because it will not be an economic solution.

Well maybe but ...

I actually fully disagree with this notion and believe that a slow entry into Earth orbit is the BEST solution. The problem is to find a good way to do it - not easy, but I do not believe that it cannot be done.

No good me just leaving it there, I have to propose a method that may be possible to show that it may be possible so here goes;

Reading the other posts I noticed a common complain to crawling into space is that you would need to take a lot more fuel with you, and in so doing you would make your journey more expensive.

I suggest crawling into space with absolutely no fuel whatsoever on board your spacecraft. I propose this using one of three methods (however there are other possiblilities).


METHOD 1 - ENERGY TRANSFER FROM EARTH
-------------------------------------

This method would probably be best used for the first part of our launch. Mazer beams transfer energy to our spacecraft instead of realying on heavy on-board fuel (and fuel tanks, and fuel to carry the fuel).

The spacecraft itself would probably be only marginally heavier than its payload, but would probably be spread over a large volume (designed along the lines of a airship).

Once the spacecraft is flying free of the clouds its second (and eventually primary) fuel source would kick in - solar energy.


METHOD 2 - SOLAR ENERGY
-----------------------

Our spacecraft would be one giant flying solar panel like this NASA project.



NASA's solar aircraft

The helios project is an aircraft which can attain an altitude of 100,000 feet (about 30KM). If the design was expanded, used modern materials, and was assisted by ground based mazer beams (microwave version of a lazer) we may be able to boost the altitude to somewhere between 40 and 60 KM's. The last stage would then involve boosting the craft into low Earth orbit. For this we may need fuel, but not from Earth.

I propose that the last leg could be achieved by sending rocket fuel to our spacecraft from - THE MOON !!!


METHOD 3 - LIFT IT FROM ABOVE
-----------------------------

If a lunar base were established on the moon, rocket fuel could be manufactured from water deposits at the poles. As resources start to dwindle we would have to look to acquiring our fuel from further afield (Mars, Asteroids, Comets ...), but for the time being there should be enough to serve our purposes.

The Lunar station would be powered by a combination of nuclear and solar energy. The nuclear reactors would be designed to utilise the He3 and He4 which are in plenty of supply on the lunar surface. The post would be mostly automated, and although there would be a few people manning the operations, the bulk of the work would be achieved by telepresence workers operating robots from Earth.

The lunar base would also use some local materials to construct "lifters" which would be used to raise our spacecraft (or probably just the payload) to the desired orbit.

Phobos

<font size=-1>[ This Message was edited by: Phobos on 2002-07-08 19:44 ]</font>

[Chip]

A similar idea was done in one of the British Mouse That Roared comedies in the 60's. Salvage 1 also had a terrific opening scene where Andy landed in a very cool WWI Nieuport 28 (for you pilots out there). - But getting back to astronomy (sort of) -- the question remains - if you had some kind of super duper engine that didn't blow up under constant enormous pressure, and a super duper fuel that constantly provided enough thrust to cause your rocket ship to continue to slowly rise, would you be able to eventually escape Earth's gravity and go to the moon -- though more slowly than normal escape velocity?

(I suspect that achieving 11 KM per second escape velocity though "hard" to do with household tools, is easier to achieve from a engineering point of view, than all the fuel needed to rise up majestically. Besides, if you had that fantastic engine and fuel, why waste more of the fuel on a "slow" launch? Why not blast off into escape velocity, and then have all that extra gas left fly around and explore Mars?

In a sense big rockets do lift slowly at the very beginning of a launch, and build up velocity from there. Present rocket fuel isn't too far removed from the fuel discussed in Salvage 1.

Also, keep in mind that if you could go to the moon in your car at 60 mph - it would take many months, and many years to get to Mars. [img]/phpBB/images/smiles/icon_wink.gif[/img]

[Wiley]

On 2002-07-08 19:07, Chip wrote:
But getting back to astronomy (sort of) -- the question remains - if you had some kind of super duper engine that didn't blow up under constant enormous pressure, and a super duper fuel that constantly provided enough thrust to cause your rocket ship to continue to slowly rise, would you be able to eventually escape Earth's gravity and go to the moon -- though more slowly than normal escape velocity?

Yes.

