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space elevator 3
- Thread starter eezworf
- Start date
I met the people involved with the space elevator at a forum fo high-tech investors. Believe me they are quite serious, and include a number of very sharp people, This is not a hoax, but they will be dependent on technology breakthroughs in nanotubes to be successful.
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I'm afraid that the "serious investors" are involved with "serious scam artists" (my quotes). This orbital elevator, I assume, is the scheme I saw in OMNI magazine (that paragon of engineering accuracy and knowledge) a decade or so ago. It involved a cable loop, 44,000 miles in circumference, a geostationary satellite with a pulley and a similar pulley on the ground; a payload on the ground is hooked onto the cable and a motor on the ground turns the crank and the payload is hoisted into orbit. This violates a number of laws of physics, conservation of angular momentum comes immediately to mind. A slight twist to this scheme is to have an equal mass aboard the satellite, hooked onto the cable as it is cranked. This allows the net angular momentum of the system to not change; however, the angular momenta, potential and kinetic energies of the "up" mass and that of the "down" mass must be changed by the force in the cable. While a geostationary satellite appears to be hovering over a spot on the Earth, it is really travelling at roughly five plus miles a second; this velocity would have to be imparted to it by a cable that is running perpendicular to this direction of travel.
If any of the investors are interested, I have a few concepts of my own they might be interested in.
If any of the investors are interested, I have a few concepts of my own they might be interested in.
EUPlanetLanders
New member
nhughes, I'm afraid but you are partly right and partly wrong.
What you describe is laughable as elevator, true. But that it's not the current concept.
AFAIK, orbital elevators are fixed space Structures, more like "Space stairs", ON which loads are transported, usually by means of induction/magnetic motors
They are veryadvanced concept and, in my opinion, still very SF-like.
They work like this: the base of the elevator is connected somewhere on Earth's equator, the "tip" is somewhere up there in space. The length of the elevator is not important but the whole structure MUST have a property: its COG must be at the geostationary orbit level to be orbitally stable. Some schemes require a big equilibrating mass (a captured asteroid usually) on top, to achieve the COG requirement.
The main drawbacks to this scheme are two:1) the asteroid and 2) the enormous tensional forces.
POint 2 is the reason why joe922 was speaking of technological breakthroughs: at the moment there is no material able to resist the tension generated by its own weight under these orbital conditions.
A further problem would be the electrical induced currents (make a google search on tethered satellites) but I think this post is long enough now.
What you describe is laughable as elevator, true. But that it's not the current concept.
AFAIK, orbital elevators are fixed space Structures, more like "Space stairs", ON which loads are transported, usually by means of induction/magnetic motors
They are veryadvanced concept and, in my opinion, still very SF-like.
They work like this: the base of the elevator is connected somewhere on Earth's equator, the "tip" is somewhere up there in space. The length of the elevator is not important but the whole structure MUST have a property: its COG must be at the geostationary orbit level to be orbitally stable. Some schemes require a big equilibrating mass (a captured asteroid usually) on top, to achieve the COG requirement.
The main drawbacks to this scheme are two:1) the asteroid and 2) the enormous tensional forces.
POint 2 is the reason why joe922 was speaking of technological breakthroughs: at the moment there is no material able to resist the tension generated by its own weight under these orbital conditions.
A further problem would be the electrical induced currents (make a google search on tethered satellites) but I think this post is long enough now.
- Thread starter
- #5
Wow long time between responses. As a follow up, since my original post I looked further into this topic. While it is still pretty SF, it is close to realization, or the proponents are very convincing. I say this becuase NASA has pumped several million dollars into a group to explore the possibility. The key technology is carbon nanotubes. The strength of this material would make it possible if it could be produced in large, continuous quantities. I beleive the group doing the research is on the website While I am skeptical, I assume NASA has given the project some consideration as to feasibility before providing research funds.
Are you kidding me?????? A rigid structure tall enough so that its center of gravity is at geosynchronous altitude???? Come on. As an engineer I am ashamed of having absurd concepts such as this attributed to my profession. Millions of dollars spent???? Billions on single stage to orbit???? I am appalled.
It does seem incredible. One suggestion for how it would be built is to build a factory at geostationary orbit, then have it start building cables in opposite directions, directly toward the Earth and directly away from it. The COG would stay at geostationary orbit, and tidal forces would stretch the cables taut. Eventually the lower end would reach close enough to the earth to be reachable somehow, perhaps even anchored to the ground. Another way is to build a little sky elevator one to hoist other cables up in a kind of pyramid scheme.
