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I just read another great article by Jeffery Bell.
http://www.spacedaily.com/news/oped-05zy.html
In this article he correctly points out the difficulties of reaching orbit in a single stage reusable vehicle. Basically the meat of the article is that to reach orbit in a SSTO you need a dry mass weight of only about 8%, meaning that your vehicle must me 92% fuel by weight.
Obviously, contractors and NASA have been feeding us pipe dreams with the DC-X and the like that don't even come close to meeting this weight requirement. Projects such as these have just been an exercise in pork for the aerospace giants apparently.
So my question is this...
Why isn't NASA seriously considering alternatives to the 'take the fuel with you' approach?
What happened to dreams of building a rail gun like launch facility to accelerate small spacecraft up to say Mach 1 before turning on the engines?
Yes, I know this would be a huge engineering task that would require miles of track to be built, but if we can build super-colliders on the same scale, then why is this out of our reach?
Also, why isn't NASA, Boeing or Lockheed looking into a two stage transport the likes of which was used by Burt Rutan to capture the X-prize? Granted, NASA could get 1-3 people to orbit like this and not much else, but it isn't unmanned transport that is terribly expensive. Cargo and supplies could be launched seperately on traditional rockets that are much cheaper and not as safe.
Here's what I am envisioning...
Stage One: A supersonic vehicle capable of carrying the stage 2 vehicle reaches an altitude of about 20,000 feet traveling at Mach 2-3. It then drops the stage two vehicle and returns to the landing strip.
Stage Two: Already traveling near Mach 3 fires its rockets clear of the atmosphere and begins to build the needed velocity to reach orbital speed. This stage will include a capsule for the crew to re-enter the atmosphere safely while the spent stage two re-enters under auto pilot to be reused if it survives intact AND is cheaper than replacing.
Surely this is much safer than the shuttle we now use for several reasons. Capsules have never let us down when it comes to re-entry. They are tried and true tech while being relatively inexpensive as well. The stage two vehicle/glider wouldn't suffer from the same re-entry pains as the shuttle being much smaller and lighter without a crew compartment.
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Finally I have a physics question for someone like GNCRevenger. Would the fuel needed to reach orbit be reduced by using an elliptical plan of attack rather than a circular one?
Let me explain, we current reach orbit by using Hydrogen/Oxygen burns for an extremely high exhaust thrust so that we can reach 25,000 mph in what, two minutes?
Why not gain more altitude with a slower, continuous burn going straight up at say 80 degrees to the plane of Earth till we are say 10,000 miles above the Earth where the orbital velocity needed is much less. Then we could use the pull of The Earth to our advantage couldn't we? Once we start to fall back towards Earth, we could accelerate toawrds the edge of the atmosphere in a second burn, just barely miss it, and sling shot to the other side. Then once we have the needed speed, we could use a few well timed burns to round out our orbit could we not?
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I guess the basics of the engine and fuel used comes down to an effiencency question for can we go slowly to reach orbit or can we get there by rapidly burning the fuel.
Going slowly means more time and that means more fuel no matter how you look at it.
So a large scale push or burst gets the greatest delta v for forward motion.
The solid fuel srb's that the shuttle uses burn for approximately 2 minutes which is enough to get you to the suborbital ceiling of 62 miles.
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I thought DC-X had promise as a demonstrator--certainly as a lander. Place that atop the Magnum/Longfellow SD HLLV with four SRBs--and there is your direct ascent NOVA mission to the lunar poles right there.
You know the X-33 VentureStar was actually a J. Northrup design? He kept getting his cough-drop bottle confused with his suppository bottle at the home--with interesting results there at the home. So he took his bic lighter, and fused up a lozenge that was half cough-drop--half suppository. He put one hybrid in each hole so he knew he was covered.
But he put them all in the full bottle--which he threw away thinking the empty bottle had his medicine--and he died.
So some Lockheed-martin spies saw one of his lozenges---and that's where they came up with the VentureStar /X-33 design. They then tried to take it to Marshall--but took a wrong turn to the Alabama group home for retards.
