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"he on board hyd/oxy would run the SSME's for only 23 seconds."
Thats no where near enough. Shuttle burns its engines for like eight minutes.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Yeah but the total launch weight of the STS is like 4.5 million pounds just to get 63,500 lbs into orbit. 6 seconds of fuel is wasted on the ground before launch whereas this one wastes none. The STS external tank is an aerodynamic and weight burden (not to mention safety hazard) and it's left to the ocean. The STS has to be moved from horizontal to vertical for launch.
If somehow this idea could be perfected it definately has some advantages over the current system. It could fly on it's own to launch locations and it's jet engines would provide more landing options.
Better performing jet engines maybe? If this could get to 100,000 feet and mach 3 on two jet engines alone then fire up the SSME's, they produce 100,000 more pounds of thrust in a vacuum.
You sure SRB's are not a benefit? They seem to produce twice as much thrust as their weight and they can be ejected, plus NASA uses them so they can't be that bad.
Is there any hypothetically better rocket fuel other than hydrogen?
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Better performing jet engines maybe? If this could get to 100,000 feet and mach 3 on two jet engines alone then fire up the SSME's, they produce 100,000 more pounds of thrust in a vacuum.
It won't make enough of a difference. Your vehicle still would not be able to get anywhere near orbit. There is a reason why the STS is 90% fuel at launch. It has to be, or it will not be capable of getting into orbit. Even starting at mach 3 and 100,000 ft, your vehicle would still need a mass ratio almost that high to get to orbit.
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If you take your vehicle to have a dry mass of 293,500 lbs and a hydrogen/oxygen fuel mass of 397,394 lbs, then the vehicle total mass is 690,894 lbs. The rocket equation ratio is 690894/293500 = 2.35, which is the natural log of 0.85. In other words, your vehicle will reach 85% of the exhaust velocity of the propellant. Assuming your jet "first stage" gets you above most of the atmosphere, your SSMEs will give an exhaust velocity of 10,000 mph. So your shuttle will get to about 8,500 mph; less than half of orbital velocity. It will barely get into orbit around Mars.
Starting from sea level, a vehicle must achieve 22,000 mph to go into low orbit. Hydrogen-oxygen gives an exhaust velocity of 10,000 mph in a vacuum and about 8,000 mph at sea level. But neglecting the sea level situation (for illustrative purposes), your vehicle must achieve 22,000/10,000 = 2.2 times as much velocity as the exhaust velocity. The natural log of 2.2 is 9, which means your vehicle must be 8/9 fuel by weight. Considering that the exhaust is slower at sea level explains the common 9/10 figure people have mentioned.
This is one reason space travel is difficult.
-- RobS
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"Is there any hypothetically better rocket fuel other than hydrogen?"
No. Not as far as a practical fuel... you could use slush hydrogen to decrease your fuel tank mass a little, but it isn't more efficent then liquid.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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How do you determine the maximum altitude an aircraft can fly at?
I know weight vs thrust are the main factors, then wing surface area, and to some degree the wings shape.
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How do you determine the maximum altitude an aircraft can fly at?
I know weight vs thrust are the main factors, then wing surface area, and to some degree the wings shape.
It's complicated, but it boils down to the balance of forces. As altitude changes, the air density changes. This has the effect of decreasing your thrust, drag, and lift. Of the four basic forces acting on the aircraft, the only one that doesn't change is the force of weight.
For your maximum altitude, your lift force has to match the weight of the aircraft. Then the engine thrust has to match the drag force.
There are many things you can do to increase the value of the lift force. The 2D lift coefficient is determined by your airfoil cross section. The 3D lift coefficient takes the 2D coefficient into account but also has the wing's planform shape as a variable. Wings with high aspect ratio (like sailplane wings) create higher lift, while swept and delta wings create less lift. Wing area is also important.
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How much thrust would the following delta wing shaped aircraft:
Width: 120' at the end
Length: 160' long
weight: 726,000 pounds
Wing surface area: 9,600 sq ft
need to go mach 1 or 2 at 100,000 feet?
