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You don't need large boosters, but it helps. The atmosphere provides drag, and that requires propellant to fight against, so you want to get out of the atmosphere as soon as possible. One complication is that the faster the rocket travels in the atmosphere, the more drag it creates. On lift-off when the rocket is still travelling slowly there is neglegable drag, so you want to accelerate as much as possible. Once you achieve supersonic speed you would want to scale back the acceleration because further acceleration increases drag which wastes propellant. That is why Rockets often use large boosters for initial lift-off.
You could use the larger SRB's from the Shuttle instead of the expendable SRB's from Titan. The Shuttle SRB's are reusable, but recovering, refurbishing and refueling them cost something like 90% the price of new ones.
You could design a reusable launch vehicle that does not use strap-on boosters of any kind, liquid or solid. Current work on a Two Stage To Orbit (TSTO) reusable launch vehicle would have a large spaceplane that does not have a heat shield lift the orbiter to high altitude and speed, then fly back. The orbiter would push on to orbit.
You could also design a Single Stage To Orbit (SSTO) reusable launch vehicle using a NTR engine. The waste product from nuclear fission is highly radioactive so you have to decide if you really want to use nuclear for a reusable launch vehicle. Nuclear may be better for an expendable launch vehicle, and that raises the question of whether an expendable booster for lift-off is better vs a larger core stage.
Exact numbers are harder to calculate for a launch vehicle. Notice my calculations for Shuttle-C included the same engines, same thrust, same acceleration, same total launch weight; I just reduced fixed mass to increase payload capacity. That made the calculations easy. Designing a launch vehicle from scratch is much harder. Exactly how much propellant will be wasted fighting drag is an aerodyanic calculation, and dependant on what altitude you accelerate to supersonic speed.
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basic question probably but just to be sure: a nuclear engine is designed to be used only once in space, right ? not for lift off.
The Timberwind launch vehicle used a nuclear engine for lift-off. It had a single NTR core stage with 2 solid rocket boosters from a Titan 4B.
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and if you could jettison the wastes towards the Sun once in orbit, prior to reentry, then wouldnt you solve the waste problem?
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That's basically what Zubrin argued with his nuclear design. It left a lot of nuclear waste, but compared to the background radiation of the sun and the solar wind in general, it was, like, nothing. And the particles escape at a huge velocity, so they're going to go in the other direction quite fast. So all you have to do is direct the waste in whatever direction you don't want it.
I wonder if that new radiation shielding fabric could be useful for shielding the crew from the engine itself. That's really my main concern about nuclear propulsion.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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hmmm, nuclear for lift off... well if you are sure it's safe.
I support nuclear in space but I think that to add safety to the process, the heavy nuclar reactor could be bring in space empty, without any uranium, and the uranium could be bring separatly to the reactor, in a special container designed to withstand the worst acccident.
I have to say that the prospect of nuclear in space, like the project prometheus, is amazing of possibilities. I even wonder why it has never been done before, since a NERVA reactor was already operational 30 years ago. Good luck for NASA and you guys aeronautic engineers. I hope to see a beautiful nuclear engine soon, flying over Mars. I think it's a good way to spend taxes that to develop such new technologies.
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If the reactor is off, even with uranium on board, as someone at NASA said, its about as dangerous "as a pile of dirt."
I don't recall a nuclear submarine blowing up in the past 50 years, so why should we expect a nuclear spacecraft to blow up anytime soon either?
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and if you could jettison the wastes towards the Sun once in orbit, prior to reentry, then wouldnt you solve the waste problem?
Escape from Earth orbit takes a lot of fuel. Reducing interplanetary velocity to fall into the sun takes even more. It isn't practical to throw anything into the sun. It is easy for the military to use nuclear engines to through atomic bombs; the bombs would release MUCH more radiation than the engines. The Pluto nuclear ramjet developed in the late 1950's and early 1960's use an unshielded plutonium reactor and let the fission products escape with exhaust. That was a very dirty engine, but it was a cruise missile designed to carry multiple fusion bombs. Peaceful applications become more difficult. A Trans-Mars Injection stage that propels a spacecraft to Mars is easy because the spacecraft is already leaving Earth orbit. You could park the spent stage in solar orbit or impact it into Mars. The Jupiter Tour mission would leave the engine in Jupiter orbit, where the radiation belts have much more radiation than the largest nuclear engine. I don't know where the waste from a nuclear launch vehicle would go. Perhaps collecting spent stages and lashing them together in a junk yard in medium Earth orbit. Medium orbit is sufficiently stable that satellites stay there; there is no atmosphere to cause orbital decay. However, Earth's radiation belts are in medium orbit. To avoid the radiation satellites are placed in low or high orbit, outside the radiation. Those radiation belts may be an appropriate place to park spent nuclear stages, but you would have to reserve enough propellant to move the stages there.