"UH!--we use composite tanks for hydrogen, and leaky as a sieve engine...drool."
And you know the rest.
My plan for the SSTO problem?
Get all the engineers who support it.
...line them up...
----and have them shot.
problem solved.
Now let's get back to Heavy Lift--something we know works.
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Hmmmm I didn't realize the numbers were so bad for the ol' DC-X... with a much denser fuel and far less gravity and drag, it might still work for Mars though. It sure scared the Commies though, since the DC-I was advertised to cheaply haul anti-ICBM interceptors to orbit.
I don't share Bell's pessimism about the CONCEPT of the X-30, because an air-breathing SCRAMJET engine throws the rocket equation out the window, because you have "free" reaction mass and oxidizer. That isn't to say that it wouldn't be extremely difficult to build of course, and is probobly a little beyond our technology even with a >$25Bn investment, but it still more plane than rocket.
The problem with using a rail launch or a low-speed/low-altitude air launch is really pretty simple, that they don't contribute enough velocity to the vehicle to save much fuel. You are only talking a few percent of the total velocity required to reach orbit, and even after the assisted launch, you are still wallowing around in the thicker lower atmosphere. The logistics involved with the rail launch are particularly bad unless you need a large number of launches, but if you need a really BIG number, then they aren't good either.
Air-launching a conventional capsule with a recoverable upper stage is not a horrible idea if all you need is a capsule, but its a terrible arrangement if you want cheap, routine spaceflight. It is very very simple, that the entire vehicle - ALL of it - must be able to return to a runway, preferably at the launch site. A capsule can't, so its out. If the upper stage is already pushing the capsule to orbit, then it makes better sense to make the fly-back upper stage also carry your crew/payload. We are alot better at making spaceplanes now, and with the use of slushed Hydrogen largely solves the fuel tank volume problem. Total, easy reuseability is the only possible justification to go to so much trouble.
The best arrangement is a LARGE carrier plane with either conventional jet engines and large kerosene rockets, or combined-cycle turbo/ramjet engines like on the SR-71 Blackbird, except bigger and augmented with Liquid Oxygen. This vehicle would take off from a runway, perhaps produce its LOX in flight, and then sprint up to high speed and altitude - say Mach-6 at 100,000ft - then seperate from the spaceplane. The spaceplane itself would be a slightly streamlined lifting body, perhaps like the Shuttle-LSA, and carry a payload preferably as large as the Russian Proton rocket. It would be powerd by conventional but advanced bell-nozzle engines, fed by slushed hydrogen, and maneuver with storables. The heat shield would be all metal except for RCC leading edges and nose cone (or maybe robust active cooling) and return to the launch site for runway landing.
These technologies now exsist or will soon in an acceptably advanced form, however the size of the vehicles involved would still demand an extremely expensive development, perhaps on the order of $20-30Bn. Two different models of orbiter would also be built, one purely for cargo and one for crew, where the latter would have enough mass to accomodate secondary heat shielding or perhaps even an ejectable reentry-hardened/self-righting cabin. The "trick" to the project would be to rely on the carrier plane to reach high altitudes and speeds to minimize the size of the orbiter.
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Now for the orbital mechanics...:
"we could use a few well timed burns to round out our orbit could we not?"
Short answer: no you can't.
The current way of getting into orbit with rocket engines requires the least amount of energy, there are no better, easy, sneakier, smarter ways. The mechanics of orbital flight, if you don't bother with much math, are pretty easy. You have to build up velocity tangent to the Earth, or else Earth's pull will pull you right down again. You have got to have this velocity, and this velocity isn't free, you have got to get it from someplace. Getting it from converting altitude into velocity won't help you, because of the huge amount of energy needed to reach said high altitude vastly exceeds simply using the energy to gain velocity directly.