Escape velocity is initial velocity you need to overcome gravity. This is a actually a pretty simple calculation. Neglecting air resistance, the final energy must equal the initial energy

K₀ + U₀ = K_f + U_f

where K is the kinetic energy and U is potential energy. The final state is at infinity so U_f = 0 (the pull of gravity is zero) and assume the final velocity is zero (K_f = 0). This leads to

K₀ + U₀ = 0.5 m v^2 - G M m /r = 0

And finally

v_esc = (2 G M / r)^(1/2)

where for our case M is the mass of the earth and r is the radius of the earth.




<font size=-1>[ This Message was edited by: Wiley on 2002-07-08 20:03 ]</font>

[roidspop]

You still have to have reaction mass...something to throw away. The air would work just fine up to an altitude of maybe 50k ft or better. Above that, you have to lug along whatever it is that you're going to toss away for thrust. The slower you go about gaining velocity, the more stuff you have to carry.

I like the beamed power. How about combining the Roton space-helicopter idea with laser/maser power beaming? The rotors apparently give you a terrific specific impulse, and using ground power instead of onboard propellants to operate the tip jets would improve efficiency just that much more. The guy to talk to us about this is probably over on the Lunar Hoax thread...Jay Utah eats this stuff for breakfast.

Everything else you propose sounds good. Now, run for President!

[Wally]

they come into the atomshpere fast and firction heats it up,,,

Actually, I heard (or read. Probably here somewhere) that it isn't friction that causes the heat at reentry. It's actually the compression of the air by the module that causes it to heat up.

[DaveC]

Well, compressing a gas certainly does cause it to heat up - that's the principle behind a diesel engine which uses a 22+:1 compression ratio to ignite the fuel/air mix in the combustion chamber without a spark plug, so it makes sense that air compression is at least partly responsible for heating of a space capsule upon reentry. Undoubtedly friction is also a factor - maybe one of or thermodynamics or rocket science experts can tell us the relative contributions of each mechanism.

[traztx]

Well since we're talking future... how about antimatter rockets?

You need a facility that receives energy and uses it to generate antiparticles and store them in a field. Then transport the trap to the rocket. Just a little bit should do the trick.

The engine can shoot antiparticles at a target which becomes a gamma ray focused towards some shielding on the planet.

Light, yet refreshing.
--Tommy

[Totally Skeptical]

When a rocket lifts off it is starts a 0ft/s and gradually accelerates. The idea of escape velocity is flawed in it its basic premise , as so much of science in these dark ages of science. As I understand it, escape velocity is defined as the he velocity needed for a celestial body or artificial construct to overcome the gravitational pull of another, larger body and not fall back to that body's surface. Escape velocity is determined by both by the mass of the larger of the two bodies and by the distance of the smaller object from the smaller object's center of mass. Depending on its initial trajectory, a smaller body traveling at precisely the escape velocity for it's distance from the larger objects center will enter a orbit around the larger body. A bit higher and the distance will gradually increase, with an acceleration. The escape velocity at the Earth's surface is about 11.2 kilometers per second (25,000 miles per hour) but decreases as altitude or more properly distance from the Earths center of gravity increases. Escape velocity is one of those catch phrases that really makes no sense and has no definition quantification. It is not nessecary to reach escape velocity of leave Earth but constant thrust would need to be applied. In most space vehicles escape velocity is not reached until well into the burn sequence. In my opinion "escape velocity" would better be a called balanced orbital velocity, but hen I am not a rocket scientist nor do i have a PhD.

[Totally Skeptical]

The real breakthrough will come when we discard the 'gravity well' idea and understand what gravity actually is. In my own presentments I have been able to overcome the force of gravity using much less energy than any conventional design currently in use, and the concept is based totally on mechanical concepts. The most complicated idea is seldom the best, as Werner Von Braun proved by essentially copying ancient chines techinolgy.
I give you all a hint and see if you can figure it out.

I got to thinking about an article I read years ago in a technical publication concerning new automobile engine designs. There was a certain engine developed back in the 80's by GM (a 4.3 liter V-6) that had an unusual tendency to put an upward force on it's engine mounts while it was running, caused by particular unbalance inherent in the design. In my own personal experiments it takes less that two horsepower to lift 100 pounds to any altitude desired.
Drawbacks are a control-ability issue that would require sophisticated computer control to solve that i d not have the resources or knowledge to solve, and the problem that mechanical failure is inevitably catastrophic and unacceptably dangerous to anyone riding in such a machine or who happened to be under it when it was in operation.
Total redundancy would be required. I am certain this technology is already in use with the military skunk works division and responsible for the triangular shaped craft so many people are seeing. It is most probably nuclear powered

My own attempts at remote control of the aforementioned anti gravity machine have resulted in some extremely hair raising failures, but proved the concept viable and very efficient.