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That's naivety speaking, there. There's no rational reason to believe that the nuclear industry would have been less destructive than the coal industries. Simply looking at the benefits of using the energy itself isn't enough, you have to look at the whole picture.
But then again... we learn from history that we learn nothing from history.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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I didn't realize the US had a bill prohibiting recycling nuclear waste. That is the only reasonable thing to do with waste from a nuclear power plant. Such prohibition is just plain stupid. However, that doesn't answer the question of where the spent stage from a nuclear launch vehicle will go. Spent stages from chemical rockets are allowed to fall back to Earth and land where ever. The US likes to drop them in an ocean and just leave them there. Russia drops some stages on wilderness areas; I don't know if they recover them. The engines have high grade titanium so recycling spent rocket stages would be quite useful. (Whacking a cariboo is about as likely as whacking a whale.) Waste from a TMI stage or Jupiter Tour spacecraft is not an issue, but where does the spent fuel from a nuclear launch vehicle go? You could design a nuclear SSTO RLV and have robotic equipment remove spent fuel rods after it returns to Earth. Those spent fuel rods could be recycled like nuclear waste from a power plant. :;): But where would the spent nuclear fuel from an expendable launch vehicle go? The uranium from a reactor that has never been turned on is about a dangerous as a pile of dirt, but after the reactor has operated the nuclear waste is quite radioactive. I could live with dropping sealed fuel rods or capsules in the ocean as an emergency procedure in case of catastrophic failure, but I don't think it is a good idea for normal operations.
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So, for an SSTO we recycle the fuel rods, and in normal procedure, we don't have to worry about the nuclear waste?
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Currently recycling waste is more expensive then mining new urainium barring ore, not including the cost of building the reprocessing plant. Eventually the cost of reprocessing will be cheeper, but not at the moment.
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Currently recycling waste is more expensive then mining new urainium barring ore, not including the cost of building the reprocessing plant.
What is the cost of long term storage of nuclear power plant waste? You have to compare the cost of reprocessing against the total of long term waste storage and mining new ore. As long as waste storage is government subsidized and reprocessing is not, it will always appear that new ore is cheaper.
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Hmm, obviously recycling has more long term benefits over not recycling; especially if you consider the environmental damage caused by not recycling, not just the storage costs. I too, didn't know that the recycling issue was banned, so I was surprised when I read that. If anything, you'd think that they would make recycling paramount to running reactors, with requirements that you recycle all your waste or whatever.
Anyone know if Canada's nuclear reactors are able to recycle? I hear they're moving in that direction up there.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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Josh, banning recycling is a good way for anti-nuke people to create an issue-they can now say that the waste has to be stored, which is terrible for the environment.
They say that recycling can be used to make weapons-grade plutonium...but if anybody wanted to do that, they would do it anyway! I think the best solution is to have breeders, but have them monitored, as the North Korean reactors were. This ensures that breeders aren't used for weapons. Of course, this eliminates a huge part of the anti-nuke incentive, so anti-nuke people rail against it as much as possible!
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Um, I'm more inclined to believe it has to do with the fact that they would have to build new reprocessing facilities, which would probably be against the whole act of banning nuclear reactors itself. Which actually makes sense now that you think about it. They banned it without thinking.
Like I said in the greenpeace commercial thread, the real downside to nuclear material is the whole regulatory aspect. Any of the environmental stuff can be taken care of.
I read that if only half the world ran on nuclear power (yes, using breeder reactors), we'd only have 2 years of uranium from proven deposits. But the oceans have billions of tons of uranium. So if we are to go in that direction, it'd be advizable to work on extracting uranium from seawater.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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I had heard 2,000 years without breeders. Maybe it was 2 millenia?
Nuclear reactors arent banned here-but breeders aren't used because of the supposed weapons potential.
