Posted on 09/23/2005 2:45:56 PM PDT by tricky_k_1972
This is an excerpt of a very lengthy explanation of what a nuclear SSTO (Single Stage To Orbit) fully reusable rocket would look like. The full article can be found at the link above.
In this section I describe a huge nuclear powered rocket launcher. I will repeat and expand upon many of the points I made above, because I don't want to throw cryptic acronyms around. I want people to understand just how powerful we can make this rocket if we decide to do it.
The most important difference between our new booster and the Saturn V is in the engines. The Saturn V used five massively powerful F1 engines in the first stage, burning kerosene and liquid oxygen. The mighty F1 produced 1.5 million pounds of thrust. Despite its large size and power, the F1 was a very "relaxed" design. It ran well inside the possible performance envelope. The reason it did so was to increase reliability. This is a sound design principle, so I will apply it to the new launcher wherever possible.
For an engine, I will designate a Gaseous Core Nuclear Reactor design, of the Nuclear Lightbulb subvariant. I like the gas core design for a number of reasons, and the nuclear lightbulb variant for several more.
To recap, the efficiency and power of the thruster is based on the difference in temperature between the fissioning mass and the reaction mass. If you run a solid core NTR much above 3000 C, it melts. This provides a firm "ceiling" on how efficient a solid core reactor can be. A gas core design STARTS melted. In addition, since all of the structure of the fuel mass is dynamic, a gas cored reactor is inherently safer than a solid core device. If a "hot spot" develops in a solid core, disaster ensues. If a hot spot develops in a gas core, the hot spot superheats and "puffs" itself out of existence. A gas core reactor is expected to operate at temperatures of 25,000C. The much higher temperature gradient makes the thruster inherently more efficient.
Second, a solid core reactor has a "fixed" core, since it is solid. A gas core reactor does not, and the radioactive fuel is easily "sucked" out of the core and stored in a highly non-critical state completely out of the engine! The fuel storage system I propose is a mass of thick walled boron-aluminum alloy tubing. As I said above, the fuel proper is uranium hexaflouride gas. UF6 is mean stuff, but we have decades of experience handling it in gaseous diffusion plants, and common aluminum and standard seals are available which resist attack from it. It is stoichiometric, fluorine is low activation, and UF6 changes phase at moderate temperatures, allowing it to be converted from high pressure gas to a solid and back again using nothing fancier than gas cooling and electrical heaters. This naturally makes dealing with the engine easier.
In addition, the design of the gas core allows the addition and removal of fuel "on the fly." The core can also have its density varied by control of the vortex, which directly affects criticality. Both of these elements allow very potent control inputs to be applied to a gas core reactor which are very stable and unaffected by the isotopic condition of the fuel mass.
Also, to repeat, due to the extremely high temperature gradient in the motor, the main cooling of the fissioning mass is not conductive but radiative, a mode which is inherently less susceptible to perturbations. (Having no working fluid for cooling means no material characteristics for the working fluid must be considered.) This radiative cooling mechanism is what allows the "lightbulb" system to work. The silica bulb just has to be transparent enough to let the gigantic power output of the fissioning core flow through, while keeping the radioactive material of the core safely contained inside the thruster. No radioactive materials leak out of the exhaust, it is completely "clean."
Third, a gas cored reactor has several potential "scram" modes, both fast and slow, and the speed of the reaction is easily "throttled" by adding and removing fuel or by manipulating the vortex. A 'scram' is an emergency shutdown, usually done in a very fast way. For example: a gas cored reactor can be fast scrammed by using a pressurized "shotgun" behind a weak window. If the core exceeds the design parameters of the window, which are to be slightly weaker than the silica "lightbulb," then the "shotgun" blasts 150 or so kilos of boron/cadmium pellets into the uranium gas, quenching the reaction immediately. A slightly slower scram which is implemented totally differently is to vary the gas jets in the core to instill a massive disturbance into the fuel vortex. This disturbance would drastically reduce criticality in the fission gas. A third scram mode, slightly slower still, is to implement a high-speed vacuum removal of the fuel mass into the storage system. Having three separate scram modes, one of which is passively triggered, should instill plenty of safety margin in the nuclear core of each thruster. Extensive work was done on gas core reactors, and 25 years ago several experimental designs were built and run successfully. There were technical challenges, but nothing that seems insurmountable or even especially difficult given our current computer and material skills.
