[texaslabrat]

belbear wrote:

Radiating waste heat into deep space isn’t so difficult, on condition you shield your radiator from the sun. After all, space shows us a 3 Kelvin black-body and that’s really cold.

Right, but that is purely radiative cooling, which as I understand it isn’t nearly as efficient as conductive or convective cooling — there’s a reason that thermos bottles use vacuum flasks. As “cold” as space may be, you can cool things far more efficiently on earth by, for example, dumping heat into a lower temperature fluid. (I’m sure that some one with way more technical expertise could clarify what sized radiator would be needed to dump 5MW of heat into space.)

Sure, radiative cooling is less efficiënt than convective/conductive, but in space that’s all you’ve got, unless you vent precious matter (such as the flash-evaporative cooling the Space Shuttle uses when its payload doors are closed)

Radiator size is not the only issue here, temperature is one too. Radiative cooling becomes more efficiënt with rising temperature (look at the Sun, that’s a very efficient radiator), so all you need to make your radiator panels smaller is to make ’em hotter.

blackbody radiation is proportional to T^4 (where T = absolute temperature…eg Kelvin or Rankine).

I don’t imagine a FF spaceship at full trust using the kind of big, shiny radiators like the ISS has, I imagine them being rather small, sturdy and glowing hot. Using high-temp coolants such as molten metal rather than ammonia. Since energy is not such a scarce commodity on board a FF vessel as it is in a solar-powered one, a two-stage cooling process that steps up the temperature using some sort of refrigerator cycle can be used.

Why in the world would you want to do that? Who cares how big the panels are *IN SPACE*? There’s no drag, and surface area has very little correlation to mass in the absence of large dynamic loads. You say that energy isn’t scarce with FF..I beg to differ. Purposely *wasting* energy on an active cooling mechanism such as you’ve described necessarily means a bigger power source, and a bigger cooling system, and bigger radiator panels anyway. It’s basically the rocket equation to some degree. Efficiency = good. Passive cooling = efficient. Therefore, Passive cooling = good 🙂

Actually both types of radiators would be needed, one high-temperature for the high-grade waste heat from the reactor and one low temperature for low-grade waste heat from electronics and life support.

p.s.: you got your quotes wrong…

If you make the panels big enough, you’d only need a single set. The hull can also be used as a heat-sink/radiator with proper design. Again, simplicity is the key.

[texaslabrat]

edit: nm…that post didn’t even make sense to me after I thought about it.

[texaslabrat]

HermannH wrote:

As I mentioned before, an F-16 (a small, single-engine, lightweight fighter) in full afterburner consumes the rough equivalent of 300 MW. The top speed of an F-16 in full afterburner is about Mach 2.0 at altitude. Believe me, you’re gonna need power in the GW scale to even think about a hypersonic high-altitude first stage or a hypersonic trans-continental aircraft. As a “fun fact” comparison, each of the 5 Saturn V first-stage engines consumed a heat-content equivalent of over 30GW. It’s hard to wrap your head around the shear power requirements needed for high-performance flight..but they are indeed quite steep.

This is the crux of the story. The F-16 can generate power at a rate of 300 MW, but only for about an hour or two. After that the tank is empty.
A FF reactor will probably never produce enough power to lift itself into low earth orbit. The power to weight ratio is way too small.
Once you are in orbit and want to travel to distant planets or solar systems the story is different: you can let the engine burn for days or months and keep picking up speed. 5 MW for a couple of months beats 300 MW for a couple of hours.

Actually, an F-16 can produce 300MW for about 11 minutes before the tanks go dry so it’s far worse than even that scenario. But it’s apples-to-oranges since a FF-powered craft would, for all practical purposes, never run out of fuel and thus could take a longer path to achieve a given speed and altitude as long as it could get off the ground in the first place. My main point (as you’ve mentioned) is that the power-to-weight and power-to-volume of FF would have to be DRASTICALLY improved from today’s concepts/prototypes to be suitable for flight due to the enormous amounts of power required. Not saying it can’t happen (never bet against the ingenuity of motivated engineers)…just that there are probably easier technical avenues for achieving orbit and subsequent space flight (eg space elevator + FF-powered ion engine).

