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| Topic: A different path to space | |
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I was impressed by the students that flew a high altitude balloon up to the edge of space.
I wonder what would happen if they attached a pulse ion engine and attempted to thrust a payload to orbit from the point they reached. The atmosphere should be thin enough at that altitude as to present very little resitance. It would be a much slower trip to orbit than conventional chemical thrust. (and a lot less expensive). It might have the added benefit of allowing a slow reentry to the same point. With a nice gentle re-entry. (if the forces can be balanced by ion thrusters) |
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Edited by
jrbogie
on
Sun 10/16/11 05:32 AM
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true, the atmosphere is very thin that high but along with very little resistance comes very little lift capability. gravity would still be in effect and without lift it'd be a short trip from the balloon back to terra firma. airspeed is needed to create aerodynamic lift and at high altitudes the TRUE airspeed needed is very high. we'd have to get into the definition of true airspeed to fully discuss the topic but suffice it to say that the further apart air molecules are, a thin atmosphere, the faster a craft would have to fly to get the molecules to provide lift. we can get deeper into it all if you'd like but i'll leave it at this; great speed is required to either overcome the effects of gravity to obtain orbit or to proved lift at altitude to overcome the effects of gravity to stay aloft within the atmosphere.
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Without the friction of air (with the baloon providing lift to the point of thrust)...
an Ion drive should theoreticlly 'sprial' the craft into the desired orbit... from that altitude, as it slowly builds momemtum. would require (depending upon payload) .3 g thrust over approximately 8 to 10 hours... Orbit |
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math.
at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. |
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about 12 km/sec!
Escape Velocity. |
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math. at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. One does not release the balloon (you will need it to soft land upon return). The craft would stay at altitude until it builds up enough km/s to sprial to a higher orbit. Once it has done that orbital dynamics take the place of lift. (8 to 10 hours to orbit vs but a few minutes by very expensive chemical thrust). |
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math. at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. One does not release the balloon (you will need it to soft land upon return). The craft would stay at altitude until it builds up enough km/s to sprial to a higher orbit. Once it has done that orbital dynamics take the place of lift. (8 to 10 hours to orbit vs but a few minutes by very expensive chemical thrust). well eight to ten hours at three g's acceleration would still end up with a speed far greater than orbital speed. and once you are in orbit how do you slow down in the atmosphere enough to land? how do you build a balloon that can withstand the heat build up due to friction? anyway, if you really think your idea would work you can be a multimillionair if you can sell it to somebody who agrees. but your balloon will never reach a high enough atmospere that will allow a craft to overcome the aerodynamic affects. it will need a dense enough atmosphere to remain boyant and the affects of drag will always hinder the smaller amounts of acceleration an ion engine might produce which would be way below the three g's you're talking about. and now keeping the balloon in tow will provide even more drag that will need to be overcome. it simply won't work but as i say, sell your idea and you'll be rich but i'm far from sold. |
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math. at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. One does not release the balloon (you will need it to soft land upon return). The craft would stay at altitude until it builds up enough km/s to sprial to a higher orbit. Once it has done that orbital dynamics take the place of lift. (8 to 10 hours to orbit vs but a few minutes by very expensive chemical thrust). well eight to ten hours at three g's acceleration would still end up with a speed far greater than orbital speed. and once you are in orbit how do you slow down in the atmosphere enough to land? how do you build a balloon that can withstand the heat build up due to friction? anyway, if you really think your idea would work you can be a multimillionair if you can sell it to somebody who agrees. but your balloon will never reach a high enough atmospere that will allow a craft to overcome the aerodynamic affects. it will need a dense enough atmosphere to remain boyant and the affects of drag will always hinder the smaller amounts of acceleration an ion engine might produce which would be way below the three g's you're talking about. and now keeping the balloon in tow will provide even more drag that will need to be overcome. it simply won't work but as i say, sell your idea and you'll be rich but i'm far from sold. I think everyone missed the period above ( .3 g ) |
