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#11
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Small, cheap, reusable rocket launcher
dan wrote:
Back in the 50's when no one knew if spaceflight was even possible, several tests were made with sounding rockets launched by balloon at high altitude. However the payload capability of even very large balloons declines at extreme altitude, and launching a large balloon is tricky. Because of the long period climbing to launch altitude cryogenic propellants were not practical. Ultimately it was not possible to carry rockets capable of getting into orbit. A similar problem will occur with rotorcraft. It will not. The helicopter can fly much faster than the balloon. If it flies vertically at the rate of 33 meters per second, it will reach the altitude of 30 kilometers in 15 minutes. Liquid oxygen and liquid methane will not evaporate in 15 minutes. On the other hand, a fixed-wing aircraft.i.e. the B-70, can indeed be designed to carry a large payload at high altitude. While a large blunt cone would have to much drag for external carriage on an aircraft, a saucer-shaped vehicle could be carried and launched edge first and re-enter flat side first; this is pretty much what Rutan's SpaceShip One does with its pivoting tail. This can spread the heating over a large area as with the Apollo Capsule, reducing thermal loads. The airplane is superior to rocket as a means of transportation through the troposphere because it is slower and much more reusable. It is however not as slow as the helicopter, and the separation of the rocket launcher and its cargo from the airplane is tricky due to the aerodynamic drag. |
#12
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Small, cheap, reusable rocket launcher
Andrew Nowicki wrote:
The problem is how to bring the balloon or the airship back to the earth -- you would have to release lots of expensive hydrogen. Joe Strout wrote: Why? Normal airships don't release lifting gas; they compress it, by inflating internal bladders with air. I don't see why it should be any different for this application. I was not familiar with this technology, but it seems that it may be troublesome to use it in a balloon or an airship that reaches the altitude of 30 km. The problem is that atmospheric pressure at the altitude of 30 km is about 100 times lower than the sea level pressure. You would need two bladders: one of them would hold all the helium at the sea level, the other would hold all the helium at the altitude of 30 km. It takes lots of energy to pump all the helium from the big bladder to the small one. Furthermore, as you compress the helium by the factor of 100, it heats up a lot, so you have to cool it. Thin air is not a good coolant, so the cooling is slow. It would be interesting to calculate how much time it would take to compress and cool all the helium. Andrew Nowicki wrote: Leik N. Myrabo experimented with this idea some 20 years ago. It works, and it is not very expensive. The microwave electronics would cost about $100 per 1kg of the rocket weight. (Batteries cost about $200 per 1kg of the rocket weight.) I did not mention microwaves because the safety concerns would drive up the cost. Joe Strout wrote: But they reduce the logistical issues. I wonder whether the safety issues can be mitigated by careful selection of the wavelength used. There is some info he http://radsafe.berkeley.edu/nir1101c.html The idea is not stupid, but it would take some effort to develop this technology. Batteries are probably less efficient, but they are easier to use. Magnetrons are used to generate long microwaves. Low frequency magnetrons are more efficient than high frequency magnetrons. Microwave ovens have magnetrons which operate at a frequency of 2.45 GHz and have efficiency of about 70%. Magnetrons operating at 915 MHz frequency have efficiency of about 85%. Magnetrons cost about $0.1/W. Gyrotrons can produce short microwaves ( 3 mm) which are easy to focus into a narrow beam, but their efficiency is low (15%-60%). The maximum frequency is about 170 GHz. Gyrotrons cost about $1/W. Atmospheric absorption of microwaves: http://www.submm.caltech.edu/cso/weather/atplot.shtml |
#13
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Small, cheap, reusable rocket launcher
In article ,
Andrew Nowicki wrote: dan wrote: Back in the 50's when no one knew if spaceflight was even possible, several tests were made with sounding rockets launched by balloon at high altitude. However the payload capability of even very large balloons declines at extreme altitude, and launching a large balloon is tricky. Because of the long period climbing to launch altitude cryogenic propellants were not practical. Ultimately it was not possible to carry rockets capable of getting into orbit. A similar problem will occur with rotorcraft. It will not. The helicopter can fly much faster than the balloon. If it flies vertically at the rate of 33 meters per second, it will reach the altitude of 30 kilometers in 15 minutes. Liquid oxygen and liquid methane will not evaporate in 15 minutes. I question whether that rate can be maintained at high altitudes. Both an airplane and a helicopter rely on air (or some other gas) for there to be any power usable for lifting. On the other hand, a