A big reason for this is due to gravitational losses: the reason why you need so much thrust for a rocket is more subtle then you might think, that the basic rocket equation doesn't take into account... The reason why a slow acent requires more fuel than a fast acent is that the rocket engine requires a certain amount of fuel continuously to produce a certain amount of thrust. You need a minimum amount of thrust to counteract gravity continuously, which does not go into accelerating your vehicle. The more time you spend fighting gravity, the more of this fuel is wasted just to keep you from plummeting back to Earth. This is why rockets generally want to start building up tangent velocity as fast as they can, bascially as soon as they clear the thickest atmosphere, because the more tangent velocity you have, the time and fuel you have to spend to counteract gravitational losses.
This is why climbing straight up to orbital altitude before making any tangential velocity is silly, because you have to spend fuel to fight gravity the whole way instead of reducing your gravitational losses as soon as possible after liftoff.
Oh! And before I forget, you might wonder how you can use the rocket equation to estimate launch vehicle payloads if you don't factor in gravitational losses? The actual delta-V needed to reach orbit is less then what the launch vehicle can actually accomplish, with the "extra" being to counteract gravitational and drag losses. This is assuming that most rockets have relativly similar thrust/mass ratios, which is not always a good assumption. The big Delta-IV HLV has horrible gravitational losses, while "The Stick's" high thrust SRB and SSME configuration would have relativly low losses.
Edit: Side note, spaceplanes or anything that uses wings/lift-body for lift have one edge, that the added lift counteracts gravitational losses without burning fuel and reduces the thrust requirements somewhat, but at the cost of wing mass. If you need lift to glide/fly anyway, then they can come in handy.
[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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That was one of the best articles I read by Jeffery Bell, although I did find this quote,
I've been monitoring the large volume of Web chatter about these plans, and have noticed a disturbing theme therein.
Many Space Cadets are expressing dissatisfaction with these leaked NASA plans. They say that the Shuttle-derived boosters are too primitive, too expensive to develop, too expensive to operate, and not inspiring enough. They can't understand why we will be returning to the Moon with rockets and space capsules that look like minor variations of those used in the Apollo program 40 years ago.
slightly offensive.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
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Yeah, he was laying it on a little thick...
I am trying to think of an easier way to explain the mechanics of getting into orbit... anybody else have a better way to say it?
The long and the short of it, the less TIME you have to fight gravity before reaching orbital velocity, the less total fuel you need.
[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, he was laying it on a little thick...
I am trying to think of an easier way to explain the mechanics of getting into orbit... anybody else have a better way to say it?
The long and the short of it, the less TIME you have to fight gravity before reaching orbital velocity, the less total fuel you need.
There is the work equals force times distance thing. If you burn your fuel before gravity slows you down you do the same force over a larger distance thus you impart more energy on the ship. As for the path, forces perpendicular to the velocity only change the direction and not the velocity. Thus they don’t slow you down. I am thinking though it is not the energy we want to change but rather the angular momentum.
The angular momentum of an object about a point is equal to the cross product of the position vector and the velocity vector. If you fire your engines tangential to the earth all energy goes into increases the angular momentum of the rocket about the earth. If you fire the rockets straight up no energy goes into increasing the angular momentum of the rocket about the earth.
This actually seems consistent about what I’ve heard where you can alter the orbit of an asteroid the most if you give it a push when it is furthest away from the sun. So if you fire your rocket straight up. You want to fire it again at the exact moment it starts to fall back down and you want to fire the engines in a direction that is perpendicular to the vertical.
edit: I have a homework question for someone. Find an algebraic relation between: the eccentricity of the orbit, the energy and the momentum.
For my homework question I might try to find a vector differential relation between the position vector, velocity vector, thrust vector and gravitational losses.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
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The best arrangement is a LARGE carrier plane.... ... The spaceplane itself would be a slightly streamlined lifting body, perhaps like the Shuttle-LSA, and carry a payload preferably as large as the Russian Proton rocket.
So it will be huuuge and expensive, but possible... Interesting start.
