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the below notes contain the specs needed. my answers are as follows.
1) what would be the escape velocity/speed of a vehicle that is leaving earth and traveling into outer space?
A1: any vertical velocity / speed above zero.
2) how much force would the vehicle first need to accelerate itself vertically off of the ground?
A2: a force greater than 1 kilogram force.
3) how much extra force above the required lift off force would the vehicle need to acquire a vertical acceleration of 1 meter per second per second?
A3: None.
4) as the vehicle achieves vertical acceleration and as the vehicle gets further away from the earth and thus further away from the pull of the earths gravity wouldn't the vehicles vertical velocity and vertical acceleration increase due to the increased distance from the center of the earths mass if the vehicle is propelling itself with the same amount of force that it used for lift off?
A4: Yes.
notes:
a) the mass of the vehicle is 1 kilogram.
b) there is no fuel , the vehicle can provide a constant force for propulsion and so propels itself.
c) the vehicle has stabilization equipment to keep the vehicle in a vertical posture.
d) and of course taking into consideration that building such a vehicle is possible.
e) the vehicle can only lift off the ground and travel vertically not horizontally.
f) and assuming there is no air or downward wind resistance.
In general your summary is correct. I have a few comments. Generally the definition of 'escape velocity' is the required unaccelerated initial speed required to escape into space and not return. That would be something like firing a cannon vertically. You use suggests a constant acceleration. In that case any acceleration greater than the force of gravity at the surface of the Earth will allow escape. That is what I think you mean when you say "any vertical velocity / speed above zero".
For your second point you can generalize it to say 'any force greater than the mass of the vehicle'.
For your third point I'm not sure exactly what the value would be.
Your 4th item is a little trickier. My feeling is that you are approximately correct. Again this depends on a constant acceleration drive, which doesn't expend mass from the vehicle. That is the problem with today's space vehicles. We have to expend huge amounts of energy to achieve the acceleration required to get to space. But we have to start with full fuel tanks, and that fuel has to be accelerated too. Most of the fuel used to launch a space vehicle is used just to lift the fuel.
As far as a purely vertical takeoff is concerned we don't do it because the real world doesn't work according to our simplified models and we have to work with what we have.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
Your mostly correct , but there are issues that need picking. ie...
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In general your summary is correct. I have a few comments. Generally the definition of 'escape velocity' is the required unaccelerated initial speed required to escape into space and not return.
escape velocity would send the vehicle away from the earth and at the same time once the vehicle stopped accelerating away from the earth the vehicle would then begin to gradually decelerate due to the gravitational attraction between the vehicle and the earth until the vehicle comes to a stop and at that time the vehicle would begin to accelerate towards the earth or towards the largest gravitation field that it is attracted to.
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For your second point you can generalize it to say 'any force greater than the mass of the vehicle'.
true , because the mass is only 1 kilogram on the earth , so in generalizing it you are correct as the any force above 1 kilogram force would not stand correct on a planet with a stronger or a weaker gravitational field.
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For your third point I'm not sure exactly what the value would be.
the constant verticle acceleration of the vehicle with a force greater than the mass of the vehicle would give the vehicle constant acceleration , there is no exact value here as any value of force can always be lowered which in turn lenghtens the time required to lift off.
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Your 4th item is a little trickier. My feeling is that you are approximately correct. Again this depends on a constant acceleration drive, which doesn't expend mass from the vehicle. That is the problem with today's space vehicles. We have to expend huge amounts of energy to achieve the acceleration required to get to space. But we have to start with full fuel tanks, and that fuel has to be accelerated too. Most of the fuel used to launch a space vehicle is used just to lift the fuel.
all true except the approximately correct part because I did include in the specs that the vehicle supplies its own propulsion and the vehicle has a mass of 1 kilogram.
but I should have also noted that the vehicle does not throw mass away from the vehicle in order to achieve propulsion.
and with the common laymans type of rocket propulsion systems that are still currently used I can understand how it would be easy to think that my answer might be incorrect even though it was not.
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As far as a purely vertical takeoff is concerned we don't do it because the real world doesn't work according to our simplified models and we have to work with what we have.
a more correct statement would be that we dont do it because of the tools that we are allowed to use to accomplish a goal due to economic and political reasons.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
escape velocity would send the vehicle away from the earth and at the same time once the vehicle stopped accelerating away from the earth the vehicle would then begin to gradually decelerate due to the gravitational attraction between the vehicle and the earth until the vehicle comes to a stop and at that time the vehicle would begin to accelerate towards the earth or towards the largest gravitation field that it is attracted to.
Escape velocity is defined as the velocity that a mass must have to escape completely from a planet's gravitational field. It is the speed that the mass must have with no further acceleration, other than the gravitational attraction between the planet and mass. It is, as I said above, like being shot out of a cannon. There is one impulse, then it just coasts. Your system would reach escape velocity at some point above the Earths surface. Just how far would depend on the actual acceleration of the vehicle. Once it had reached that velocity then it would keep on gaining velocity as long as the vehicle's propulsion system continued to operate.