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Dook, I'd suggest you pick up a book like "Fundamentals of Aerodynamics" by John D. Anderson for the answers to these complicated questions that are too lengthy to be answered on this forum.
If you want a short answer, why don't you look at the specs for aircraft with similar dimensions and performance profiles? There aren't too many planes like that out there, but the SR-71 and B-58 should at least steer you in the right direction. Also keep in mind that thrust is almost directly proportional to atmospheric density, so get the standard atmospheric tables out and be prepared to adjust your thrust levels for that altitude.
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Already looked at the SR-71, you can download the flight manual online now.
The SR-71 is a delta shape, 120,000 lbs full of fuel and each J-58 engine put out 34,000 lbs of thrust at sea level but the moveable intakes produce something like 54% of the forward thrust at high altitudes.
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The SR-71 is a good starting place for a jet carrier plane that a slush-hydrogen fueled spaceplane would ride on. Although no engines exsist today that would be appropriate, such engines are not beyond current technology. The SR-71's engine was special, because it was a combination turbojet and ramjet engine, where the intake would be positioned to operate the engine in turbojet mode at low speeds, but repositioned to funnel air around a turbine bypass and act as an almost-pure ramjet engine. Ramjet engines are superior in the Mach 3-6 range or so, and having them built-in to your regular jet engines would save lots of weight and money. Using the SR-71s J5s or the ATF F-119 fighter jet engines for a huge carrier plane probobly isn't a good idea, a smaller number of bigger engines would be preferred.
Even with a combination turbojet/ramjet engine though, you still aren't going to reach high enough speeds to keep the spaceplane's fuel bill low enough. Since Scramjets are probobly out of the question given their low state of maturity and nessesitty that the carrier plane be built around them to work, that option is out too. So I think there are two possible routes:
-Equip the carrier plane with regular turbojet/turbofan turbine engines and LOX/kerosene engines, perhaps with LOX loaded in mid-flight by ACES type system to lower takeoff weight.
-Equip the carrier planes' turbine/ramjet engines with LOX injectors to boost their performance for short periods to reach higher speeds and altitudes.
If you can get up to Mach~6 and ~100,000ft+, then the spaceplane powerd by slushed hydrogen starts getting smaller fast.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Even with a combination turbojet/ramjet engine though, you still aren't going to reach high enough speeds to keep the spaceplane's fuel bill low enough. Since Scramjets are probobly out of the question given their low state of maturity and nessesitty that the carrier plane be built around them to work, that option is out too. So I think there are two possible routes:
-Equip the carrier plane with regular turbojet/turbofan turbine engines and LOX/kerosene engines, perhaps with LOX loaded in mid-flight by ACES type system to lower takeoff weight.
-Equip the carrier planes' turbine/ramjet engines with LOX injectors to boost their performance for short periods to reach higher speeds and altitudes.
If you can get up to Mach~6 and ~100,000ft+, then the spaceplane powerd by slushed hydrogen starts getting smaller fast.
There is one other way to get such a carrier to increase speed fast. Let it get to a decent height using regular jet engines but when high enough it switches to the rocket that it was carrying and ascends to 100,000 feet. Where we can seperate the actual spaceplane.
Advantages are that speeds in excess of mach 6 are available without requiring very complicated new jet engines and or scramjet technology. This leads to a lighter upperstage needed and a bonus to cargo carrying capacity of such.
Disadvantages are that you would require a rocket motor that can be reused reasonably easy and it would have two seperate engine systems on board the carrier aircraft.
still a possibility.....
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
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My concern with these HTOL spaceplane systems is the separation of the orbiter from the mothership. While it might be possible to build a Mach-6 mothership, the ability to separate the orbiter for staging appears sporty at best. The closest we've ever come towards trying was the D-21 launched by the Blackbird. The D-21 was launched at Mach 2, and even still there was an instance where the D-21's control surfaces failed and the drone crashed into its mothership.
I don't know if mounting the orbiter on top of the mothership or below it will make a big difference in ensuring a safe separation. Perhaps the best approach is to accelerate to Mach 3 with turbojets, get above Mach 5 with ramjets, then ignite a rocket engine and enter a steep climb. The orbiter would be released just before apogee, so it's in the proper attitude whe its own engines ignite.