Now, I know there have been numerous discussions already about minimal launch-capacity, but this one is too good to let go.
If the system you describe is possible, launchprices would go down dramatically. So, you could do more launches for the same price.
What would be the minimal launch capacity to make this worthwhile? Proton categories are good, but a smaller system would be cheaper to develop build, service... So how small exactly?
at one point, lauching, say 50kg a throw even at incredibly low launchprizes becomes totally impractical, to say the least... But what *would* be practical In a scenario where existing expensive boosters could throw huuge stuff, if really needed...
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Its all about the customers
With improved Russian "Soyuz-II" or Angara and Elon's Falcon V/IX over here, the launch market for space satelites - barring some "killer app" - is too well served by cheap rockets to compete with a "no really" type RLV. (I use the term "no really RLV" for a vehicle that is what Shuttle promised to be, biweekly flights for <$1000/lbs.)
So if comm/weather satelites are out, what does that leave? A "space hotel chain" or the government. The former wouldn't need as much payload, say about as much as the ESA ATV or say a crew of eight, but given the small number of would-be weekend astronauts, the chances affording the development of a $10Bn "mini" version are pretty slim.
So that leaves just NASA, or in general, government spaceflight. What are the payloads that NASA or the USAF or intelligence agencies interested in launching? The USAF will already have a low-cost way to put small payloads into orbit by then (like cellular SBR), so tailoring a "mini" version with a bit more payload then a Falcon-I doesn't make much sense. What else would the USAF need? Hmmm lets see here...
-SBIRs satelites, probobly of similar or slightly larger scale to GPS satelites (Delta-II/Delta-IVM) and about as numerous, but this market vanishes when the constellation is complete.
-Spy satelites with large-diameter optics or antennas, but you might not need that if you use smaller satelites with folding aperatures. Since we don't know much about spy sats, this is kind of sketchy.
-The biggie... space-to-space and space-to-Earth weapons. This would require bigger (Proton sized) and more frequent launches.
Then comes NASA... NASA obviously needs pretty hefty payloads to support a Moon base and eventually a Mars base, and I think that the minimum size that makes sense is a Proton sized vehicle, which is the same as the maximum payload capacity of a current VSE Lunar lander and about half the DRM Mars lander. The ability to carry at least eight passengers with "luggage" should also be a requirement, since you could put that many into a slightly uprated NASA-DRM hab if you removed the laboratory spaces. Perfect for Mars base crew rotations.
I also don't think that there is going to be a space station by the time this bird' would be flying, so the notion about using it for ISS/etc resupply is out. Since most of the bulk materials will be made on the Moon and Mars, then the need for small resupply flights is probobly also nil. So to summerize...
-There is a possibility of a 10MT class need for a signifigant but not huge number of launches for USAF future SBR/SBIRs/spy sat needs, but this market would dry up after a few years of launches or Falcon-V might eat the RLV's lunch. It is not likly NASA would need such a vehicle since the ISS will no longer exsist, and you need signifigant fuel & hardware to propel even supplies or light/medium equipment to Moon/Mars.
-NASA will definatly need a 20MT class vehicle in the long run, probobly closer to when the money will be available for Shuttle-II, and the USAF will also need it if the weaponization of space occurs. This would be much more a "sure thing" by comparison to the 10MT version, and selling flights for large spy sats or weather/comm sats on the side would bring in some business too. You might even be able to make a little money from space tourists using the the thing.
I won't say that a 10MT version is outright useless, but I think that the situation points to the 20MT version being the better investment.
[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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The more time you spend fighting gravity, the more of this fuel is wasted just to keep you from plummeting back to Earth. This is why rockets generally want to start building up tangent velocity as fast as they can, bascially as soon as they clear the thickest atmosphere, because the more tangent velocity you have, the time and fuel you have to spend to counteract gravitational losses.
Granted GCNR, but doesn't this assume that the efficency of a slow and fast burn rocket are the same?