The engine I propose is this:
A Gas cored NTR using a silica lightbulb. The silica bulb is cooled and pressure-balanced against the thrust chamber by high pressure hydrogen gas. The cooling gas from the silica bulb is used to power three turbopumps "borrowed" from the Space Shuttle Main Engine. These pumps are run at a very relaxed 88 percent of rated power at their maximum setting. The three pumps move 178 kilos of liquid hydrogen per second combined. Most of this is sprayed into the thrust chamber. A portion of the liquid hydrogen is forced into cooling channels for the thrust chamber and expansion nozzle, where a portion of it is bled from micropores to form a cooling gas layer. The gaseous hydrogen that is not bled then flows down the silica lightbulb to cool it, and the cycle finally goes into powering the turbopumps.
This engine produces 1,200,000 pounds of thrust, with an exhaust velocity of 30,000 meters per second, from a thermal output of approximately 80 gigawatts. This equates to an Isp of 3060 seconds. Several sources state that a gas core NTR can exceed 5000 seconds Isp, so 3060 is well inside the overall performance envelope. The three turbopumps from the SSME are run at low power levels, and even losing a pump allows the engine to continue running as long as there is no damage to the nuclear core. Lets assume this design is able to achieve a thrust to weight ratio of ten to one, so the engine and all of its safety systems, off-line fuel storage, etc, weighs 120,000 pounds. I think we can build this engine easily for 60 tons.
We have the engine. Now to design the entire vehicle.
Since we are using the Saturn V as our template, we will make the new machine about the same weight, or six million pounds launch weight. With our engines giving 1.2 million pounds of thrust, we need at least five to get off the ground. But, since we have the power of nuclear on our side, we will use seven engines instead of five. Why seven? The most vulnerable moments of a rocket launch are the first fifteen seconds after launch. If we have to scram a motor in those fifteen seconds, having two extras is very comforting. Engine failures further along the flight profile are much easier to recover from, and having two spare engines allows us to be very "chicken" on our criteria for scramming a motor. We can shut one down even at one second after launch if we need to with no risk of crashing the entire vehicle. This further lowers the risk of nuclear power as a means of getting off the earth. With seven engines, we have a thrust of 8.4 million pounds available. In addition, the turbopumps can "overthrottle" the engines easily in dire straits. This gets more thrust at the expense of less Isp.
Let's design the vehicle for a total DeltaV of 15 km per second. This is very high for a LEO booster, but the reason for it is to allow enough reaction mass to perform a powered descent. In other words, this is a true spaceship, that flies up and then can fly back down again.
The formula to calculate DeltaV from a rockets mass is: DeltaV = c * ln(M0/M1).
'c' is exhaust velocity of the engines and equals 30,000 m/s.
'ln' is the natural log.
'M0' is the initial mass of the vehicle, and we have set this to be 6 million pounds.
'M1' is the mass of the vehicle when it runs dry of reaction mass.
The value of M1 is what we need to find, since we know we want a total DeltaV of 15,000 m/s.
Doing a little simple math, we find we need 2,400,000 pounds of reaction mass. Since we are using liquid hydrogen, we can now calculate the size of the hydrogen tank needed, which is 15,200 cubic meters. This works out to be a whopping 20 meters in diameter and 55 meters long!
We look at the Saturn V and find our new booster is going to be quite plump compared to the sleek Saturn V, but we have no choice if we want to use liquid hydrogen as reaction mass. Since hydrogen is the best reaction mass physics allows, and is cheap, plentiful, and we have decades of experience handling it, we will use it.