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What about designing a complete spaceplane that has in-built turbojet engines and a nerva style strap on booster that would be removed in orbit. We could deliver all the requirements for earth orbit with significant cost savings including the recycling of nerva engine systems to moon and other planet vessel platforms.
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What about designing a complete spaceplane that has in-built turbojet engines and a nerva style strap on booster that would be removed in orbit. We could deliver all the requirements for earth orbit with significant cost savings including the recycling of nerva engine systems to moon and other planet vessel platforms.
We are not going to build a one piece shuttle from ground to orbit, because it would be too heavy with present day technology. You would have to have two or three types of engines to get the efficiency in each part of the assent that it would make it impossible to do it. It would increase the weight too much. That why the rocket has stages and the shuttle has a throw tank and two solid buster. With present day technology or technology for the forseable future, the best we can hope for is a two piece shuttle. One piece being the carrier plane and the other being the orbiter.
Larry,
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Thats not entirely true MR... Martian Tristar here is talking about a NERVA NTR engine, a nuclear rocket engine. With one of those, then a SSTO spaceplane on paper starts looking much more plausable. The trouble is, of course, the radiation: that shielding for the crew would defeat the mass savings of using an NTR engine, and if there were a failure... well... lets just say that you don't want to be down-wind of the crash site for a few years. The size of the NTR engine needed would also be quite large and might itself present weight problems. The extra-large liquid hydrogen tanks would be a drag/reentry problem too.
I think one of the absolute "if it can't then it don't fly" requirements is that everything about the launch vehicle has to come back down, or else you'll never be able to take advantage of economies of scale that make an RLV worthwhile to begin with. It should be reliable enough to be able to reintegrate, in a pinch, without anything more then a 24hr diagnostic/inspection and no more then a few days in normal operations.
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"My concern with these HTOL spaceplane systems is the separation of the orbiter from the mothership"
The best options are probobly to slide the spaceplane directly backward off rails, which would perhaps extend (retractable?) from the rear of the carrier, and then nose up and ignite its engines... Like a missile rail, only backwards. Or, the spaceplane would seperate straight up and the carrier plane would nose down. Perhaps use some of the engine bleed to give the spaceplane a "push" away from the carrier.
How much of a problem is this due to air pressure/lift?
"...get to a decent height using regular jet engines but when high enough it switches to the rocket that it was carrying and ascends to 100,000 feet... without requiring very complicated new jet engines."
You are going to need new jet engines anyway since no exsisting production engine can give you that kind of altitude or speed performance on such a scale, and you would have to develop a highly reliable reuseable kerosene rocket for the carrier plane. If turbine/ramjet combination engines boosted with a little LOX can do the job, they would be preferable to rockets since they are more difficult to reuse. Rocket engines and the extra kerosene would add tons to the weight too.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Thats not entirely true MR... Martian Tristar here is talking about a NERVA NTR engine, a nuclear rocket engine. With one of those, then a SSTO spaceplane on paper starts looking much more plausable. The trouble is, of course, the radiation: that shielding for the crew would defeat the mass savings of using an NTR engine, and if there were a failure... well... lets just say that you don't want to be down-wind of the crash site for a few years. The size of the NTR engine needed would also be quite large and might itself present weight problems. The extra-large liquid hydrogen tanks would be a drag/reentry problem too.
Radiation shielding for the crew should not be a huge problem. The most natural configuration would put the crew in the front and the engines in the back, meaning that almost the entire vehicle is acting as a buffer between the two. It also makes sense to use NTR in a horizontal takeoff/landing vehicle, because that means the engines can be smaller as it does not need a T/W ratio greater than one. However, the environmental problems are still considerable.
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"Radiation shielding for the crew should not be a huge problem."