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math. at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. One does not release the balloon (you will need it to soft land upon return). The craft would stay at altitude until it builds up enough km/s to sprial to a higher orbit. Once it has done that orbital dynamics take the place of lift. (8 to 10 hours to orbit vs but a few minutes by very expensive chemical thrust). well eight to ten hours at three g's acceleration would still end up with a speed far greater than orbital speed. and once you are in orbit how do you slow down in the atmosphere enough to land? how do you build a balloon that can withstand the heat build up due to friction? anyway, if you really think your idea would work you can be a multimillionair if you can sell it to somebody who agrees. but your balloon will never reach a high enough atmospere that will allow a craft to overcome the aerodynamic affects. it will need a dense enough atmosphere to remain boyant and the affects of drag will always hinder the smaller amounts of acceleration an ion engine might produce which would be way below the three g's you're talking about. and now keeping the balloon in tow will provide even more drag that will need to be overcome. it simply won't work but as i say, sell your idea and you'll be rich but i'm far from sold. Was not three G's of thrust... It was POINT 3 G's (.3g). You do not slow down in the atmosphere. You sprial in to a point where your deceleration puts you at a 'slow' ground speed and simply 'ease' into the atmosphere. Altitude at which 'drag' from atmosphere and thrust balance is 75 miles (roughly). Altitude reached by the students was 100 thousand meters. Atmosphere at that altitude is not even holding the balloon well. It poses no large 'friction' factor. Baloon is not in 'tow' it must be an intergral part of the structure. (which would require some method of evacuating a portion of Helium to prevent baloon 'bag' from bursting once orbit is achieved). |
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Was not three G's of thrust... It was POINT 3 G's (.3g). You do not slow down in the atmosphere. You sprial in to a point where your deceleration puts you at a 'slow' ground speed and simply 'ease' into the atmosphere. Altitude at which 'drag' from atmosphere and thrust balance is 75 miles (roughly). Altitude reached by the students was 100 thousand meters. Atmosphere at that altitude is not even holding the balloon well. It poses no large 'friction' factor. Baloon is not in 'tow' it must be an intergral part of the structure. (which would require some method of evacuating a portion of Helium to prevent baloon 'bag' from bursting once orbit is achieved). ah, my appologies. i did miss the decimal point. okay, let's assume .3 gs acceleration. first of all, ground speed has nothing in the least to do with anything. when speaking speed as regards aerodynamics, airspeed is all that matters. with any increase in airspeed, there will be an increase in drag equal to the airspeed increase squared. that means if you double the airspeed you will QUADRUPLE the drag coeficient. when you do finally reach the point where drag and thrust balance, as you say '75 miles [qoughly]' all accerleration stops. when lift balances out weight and thrust balances out drag the aircraft is in a state we refer to as "straight and level unaccelerated flight." think of an airliner cruising at altitude. the point being, how do you maintain even .3 g acceleration while the craft is in the atmosphere? as far as i know, ion propulsion is an idea for use in outer space where there is no atmosphere. we have electric motors that can produce much more than the .3 g's you're talking about to accelerate to the point that thrust and drag are in balance. that's the problem. you need a propulsion system that can produce enough thrust that drag NEVER balances out so that you can leave earth's atmosphere. i think where you're having a problem is with your thinking of engines producing x number of g's or acceleration. propulsion systems do not measure power as such. weight, altitude, temperature, or being in outer space will all play a role in the ammount of acceleration any given craft will maintain. you say an ion engine will maintain .3 g's acceleration for eight to ten hours even in the upper atmosphere but you've not explained how it will do that. for an aircraft to maintain acceleration it must have an engine powerful enought to overcome the greatly increased drag that builds up as the airspeed increases. if that were a simple matter i can assure you that boeing would produce an airliner that can do just that. fact is, it ain't a simple matter. |