When it is built, you ride an elevator up to the far end. That far end would be whipping around at much higher than Earth escape velocity, so to launch that coummuter bus to the Moon, you just let go of it and it sails away, like a rock from David's (the Goliath-killer) sling. The entire structure will have lost some kinetic energy and its orbit will shrink a little, so it would need some way to correct its orbit (maybe by running electrical current through it to push against the Earth's magnetic field.)
It would seem crazy, but once it is built you can have relatively cheap interplanetary space flight, with no limit on payload. Also, it might not be practical on Earth, but it might be practical on the Moon or even Mars, perhaps even using existing materials like steel. People have suggested it as a way to return mined materials from fast-spinning asteroids.
And the earliest source of the idea I am aware of is the source of so many other visionary ideas, Arthur C. Clarke, in his 1979 novel, Fountains of Paradise. He imagined using diamond cables, but he later suggested buckminsterfullerene, aka carbon nanotubes.
This wikipedia article has a nice rundown of the design issues, costs, etc.
When it is built, you ride an elevator up to the far end. That far end would be whipping around at much higher than Earth escape velocity, so to launch that coummuter bus to the Moon, you just let go of it and it sails away, like a rock from David's (the Goliath-killer) sling. The entire structure will have lost some kinetic energy and its orbit will shrink a little, so it would need some way to correct its orbit (maybe by running electrical current through it to push against the Earth's magnetic field.)
It would seem crazy, but once it is built you can have relatively cheap interplanetary space flight, with no limit on payload. Also, it might not be practical on Earth, but it might be practical on the Moon or even Mars, perhaps even using existing materials like steel. People have suggested it as a way to return mined materials from fast-spinning asteroids.
And the earliest source of the idea I am aware of is the source of so many other visionary ideas, Arthur C. Clarke, in his 1979 novel, Fountains of Paradise. He imagined using diamond cables, but he later suggested buckminsterfullerene, aka carbon nanotubes.
This wikipedia article has a nice rundown of the design issues, costs, etc.
This is an interesting twist on the space elevator hoax. Let's look at the basic concept of conservation of momentum. (not to mention the energy needed to transport the geostationary factory and its raw materials to geo orbit) Orbital (or any other object's) angular momentum is equal to w**2*r where w is rotational rate and r is the radius. Thus an object attached to an orbiting vehicle that is closer to Earth than the orbital altitude is forced to move forward relative to the vehicle; an object at a higher altitude falls behind. Thus the cables streamed out from the geo factory would be forced into a line leading and trailing the vehicle. This would dominate the dynamics of the cable if it were only a few miles long, let alone 22000 miles. This concept, as well as all the others, violates basic laws of physics.
If there truly is significant money available to study the space elevator, please let me know. I will become an advocate and request financial support for my studies. This takes advantage of a more basic law than any of physics, the one about one being born every minute first (???) promulgated by P.T. Barnum.
If there truly is significant money available to study the space elevator, please let me know. I will become an advocate and request financial support for my studies. This takes advantage of a more basic law than any of physics, the one about one being born every minute first (???) promulgated by P.T. Barnum.
- Thread starter
- #9
Mr. Hughes,
I assume you were not serious as I already stated NASA has provided funding for this particular "hoax". Perhaps you should instead get a job with them, as you are obviously much smarter, being able to dismiss this based on basic laws of physics, where the obviously uneducated types at NASA gave them money. Or perhaps you could put your doubts on hold for a moment and look at the link I posted. Perhaps you, not NASA's engineers who do this for a living, are missing something.
Nothing wrong with being critical, assuming you are the only one who is being critical is a little egocentric, don't you think?
I assume you were not serious as I already stated NASA has provided funding for this particular "hoax". Perhaps you should instead get a job with them, as you are obviously much smarter, being able to dismiss this based on basic laws of physics, where the obviously uneducated types at NASA gave them money. Or perhaps you could put your doubts on hold for a moment and look at the link I posted. Perhaps you, not NASA's engineers who do this for a living, are missing something.
Nothing wrong with being critical, assuming you are the only one who is being critical is a little egocentric, don't you think?
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Mr. Worf,
I am, and have been, a spacecraft dynamics and attitude control engineer for pushing thirty years. I have a Bachelor's degree in Aerospace Engineering and an MSME. I have worked for three of the largest Space/Defense contractors as well as the Federal Government during my career in this field. In this time I have known engineers and scientists (a small number) whose scruples are such that they would not hesitate to convince naive decision makers, who control the money, of whatever it takes to receive said money. I have seen many millions of dollars wasted on projects on which the technically knowledgeable personnel have no expectation of success. The fact that NASA is funding this concept may confer apparent legitimacy to it, but it does not mean it is based in reality.