A design height of 105 meters seems reasonable. We assign 15 meters to the engines, 55 meters for the hydrogen tank, 5 meters for shielding and crew space, and a modular cargo area which is 30 meters high and 20 meters in diameter. This is enough cargo space for a good sized office building!
How heavy is the rest of the vehicle? Well, we already decided that the engines are going to weigh 120,000 pounds each, for a total of 840,000 pounds. (To make a comparison, the entire Saturn V, all three stages, engines and all, weighed a mere 414,000 pounds dry.)
Let's splurge here. With nuclear power, we have the power to splurge. Let's use 760,000 pounds to build all of the structure of the new booster. We use thicker and stronger metal, we use extra layers of redundancy, we make it strong and safe and reliable.
We have now used 2,400,000 pounds for reaction mass, 840,000 pounds for the engines, and 760,000 pounds for the rest of the ship's dry structure. This adds up to 4,000,000 pounds, fully built, fully fueled, ready to launch.
But we said at the beginning, the booster has a design launch weight of 6,000,000 pounds! If it only weighs 4 million pounds ready to launch, the rest must be cargo capacity.
This machine has a Low Earth Orbit cargo capacity of TWO MILLION POUNDS.
It is fully reusable. We gave it enough fuel to fly back safely from orbit.
It has MASSIVE redundancy and multiple levels of safety mechanisms.
Its exhaust is completely clean: It is very difficult to make hydrogen radioactive in a fission reactor. It basically can't happen.
It flies to space with a thousand tons of cargo, and flies back using some gentle aero-braking and its thrusters with another thousand tons of cargo.
This means it has eight times the cargo capacity of the Saturn V, which was not reusable at all. No longer will the Saturn V be the mightiest American rocket. No more resting on our laurels.
With this sort of performance potential, can anyone argue that NTR's are NOT the only sensible course for heavy lift boosters?
There are risks, of course, but careful design and the proper launch site can easily mitigate those risks so that the huge advantages of nuclear propulsion can be realized.
hrmnnnnnnnnnnn...
The winner could wait for his flight into space, or sell the ticket to the highest bidder, tax-free.
The excitement of the lottery winnings alone would push the entrants to make more investments. Maybe it could be in five dollar increments.
That's a great addition to the program, my only concern is that it gets the federal government into the gambling arena, which I feel is dangerous territory if other groups try to apply it to all their pet projects, of course that could also be said of my original idea.
Ok, I've got the solution. If this is designed as an extra voluntary tax, then it avoids all the problems of other groups attempting to glom onto the idea and turn the entire federal budget into a reactionary self-serving crap heap.
If you wish to spend $5.00 more in taxes for a chance at a future space flight or the ability to sell that opportunity after winning it on the open market, then you can.
As long as each had its own separate write-off, who cares?
This is all voluntary taxation money, so it shouldn't affect anyone else.
How about a tax write-off lottery to buy Baja from Mexico? Nice estate as the prize!
Acronymically speaking, GMTA.
I love this.
If the enviro weenies want extra money, fine, name a forest after someone.
If the welfare people want extra money, fine, offer up a free house.
Nobody ever gets an increase in their line item unless they offer a reason and a benefit, and it's strictly voluntary.
Somebody please tell me what’s wrong with this cause it sounds to good to be true.
I'm not sure what you mean by your first statement quoted above, but I would like to suggest a multiplier effect, that good ideas or good reasons get a dividend from a tax deduction to assist in the project. That is, if you can state a really convincing reason why your idea is of benefit to the world, you can add to your voluntary contribution by an amount deducted from your tax burden.
What's wrong with it is that it doesn't really reduce the tax burden, but by having voluntary donations flowing into worthwhile projects, the tax burden could be reduced gradually as those projects pay off.
I remember reading a (obviously) Science Fiction story in which every dollar of tax burden had to be allocated by the taxpayer to his choice of benefit programs. The tax form was horrendously long, but at least you had the choice of supporting the programs that appealed to you, and rejecting (defunding) those that did not!