I don't know about that, the radiation shield for the USAF nuclear bomber program weighed quite a bit. The amount of thrust needed for a nuclear engine also dictates a pretty large reactor, which will produce far more radiation then a little RL-10 sized space-only engine.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I will explain a bit more, the NTR Engine would be a strap-on booster , aerodynamic in design to fit with the design of the spaceplane, second the nuclear drive will not activate until 38-45, 000 ft in the air. Yes, I have some concerns size and capacity of the drive system that is where research and testing plays a part in the development. Once out in space orbiting earth the NTR booster is removed and remains in orbit, the spaceplane only returns with cargo or returning personnel. In case of in-flight emergency the strap-on booster can separate from ship and have a parachute recovery system installed with GPS locator system.
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I think that you are underestimating the potential risk and how the limited bennefit of such an arrangement is, MT.
If your vehicle fails... aerodynamic problems, engine explodes, whatever that prevents you from reaching orbit, then that reactor is going to come back down while it is still "hot" and producing intense radiation for weeks or months, even if it is shut off.
If the reactor casing were to fail, especially if you were reentering at a high speed, then its deadly contents could do the worst possible thing... be spread over a large area. Instant fallout cloud, no warning, no defense. Normally I am very supportive of nuclear energy and dismissive of parinoid concerns, but not this time... this really does have the potential to kill thousands or tens of thousands of people.
If the reactor does come down intact, it will still kill anyone in the vicinity and will be very hard to recover since you can't aproach it. This is a moot point anyway, since you can't risk the possibility of the fuel casing failing.
The bennefits of an NTR engine are also more limited then you think. A large enough engine will still be much heavier then a comperable chemical engine of similar thrust, and the fuel tanks must be much larger. This latter point both increases the mass of the tanks needed, but also increases how strong they must be to support the dynamics on the vehicle since they are bigger.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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GCNRevenger,
It is better ( larger spaceplane ) than using our current stuff like rockets to expand the human race into space. We will need to start using large capacity drives starting with NTRs then moving to thermo-plasma propulsion, and then do more research to accelerate faster off the planet.
I am talking about testing the drive system on earth , In one of the nuclear declared zones and test all the different drive assemblies to find out the best and most thrust/fuel/ weight ratio. Model the spaceplane in computers and wind tunnel test the design. I am not talking about construction of the NTR yet. I would then work at spaceplane construction and testing as an aircraft first. At the same time as full size spaceplane testing and evluation a full size NTR would be tested and fuel / thrust testing including calibration of the drive system for the most efficient capacity. Then finally put the spaceplane and booster together in the nuclear decalred zone.
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So your shuttle will get to about 8,500 mph; less than half of orbital velocity.
Almost half orbital speed on 1/4th the launch weight of the space shuttle! That's pretty good.
But your figures were a little favorable. You did not include the F119 engines and 20,000 lbs of jet fuel, well 10,000 by the time the vehicle gets up to that altitude. The actual weight would be 26,000 lbs heavier.
It seems to me that the idea only needs a little more something.
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No, you do not understand Tristar... since it is an actual space vehicle, it could crash anywhere in the world. You simply cannot count on it to crash only near the launch site, that just isn't realistic. If your vehicle failed, it will become a giant out-of-control ICBM.
Furthermore, since the reactor casing must be light weight and it must have holes in it for liquid hydrogen and the rocket nozzle, I don't think it will be very practical to develop a completly reentry-proof/impact-resistant reactor. It will never be crash-safe and light enough.
Using a NTR engine will probobly never be safe enough for a launch vehicle to be worthwhile. Oh, and plasma rockets (eg VASIMR) will never produce enough thrust to even get their own weight off the ground, much less their fuel or the rocket.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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GCNRevenger,
When we design future spaceplanes, or larger spacecrafts, all will be powered by nuclear type drive and power systems. Yes the risks are their for radiation and other issues regarding the use of nuclear reactors. But the benefits outway the specific risks, if the risks can be managed.
We need a space vessels to be able to take 20-35 personnel, their belongings and cargo into orbit and back. A large spaceplane would be the answer, but the design, weight, thrust, and fuel consumption all need to be worked out. NTR Engines are part of the mix because they provide increased thrust to weight ratio compared to the same chemical engines.