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Was not three G's of thrust... It was POINT 3 G's (.3g). You do not slow down in the atmosphere. You sprial in to a point where your deceleration puts you at a 'slow' ground speed and simply 'ease' into the atmosphere. Altitude at which 'drag' from atmosphere and thrust balance is 75 miles (roughly). Altitude reached by the students was 100 thousand meters. Atmosphere at that altitude is not even holding the balloon well. It poses no large 'friction' factor. Baloon is not in 'tow' it must be an intergral part of the structure. (which would require some method of evacuating a portion of Helium to prevent baloon 'bag' from bursting once orbit is achieved). ah, my appologies. i did miss the decimal point. okay, let's assume .3 gs acceleration. first of all, ground speed has nothing in the least to do with anything. when speaking speed as regards aerodynamics, airspeed is all that matters. with any increase in airspeed, there will be an increase in drag equal to the airspeed increase squared. that means if you double the airspeed you will QUADRUPLE the drag coeficient. when you do finally reach the point where drag and thrust balance, as you say '75 miles [qoughly]' all accerleration stops. when lift balances out weight and thrust balances out drag the aircraft is in a state we refer to as "straight and level unaccelerated flight." think of an airliner cruising at altitude. the point being, how do you maintain even .3 g acceleration while the craft is in the atmosphere? as far as i know, ion propulsion is an idea for use in outer space where there is no atmosphere. we have electric motors that can produce much more than the .3 g's you're talking about to accelerate to the point that thrust and drag are in balance. that's the problem. you need a propulsion system that can produce enough thrust that drag NEVER balances out so that you can leave earth's atmosphere. i think where you're having a problem is with your thinking of engines producing x number of g's or acceleration. propulsion systems do not measure power as such. weight, altitude, temperature, or being in outer space will all play a role in the ammount of acceleration any given craft will maintain. you say an ion engine will maintain .3 g's acceleration for eight to ten hours even in the upper atmosphere but you've not explained how it will do that. for an aircraft to maintain acceleration it must have an engine powerful enought to overcome the greatly increased drag that builds up as the airspeed increases. if that were a simple matter i can assure you that boeing would produce an airliner that can do just that. fact is, it ain't a simple matter. I said .3g's of THRUST. (much different than acceleration). Sir I know this is possible. I watched a demostration by MIT students a few years ago in which the students tested an Ion engine. (at sea level in California - would this not be IN ATMOSPHERE) that engine burned far more hours then the 8 or so I think would be required (and at a far higher thrust than .3g's. Acceleration would be slow to build up in the upper atmosphere. However once it did it would no longer BE in atmosphere and drag then becomes a planetary phenom that has no bearing. You dont THRUST with the Ion Engine until the balloon reaches the altitude where drag caused by friction is at the best ratio versus your structure. |
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I said .3g's of THRUST. (much different than acceleration). 0.3 g is a measurement of acceleration. |
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Have you given any thought to the size of balloon you would need to lift an ion engine of any size plus some sort of decent sized payload to the stratosphere?
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that's the problem. the 'slowly builds momentum' part. how does the craft stay in the thin air after release from the balloon until it finally builds orbital speed? what provides the lift required while it slowly spirals into orbit. three g's is about what the shuttle astronauts experience during launch and can hardly be called 'slowly building momentum'. have you ever felt 3 g's? imagine your body weighing three times what it weighs. no human has ever withstood three g's for ten hours. not even close. i wonder how fast the shuttle would be going if it could maintain that acceleration for eight to ten hours especially once it reached thin atmosphere and beyond? likely millions of mph if you did the math. at any rate, there is simply no way to deal with lift in an atmosphere, especially a thin atmosphere, that does not involve lots of airspeed. in any atmosphere there are four forces acting on an aircraft. gravity [load factor], lift, drag and thrust. until the craft has escaped the atmosphere and reached orbital speed drag must be overcome by thrust and lift must counter gravity if the craft is to remain aloft. i can think of no way for a craft to slowly build momentum from zero airspeed when released from the balloon to orbital speed without an adequate amount of lift. and in a thin atmosphere the slightest amount of lift requires alot of airspeed. You don't use "lift" to propel a rocket, you use thrust. |
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Ion engines are extremely heavy and (for the foreseeable future) can only be used in outer space. .3 gees of thrust is a huge amount for an ion engine and would not be able to life a balloon vehicle out of the atmosphere and Earth's gravity well into orbit.