If you wish to spend $5.00 more in taxes for a chance at a future space flight or the ability to sell that opportunity after winning it on the open market, then you can.
Can we find a way to apply this to defense spending; I mean we can't exactly give someone an M1 Tank? Maybe we could offer the naming of the Tank, Destroyer or Aircraft.
I love this.
If the enviro weenies want extra money, fine, name a forest after someone.
If the welfare people want extra money, fine, offer up a free house.
Nobody ever gets an increase in their line item unless they offer a reason and a benefit, and it's strictly voluntary.
Somebody please tell me what’s wrong with this, because it sounds to good to be true.
In the era when AOL can absorb Time-Warner for $166 billion we can still talk about $5 chits. It's a miracle.
In other words current taxes stay static. Your budget line item only gets an increase by voluntary taxation.
Yes, but were talking about "$5 chits" across the entire US, and it's all voluntary.
The entire world was stunned when the whole structure lit up the ocean like a second sun as the nuclear rockets blew a trail of fire nearly two miles long from hundreds of rocket exhausts, and the “casino” lifted off and went directly into orbit!”It is a quote from a planned chapter of a future book, which is basically a love affair with the idea of manned exploration and exploitation of space.
I heard some 'poor guy' complaining that he couldn't get out of Houston because he couldn't cash his GovCheck. That's who would buy the $5 tickets. There is no way anything can possibly beat the corporations. The Big 100, or Big 500, might be Big enough to do outer space development. What is the corporate status of Rutan? I'll tell you, once you go corporate, the individual is out of the loop. Be on the Board of Directors, or be an employee, the Corporation will kick the individual out even if the move would be considered suicidal to business. See, corporations are inherently immortal. Sony will survive even without its guiding genius and no iPod. GM will survive even without its soul or hybrid drivetrain. Corporations will look at outer space as soon as they can get some property rights; the $5 guy doesn't know anything about property rights or corporations.
People would be jumping on it from the lottery aspect alone!
I'd have multiple winners, with perhaps every ten millionth $5 ticket being chosen at random. That's fifty million for a ride into space for someone, and who cares about who it might be? Ten million to one odds against winning, but a tax-free million if you do! Not a bad lottery!
The money will disappear into a black hole. Even Carnegie would sell short on that deal. What is the true power form of investment vehicle? The best forms of debentures? Pennies saved Old Ironsides, but only up to a point, now it's another Gov't Institution. Like the Post Office.
You’re right, and that’s precisely the problem with any gambling, whether it is the state or federal government running the program.
I am wrong, there is no way to run a program like this without it leading to disaster.
He has done a fine job of pulling together the true history of the rise of the modern corporation. Why would a writer of computer books even care enough about this to do some research and then write about it in a way that presents this dry stuff in a fascinating way? Can't say, but it fills in a big gap. Considering that America [with Japan] has emerged as far and away the power on earth, and the modern corporation is the structure behind all of that, why don't we take a good look at this modern corporation idea, where it came from, how it was implemented, who did it.
Quite the possibility. However, if a few lucky working stiffs win tickets to space, and sell them to rich individuals, those individuals will have a compelling interest in monitoring their investment. My devious plan has many aspects.
I understand your post about the ascendancy of corporations, but I'm not clear about why this would be an impediment to progress in this venture. Corporations are the active agents of investors (of which I am one), and would be powerful allies in furthering the development of space assets.
Maybe at some level of debenture. At the common stock level they are definitely forever not agents for the investors. Active and agent are the same word at root, somewhat redundous. The history of the rise of the American modern corporation is fascinating, which I never thought could be possible when I was studying physics. But, in trying to find a way to mine asteroids I have been led to study many things that I formerly viewed as attractive as [fill in your favorite noxious substance here]. The place of corporations in America and in the world seems to be vital to the present ascendancy of the West, and alone seems to make space exploration possible. How to guide it to the conquest of outer space is the problem.
How to guide a money-grubbing, socially insensitive, mindlessly immoral entity in a particular direction ... Don't tell me, now. Let me think about it ... I know this one ...
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