[pzkpfw]

Totally Skeptical, these sections of the forum are not the place to present your own personal ideas and theories, they are for current known science. You can call this censorship or whatever you like, but just please stop doing it. The internet is a big place; you can even go start your own website to present your ideas free from our rules.


And for the record:

From Wikipedia: http://en.wikipedia.org/wiki/Escape_velocity (usually a good source for a basic overview of current science):

... A rocket moving out of a gravity well does not actually need to attain escape velocity to do so, but could achieve the same result at walking speed with a suitable mode of propulsion and sufficient fuel. Escape velocity only applies to ballistic trajectories. ...

So the "issue" of this thread is mostly about the misrepresentation (or perhaps overly strong use of) of a simple term.

[Jens]

As I understand it, escape velocity is defined as the he velocity needed for a celestial body or artificial construct to overcome the gravitational pull of another, larger body and not fall back to that body's surface.

Yes, without any additional burn.

Escape velocity is determined by both by the mass of the larger of the two bodies and by the distance of the smaller object from the smaller object's center of mass. Depending on its initial trajectory, a smaller body traveling at precisely the escape velocity for it's distance from the larger objects center will enter a orbit around the larger body.

I'm not sure that's true. I think an object going at precisely the escape velocity will approach an orbit, but I don't think it will ever reach it (mathematically speaking).

Escape velocity is one of those catch phrases that really makes no sense and has no definition quantification.

A catchphrase with no definition? But you yourself defined it above. . .

In my opinion "escape velocity" would better be a called balanced orbital velocity, but hen I am not a rocket scientist nor do i have a PhD.

You can call it whatever you want, but it still exists as a physical quantity. I'm not sure what upsets you about it. It's a real figure, as you seem to understand by what you wrote above.

[Totally Skeptical]

And for the record:

From Wikipedia: http://en.wikipedia.org/wiki/Escape_velocity (usually a good source for a basic overview of current science):

It has long been established and accepted the Wikipedia cannot be used as a valid reference since anyone can post whatever they want to it. It is simply a false reference used by disinformation ops who in many confirmed caseswrite their own backups and post links to them, and this is well known you an I both.

[pzkpfw]

It has long been established and accepted the Wikipedia cannot be used as a valid reference since anyone can post whatever they want to it. It is simply a false reference used by disinformation ops who in many confirmed caseswrite their own backups and post links to them, and this is well known you an I both.

Leaving out the conspiracy angle, what you say is more or less true. However, wikipedia (with known reservations) is still a useful guide to current scientific understanding. While some people with axes to grind have been known to vandalise wikipedia pages to push their own view, a page such as the one I linked to will tend to get edited back to "correct" when this happens - because there are more people who understand science than there are cranks.

Really, the main point of posting that Wikipedia link, was to show that one of the issues you raised in your post is already well understood. Do you really want to say that what's in that wikipedia page is totally unreliable? The bit I quoted agrees with you.

Of course, you are welcome to provide your own references to current science, on this topic. It would be good for all of us.

Edit: to be more specific, in a discussion around here you don't get to write-off a reference to Wikipedia by simply saying "it's Wikipedia so it can't be trusted". You'd need to provide your own alternate references that are somehow more reliable.

(You are also welcome to start a new ATM thread (when your current ATM thread has had its 30 days) to present your own ideas on escape velocity - with whatever references you wish to provide.)

[Jeff Root]

I edited these quotes to correct several typos and other
errors, so that it says what I think the poster intended.

When a rocket lifts off it starts at 0 ft/s and gradually
accelerates. The idea of escape velocity is flawed in its
basic premise, as so much of science in these dark ages
of science. As I understand it, escape velocity is defined
as the velocity needed for a celestial body or artificial
construct to overcome the gravitational pull of another,
larger body and not fall back to that body's surface.
Escape velocity is determined both by the mass of the
larger of the two bodies and by the distance of the smaller
object from the larger object's center of mass.

That is essentially correct. It is actually the sum of the
two masses, not just the mass of the larger body, but
in many cases the masses are so different that the mass
of the smaller body can be ignored.

Depending on its initial trajectory, a smaller body traveling
at precisely the escape velocity for its distance from the
larger object's center will enter an orbit around the larger
body.