The advantage to an ion engine is that it can run for very long periods of time ... even years, but it produces very little thrust. Of course, over time, the velocity builds much higher than a chemical rocket can produce just due to the efficiencies of the fuel used. There is a new type of rocket being developed caused the "plasma drive" which is kinda sorta like an ion drive without much of the heavy equipment. It would do the job at greater than one gee and after the balloon was ditched but it still doesn't have the thrust to weight ratio of a chemical rocket. http://www.theregister.co.uk/2008/10/28/vasimr_plasma_first_stage_test/ |
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I said .3g's of THRUST. (much different than acceleration). 0.3 g is a measurement of acceleration. if you spin a ball on a string and whip it around in a circle you also apply 'acceleration'. .3g is only a measurement of acceleration if one is measuring it. If you thrust at a sufficient 'pulse' so as to provide movement in a mass that is the equivilant to the acceleration of that same mass in a .3g gravational field. And continue that thrust (in a micro gravity environment). The speed of that object will slowly increase it will increase until you stop thrusting. (or run out of fuel). Example... A spacecraft with a continous thrust engine. Thrusting at merely 1 g. (Earth normal) you can leave earth orbit... and cross the orbit of mars in but 5 or 6 days... (of course you would be going WAY to fast to stop at mars)... For the example of a POINT 3 g (.3g) continous thrust engine. In a non resistive environment (no friction) a continous .3g translates to roughly 9.6 feet per second/per second. at 1 second of thrust your velocity would become 9.6 feet per second. at 2 seconds of thrust your velocity would be 192 feet per second. at 3 seconds your velocity would be (at this point you either understand the beauty of it... or you dont) Suffice it to say that in a very low resistive environment (thin upper atmosphere) your actual 'build' in velocity would not be as good... However it would be good enough to 'turtle' your way to orbit... at MUCH less cost than the way of the 'rabit'. |
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I said .3g's of THRUST. (much different than acceleration). 0.3 g is a measurement of acceleration. .3g is only a measurement of acceleration if one is measuring it. You said that 0.3g of thrust is different than acceleration. 0.3g is acceleration. If you have 0.3g of something, you have 0.3g of acceleration. Maybe I missed your meaning; the phrase"0.3g of thrust, different than acceleration" rather invites misunderstanding. In a non resistive environment (no friction) a continous .3g translates to roughly 9.6 feet per second/per second. Yes. That's acceleration. However it would be good enough to 'turtle' your way to orbit... at MUCH less cost than the way of the 'rabit'. You haven't specified the height that you have in mind, which means the air resistance is unknown, which means we cannot know if this statement is true. You assert that it would be good enough, and maybe it would be, but we need more information to know. As someone else pointed out, its quite possible that the velocity at which that force balances resistance is too low. |
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Edited by
AdventureBegins
on
Fri 10/21/11 12:10 AM
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I said .3g's of THRUST. (much different than acceleration). 0.3 g is a measurement of acceleration. .3g is only a measurement of acceleration if one is measuring it. You said that 0.3g of thrust is different than acceleration. 0.3g is acceleration. If you have 0.3g of something, you have 0.3g of acceleration. Maybe I missed your meaning; the phrase"0.3g of thrust, different than acceleration" rather invites misunderstanding. In a non resistive environment (no friction) a continous .3g translates to roughly 9.6 feet per second/per second. Yes. That's acceleration. However it would be good enough to 'turtle' your way to orbit... at MUCH less cost than the way of the 'rabit'. You haven't specified the height that you have in mind, which means the air resistance is unknown, which means we cannot know if this statement is true. You assert that it would be good enough, and maybe it would be, but we need more information to know. As someone else pointed out, its quite possible that the velocity at which that force balances resistance is too low. Au Contrar... Did specify. (perhaps you missed it). 75 miles of altitude places one at close to the edge of the atmosphere. Resistance at the altitude is minimal. As far a 'knowing'... When the Wrights flew for the first time no one knew if it would work or not... Someone would have to test a small craft and see if it would work. I have done the math on it. Math works. The math actually works better with hydrogen than helium but there is then the added problem of 'containing' the hydrogen at high altutide (which would make the craft heavier) and safeguarding the hydrogen from explosion at low altitudes. Computer models (with object and orbital physics) 'fly' quite well. I don't have the money to build a working one. (or I would have built it a few years ago when I first had the idea). |
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Au Contrar... Did specify. (perhaps you missed it). You're right, I'm wrong, about stating the altitude. |
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Ion engines are extremely heavy and (for the foreseeable future) can only be used in outer space. .3 gees of thrust is a huge amount for an ion engine and would not be able to life a balloon vehicle out of the atmosphere and Earth's gravity well into orbit. The advantage to an ion engine is that it can run for very long periods of time ... even years, but it produces very little thrust. Of course, over time, the velocity builds much higher than a chemical rocket can produce just due to the efficiencies of the fuel used. There is a new type of rocket being developed caused the "plasma drive" which is kinda sorta like an ion drive without much of the heavy equipment. It would do the job at greater than one gee and after the balloon was ditched but it still doesn't have the thrust to weight ratio of a chemical rocket. http://www.theregister.co.uk/2008/10/28/vasimr_plasma_first_stage_test/ I didn't say this well. No ion drive could get out of the atmosphere and into orbit. It simply does not have the thrust to weight ratio. "It would do the job at greater than one gee ..." really doesn't mean anything since ion drives cannot develop that kind of thrust. Starting out at the height of a balloon is a big help since it is now a shorter distance to orbit, but an ion drive won't provide the lift to get you there. |
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