Originally Posted By: Paul
all true except the approximately correct part because I did include in the specs that the vehicle supplies its own propulsion and the vehicle has a mass of 1 kilogram.
but I should have also noted that the vehicle does not throw mass away from the vehicle in order to achieve propulsion.
The reason I said approximately is that I didn't stop to do a calculation, so I can't be sure that you are completely correct. You are correct that you said the vehicle was under constant acceleration and I understood that it did not expend any mass in maintaining that acceleration. What changes then is the net acceleration, that is the sum of the acceleration down provided by the Earth's gravitational field and the acceleration upward provided by the vehicles propulsion system. I added the rest about modern rockets because I just wanted to be complete.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
A misnomer is a word or term that suggests a meaning that is known to be wrong. Misnomers often arise because the thing named received its name long before its true nature was known. A misnomer may also be simply a word that is used incorrectly or misleadingly
the gravity from any body in space/the universe will be felt by all other bodies in space / the universe.
the vehicle will slow to a stop and then accelerate back towards the earth. unless other gravity fields become involved.
think of it this way.
if the initial force applied to achieve enough inertia to vertically propel the vehicle were a mere 1.001 kgf then the vehicles vertical acceleration would be the result of a mere .001 kgf due to the 1 kg downward force of gravity.
a=F/m
(a) .001 = (F) .001/(m) 1
so its acceleration would be a mere 0.001 mps^2 as it left the surface of the earth and headed into space.
and the vehicles vertical acceleration would constantly increase due only to the decreasing force of gravity felt by the vehicle and the constant vertical propulsion force of 1.001 kgf.
so the vehicle would not be traveling very fast as it entered into low gravity above the earth.
I haven't calculated the vehicle speed at this point but at this point the propulsion could be shut down and the vehicle would slow to a stop due to the attraction of gravity between the earth and the vehicle and then begin accelerating towards the earth due to the attraction of gravity between the earth and the vehicle.
so its all pretty much like you said below , in fact this is exactly what I would expect to happen myself.
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What changes then is the net acceleration, that is the sum of the acceleration down provided by the Earth's gravitational field and the acceleration upward provided by the vehicles propulsion system.
the propulsion goes to zero and the gravity is constant so the vehicle slows to a stop and then accelerates toward the earth.
you would pretty much need a computer program to calculate the different elements involved in slices of time as would be needed to get much further in the discussion.
I just keep hearing the term "escape velocity" being misrepresented on tv and movies as if an object needs only to gain a specific speed in order to leave the earths atmosphere and head into space.
ie .. a set speed which is not correct.
heres an example of a free fall from 128,000 feet above surface.
notice the acceleration as soon as he leaves the platform.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
escape velocity is a term that is a misnomer ie .. from the escape velocity wiki page I linked to
That is correct in the sense that the term escape velocity is generally used to refer to what it would take to get completely away from the planets surface. This of course would vary depending on the mass of the 'planet'. They talk sometimes about the escape velocity of a comet. That is low enough that you could get away just by jumping. I think it can be a useful measure, but it does have to be used with care. If you were in a balloon at extreme altitude, like the man in the video, the escape velocity would be slightly lower than from the surface. Not much, because even that height isn't much further, relatively, from the center of the Earth than the surface is.
Escape velocity of course also includes the provision that the projectile's velocity with respect to the Earth would never fall to 0. And of course it is talking about a simplified system that contains only the Earth and the projectile. Other gravity fields will have a large effect on the actual velocity of the projectile.
Originally Posted By: Paul
you would pretty much need a computer program to calculate the different elements involved in slices of time as would be needed to get much further in the discussion.
All you need is calculus and it can be done by hand. It isn't always easy, but it can be done.
If you have a long enough acceleration period then you can achieve escape velocity. Your 1.001 kgF would do the job if it kept up long enough. And of course the escape velocity would be getting lower as the vehicle got higher.
And of course escape velocity implies a single impulse like being shot from a cannon. The only proposal that I have ever heard of that approximates that is a mass driver (rail gun) that would throw things into space from a high mountain. Not very practical for anything that is at all delicate, like people.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
I was talking about using the elements involved in a computer program to give the precise predictions of the entire process in slices of time.
you could use calculus to get an approximate prediction of a single slice but you would need to perform a single calculation for each slice of time and that could take years to perform if you wanted the entire process sliced up into slices that are each 1000th of a second to achieve a precission set of calculations.
