annodomini2
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annodomini2Participantjamesr wrote:
Air with a turbine is only practical up to about Mach 2.5 at which point the air temperature entering the engine is so high that it literally melts the engine.
You can use a pre-cooler such as the SABRE design from Reaction Engines in the UK http://www.reactionengines.co.uk/
They are aiming to be able to have one engine that can seamlessly accelerate from 0 through mach 5, thetransition to using a small onboard oxygen tank to morph into a rocket for the last bit to orbit, then all the way back.
(incidentally they are based on the same site at Culham where the JET and MAST tokamaks are)
I know, but this would intend to use purely air, no cryogenic hydrogen available to cool the inlet, generating that kind of cooling would require huge amounts of energy. If you’re carrying hydrogen as reaction mass why bother with an f2f freactor.Dumping the heat may be a problem.
annodomini2ParticipantFerret wrote:
What we’re talking about I think – to be quite vague – is a technology that best converts between energy and matter. The more of the latter you have, the more effective the propulsion system will be in this sea of gas and gravitation. Sound right?
Generally, a rocket engine is more effective in terms of fuel used when it puts more energy into less matter. Energy means kinetic energy. Thus, an efficient rocket engine has higher exhaust speeds for less matter exhausted. For atmospheric engines things change a bit, since air may be taken in and used as the exhaust. But basically you still want to use the least amount of fuel.
Now for FF atmospheric propulsion, one would probably have to send the FF ion jets into a heating chamber, where they heat the air, which is then expelled to the back. It is much like a turbojet or a ramjet engine, only you use the FF exhaust to heat the air instead of burning some petroleum fuel. In terms of fuel used, this is much more efficient than a jet engine, since you use nuclear energy and the fuel quantity is some 1 000 000 times smaller. It remains to be seen whether it is more efficient in terms of engine mass, too. You don’t want a huge, heavy engine to do the same work as a jet engine. If you wanted that, the solution were right around the corner: a thermal nuclear fission reactor powering an aircraft engine. Think about an aircraft carrier power source on an airplane.
Nuclear propulsion has been tried:http://en.wikipedia.org/wiki/Nuclear_aircraft
The main issue that it wasn’t continued was political, due to fear of a Fission reactor crashing in a populated area.
The main technical issue was weight, reactor + shielding being quite heavy.
Like most technical issues there are solutions to these problems, but there are obviously practical limits.
For FF, the main issue for space use in an orbital launch capacity is you are effectively trading weight. Yes you have less actual fuel, but the reactor itself has a large mass and your propulsive element still needs to be there.
Air with a turbine is only practical up to about Mach 2.5 at which point the air temperature entering the engine is so high that it literally melts the engine.
Ram systems can work to higher speeds, but they are not self starting, so you need multiple propulsion elements. Using an electric heat source would require the system to generate ridiculous temperatures as you need to maintain sufficient deltaT to generate thrust. See SR-71.
Above about Mach 5-10 you’ll need internal mass to throw out the back as the temperatures will well exceed the limits of the materials we have today.
Starlite was a possibility, but unfortunately Maurice Ward died last year and as far as is public, he took the recipe with him.
As you state more speed/energy can result in reduced mass, but there is a limit, in the sense that, above a certain temperature you’re effectively throwing a hugely powerful ion beam out the back of the engine. This would (at least) create the same political issues as with flying a Fission reactor, if not more.
annodomini2ParticipantPlasma propulsion for in Earth Atmosphere (I’m not saying for other planets in the solar system) isn’t practical due to the ionising radiation.
For planetary bodies with little or no atmosphere, relative to their minimum orbital velocity such as the moon or Mars, rail launch could be used. (A fusion reactor could be one possible power source).
In Earth atmosphere, you could, in theory, use a reactor to produce heat and convert water to steam, unfortunately this has major weight and efficiency issues (it was considered with Fission reactors in the ’60s). Designs that are currently being developed, such as Skylon would make these look big and heavy.
What would be needed is a revolutionary technology that could produce an adequate force, using only electricity or some other form of energy as a power source and no mass ejection. As far as I am aware, no one has achieved this yet.
annodomini2ParticipantBreakable wrote: If fusion (or other cheap/clean energy approach) does not succeed we can only a marginal space program.
You cannot rationally be building huge space ships if most of your planets population is living below the level of poverty.Since when did rationality come into a Politicians/Dictators mind?
annodomini2Participant@BSFusion, To me you are coming across as trolling to promote you’re own concept.
annodomini2ParticipantAnyone considered making a MEMs DPF?
annodomini2ParticipantRe: Spacecraft,
I doubt FF would be used as a power source to get on orbit. The vehicle mass would be excessive and other than superheating material for mass ejection there are currently no known propulsion systems that could use electricity and generate sufficient thrust to get a manned space vehicle off the ground. (That don’t produce excessive amounts of ionising radiation in the process).
If an FF was used as a power source on a space vehicle I would see it being used more for deep space, rather than on orbit. Shielding is less of an issue of mass in this situation as the crew will need shielding anyway.
Again on a base, on the moon for example, I would have thought burying it would be more beneficial than taking shielding with you.
annodomini2ParticipantThe other issue being a large component of that energy usage is also transport and heating (in colder climates).
The article only seems to discuss electricity generation, which FF is ideal to compete with, but what percentage of that usage is purely for electricity generation?
The main one that will take more time to replace is heating, the transport cycle is usually around 10-15years for the bulk of the market, so if electric based vehicles became widespread and cheaper (may take some advancement here as well), transport could be converted quite easily.
The issue is heating, many countries which developed with large gas reserves, their heating systems in the properties tend to be based around gas fired heating systems, which do not in themselves easily convert to electricity. The users of these systems will be quite averse to changing them due to cost. Unless the electricity is so cheap that the change will pay for itself within a few years.
Converting purely to ‘renewables’ as they like to be called, is not practical or cost effective, certainly in the short term and other systems need to be in place for the bulk of the generation due to the general intermittent nature of a lot of these systems.
Climate change can happen and has happened many times before, whether or not humans are influencing the climate as significantly as some people would like to make out is unclear at this time.
Whether climate change will cause the doomsday scenario a lot of extremists declare is also subject to more investigation.
annodomini2ParticipantTheir largest shot was 1.694 Mj with 370TW of laser power, so iro 4.5ns.
At 500TW, so it would 2.289Mj for the same duration.
annodomini2ParticipantDon’t know if this is of any help, but something to consider.
annodomini2ParticipantRezwan wrote: Great newsletter, Derek!
My favorite comment: “Going to war for energy is like burning down your house for heat.” by AC. Where are those comments to be found online?
And who is AC – does AC have a twitter account?
Anonymous Coward perhaps?
annodomini2ParticipantWarwick wrote:
At least LPP don’t have to fear for their lives for the time being, until the big boys feel threatened. (Maybe it’s a good thing there’s little coverage!)‘Quiet’ black helicopter hovering over your current location? 😉
annodomini2ParticipantBrian H wrote:
FYI here are photos taken previously of an insulator, and one that appears to be damaged.
Remember that ‘secret’ insulator formulation? Starlite: http://www.telegraph.co.uk/technology/5158972/Starlite-the-nuclear-blast-defying-plastic-that-could-change-the-world.html
Might be worth seeing if Maurice Ward has finally broken down and filed a patent!
It’s a thermal insulator, no word on electrical properties.
annodomini2ParticipantGraphene is a conductor not an insulator.
annodomini2ParticipantOne suggestion would be, if the math is going to go beyond the ‘high school level’ that references to sites teaching the mathematical concepts used??
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