You seem to have a good grasp of nuclear physics, so help me understand why we can't acheive much higher thrust from a nuclear powered rocket? I understand that the force of a rocket's engines are directly related to the speed of a rocket's exhaust.
So my question is this: can a small reactor be used to super-heat air, perhaps even incoming air from the surrounding atmosphere, or stored air to produce a thrust greater than that of conventional rockets?
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What would the 'no really' RLV offer re: $/kg ?
You make it sound on par with Falcon launchers, but wouldn't it be an order of magnitude cheaper?
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I don't think you have a good grasp of rocket mechanics deagle, a fast burn will build up orbital velocity more quickly, and hence will not have to fight gravity for as long, thus wasting less fuel to fight gravitational losses. A slow "burn" has absolutely no advantage whatsoever as far as fuel efficiency is concerned compared to a "fast" burn.
Fuel efficiency, specific impulse to use the proper term, is the maximum amount of velocity change you get per pound of fuel. It has nothing to do with how fast or slow the fuel is used! It is controlled by the exhaust velocity, which is controlled by temperature in rockets, and the mass of the exhaust. A hot, light exhaust is very efficient.
However, a very efficient engine has trouble achieveing high thrust: thrust is simply momentum by a different name, and if you have a lighter propellant then you need MUCH higher velocities (and temperature) to acheive comperable thrust, or else bigger/more engines.
The temperature that rocket engines can achieve given their fuels and the materials they are made of has reached a plateu, and is not going to improve anymore. This is why rockets today aren't really much different then rockets back in the 1960's, sure ours are a little more efficient, but this is why things haven't changed much.
The mass of adding additional chemical engines is not that bad (not that good either), but since most rockets are staged then its easier to put less efficient but higher thrust engines in the lower stage, and high efficiency lower thrust engines in the upper stage, like Saturn, Atlas, or The Stick.
There is also the problem of fuel density, that the most efficient rocket fuel is Hydrogen, but Hydrogen has very low density. As such, if you need alot of it, then your fuel tanks are going to be very very big and heavy. This is yet another tradeoff between high efficiency engines, since their fuel tanks are large.
Now nuclear engines are a different ballgame...
They get their high efficiency not from their high temperature, the SSME engine runs at similar temps, but rather because it uses only Hydrogen and no Oxygen. Since you are no longer blowing Oxygen out the back, the exhaust is MUCH lighter, and so is much more efficient...
...But nuclear engines suffer the same efficiency/thrust tradeoff, that though they are efficient, their thrust isn't very good. The real killer though is that the engine itself is pretty heavy, that to build a high-thrust nuclear engine, it is going to weigh many many tonnes, which will counteract most of the improvement in efficiency! There is also the sticky matter of radiation, and unless you have "disposable" launch pads, you have to add very heavy radiation shielding too, which makes it even worse. Plus, since it burns only Hydrogen, the fuel tanks would be gigantic.
And finally, since the engine would not be in a stable orbit before it is fired, even the slight chance that the hot reactor would fail to reach orbit is enough to scare even me to death.
[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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What would the 'no really' RLV offer re: $/kg ?
You make it sound on par with Falcon launchers, but wouldn't it be an order of magnitude cheaper?
I don't think that the "big" Falcon-IX launcher can lift payloads of useful size for under the $1000/lbs.
I think its hard to say at this point, but the $1000 mark is the minimum cost reduction... the ideal would be around $25M a flight, which would be in the $500/lbs region, but that might be pretty hard to achieve. I think it could be done, but it would take a level of execution that NASA hasn't pulled off since Apollo.
Edit: Now that I think about it, the $25M mark is probobly the most expensive that would be worthwhile to develop the thing.
[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 don't think you have a good grasp of rocket mechanics deagle, a fast burn will build up orbital velocity more quickly, and hence will not have to fight gravity for as long, thus wasting less fuel to fight gravitational losses. A slow "burn" has absolutely no advantage whatsoever as far as fuel efficiency is concerned compared to a "fast" burn.