By the way, I do "do this for a living" and have for alomst three decades.
As far as being smarter than the NASA scientists, with my training and experience, many might agree that I might be.
I am, and have been, a spacecraft dynamics and attitude control engineer for pushing thirty years. I have a Bachelor's degree in Aerospace Engineering and an MSME. I have worked for three of the largest Space/Defense contractors as well as the Federal Government during my career in this field. In this time I have known engineers and scientists (a small number) whose scruples are such that they would not hesitate to convince naive decision makers, who control the money, of whatever it takes to receive said money. I have seen many millions of dollars wasted on projects on which the technically knowledgeable personnel have no expectation of success. The fact that NASA is funding this concept may confer apparent legitimacy to it, but it does not mean it is based in reality.
By the way, I do "do this for a living" and have for alomst three decades.
As far as being smarter than the NASA scientists, with my training and experience, many might agree that I might be.
- Thread starter
- #11
Mr. Hughes,
I understand that you feel your experience gives you insight into this. While I am happy to grant you that, I, by the same token grant that credit to NASA's enginers. While you feel you may exceed their abilities, I find it hard to believe you can dismiss their approval of funding in hundreds of millions out of hand. While I agree mistakes are made, it seems to me just a likely that you are making one, as they are. And though I am an engineer and DAR (Candaian equivalent to DER) I have not carried out the analysis of this to convince myself one way or the other. Just an interested party, not wanting to hold onto a belief without reference to changes in technology or understanding. I have no doubt that many experts dismissed new technologies as impossible in the past. That may or may not be the case here, I am just willing to keep an open mind. Einstien seemed pretty far out there in 1914. By 1920 what he said was accepted without question.
As always the proof is in the pudding. Since I have no money to invest, I will continue to observe with interest. Thanks for your input, I value educated opinions. I see you mention angular momentun and the difficulties it would entail in the design of such as system. Difficulties do not equal violating basic laws of physics and can be overcome with new technologies (let me define the ideal material I can make you vertually anything). What law of physics do you suggest is being violated?
David Pasquill, P.Eng, DAR
I understand that you feel your experience gives you insight into this. While I am happy to grant you that, I, by the same token grant that credit to NASA's enginers. While you feel you may exceed their abilities, I find it hard to believe you can dismiss their approval of funding in hundreds of millions out of hand. While I agree mistakes are made, it seems to me just a likely that you are making one, as they are. And though I am an engineer and DAR (Candaian equivalent to DER) I have not carried out the analysis of this to convince myself one way or the other. Just an interested party, not wanting to hold onto a belief without reference to changes in technology or understanding. I have no doubt that many experts dismissed new technologies as impossible in the past. That may or may not be the case here, I am just willing to keep an open mind. Einstien seemed pretty far out there in 1914. By 1920 what he said was accepted without question.
As always the proof is in the pudding. Since I have no money to invest, I will continue to observe with interest. Thanks for your input, I value educated opinions. I see you mention angular momentun and the difficulties it would entail in the design of such as system. Difficulties do not equal violating basic laws of physics and can be overcome with new technologies (let me define the ideal material I can make you vertually anything). What law of physics do you suggest is being violated?
David Pasquill, P.Eng, DAR
Let's do a thought experiment. Let's say that we have invented a material, unobtanium (a commonly used engineering material) infinitely strong and zero density. We have made a structure/tether to geosynchronous orbit. Remeber that strength does not equate to stiffness, so a structure made out of unobtanium 22000 miles long would act like a string (I think you'll grant me that). So now we want to raise a payload up the structure/tether, using a crawling mechanism. Since as soon as it leaves the ground it is supported by tension in the structure/tether, the weight of the payload is transfered to the geosynchronous satellite. This will pull it into a lower orbit; the satellite will no longer be geosynchronous - it will move in the prograde direction from its station. The longer this condition persists, the farther it will move.
Okay, let's say we have thrusters on board to maintain orbital position. As the payload leaves the ground, the thrusters will have to be producing thrust equal to the weight of the payload (this ignores other effects, like the necessity to accelerate the payload tangentially). As the payload climbs the structure/tether, the differential between weight and the Mw**2r centripital force will decrease, reaching zero as the payload pulls into the hangar on the geosynchronous station. I've seen estimates of days to weeks to get a payload up; so we have this thruster firing for that amount of time.