And by the way, the basic premise of the FF-powered aircraft (as envisioned by belbear in this thread) is not new. Look up “project Pluto” for a “blast from the past” 😉

[texaslabrat]

belbear wrote:

In the mean time, I’ll still be putting my money on the space elevator tho 😉

Just because a FF launcher can take off lightweight, it doesn’t even need those outrageous power levels and brutal acceleration associated with Saturn V rockets or Space Shuttles, so much less than a GW may do. Neutron shielding doesn’t need to be as heavy too. The crew compartment must of course be safe, but leaking some neutrons in the atmosphere is not really a problem. Cosmic radiation does similar all the time.

As I mentioned before, an F-16 (a small, single-engine, lightweight fighter) in full afterburner consumes the rough equivalent of 300 MW. The top speed of an F-16 in full afterburner is about Mach 2.0 at altitude. Believe me, you’re gonna need power in the GW scale to even think about a hypersonic high-altitude first stage or a hypersonic trans-continental aircraft. As a “fun fact” comparison, each of the 5 Saturn V first-stage engines consumed a heat-content equivalent of over 30GW. It’s hard to wrap your head around the shear power requirements needed for high-performance flight..but they are indeed quite steep.

[texaslabrat]

Tulse wrote:

If the power density of the fusion power sources were sufficiently high (in terms of MW/m^3 and/or MW/kg) , that’s definitely feasible from at least a basic conceptual point of view (ignoring the complexities of the actual aircraft and propulsion system design). A lot of optimization and miniturization of the fusion source will be necessary to make this kind of system do-able for atmospheric flight propulsion.

One of the “advantages” of conventionally fueled craft is that they get lighter as they travel. With a FF powerplant instead, all the weight is constant. I presume there is some crossover point where a specific fixed weight fusion generator is more efficient than than a powerplant running on conventional fuel that gets lighter over time. But it is not immediately obvious that such crossover point can be easily reached — my guess is the fusion plant in such instance would have to be very light relative to its on-the-ground, fixed instantiation.

And I’m still not convinced that there would be any major advantage to such a system. As I noted earlier, the real problem with most launch systems isn’t lack of power per se (at least not power on the scale that an FF device would generate).

I’m not convinced it would be feasible in the near-term by any stretch…fitting probably a GW of power production into a space-worthy airframe (never mind the issues of power distribution within the craft) meant to take off from a runway presents issues that are non-trivial to say the least.

And while you say that an “advantage” of a conventional plane is that it gets lighter as it travels…I’ll counter by saying that a sufficiently miniaturized power source STARTS light so therefore has a huge advantage. Not having to carry the structural weight of a changing fuel load greatly simplifies the airframe design as well as makes the balance points and other dynamic issues easier to predict and control. That was the point I was trying to get across…that you would need to make the power source VERY small and VERY light to be advantageous over a conventially fueled craft…but if you could do so…it would revolutionize air (in addition to space) travel as you could then have non-range-limited aircraft in addition to the spacecraft previously discussed. All for a bit of boron…not too shabby. Very much “pie in the sky”…but an interesting thought experiment for sure.

In the mean time, I’ll still be putting my money on the space elevator tho 😉

[texaslabrat]

Aeronaut wrote:

I’m not sure that’s true — once in space FF may make technologies like VASIMR far more practical, but the big problem will always be getting into space. I don’t see how FF will significantly change the problems of launching to orbit, at least not without other major technological advances (such as space elevators or huge magnetic launch tracks).

What do you think of a focus fusion powered turbojet/scramjet powered launch vehicle with a chemical LOX/LN2 upper stage glider (type X-33) to fill the gap from high-atmospheric hypersonic flight to orbit?