That is almost but not quite correct. Circular orbital speed
is half the square root of 2 times the escape speed at a given
distance. A small body travelling away from a larger one at
precisely escape speed will decelerate at an ever-decreasing
rate as the distance increases. The distance never stops
increasing and the speed never stops decreasing. In principle,
the bodies would end up infinitely far apart after infinite time,
with no remaining relative motion.

A bit higher [speed] and the distance will gradually
increase, with an acceleration.

The acceleration is always downward, a deceleration,
reducing the speed over time as the bodies move apart.

The escape velocity at the Earth's surface is about
11.2 kilometers per second (25,000 miles per hour) but
decreases as altitude or more properly distance from the
Earth's center of gravity increases. Escape velocity is one
of those catch phrases that really makes no sense and
has no definition quantification.

It is more properly called "escape speed", since the term
"velocity" implies specification of direction, and direction
rather surprisingly isn't relevant to escape speed as long
as the two bodies aren't on a collision course.

It is not necessary to reach escape velocity to leave
Earth but constant thrust would need to be applied.
In most space vehicles escape velocity is not reached
until well into the burn sequence. In my opinion "escape
velocity" would be better called balanced orbital velocity,
but then I am not a rocket scientist nor do i have a PhD.

I'm not a rocket scientist and don't have a PhD, either,
but I know that orbital speed is distinct from escape
speed.

As I said, circular orbital speed at any distance is half the
square root of 2 times the escape speed at that distance.
If a small body has either more or less than circular orbital
speed, and less than escape speed, then it is in an elliptical
orbit around the larger body. More precisely, the two
bodies are in elliptical orbits about their barycenter.

-- Jeff, in Minneapolis

[Van Rijn]

Depending on its initial trajectory, a smaller body traveling at precisely the escape velocity for it's distance from the larger objects center will enter a orbit around the larger body.

An object at exactly escape velocity would be in a parabolic trajectory or orbit, not an elliptical or circular one (and if it were above escape velocity, it would be hyperbolic).

It is not nessecary to reach escape velocity of leave Earth but constant thrust would need to be applied.

Actually, if it has constant thrust, and it isn't just hovering in place and doesn't hit the Earth, it will eventually reach escape velocity. If it keeps the constant thrust going after that, it will go far beyond Earth escape velocity.

Also, if it is moving away from the Earth at constant velocity (a mile an hour straight away from the Earth will do), it will eventually reach the distance where that velocity is Earth escape velocity.

[Van Rijn]

It is more properly called "escape speed", since the term
"velocity" implies specification of direction, and direction
rather surprisingly isn't relevant to escape speed as long
as the two bodies aren't on a collision course.

A couple of good points there. I was going to mention the direction/path issue myself, but saw it was covered.

[grapes]

That is almost but not quite correct. Circular orbital speed
is exactly 1/2 the escape speed at that distance.

As I said, circular orbital speed at any distance is exactly
1/2 the escape speed at that distance.

Not 1/2 (.5), but instead close to .7

It's the square root of 1/2, which is .7071...

[NEOWatcher]

When a rocket lifts off it is starts a 0ft/s and gradually accelerates. The idea of escape velocity is flawed in it its basic premise...

The people that rely on a rocket trajectory do thier computation on a lot more than escape velocity. They use more complicated math to do thier calculations because of acceleration, altitude and target location.

Escape velocity is one of those catch phrases that really makes no sense and has no definition quantification.

Perhaps to you.

It is not nessecary to reach escape velocity of leave Earth but constant thrust would need to be applied.

Completely wrong. It is necessary to reach the escape velocity at the altitude when the burn has completed. It doesn't matter how quickly or slowly you reach that velocity and altitude. The speed has more to do with engine efficiency and trajectory to get to that point.

In my opinion "escape velocity" would better be a called balanced orbital velocity

Call it what you want, but if you don't reach the velocity, you don't escape the gravity well.
Mathematically speaking, it is the conic section which separates Hyperbola and ellipse called the parabola.

but hen I am not a rocket scientist nor do i have a PhD.

Neither do I, but I do have a math background and respect the words of people who are versed in orbital mechanics.

In my own personal experiments it takes less that two horsepower to lift 100 pounds to any altitude desired.

Please start a thread in ATM. I would love to see that discussion because I have my own comments that I don't want to poison this thread with.

[Jeff Root]

Oh, good grief! I shouldn't have depended on memory!
It's been too long since I last went through the equations.
I'm going back in time and altering the past slightly...

Yet again, I thought I was done before I was done.

-- Jeff, in Minneapolis