The most efficient rockets we have today - hydrogen/oxygen - have a specif impulse of around 400 seconds. That means you can ge 400 seconds of one pound of thrust for every pound of propellant. A more exotic system - ion engines - I believe have specific impulse of around 1000 seconds, although at present they only produce fractions of a pound of thrust and require large amounts of electrical power. Okay, let's say we have ion engines that produce enough thrust to provide for a useful payload to climb the structure/tether. And let's say that the typical transit to geo orbit takes a week - 604800 seconds. The average thrust over that week will be half the weight of the payload (assuming that it climbs at a constant rate). So for every pound of payload we lift we will need to expend 604800/(2*1000) pounds of fuel or roughly 300 pounds of propellant to move it vertically to geo orbit altitude.
Also, the payload will have to be accelerated tangentially from equatorial velocity, about 1000 mi/hr, to geosynchronous orbit velocity, about 6800 mi/hr. This tangential velocity must be imparted by a tension only device which can provide tangential velocity only when deformed, much like a bowstring imparts velocity to an arrow. Watch a bow closely as you draw an arrow and you can observe that the tension in the string is far larger than the force required to pull it back - it goes, I believe, with 1/sin(angle between the string at its undeformed position and the position at any time). This sounds like very large tension force, which, of course, is also transfered to the orbiting geosynchronous station. We could make some assumptions and estimate this force but my head is starting to hurt - I think it would be very large - probably orders of magnitude larger than the thruster we calculated above.
Okay, this does not, strictly speaking, "violate a law of physics" as I suggested before. It's more that we cannot violate the laws of physics, and therein lies the problem.
Okay, let's say we have thrusters on board to maintain orbital position. As the payload leaves the ground, the thrusters will have to be producing thrust equal to the weight of the payload (this ignores other effects, like the necessity to accelerate the payload tangentially). As the payload climbs the structure/tether, the differential between weight and the Mw**2r centripital force will decrease, reaching zero as the payload pulls into the hangar on the geosynchronous station. I've seen estimates of days to weeks to get a payload up; so we have this thruster firing for that amount of time.
The most efficient rockets we have today - hydrogen/oxygen - have a specif impulse of around 400 seconds. That means you can ge 400 seconds of one pound of thrust for every pound of propellant. A more exotic system - ion engines - I believe have specific impulse of around 1000 seconds, although at present they only produce fractions of a pound of thrust and require large amounts of electrical power. Okay, let's say we have ion engines that produce enough thrust to provide for a useful payload to climb the structure/tether. And let's say that the typical transit to geo orbit takes a week - 604800 seconds. The average thrust over that week will be half the weight of the payload (assuming that it climbs at a constant rate). So for every pound of payload we lift we will need to expend 604800/(2*1000) pounds of fuel or roughly 300 pounds of propellant to move it vertically to geo orbit altitude.
Also, the payload will have to be accelerated tangentially from equatorial velocity, about 1000 mi/hr, to geosynchronous orbit velocity, about 6800 mi/hr. This tangential velocity must be imparted by a tension only device which can provide tangential velocity only when deformed, much like a bowstring imparts velocity to an arrow. Watch a bow closely as you draw an arrow and you can observe that the tension in the string is far larger than the force required to pull it back - it goes, I believe, with 1/sin(angle between the string at its undeformed position and the position at any time). This sounds like very large tension force, which, of course, is also transfered to the orbiting geosynchronous station. We could make some assumptions and estimate this force but my head is starting to hurt - I think it would be very large - probably orders of magnitude larger than the thruster we calculated above.
Okay, this does not, strictly speaking, "violate a law of physics" as I suggested before. It's more that we cannot violate the laws of physics, and therein lies the problem.
I am not the smartest guy in the world, but I can see some flaws in nhughes1's argument. First of all, I would put the tethered satellite in an orbit that is bigger than a geosynchronous orbit. The tether will now have to be in tension and any load which weighs less than the tension can climb it and have no effect on the tension that the satellite feels. The tension in the portion of the tether that is below the climbing load will be the original tension minus the climbing load. In reguard to the tangential speed, doesn't the base of the tether have the same angular velocity as the satellite at the start. After all, we are on the surface of a spinning ball.
Orbital mechanics is far beyond my knowledge but the governing equations is this application is Newton law of gravitation.
F= G* m1*m2/r^2
This equation is integrated over the mass volume of the objects in question
This will give the following result:
Given a string is orbiting a sphere, Where the mass of the string is significantly small than the mass of the sphere.