Fusion-generated electricity drives compressor fans (instead of a turbine) and fusion heated air (instead of fuel combustion) provides jet thrust. Everything fully reusable.

The rocket equation makes it perfectly clear that the space elevator is the enabling technology for meaningful space exploration. My understanding is that raising around 50G$ is a far greater challenge than incrementally increasing the tether strength.

The rocket equation does not pertain to the type of solution that belbear has proposed as the fusion-powered plane would not be consuming a mass-fraction of fuel during the initial ascent/acceleration. For the “booster” phase, yes…but at that point the fuel needed is trivial once the air-“breathing” portion has brought the craft up to the altitude and speed that a scramjet flight regime can provide.

That said, I’m certainly not discounting the usefulness of a working space elevator 🙂

[texaslabrat]

belbear wrote:

I’m not sure that’s true — once in space FF may make technologies like VASIMR far more practical, but the big problem will always be getting into space. I don’t see how FF will significantly change the problems of launching to orbit, at least not without other major technological advances (such as space elevators or huge magnetic launch tracks).

What do you think of a focus fusion powered turbojet/scramjet powered launch vehicle with a chemical LOX/LN2 upper stage glider (type X-33) to fill the gap from high-atmospheric hypersonic flight to orbit?

Fusion-generated electricity drives compressor fans (instead of a turbine) and fusion heated air (instead of fuel combustion) provides jet thrust. Everything fully reusable.

If the power density of the fusion power sources were sufficiently high (in terms of MW/m^3 and/or MW/kg) , that’s definitely feasible from at least a basic conceptual point of view (ignoring the complexities of the actual aircraft and propulsion system design). A lot of optimization and miniturization of the fusion source will be necessary to make this kind of system do-able for atmospheric flight propulsion. By way of comparison, an F-16 in full afterburner is burning fuel at a heat-content-rate of over 300MW (~60,000 lbs of fuel/hour), so consider that as the bare-minimum starting point for how much power you are going to have to provide in order to be in the right order of magnitude. And I think you meant “LOX/LH2” upper stage, right?

[texaslabrat]

Alex Pollard wrote:

I have a feeling Madoff may have a cellmate soon…

Yeah I noticed that but assumed they meant catalyst, not fuel, but then again, what kind of organisation would get something that fundamental wrong? We don’t have all that much information to judge them by, so people will understandably try to read between the lines.

Unfortunately, we are practically drowning in scams from folks who have claimed to have invented some “new physics model for energy generation” whether it be from hydrinos, nanobacteria that revolutionize pyrolysis of organic matter, or any number of other something-for-nothing energy schemes. When there is a dearth of details in the process and the only “independent” verification is from a carefully selected 3rd party rather than in a peer-reviewed published journal…well, keep a good grip on your wallet.

I really hope I’m wrong about these guys…it would be fantastic if their claims were true. But I’ve seen this movie before…and it usually ends in either a lawsuit or prison time.

[texaslabrat]

From the 08/12/09 Press release:

BlackLight says it developed a solid fuel that efficiently liberates hydrinos and then requires very little energy (in the form of heat) to reverse the chemical product back into the initial solid fuel. The system is nearly closed-loop, requiring only the replacement of hydrogen consumed when forming hydrinos, CEO Randell Mills said in a news release.

By that standard, a coal-fired plant is also nearly closed-loop..requiring only the replacement of coal consumed when forming CO2.

I have a feeling Madoff may have a cellmate soon…

[texaslabrat]

I’ve not needed to do any character assassination..I’ve only been pointing out facts. Any perceived character assassination is of your own doing through repeated demonstration of utter ignorance of high-school level physics. We’ve just been handing rope (in hopes you’ll pull yourself in from drowning)…it is you who have decided to use it to strangle yourself.