I can see how frightening change can be for you, GCN but we need to move down this road for space development in engine design and testing, we haven't since the 1950-60's and we nned to see if our new material technologies and computer technologies could improve the design, fabrication, and control of the engine system .
VASMIR Drive system could provide greater thrust then NTRs but it relays on the power requirements and only will occur when we have fusion reactors ( again for large scale space vessels only ).
Inclusion
I am suggesting a course of action that will provide the ability to move large scale personnel, and cargo into space and return complete space products to earth safely would a large scale cost, increasing the use of space and the expansion of humanity permanently into space locally and interplanetary.
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"When we design future spaceplanes... all will be powered by nuclear type drive and power systems. Yes the risks are their for radiation and other issues regarding the use of nuclear reactors. But the benefits outway the specific risks, if the risks can be managed."
Why do you think this? What are the technical concepts that lead you to conclude this? The reasons why an NTR engine is not a good idea for a spaceplane are signifigant purely from a performance standpoint:
-Radiation shield will reduce payload mass considerably
-Large NTR engines weigh many tons
-All-Hydrogen fuel tanks are bigger then H2/O2 tanks, increasing weight, drag, and reentry pressures
-Cannot be reused by any practical method unlike chemical engines due to radiation hazard
-Large NTR engines would be expensive to develop and build, while reuseable H2/O2 engines are being developed right now
These are just the logistic reasons why NTR for launch is a bad idea and will not change much with improved technology. The fact remains that if your vehicle fails to reach orbit, many kilos of the most deadly chemical substance in the world will return to Earth unpredictably and with no warning or defense. Making the reactor heavily armored to reduce how wide an area the material would be spread over would not reduce the risk far enough, and would add tons more weight to the vehicle. The risks cannot be managed in such a fasion that bennefits of using NTR engines for ground-to-orbit outweigh the technical, environmental, and political consequences...
In fact, using chemical engines would possibly be lighter overall then nuclear since NTR engines aren't far more efficent and will need all that extra shielding. And since you can't bring them back to Earth, your spaceplane therefore isn't a true RLV. I should also point out that NERVA/Timberwind type engines cannot be improved on much, since they already operate very close to the melting point that the reactor is made of. Ultrahigh temperature ceramics are nearing a plateu, since the bonds between the atoms themselves have an upper strength limit. And if it melts... kaboom.
"I can see how frightening change can be for you"
Please, do not try to insult my intelligence with nonsense like this. You do not even know the facts of what you are talking about, or the faintest notion about how deadly a "hot" reactor's contents are. I am as pro-nuclear a person as you will find, I openly scoff at anti-nuke environmentalists, cheer when NASA wants NTR for Mars ships, and even my name (N=Nuclear) is an homage to a brilliant reactor concept... But not this time, the bennefits of using a NERVA or Timberwind type engine for a spaceplane or general ground launch simply do not make sense given their problems.
"VASMIR Drive system could provide greater thrust then NTRs but it relays on the power requirements and only will occur when we have fusion reactors"
No they won't. VASIMR engines are large, heavy devices with their cryomagnets, radiators, and other equipment plus they can't generate much thrust, because the more efficent an engine is the less thrust it can produce for a given energy input. Simple thermodynamics, it will have little more thrust then an ion engine, and would not even be able to lift its own weight even if you don't count the reactor mass.
A fusion reactor or a next-generation fission reactor won't change this situation either, since they can produce a little power continuously with high efficency per-pound, but they can't produce huge amounts of energy without sacrificing efficency... which defeats the purpose. Fusion reactors imparticularly are likly to be heavy even though they are efficent. If you build a bigger reactor to try and give a VASIMR engine enough thrust to go from ground-to-LEO, then the reactor gets heavier too, so you will never make it.
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Oh, and before you go off on some "you don't believe in our abilities" etc etc, no amount of human technology can change the laws of physics, such as the maximum strength between chemical bonds in ceramics, or the unchanging half-life of radioactive elements. The best we can do is push technology to work within these limitations, and as far as solid-core fission engines go, we have essentially reached these limits.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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