The string will line up pointing towards the sphere, the longer the string, the stronger the forces that will point it towards the sphere.
The prime example of this phenomenon is the moon orbiting the earth, the rotation of the moon about its own axis has degraded so the same face is always pointing toward the earth. The earth is trying to do the same thing toward the moon and the sun as evidenced by the tides of the seas.
The basic orbital mechanics that you have been describing only applies to bodies taken about its mass centroid as whole bodies assumed to be concentrated at the centroid, applicable only to the limits of the assumptions. The space elevator equations require the full volumetric integration of both the elevator and the earth to understand the process.
Hydrae
F= G* m1*m2/r^2
This equation is integrated over the mass volume of the objects in question
This will give the following result:
Given a string is orbiting a sphere, Where the mass of the string is significantly small than the mass of the sphere.
The string will line up pointing towards the sphere, the longer the string, the stronger the forces that will point it towards the sphere.
The prime example of this phenomenon is the moon orbiting the earth, the rotation of the moon about its own axis has degraded so the same face is always pointing toward the earth. The earth is trying to do the same thing toward the moon and the sun as evidenced by the tides of the seas.
The basic orbital mechanics that you have been describing only applies to bodies taken about its mass centroid as whole bodies assumed to be concentrated at the centroid, applicable only to the limits of the assumptions. The space elevator equations require the full volumetric integration of both the elevator and the earth to understand the process.
Hydrae
To Timelord:
You're correct - the angular velocity, w, of the mass "climbing" the "tether" remains constant, but the angular momentum is equal to mwr^2. Angular momentum of the mass increases as the square of the radius from the center of rotation. This increase in angular mometum must come from somewhere - Newton and God say angular momentum is always conserved. Either the angular momentum of the orbiting station, irrespective of its original momentum (an interesting dynamics problem - a mass at higher than geo altitude at geosynchronous rotational rate attached to a tether - the big fallacy many people make is confusing what they see when they swing a rock on a string with the interaction between gravity and centripetal force) will decrease proportionately or an external force (thrust?) must be applied to make up the difference, either to the orbiting station or to the climbing mass. The same priciples I outlined in my earlier missive apply - I made assumptions about what the system would look like to get some numbers. This increase in angular momentum is another way of viewing the required increase in velocity. Trust me, constant angular velocity does not translate into no need to accelerate a body going to geosynchronous (or any other) orbit. Geosynchronous orbit is the same as any other orbit (it requires the correct angular momentum, velocity, energy, altitude, etc.) with the minor proviso that its angular velocity happens to match that of the Earth.
To Hydrae:
You are referring to the gravity gradient effect. This is, indeed, the reason that the Moon always shows one face to the Earth and Mercury always shows one face to the Sun. Gravity gradient torque is proportional to (r X Ir)/R^3 where r is the radial unit vector from the central body, R is the distance from the center of the central body and I is the inertia matrix of the body in orbit (X is the vector cross product operator). Gravity gradient is used to stabilize some vehicles, dump internal momentum for others. Notice that it is proportional to 1/R^3 - it decreases very rapidly with altitude. It will, I think, be orders of magnitude smaller than the forces exerted by conservation of orbital momentum, etc. By the way, it took billions of years for the Moon and Mercury to stabilize with their rotational periods equal to their revolutionary periods.
I stand by my assertion that a space elevator is - the appropriate word eludes me. I hesitate to insult by using the words that immediately come to mind, but I refuse to dignify the concept with any word that suggests that it merely suffers from difficult complexity or a lack of sufficiently advanced technology.
I hope you all had a nice Mother's Day.
You're correct - the angular velocity, w, of the mass "climbing" the "tether" remains constant, but the angular momentum is equal to mwr^2. Angular momentum of the mass increases as the square of the radius from the center of rotation. This increase in angular mometum must come from somewhere - Newton and God say angular momentum is always conserved. Either the angular momentum of the orbiting station, irrespective of its original momentum (an interesting dynamics problem - a mass at higher than geo altitude at geosynchronous rotational rate attached to a tether - the big fallacy many people make is confusing what they see when they swing a rock on a string with the interaction between gravity and centripetal force) will decrease proportionately or an external force (thrust?) must be applied to make up the difference, either to the orbiting station or to the climbing mass. The same priciples I outlined in my earlier missive apply - I made assumptions about what the system would look like to get some numbers. This increase in angular momentum is another way of viewing the required increase in velocity. Trust me, constant angular velocity does not translate into no need to accelerate a body going to geosynchronous (or any other) orbit. Geosynchronous orbit is the same as any other orbit (it requires the correct angular momentum, velocity, energy, altitude, etc.) with the minor proviso that its angular velocity happens to match that of the Earth.