Who said anything about U235? You do realize that’s not the only radioactive element in the universe, right? U238 (which is FAR more common) has a half-life of about 4.5 billion years. Potassium 40 has a half life of 1.25 billion years. Thorium 232 has a half life of of 14 billion years. But I suppose you don’t believe in that stuff now that it refutes (yet again) your hypothesis.

I’m not about to list a play-by-play evolution of the earth’s heat history as fact, because I wasn’t there (though there are a number of models/theories which account for the things we observe today). But we *are* here now..we CAN measure heat flux, we CAN measure the loss of rotational energy of the earth, we CAN measure the distance that the moon is from the earth, and we CAN measure the half-lives of the most abundant naturally occurring radioactive materials.

But since you “don’t believe in that stuff” when it contradicts any notions you have…of course it’s unimportant. I’d be interested to hear Eric’s take on this since you keep invoking his name. Eric bucks the mainstream when it comes to cosmology, sure (since the big bang theory IS theory since none of us was around to actually witness it)…but he has a VERY firm grasp on modern physics (hence the FF project) and the scientific method which you seem oblivious to.

Or there’s another compelling theory: You are a troll who disagrees with anything and everything in order to incite a reaction from people. I think that’s actually far more likely than the demonstrated lack of thought you’ve shown thus far. Either way, I feel sorry for anyone who must rely on your critical thinking skills.

[texaslabrat]

Well, I’m glad you are ok with being wrong…it must come with practice.

And I think you need to work on your scientific lingo…actually MEASURING things is not a “theory”. The items I cited (did you even bother to read any of them? doubt it since you might actually have to admit the data don’t match your assumptions) are MEASUREMENTS. The theory comes in to make sense of said MEASUREMENTS. Just because the MEASUREMENTS don’t agree with your pet theory doesn’t invalidate them…especially when they have been continually confirmed and refined over time by independent researchers using a variety of methods.

Taking these MEASUREMENTS, combined with a simple conservation of energy calculation (I suppose you don’t believe in that, either?) trivially shows the situation that your assumptions are completely wrong. This isn’t an issue of philosophy..it’s about black and white, right and wrong, cold hard math. On a SCIENCE-based website..that distinction is important. Now that you’ve proven yourself incapable of processing new information and adjusting your own assumptions (you know, practice the “scientific method”)…I don’t think anyone will be taking your input seriously going forward. And that is my purpose with this exchange (since you asked) after you proved yourself to be incorrigibly unable to be educated. I suppose you’ll be arguing for the flat-earth theory next.

Have a nice day.

[texaslabrat]

I know I said I wouldn’t teach the unwilling..but seeing such misguided scientific lack of knowledge on this board bothers me for some reason. So here goes.

The heat flux out of the earth is known to be around 44TW (look it up). This should help get you started:
http://www.google.com/search?hl=en&client=firefox-a&channel=s&rls=org.mozilla:en-US:official&hs=4uV&q=heat+flux+out+of+earth+44tw&aq=f&oq;=&aqi;=

For tidal forces to be responsible for this, the earth would need to be losing rotational energy at the rate of *at least* 44TW as tidal friction is a consequence of trading rotational energy for heat and orbital acceleration (of the moon with respect to the earth, and of the earth with respect to the sun). Unfortunately for your “theory”, the earth is not losing rotational energy at this rate…rather it is losing rotational energy at roughly 4TW (the exact number is complicated to compute due to not-quite-spherical shape and non-uniform composition plus the un-flattening of the poles which tends to increase the speed of rotation while the frictional forces slows it down…but the rough number with a spherical assumption is good enough to show order of magnitude). There are on-going gravimetric satellite-based surveys which keep track of these issues. Much of that is explained (with citations) here:
http://74.125.113.132/search?q=cache:-gk-ok_CbiUJ:eprints.ictp.it/165/01/moon.ps+earth+loss+rotational+energy&cd=10&hl=en&ct=clnk&gl=us&client=firefox-a

