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| Topic: A different path to space | |
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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. as massagetrade said. acceleration IS measured in g forces. you feel 1 g on you right now meaning you are affected by an accelerative force of one g as gravity accelerates you toward earth. propulsion is measured in pounds of thrust. an increase in drag is always directily proportional to the increase in airspeed squared no matter how high up or thin the atmosphere is. to maintain any excelerative force, .3 g's or whatever, will result in an ever increasing airspeed along with four times increasing drag. there is no 'best ratio' for drag caused by friction that i know of. a ratio of what compared to what? drag everywhere increases with the square of the airspeed increase. i don't care how high in the atmospere you go, as long as you remain in the atmosphere induced drag, [that produced by angle of attack], form drag[produced by the aircraft structure] and parasite drag [produced by engine nacelles, attenaes, etc.] will continue to build as airspeed increases. it would require an engine producing an ever increasing thrust/weight ratio in order to maintain acceleration at .3 g's for for any extended period of time while operating in even the thinest atmosphere. during a shuttle launch the thrust/weight ratio is ever increasing as the engines burn off heavy fuel and the craft becomes lighter. that's why it can maintain the approximately 3 g's acceleration to escape earth's atmosphere. and you still haven't explained how you'd slow your craft down from the approximately seventeen thousand mph required to sustain low earth orbit to re-enter the atmosphere without very heavy thermal protection which would add to the weight of the craft. i can assure you that if there were a means of lowering the effects of drag, heat, friction, etc., the airlines and nasa would have been all over it by now. but drag will not just go away and it's affect as airspeed increases will always remain the square of the speed increase. |
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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. of course you don't use lift to propel a rocket. you don't use lift to propel anything. lift is used to counter the effect of gravity or accelerative force. it requires twice the lift to maintain a level sixty degree banked turn than the lift required at straight and level flight for instance. for a rocket, or any powered craft, to accelerate upward without lifting devices such as wings will require thrust in pounds exceeding the weight of the aircraft in pounds. that's what's been forgotten here. how to produce the lift to maintain the craft aloft while it accelerates in the amosphere. if we had some idea of what the craft would look like, we could more readily talk about drag, thrust, lift and the affects of gravity and acceleration. |
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Massagetrade is right, gees are measures of acceleration, not thrust. You can easily calculate the gees given a thrust if you know the weight of the system. A rocket supplies "lift" according to how much of the thrust is directed normal to the Earth's surface (or whatever gravity well from which the rocket is attempting to escape.
The thrust of an ion engine is also measured in energy. The new Vasimr ion engine can produce 20 kilowatts last time I checked, maybe more now, but that would not get you into orbit even if a payload wasn't attached. Ion drives are not for near Earth operation. They could, however, reduce the time from Earth orbit to Mars orbit from six months to thirty nine days. http://www.universetoday.com/60171/ion-drive/ |
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I love science, it really is awesome when you take the time to learn the distinctions between various scientific terms, I find it really enriches my understanding of the world. It also makes it easier to speak with scientists or engineers.