To Hydrae:
You are referring to the gravity gradient effect. This is, indeed, the reason that the Moon always shows one face to the Earth and Mercury always shows one face to the Sun. Gravity gradient torque is proportional to (r X Ir)/R^3 where r is the radial unit vector from the central body, R is the distance from the center of the central body and I is the inertia matrix of the body in orbit (X is the vector cross product operator). Gravity gradient is used to stabilize some vehicles, dump internal momentum for others. Notice that it is proportional to 1/R^3 - it decreases very rapidly with altitude. It will, I think, be orders of magnitude smaller than the forces exerted by conservation of orbital momentum, etc. By the way, it took billions of years for the Moon and Mercury to stabilize with their rotational periods equal to their revolutionary periods.
I stand by my assertion that a space elevator is - the appropriate word eludes me. I hesitate to insult by using the words that immediately come to mind, but I refuse to dignify the concept with any word that suggests that it merely suffers from difficult complexity or a lack of sufficiently advanced technology.
I hope you all had a nice Mother's Day.
>>>>Angular momentum of the mass increases as the square of the radius from the center of rotation. This increase in angular mometum must come from somewhere - Newton and God say angular momentum is always conserved.
As I see it, yes, angular momentum is conserved. The rotation of the earth slows when you hoist your payload. This is because the center of gravity of the earth asteroid system shifts twards the asteroid. But no fears, the angular momentum of the earth is close to infinatly bigger than any object we will ever be hoisting...I hope.
Lucas
As I see it, yes, angular momentum is conserved. The rotation of the earth slows when you hoist your payload. This is because the center of gravity of the earth asteroid system shifts twards the asteroid. But no fears, the angular momentum of the earth is close to infinatly bigger than any object we will ever be hoisting...I hope.
Lucas
Grayocean,
All you say is true. The problem is how to transfer angular momentum, in this case from the Earth, to the payload climbing the tether. Any structure that is 22,000 mile long will NOT support any bending moment which is what would be required for the structure to provide the angular momentum to the payload. Such a structure, if it could be built, would support ONLY tension; any compressive load would cause immediate buckling as would any bending moment. Think of a high (1000' ??) radio tower with its guy wires removed - not very stable. Now think of a structure roughly 120,000 times as high!!!!!
I stand by my position that a space elevator is impossible.
All you say is true. The problem is how to transfer angular momentum, in this case from the Earth, to the payload climbing the tether. Any structure that is 22,000 mile long will NOT support any bending moment which is what would be required for the structure to provide the angular momentum to the payload. Such a structure, if it could be built, would support ONLY tension; any compressive load would cause immediate buckling as would any bending moment. Think of a high (1000' ??) radio tower with its guy wires removed - not very stable. Now think of a structure roughly 120,000 times as high!!!!!
I stand by my position that a space elevator is impossible.
Not shorten the rope, lengthen the unidirectional unobtainium crystalline structured cord to 40,000+ miles. Make gravity negligible. The Centrifugal force that keeps the asteroid in orbit is not the gravity of the earth, but the tension of the cord. mv*v/r + GmM/r*r = Tension in unobtainium cord.
Example one, a bowling ball and golf ball tied together and spinning in free space. Now there is no reason why an ant with his own Niel Armstrong space suit could not walk from the surface of the bowling ball to the surface of the golf ball. In this case where gravity is essentialy zero he better not let go, but it helps having six legs.
No torque needs to be applied to move the ant or make the system spin slower.. Angular momentum will conserve itself. Example two, a spinning figure skater, by pushing her arms out, her spinning will slow, but angular momentum will remain constant because her angular inertia will have increased.
Hope this helps clear it up.
Lucas
Example one, a bowling ball and golf ball tied together and spinning in free space. Now there is no reason why an ant with his own Niel Armstrong space suit could not walk from the surface of the bowling ball to the surface of the golf ball. In this case where gravity is essentialy zero he better not let go, but it helps having six legs.
No torque needs to be applied to move the ant or make the system spin slower.. Angular momentum will conserve itself. Example two, a spinning figure skater, by pushing her arms out, her spinning will slow, but angular momentum will remain constant because her angular inertia will have increased.
Hope this helps clear it up.
Lucas
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