As for comparing the Moon’s tidal influence on Earth vs Jupiter on Io…..ROFL. That’s like saying because they both contain water that my swimming pool is just like Lake Superior. They aren’t even in the same zip code in the strength of effects. As an example…Io’s rocky surface rises and falls *100 meters* due to the tidal forces from Jupiter. Compare this with the few-meter (at most) motion of *water* on earth coupled with the centi-meter scale of solid surface movement. And these effects are spread throughout the earth’s structure rather than being concentrated in the core with the lion’s share at the surface. Now, if you were talking 2 billion or so years ago when the earth was rotating much faster and the moon was much closer…then yeah, tidal heating was a significant player. But it’s been a very long time since tidal forces competed with radiogenic ones for the heating of the core and subsequent thermal flux out of the earth.

And as for volcanism on Venus…plate tectonics plays a huge role in volcanism, and on Earth water plays a huge role in plate tectonics. Since Venus doesn’t have large oceans…well, you do the math. At this point, we don’t know enough about Venus to make conclusions and most of our theories regarding its internal structure are educated guesses. Given its retrograde rotation and other “weird” aspects, I’d be careful about trying to make apples-to-apples comparisons with Earth.

[texaslabrat]

edit: nm…it’s not my job to teach those who refuse to learn.

[texaslabrat]

dash,

Since you seem so enamored with Wikipedia as your end-all-be-all reference source (discounting any other sources, it seems), here’s a Wikipedia article for you:

http://en.wikipedia.org/wiki/Tidal_acceleration

The gravitational torque between the Moon and the tidal bulge of the Earth causes the Moon to be promoted in its orbit, and the Earth to be decelerated in its rotation. As in any physical process within an isolated system, total energy and angular momentum are conserved. Effectively, energy and angular momentum are transferred from the rotation of the Earth to the orbital motion of the Moon (however, most of the energy lost by the Earth is converted to heat, and only about one 30th is transferred to the Moon). The Moon moves farther away from the Earth, so its potential energy (in the Earth’s gravity well) increases.
…
The dissipation of energy by tidal friction averages about 3.75 terawatts, of which 2.5 terawatts are from the principal M2 lunar component and the remainder from other components, both lunar and solar.[3]

While I haven’t verified the numbers myself, they seem to be in the same ballpark as what I remember calculating in my astronomy class years ago in college. As I said before, the tidal forces certainly contributed a non-zero component, but are far and away a minor player in core heating here (since that 3.75TW is the combined effects of all tidal friction across the entire structure of the earth and most notably in the ocean). If the majority of the heat being produced in the core (and subsequently conductively/convectively transferred to the surface to be radiated into space) were due to tidal forces as you claimed, 1) the earth would necessarily have to slow its rotation considerably more than observed 2) the earth would need to increase its orbital distance from the sun considerably more than has been observed or 3) the moon would need to increase its orbital distance from earth considerably more than has been observed or 4) some combination of 1-3 that satisfies conservation of energy of the earth-moon-sun system. The net total of the tidal forces across the entire structure of the earth are a factor of roughly 10 less than the heat being observed being generated from the core alone. I’m not sure how one could more succinctly explain that you are wrong, so I’ll just leave it at that.

As jamesr said, being skeptical can be a good thing when accepted dogma is attached to assumptions or guesses and forced upon us via indoctrination. However, when you are trying to argue against (easily) observable fact just to be “a free thinker”…well, let’s just say the impression you leave is probably not what you are shooting for.

[texaslabrat]

dash wrote:

The reason the Earth’s core is still molten, and not cooled and hardened, is radioactive warming. We’re standing on a big, slow reactor!

I don’t believe that theory.

-Dave

Regardless if you believe it or not…it’s true 😉

http://www.newscientist.com/article/mg18725103.700 is just one of many studies confirming it.

The tidal forces exerted by the moon on the earth (and conversely by the earth on the moon) pale by comparison to those imposed on Io by Jupiter. While tidal forces certainly can play a *role*…they are far and away minor players in the heating phenomenon.

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