I would not use calculus , I would use standard math code to build the program and fully rely on the preciseness of classical physics math to deliver a precise prediction that could be analyzed in depth.
all because the propulsion force vs resistance will undergo a constant change which will result in a constant difference in the acceleration thus the vertical velocity of the vehicle.
but you could get somewhat of a close proximity guess using a single calculation using calculus if that is all you wanted.
and if using a computer program you could adjust the 1.001 kgf down as you get further away from the earths center as the resistance decreases to achieve a constant velocity of say .001 mps vertical velocity or lower.
which is why I get upset when I watch a tv show or a movie that says things like escape velocity must be 40,000 mps or what ever they use when I know that its wrong.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
you simply pop a vehicle into existence for each direction needed , and adjust the speed as needed , and if any unforseen problems pop up ! you simply invent a new word and blame it on the new word and then you build a complete volume of bookshelf fillers to accompany the finding ? of the new word.
and form a group of people to believe in the new word.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
Orac is bringing up some questions that plague actual launches where the aim is to get into a particular orbit. The general idea of escape velocity includes a number of simplifying assumptions. Your idea also contains a number of simplifying assumptions. You have addressed some of them such as only going vertical. In one of your later ones you actually mention some other problems such as air drag. But for the simple solution that you have discussed those are mostly ignorable. Just getting away from the Earth can be done as you say, with a very small acceleration, as long as it is greater than the Earth's gravitational attraction, which of course does vary with height. A small acceleration maintained over a long period of time is just as good as a large acceleration for a short period of time. In a real world situation where somebody is trying to launch something such as a satellite that won't work very well. There is no good way to achieve the very low acceleration over a long period of time.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
In a real world situation where somebody is trying to launch something such as a satellite
this could easily be a real world situation , we have already seen that a balloon can lift a considerable payload to 128,000 feet.
you have mentioned a rail gun.
we know that high velocities are not needed to acquire a low earth orbit where the majority of satellites are placed.
connect the dots.
use several balloons to lift a rail gun that accelerates a satellite payload into the 7.8 km/s LOE.
millions are saved each launch because the balloon / rail gun launch platforms are reuseable which is the main cost involved in a satellite launch which converts into billions as the platforms are reused multiple times.
it would basically be a zero fuel cost launch because the gasses used to inflate the balloons can be pumped into cylinders and reused in latter launches.
and the rail gun could be solar powered by a solar cell array placed on the exterior of the balloons and charge up a capacitance bank to feed electricity to the rail gun = no heavy batteries!
look at a cell phone , its really tiny , it can perform the same task as the old multi story computers that filled several floors of buildings did in the 1950s ...
but were stuck in the 50's with the propulsion systems that we use today.
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that won't work very well. There is no good way to achieve the very low acceleration over a long period of time.
well maybe not the 0.001 mps but that was just a easily calculated and easily discussable example without complicating the issue.
I think it could be done , even to resupply the ISS , among other things such as cleaning up the space junk.
the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph; 667 kn), or a kilometre in 2.914 s
mach 10 = 3.4 km/s with atmospheric air as the medium
with hardly no resistance to movement at 128,000 ft from air and only the resistance of gravitational forces acting on the payload the 7.8 km/s needed for LOE should or might be obtainable.
if not then a small rocket to assist the railgun perhaps.
still I think it should be doable.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
Well, a balloon lifted rail gun might have some engineering difficulties to overcome. The first thing that comes to mind is stability. To launch a payload into orbit you have to have very fine control of the trajectory. Launching from a rail gun would mean the trajectory would be primarily ballistic. A ballistic launch really needs to be very precisely positioned to be able to hit the correct orbit. I don't say it couldn't be done, but it would be tricky. The rail guns I have seen discussed would be ground based, so the location would be known exactly.
The next is energy. Rail guns are power hungry. The power requirement for a rail launch might be only 10%* of the power for a rocket launch, but it comes in one big burst. That would mean some kind of high power storage device that could be discharged quickly. Many systems that use power bursts use capacitor storage, but storing that much in capacitors might be problematical. An example of a system that uses capacitor storage for a brief burst in an electronic camera flash. Any way that again might be possible, but it too would be tricky.
And did I mention that a rail gun would be long? I would expect it to be something on the order of a kilometer long. Once again the engineering to get that lifted and stabilized would be tricky.
So it might be possible, but there would definitely be some serious engineering challenges.
And I forgot to mention acceleration. Manned space flights use lower acceleration launches than unmanned flights, because people can't take the acceleration that machines can. Even then unmanned payloads will still have to be able to take the acceleration of a launch system that has all of its acceleration in 1 Km. Current launch systems have main stages that run for at least a couple of minutes, which takes them a lot further than 1 Km. So acceleration for a rail gun would probably be much higher. This could produce problems for payload designers.
* 10% is an approximate value, based on the mass ratios of current launch vehicle to payload weights. I'm certainly not going to stick my neck out and say it would be much lower than that.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
You have addressed some of them such as only going vertical.
Vertical to what?