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I haven't taken the time to read the treaty. I thought the reason no new contrcuction of plants was because they were banned completely... odd.
Anyway, I said half the world, the numbers you probably read were talking about the US alone or they probably included seawater deposits.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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actually, bush has approved permits for new construction, which is a good sign!
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Anyone know if Canada's nuclear reactors are able to recycle?
I checked Ontario Power Generation's web site. They are separating non-radioactive waste from radioactive waste to reduce the quantity of low level waste that has to be stored. However, they don't recycle spent fuel. They store it in a pool for 10 years, then in dry storage for 50 years. They are building a geologic storage facility (burying it) in an old uranium mine. That mine has radioactive tailings anyway.
They do have some interesting uses for isotopes, however. Cobalt-60 is used to irradiate food to sterilize it. They claim to produce 80% of the world's cobalt-60. Tritium is used for medical examinations as a radioactive tracer. One use I thought wouldn't be seen again is luminescence. Emergency exit signs are made with tritium and phosphorus.
Since the heavy water moderator of a CanDU reactor produces more tritium than any other device in the world, ITER (International Thermonuclear Experimental Reactor) is being built next to the Darlington Generating Station. The tritium will be used for nuclear fusion experiments.
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I made a mistake! Yes, I admit it!
Using NERVA, you get 60% fuel mass, 20% structural mass, and 20% payload mass to orbit. Thusly:
125,000 kg launch mass gets you 25,000 kg to orbit (shuttle equivalent) as payload.
600,000 kg launch mass gets you 120 tonnes to orbit as payload. I choose 600,000 kg because it can be launched off an airstrip.
2 million kg launch mass (shuttle equivalent) gets you 400-500 tonnes to orbit as payload.
These numbers represent a 16 fold increase in efficiency over the shuttle. A number of options have been discussed at space.com in my thread, including using the reactor to crack water into more fuel, among other things.
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Here is a really rough calculation:
If you take the X-33 and replace the two XRS-2200 linear aerospike engines with two Timberwind 75 nuclear thermal rocket engines, the result would have the same launch mass (123,800 kg) but a lift capability of about 15,000 kg to 185 km orbit at 28? inclination. That includes 2,200 kg for the mass difference between XRS-2200 and Timberwind 75 engines, an internal cargo bay, and all LH2 propellant tanks instead of LOX/LH2 mixture.
This is using an existing engine. If you use a liquid core NTR instead of a pebble bed fast reactor then the Isp increases to 1600-2000 seconds instead of 1000 seconds in vacuum. A liquid core reactor still seals the fissionable fuel to separate it from propellant. A droplet reactor or gas core reactor exposes the fissionable fuel directly to propellant. That expels all fission by-products with the exhaust, and a little fissionable fuel is lost as well. They could be used for interplanetary flight, but would be too dirty for use in atmosphere. A sealed liquid core reactor, however, could be used for a launch vehicle. The higher temperature of the liquid core reactor splits H2 into mono-atomic hydrogen which is most of the reason for the higher Isp.
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My rough calculation was based on maintaining the same delta-V as VentureStar for its launch into LEO. Sticking with that the propellant for a 2-engine Timberwind 75 version of X-33 would have 77,986 kg of liquid hydrogen propellant. The original suborbital configuration of X-33 had 95,200 kg propellant, but with a 5.5 ratio of oxygen to fuel that means only 14,646 kg of LH2. Liquid hydrogen requires a much larger tank than liquid oxygen; that may require larger structure and heat shield. I checked: LOX has a density of 0.01393 m^3 per kg, LH2 is only 0.00086 m^3 per kg. That means the original X-33 would have a LOX tank with 69.28 m^3 volume, and 204.0 m^3 LH2. The 2-engine Timberwind 75 configuration would require 1086.3 m^3 tank for LH2, or more than the total of LOX and LH2 within the body of X-33. If you used a liquid core NTR with the same thrust and mass as a pair of Timberwind 75 engines but with 1800 second Isp then it would require only 52,535 kg propellant, but that is still 731.8 m^3 in volume. So using NTR engines requires a substantial redesign. It's enough to make one think about a balloon tank that could be collapsed and stowed for re-entry. Is that possible at cryogenic temperatures?
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what if you stored the H2 as water and used the reactor to split the water into hydrogen in-flight?
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