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Edited by
AdventureBegins
on
Fri 10/21/11 08:02 PM
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Massagetrade is right, gees are measures of acceleration, not thrust. You can easily calculate the gees given a thrust if you know the weight of the system. A rocket supplies "lift" according to how much of the thrust is directed normal to the Earth's surface (or whatever gravity well from which the rocket is attempting to escape. The thrust of an ion engine is also measured in energy. The new Vasimr ion engine can produce 20 kilowatts last time I checked, maybe more now, but that would not get you into orbit even if a payload wasn't attached. Ion drives are not for near Earth operation. They could, however, reduce the time from Earth orbit to Mars orbit from six months to thirty nine days. http://www.universetoday.com/60171/ion-drive/ Actually I do stand corrected. What I should have said is... An ion engine capable of providing a continous thust OF specfic impulse such that it would propel the structure mass at the equivalant of .3 g's of acceleration.; Much easier to simply say .3 g's of thrust... I am not used to speaking to those that are capable of understanding the long version. The reason why an Ion drive has not been well tested in near Earth application is because there is currently no emphasis on such... Students that built the craft which intercepted an asteriod used their engine in near earth (it worked just fine). why not try it from just below LEO... If it works it would be well worth the effort. (would revolutionize space flight) Kinda irritating to give out for free something that might be a brilliant idea. Only to have it picked apart... Not as a false concept but because I DID NOT SHOW MY WORK. EEEEEK... If you have not run an experiment it does not mean the concept is invalid... Would cost but a bit more to build than a weather balloon for a simple test craft. |
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Edited by
AdventureBegins
on
Fri 10/21/11 08:10 PM
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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? approximately 1000 cubic feet per 12b to 15 Lbs of payload/structure (depends upon lift gas/structure density and if you attach or do not attach atmosphere breathing engines to 'help' at low altitudes). I have a computer model (way more than just thought). I also have a scale model that I have used in the tunnel and have 'free dropped' for atmospheric dynamics tests. Yep... Bit o' thought. |
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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. 'Lift' will not get you to orbit. Thrust such that your velocity equals the velocity needed to attain a particular orbit. (Or escape velocity if you want to go further) 'lift' has no value in space. (plus some ability to manuever) |
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Yep plasma drive is a great concept.
The fuel for it requires more processing (therefore more expensive) than what you would need for Ion. But it does potentially have a greater thrust/weight than Ion. Fuel is actually the problem with chemical rockets. That thrust to weight ratio you mentioned goes away real quick. Because the 'burn' to 'empty' ration is to high. Once you hit 'empty' it don't matter what your thrust to weight is... You aint got none. The rabit gets tired and must rest. While the turtle just keeps ploding along. |
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Edited by
metalwing
on
Sat 10/22/11 02:58 AM
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Massagetrade is right, gees are measures of acceleration, not thrust. You can easily calculate the gees given a thrust if you know the weight of the system. A rocket supplies "lift" according to how much of the thrust is directed normal to the Earth's surface (or whatever gravity well from which the rocket is attempting to escape. The thrust of an ion engine is also measured in energy. The new Vasimr ion engine can produce 20 kilowatts last time I checked, maybe more now, but that would not get you into orbit even if a payload wasn't attached. Ion drives are not for near Earth operation. They could, however, reduce the time from Earth orbit to Mars orbit from six months to thirty nine days. http://www.universetoday.com/60171/ion-drive/ Actually I do stand corrected. What I should have said is... An ion engine capable of providing a continous thust OF specfic impulse such that it would propel the structure mass at the equivalant of .3 g's of acceleration.; Much easier to simply say .3 g's of thrust... I am not used to speaking to those that are capable of understanding the long version. The reason why an Ion drive has not been well tested in near Earth application is because there is currently no emphasis on such... Students that built the craft which intercepted an asteriod used their engine in near earth (it worked just fine). why not try it from just below LEO... If it works it would be well worth the effort. (would revolutionize space flight) Kinda irritating to give out for free something that might be a brilliant idea. Only to have it picked apart... Not as a false concept but because I DID NOT SHOW MY WORK. EEEEEK... If you have not run an experiment it does not mean the concept is invalid... Would cost but a bit more to build than a weather balloon for a simple test craft. I think you misunderstand. Ion/plasma type engines are, by nature, very heavy but produce low amounts of thrust. The big advantage to one is that it can run for very long periods of time and uses it's fuel more efficiently than a chemical rocket. Your concept of going from