Obviously you didn't understand my question, but that's ok. Thanks for the 'in-depth' explanation of basic physics...
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I don't think you have a good grasp of rocket mechanics deagle, a fast burn will build up orbital velocity more quickly, and hence will not have to fight gravity for as long, thus wasting less fuel to fight gravitational losses. A slow "burn" has absolutely no advantage whatsoever as far as fuel efficiency is concerned compared to a "fast" burn.
Obviously you didn't understand my question, but that's ok. Thanks for the 'in-depth' explanation of basic physics...
No, I knew where your question was going, and I figured that giving you the background why it wouldn't work would be more effective.
[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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No, I knew where your question was going, and I figured that giving you the background why it wouldn't work would be more effective.
But you didn't understand my question so how could you know where it was going???
Any grade school science student can understand such a basic notion of physics. Obviously the slower a rocket travels the longer it will be fighting a body's gravity. My question had nothing to do with the duration of a rocket flight, just efficency.
That's why I asked the forums about nuclear propulsion as a viable option. To ascertain if the higher temperatures that could be produced would lead to a more efficent rocket.
As for the radioactive waste produced that you mentioned, why couldn't we use nuclear energy in a closed environment that would not involve dumping radioactive particles into the air?
Is there not a way that we could pass air over a reactor and use that air as thrust?
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"Why not gain more altitude with a slower, continuous burn"
Sure sounds like you meant that a slower burn was supposed to be better compared to a faster one...
I already mentioned that engine temperatures have plateued because no known material can handle the temperature, nuclear or chemical powerd. RCC materials are already used in Shuttle rocket nozzles, and both NERVA type and Timberwind nuclear engines use cores made with graphite if memory serves. They aren't going to get any hotter.
The problem with radioactive exhaust is pretty simple, that due to the extreme temperatures, supersonic flow of dense hydrogen gas, and the combintation of the two can corrode most any known material then you WILL lose some of the core material out the back of the engine. Some of it is going to ablate off of the fuel elements and be caught up in the exhaust and leaked out the back.
I personally think that the amount lost if dispursed over a wide area will probobly not be a problem, but using it for ground launch would concentrate alot of the material near the pad, which isn't acceptable. Without massive radiation shielding, the pad itself would become dangerously radioactive too. The biggest scarry thing though would be if the core failed and blew up in flight before reaching orbit, and THAT would create a nuclear wasteland like the "Space 4 Peace" nutsos shreik about.
Unfortunatly there isn't a good way around this, since if you were to add a thick coating of RCC over the nuclear fuel elements, it would act as an insulator and cause them to overheat and fail. You have got to have the fuel in close proximity to the propellant or else the whole thing will melt. So no, you can't really have a "sealed" nuclear engine. Passing hypersonic air over the core elements would be even worse, since Oxygen at extreme temperatures is powerfully corrosive. Remember that C + O2 -> CO2? The core would rapidly disolve at high temperatures.
There just isn't much bennefit using a nuclear engine for launch I don't think, you would need a huge amount of thrust as far as nuclear engines go, and would hence need a very big and heavy reactor. This reactor would produce gobs of radiation, and likewise need a heavy duty radiation shield. Plus, since it uses only Hydrogen, the fuel tanks would be pretty bulky too... Yes it would increase payload by ~50%, but I don't think its worth the expense or risk.
[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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"Why not gain more altitude with a slower, continuous burn"
Sure sounds like you meant that a slower burn was supposed to be better compared to a faster one...
Different propellants have different reaction velocities, that's what I meant. Taken out of context I can see how you might reach that conclusion. However, the overall topic is about rocket efficency.
As for the nuclear option, what about this...
Why not use a reactor to produce electricity which could then genrate a magnetic feild that forces air out of the back of our rocket at much higher speeds and without the dangerous heat you mentioned?
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Use a nuclear plant to generate electricity to improve engine efficiency for launch? Novel, but not very practical:
Do not forget the distinction between energy and power, the former you already know about, but don't forget that the later is time-dependant; power is the amount of energy per time.