fixed-wing aircraft.i.e. the B-70, can indeed be designed to carry a large payload at high altitude. While a large blunt cone would have to much drag for external carriage on an aircraft, a saucer-shaped vehicle could be carried and launched edge first and re-enter flat side first; this is pretty much what Rutan's SpaceShip One does with its pivoting tail. This can spread the heating over a large area as with the Apollo Capsule, reducing thermal loads. The airplane is superior to rocket as a means of transportation through the troposphere because it is slower and much more reusable. It is however not as slow as the helicopter, and the separation of the rocket launcher and its cargo from the airplane is tricky due to the aerodynamic drag. If it can reach 30 kilometers, the drag will be small. -- This address is for information only. I do not claim that these views are those of the Statistics Department or of Purdue University. Herman Rubin, Department of Statistics, Purdue University Phone: (765)494-6054 FAX: (765)494-0558 |
#14
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Small, cheap, reusable rocket launcher
In article ,
Andrew Nowicki wrote: dan wrote: Back in the 50's when no one knew if spaceflight was even possible, several tests were made with sounding rockets launched by balloon at high altitude. However the payload capability of even very large balloons declines at extreme altitude, and launching a large balloon is tricky. Because of the long period climbing to launch altitude cryogenic propellants were not practical. Ultimately it was not possible to carry rockets capable of getting into orbit. A similar problem will occur with rotorcraft. It will not. The helicopter can fly much faster than the balloon. If it flies vertically at the rate of 33 meters per second, it will reach the altitude of 30 kilometers in 15 minutes. Liquid oxygen and liquid methane will not evaporate in 15 minutes. On the other hand, a fixed-wing aircraft.i.e. the B-70, can indeed be designed to carry a large payload at high altitude. While a large blunt cone would have to much drag for external carriage on an aircraft, a saucer-shaped vehicle could be carried and launched edge first and re-enter flat side first; this is pretty much what Rutan's SpaceShip One does with its pivoting tail. This can spread the heating over a large area as with the Apollo Capsule, reducing thermal loads. The airplane is superior to rocket as a means of transportation through the troposphere because it is slower and much more reusable. It is however not as slow as the helicopter, and the separation of the rocket launcher and its cargo from the airplane is tricky due to the aerodynamic drag. Andrew, the record altitude that a helicopter has flown with only a pilot is 8,848 meters (29028 feet). To scale this up to a vehicle capable of carrying a rocket of significant weight for say a 1000 kg orbital payload would be akin to scaling up the Golden Gate Bridge to span from San Francisco to Hawaii. -- Mike Some say we must tax corporations more. What they do not understand is that corporations do not pay taxes. One of our governments conditions for their existence is they collect the taxes from their customers and pass them to the government. Mike Swift |
#15
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Small, cheap, reusable rocket launcher
Damon Hill wrote: wrote in news:1153423748.965872.310530 @i42g2000cwa.googlegroups.com: As I understand it, helicopters are unable to rescue people off Mount Everest, K2 or other mountains. It seems that the Pakistani army has special helicopters that can go up over 6,000 metres. A helicopter has recently landed on top of Everest, but I doubt it had any payload beyond the pilot. I didn't think helicopters could go that high myself. http://www.greatoutdoors.com/publish...licopteronever estmakeshistory/ I think the link is wrong - I found it here http://www.greatoutdoors.com/publish...ory/index.html interesting article |
#16
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Small, cheap, reusable rocket launcher
Damon Hill wrote: wrote in news:1153423748.965872.310530 @i42g2000cwa.googlegroups.com: As I understand it, helicopters are unable to rescue people off Mount Everest, K2 or other mountains. It seems that the Pakistani army has special helicopters that can go up over 6,000 metres. A helicopter has recently landed on top of Everest, but I doubt it had any payload beyond the pilot. I didn't think helicopters could go that high myself. http://www.greatoutdoors.com/publish...licopteronever estmakeshistory/ --Damon Quote: "The remarkable Eurocopter flight breaks the World Record for the highest altitude landing and take-off ever, for any flying machine on Earth, and sets an undeniable milestone in the history of aviation." I don't think this record will be beaten any time soon! |
#17
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Small, cheap, reusable rocket launcher
Andrew Nowicki wrote:
The helicopter can fly much faster than the balloon. If it flies vertically at the rate of 33 meters per second, it will reach the altitude of 30 kilometers in 15 minutes. Liquid oxygen and liquid methane will not evaporate in 15 minutes. Herman Rubin wrote: I question whether that rate can be maintained at high altitudes. Both an airplane and a helicopter rely on air (or some other gas) for there to be any power usable for lifting. The helicopter needs two sets of propellers/rorors: small propellers used at low altitude and big propellers used at high altitude. Another option is to use two helicopters having different size propellers: first stage helicopter and second stage helicopter. If we choose this option, there is no need to drop batteries on the parachutes. Andrew Nowicki wrote: The airplane is superior to rocket as a means of transportation through the troposphere because it is slower and much more reusable. It is however not as slow as the helicopter, and the separation of the rocket launcher and its cargo from the airplane is tricky due to the aerodynamic drag. Herman Rubin wrote: If it can reach 30 kilometers, the drag will be small. I disagree. The lift is constant regardless of altitude because the airplane mass is constant. To keep the lift constant you have to fly it faster at high altitude. When you fly faster, you increase both lift and drag. You can increase lift without increasing drag if you have variable geometry wings -- they are common in commercial aircraft. If you want to reduce cargo drag, canard wings are probably better than variable geometry wings. Both methods reduce the cargo drag, but not as much as the helicopter with two sets of wings or the two stages of the helicopters. I guess you could try using two stages of airplanes: one having small wings and propellers and the other having big wings and propellers. Well... you still cannot beat the helicopter, and dragging the big airplane through the dense troposphere is a major nuisance. It is easier to drag big helicopter propellers through the dense troposphere than the big airplane wings because the propellers are smaller than the wings. Because they are smaller, the can be very flat and yet lightweight. Flat things do not generate much drag. Airplane wings cannot be flat because they are big and because big flat wings would be too weak. This fact is explained by the Cube-Square Law which states that as scale is reduced, properties which are a function of volume (mass) will decrease faster than those which are a function of area (thrust and strength). |
#18
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Small, cheap, reusable rocket launcher
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#19
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Small, cheap, reusable rocket launcher
Mike Swift wrote:
Andrew, the record altitude that a helicopter has flown with only a pilot is 8,848 meters (29028 feet). To scale this up to a vehicle capable of carrying a rocket of significant weight for say a 1000 kg orbital payload would be akin to scaling up the Golden Gate Bridge to span from San Francisco to Hawaii. Apparently you have not read the first post of this thread. The helicopters cannot fly above the altitude of 8,848 meters because their internal combustion engines choke in the thin air. If you replace the engines with electric motors and replace small rotors/propellers with big ones, they can fly much higher. |
#20
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Small, cheap, reusable rocket launcher
In article ,
Andrew Nowicki wrote: Andrew Nowicki wrote: The helicopter can fly much faster than the balloon. If it flies vertically at the rate of 33 meters per second, it will reach the altitude of 30 kilometers in 15 minutes. Liquid oxygen and liquid methane will not evaporate in 15 minutes. Herman Rubin wrote: I question whether that rate can be maintained at high altitudes. Both an airplane and a helicopter rely on air (or some other gas) for there to be any power usable for lifting. The helicopter needs two sets of propellers/rorors: small propellers used at low altitude and big propellers used at high altitude. Another option is to use two helicopters having different size propellers: first stage helicopter and second stage helicopter. If we choose this option, there is no need to drop batteries on the parachutes. Andrew Nowicki wrote: The airplane is superior to rocket as a means of transportation through the troposphere because it is slower and much more reusable. It is however not as slow as the helicopter, and the separation of the rocket launcher and its cargo from the airplane is tricky due to the aerodynamic drag. Herman Rubin wrote: If it can reach 30 kilometers, the drag will be small. I disagree. The lift is constant regardless of altitude because the airplane mass is constant. This would be the case if the air density was constant. But it is not; the lift decreases with the density of the surrounding medium, and becomes 0 when there is no density outside. To keep the lift constant you have to fly it faster at high altitude. This is because of decreased pressure. Present military aircraft may reach somewhat more than 10 km, maybe 15. But at this altitude, air pressure decreases rapidly relatively. I doubt that fuel-only aircraft can reach 30 km. -- This address is for information only. I do not claim that these views are those of the Statistics Department or of Purdue University. Herman Rubin, Department of Statistics, Purdue University Phone: (765)494-6054 FAX: (765)494-0558 |
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