balloon height to orbit needs more thrust than an ion engine can produce, period. In addition, ion engines need a vacuum to work properly. Extensive research is being done on the Vasimr engine which has the potential of producing much more thrust than the standard ion engine. However, it has no chance of escaping Earth's atmosphere to reach orbit by itself. The website I posted states that clearly. Using a balloon to life a spaceship is not a bad idea. Rutan's spacecraft uses a bigger airplane to do the same job, but then leaves the "mother" behind. Your "mother" balloon would need to be left behind also. A chemical rocket could then be used to get to LEO. If the payload was an ion engine it could then travel on to wherever. Ion engines simply do not have the thrust to escape Earth's gravity, even starting at 75 miles altitude. Here is a more recent update. NASA partnership As of February 2011, NASA has 100 people assigned to the project to work with Ad Astra to integrate the VF-200 onto the space station.[15] [edit] Potential future applications VASIMR magnetic field VASIMR is not suitable to launch payloads from the surface of the Earth due to its low thrust-to-weight ratio and its need of a vacuum to operate. Instead, it would function as an upper stage for cargo, reducing the fuel requirements for in-space transportation. The engine is expected to perform the following functions at a fraction of the cost of chemical technologies: drag compensation for space stations lunar cargo delivery satellite repositioning satellite refueling, maintenance and repair in space resource recovery ultra fast deep space robotic missions Other applications for VASIMR such as the rapid transportation of people to Mars would require a very high power, low mass energy source, such as a nuclear reactor (see nuclear electric rocket). NASA Administrator Charles Bolden said that VASIMR technology could be the breakthrough technology that would reduce the travel time on a Mars mission from months to days.[17] |
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] 'Lift' will not get you to orbit. Thrust such that your velocity equals the velocity needed to attain a particular orbit. (Or escape velocity if you want to go further) 'lift' has no value in space. (plus some ability to manuever) of course lift has no value in space but you mentioned the craft 'spiraling' upward in the thin atmosphere at a high altitude. how does the craft perform this spiral maneuver without lift? how does it fly through the upper reaches of the atmosphere? will your craft rely on thrust alone? it's obvious even to nasa that the less a craft must travel through the atmosphere, especially the lower reaches, the less power it takes to reach outer space. we saw that when the x15 was dropped from a high flying b52 as early as the late fifties. and of course of late we have rutan/branson and their scheme to launch after piggy backing to altitude. but all of still requires a great deal of thrust in order to leave earth's atmosphere and those craft never reached near the speed required to orbit. perhaps if you gave us an idea of the craft you intend to haul up with the balloon would look like. then we could talk about it's feasability as a space craft. but just say it will spiral up until it reaches speed says nothing at all. how will it perform this spiral maneuver? |
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If you have not run an experiment it does not mean the concept is invalid... it'd be difficult to count the number of experiments that have been conducted at altitudes all the way up to the very top of the atmoshpere. but it's not my burden to prove your concept. you inherited the burden of proof when you began this thread. science and scientists, even amatures, live to pick apart new concepts. that's what science is all about. somebody like you comes up with an idea. somebody like me challenges you to prove that you're idea will work. perhaps you've thought of something that i haven't. great. then show me what i've missed but i can assure you that i and others here feel that you've missed quite a bit and it centers around the time that the craft must cease relying on the balloon to remain aloft until it exits the earth's atmospere completely. as a retired pilot who's flown as high as fifty one thousand feet i can assure you that the higher you go the more problems you encounter when it comes to generating lift. and without lift you've no means to accomplish this 'spiaral maneuver' you keep talking about. you say this all can be done. great, prove it to me and i've financial sources who we can take it to and we'll all be rich. |
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Edited by
wux
on
Sat 10/22/11 03:38 PM
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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. Also, if the blueprints are put up upside down on the wall, and the engineers who build the ion drive don't notice it on time, then the thing built will in fact be a negaitve ion drive, so the thing, the ion drive, will accelerat the balloon back to earth at .3 Gee. Wheezing and exhausted will the negative ion drive slowly descend back to earth, with the balloon and payload in tow. I agree with the OP, howevert, that once we find an alternative path to space, then we must put down markers on the way up, so future generations won't lose their footing and directions on the path thus carved out of the atmosphere by the pioneering iron pilots of the Ion drive (who are called Ian or Ivan, depending on whether the Russkies wipe the floor again with us, or the Scotts will be the first pathfinders). |
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