I don't think that you fully appreciate just how much power is involved with launch, that the amount of power needed is just incredible. Each one of the turbopumps on the Saturn-V's F-1 engines produced about one hundred megawatts of power, and thats just the pump!
No nuclear plant of practical mass could possibly generate more than a few megawatts of electric power, it would still produce vast amounts of radiation, and would still produce a nuclear nightmare if the engine failed to reach orbit.
Nuclear power plants geared to produce electricity operate at low power levels and temperatures, which combined with the electrical generation equipment and cooling systems, tends to make them very heavy.
Edit: The USAF ponderd coupling a Timberwind nuclear rocket to a turbine to power a space-based laser/particle weapon, and such a thing might produce the amount of power you are looking for, but it operated its cooling system "open loop" and dumped the Hydrogen coolant overboard. This coolant would be traveling pretty slow after passing through the turbine, and so if you used this to help push the rocket, the reduced efficiency from this "slow" exhaust would more than counteract the increased speed from the magnetic nozzle.
[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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Bell's criticism of DC-X's mass ratio is a bit off base in one way - DC-X wasn't a full scale prototype, nor even built the same way the full scale ship would have been. The "real" SSTO, if it had ever been built, would have been much larger and had a much higher mass ratio - the most optimistic estimates were that the real thing would have had about 90% fuel, 9% dry weight, and under 1% payload if everything worked out right.
This is not to say that a DC-X derived SSTO would necessarily have been successful - most of Bell's other arguments about the extra mass required for a fully re-usable SSTO are pretty much on target.
Now as a ship for landing/lift-off from Mars, SSTO seems to make a lot more sense.
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Bell is probobly being a little too hard on the DC-X, but not by leaps and bounds... the mass fraction of the concept is cut pretty darn close, and even a small mistake in engineering estimates or weight creep would have doomed it. Canceling DC-X was the right thing to do, since it was so risky. Betting against weight creep is almost always a losing proposition, and even a giant Shuttle ET sized version would not have margins I would feel comfortable betting on.
[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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IMHO, an SSTO is not practical unless non-chemical methods of propulsion are used.
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I wouldn't say that catagorically Vir...
Materials science really is progressing, though mostly on the laboratory scale at the moment. A relativly modest improvement in materials could make true SSTO possible. "Unobtainium" isn't so unobtainable anymore...
A DC-X style rocket, built from carbon nanofiber composites, burning slushed Hydrogen spiked with nanoscopic aluminum powder, with a radial aerospike engine(s) could possibly do the trick...
Or, a X-30 NASP style vehicle using a combined jet/ramjet engine for takeoff to high supersonic, then from there to nearly orbital velocities with a Scramjet engine fed with regenerativly heated slushed Hydrogen used to cool the vehicle's skin. Also bennefiting from next-generation composites and new ultrahigh temperature ceramics...
...Down the road a little ways, sure, but not that far.
[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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The papers in The Journal of Propulsion and Power that describe a turbojet engine to fly at mach 6 describe hydrocarbon fuel with supersonic combustion. The engines don't have a scram jet bypass; they do supersonic combustion right through the turbojet. That means supersonic airflow through the compressor blades, supersonic combustion in the combustion chamber, then supersonic airflow through the turbine blades. Yup, two airforce contractors already demonstrated them in a wind tunnel. Wind tunnel airflow is mach 6, but remember any turbojet slows airflow while it compresses so combustion is slower than mach 6 but faster than mach 1.
Combine that with LH2 scram jet and X-43A airframe and you achieve ground to mach 10. Add a Shuttle style heat shield instead of titanium skin and regeneratively cooled engine, you achieve mach 17. Add a LOX/LH2 rocket engine optimized for an upper stage and you achieve orbit. Shushed hydrogen would reduce tank size. An ultrahigh temperature ceramic would be really nice for the scram jet intake, but would RCC do?
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