The Earths axis tilts at 23 degree, I guess you might mean vertical to the earths surface in a Geostationary orbit which give you a rather strange motion to the earth orbit around the sun.
I am not sure what Paul is really trying to work with but if we are talking vertical to earths surface then you may be better googling "Space Elevator" which is a much more exact discussion of a vertical movement to earths surface.
Even with all that if you extend it too far the relativistic time effects may become significant as the higher you go the faster your instantaneous rotational velocity.
I don't get what he was trying to work out and you guys seem to switching between ridiculously small forces and rail guns. Then the rail gun is fired in mid air and it doesn't recoil back towards earth or topple over etc and hence I don't really get where Paul is going with this, which is sort of your comment above.
Last edited by Orac; 12/21/1508:44 AM.
I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
I haven't figured out where Paul is coming from with his idea, but I am trying to address just what he is saying. With the simplifying assumption that his vehicle is taking off vertical to the ground from which it is launched and ignoring all the different motions involved it would work pretty much the way he says. Allowing for the Earth's rotation the vehicle would not stay above the point at which it was launched, but it would generally work the way he says. Now there are a lot of complications to actually doing that, but with a the simplifications used in a lot of thought experiments it works pretty good. The real world has a lot of stuff that will throw him completely out, but I am ignoring those, just the way he is.
He mentioned something about the use of escape velocity in TV and movies. Maybe he just doesn't like the way that the entertainment industry messes with reality in their shows. I realize that a lot of them really get a long way from reality in their so called science.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
a 1 km long rail should not be too long to design. or too heavy to lift.
in fact the 1 km long rail could be stored in a box and as lifted the rail would unfold itself and align itself one section at a time.
made from either titanium , carbon fiber or the new really strong but lightweight metals formed with bubbles inside them to reduce weight as explained on the sagg homepage. and the rail weight would only be a matter of the number of lifting balloons used.
so proper design of the rail and lifting balloons should overcome any obstacles as to strength , length or weight.
as for the recoil , an opposing counterbalancing dummy satellite could be launched simultaneously in the opposite direction , this would remove the recoil.
as far as the rotation of the earth is concerned , small ion thrusters could be used to stabilize the overall launch platform to counteract not only the earths rotation but also the winds that are encountered.
the ion thrusters could also be used to align the satellite into its proper orbital insertion angle of attack itself after it launches vertically from the platform.
Im sure that any obstacles that may arise other than economic or political obstacles could be easily worked out if allowed.
all they need to do is just do it. everything is in place already , and theres really no reason why satellites need to be so large , and if they do then the satellites can be made to assemble themselves together in blocks after launch.
heck , the first satellite can be a programmed worker droid or an rov that assembles the satellites when they arrive in space.
this can all be done today , we just have to start and we have to stop being so negative and teaching our children things that have no value such as the escape velocity we hear or see on tv or at the movies.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
Paul, you seem to think that engineering the system you have described would be simple. I would like to point out that it would be a major engineering task. Even if we could build it with off the shelf components it would take a large design team several years. As most of it would not be off the shelf it would probably take 10 to 20 years just to design it. You can't just sit down and whip up a design overnight. It has to be done in steps with construction of proof of concept intermediates. We are undoubtedly talking about billions of dollars invested in a questionable enterprise.
And using a 1 Km rail gun does require extremely high G forces on the payloads. No humans could be launched using the system.
Bill Gill
C is not the speed of light in a vacuum. C is the universal speed limit.
I dont know the exact amount of electricity required to accelerate a 1 kilogram payload using a rail gun. else I would have that part figured out by now.
and to design a rail gun that will launch a large payload you would need to know how much electricity would be needed.
I do know that it will require electricity.
(35) 100 Watt solar panels can supply 3.5 kW of electricity to charge up a capicitor bank every hour.
4 hours of charging and the capicitor bank will have a built up charge of 14,000 Watt hours.
according to the rail gun wiki page the US Navy rail guns require 5-50 MW to launch.
50 MW = apx 14000 Watt Hours.
50 MW can deliver 1 WAtt for 14000 hours or it can last for a few seconds in a rail gun.
so the electricity should be no problem.
way back in the 1940's the united states developed and tested and deployed nuclear weapons.
there was alot more involved in the research and development of a nuclear bomb than any balloon launch system might ever dream of having associated with it.
the nuclear bombs went from theory to practice in less than 6 years.
and that was in the 1940's this isnt even the same century... there should be no problem with the design process or any other process as there are no new or unknown processes involved.
and I havent mentioned launching a human being using a rail gun , I did mention launching satellites and resupplying the ISS and cleaning up the space junk but that is all.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.
The projectile in a rail gun at that speed will become a ball of plasma
I think what you are more thinking of is a "Mass Driver" google it, which is like a rail gun but a lot friendlier on the payload. Usually it is done by coils which act as a linear accelerator.