Collecting Solar Power at 0.1au

Date: Aug 17, 2004

Collecting Solar Power at 0.1au

Date: Aug 17, 2004

Yeah, I think Stirling power conversion is 'king' in the <15Kwe range? less moving parts rugged design, idiot proof, all around full proof. some complaints of vibration on missions with humans but I believe that's been taken care of. Brayton is for mega power conversion used in airliner aircraft today more moving parts but also proven with decades of every day use.

Date: Aug 17, 2004

Thanks for your reply, Brucie! However, the concept I put forth in the original thread involved a Stirling collector to generate about 300-600 Megawatts of power. I'm not sure if it would make sense to develop larger Stirlings, banks of smaller Stirlings, or go with a Brayton/Turbine design. As you said, gas turbines have been well proven in industry and currently rate at about 50% efficient.

Date: Aug 20, 2004

Well, I'd have to agree that for small applications up to about 100KWe, Stirling Cycle engines are hard to beat. However, the rough systems I was looking at were in the thousands of of megawatts. This involves gas turbines with mechanical poweres in the neighborhood of a million horsepower.

Another possibility exhists for power conversion--it all depends on the degree of heat resistance or how cleverly it could be designed" Solar MHD. By direct concentration of sunlight from mirrors, heliostats, whatever, onto or into an absorbtion chamber possibly made out of a solid chunk of artificial saphire to heat a working fluid such as liquid sodium metal. If it's hot enough it will generate a hot, partially ionized vapor. Channeling that vapor through a strong magnetic field causes charge polarization. Placing conductive electrodes orthogonal (at right angles) to both the flow and magnetic field will yield a lot of D.C. This can be converted to A.C. and stepped up through a transformer, or perhaps the D.C. could be used as is.

The spent vapor which may now have droplets of liquid may now be channeled to a more or less conventional power generation cycle: such as a heat exchanger charged with helium to supply motive power for the Brayton Cycle turbines. This will cause condensation of the sodium back to a liquid which could then be pumped back to the solar absorbtion chamber.

The helium after it expands through the gas turbines is then directed to a first stage heat exchanger before proceeding to multistage compressors. At each stage the helium is run through other heat exchangers, forcing it to release its 'heat of compression.' Finally the high pressure helium gas (100 atm, or about 1500 psi) is directed to the main heat exchanger--the sodium condenser/helium superheaters--where it is heated to perhaps 2000 degrees F before expanding through the gas turbines.) The exact sequence of heating, expansion, compressing and cooling would have to be determined from an overall cycle analysis--it takes many iterations to determine the optimal configuration for this (which is one dissadvantage, but with new Genetic Programming algorythms for computers, it shouldn't be too hard!) With a carefully designed combined-cycle power conversion system--it should be possible to achieve efficiencies close to the theoretical limits imposed by thermodynamics, close to 70% overall efficiency I should think.

If you are interested in the production of antimatter, the first thing you should ask yourself, is what kind. Will positrons suffice, or are you looking at anti-hydrogen? Anti-hydrogen will be much more difficult to synthesize, but will eventually contain more energy overall than just positrons.

A possibilty exists for direct synthesis of antimatter via pair production. The mechanism of pair-production is thought to be an effect of the quantum vacuum. When enough energy is deposited into the vacuum as an electric field, the electric field causes polarization of the virtual particles/antiparticles there. If the energy density of a region is sufficently high, then a single pair of virtual particles gets 'plucked out' and is ripped apart by the electric field. The conversion of electric-field energy to matter-energy happens then, and the virtual pair becomes a real pair: one matter particle, and one anti-matter particle. But the required electric field is very, very high. On the order of 10^28 volts/m if memory serves.

So where can electric fields this strong be found? Well, nowhere really (unless you would like to take a little field trip to the nearest active-galactic nucleus!) but objects do exist that have really strong electric fields near them: nuclei of high-Z materials, such as uranium, tungsten, etc. Below all the shells of electrons, near the surface of their nuclei, are immensely strong electric fields. If one sneaks a photon of the right energy and polarization--the makeup energy needed to finally break down the vacuum--then pair production will occur. This is why when you slam energetic charged particles into a target in the presence of a magnetic field, you almost always observe pair productions.

Anyways, this is what it takes to make antimatter. It's not easy, it's not efficient, but it could be done. As for long term storage of the stuff--some kind of Penning trap would be needed. I don't recommend storing antihydrogen gas at high pressure in a Scuba bottle--the results you get may void your Scuba tanks warranty!

More on some other possibilities later. Chiao!

Date: Sep 5, 2004

Anti-hydrogen (i.e. molecule of 2 anitproton + positron pairs) is presumably the desired form of anti-matter if the material is to be transported from the production site. Keeping only positrons or anti-protons requires a storage ring, which is how most anti-matter is stored now. This requires considerable energy depending on the beam current, and there are losses.

http://livefromcern.web.cern.ch/livefromcern/antimatter/factory/AM-factory00.html

Date: Sep 18, 2004

Cool subject - just read through it.

Thought experiment -
Why not use microbots to build a first prototype - which goes to my
question.

How small can the system be built?

It's late and I just got the kids to bed/

anyway..

I want to take a cut of the major system to build it - first you have the energy generator - sterling space generator, then the antimatter factor, antimatter storage and then a docking port.

You don't need to generate a large amount for the first cut - rather just prove the
system.

Lets' say you go with the microbots - about 1 lb 4 in cubes - or say 10 lb - 12 in cube... the don't have to be cube shape - i offer that a base refernce and just as important

Let say the bots can hook together to make a ring ... Do you really need mile size rings or can you do it with a much smaller circumference? Say 3 feet or 1 meter...

On storage - beats me - but you do have a convient vacuum in space...Help here.

Given the cost to produce antimatter - it's a interesting notion.

Date: Sep 19, 2004

Well, I don't know about the microbots. Perhaps some kind of Von Neuman self-replicating machines that work by manufacturing more copies of themselves, and then utilizing a large number of the copies to build the industrial infrastructure. It has been variously proposed that such a bootstrap scheme could ultimately build enormous industrial infrastructure from a relatively small 'seed' plant.

As for storage of antimatter--I would assume some kind of Penning cold ion trap would do, however an efficient cool ion magetic/electrostatic confined torus might do as well. I'm not sure how much could be stored this way, probably no more than milligrams at best. For any practical interplanetary space propulsion schemes, many milligrams or even gram quantities would be needed. For interstellar, the quantities needed could be anywhere from hundreds of kilograms to thousands of tons (it all depends on how much and how fast you want to move payload. Fast, manned interstellar missions could need millions of tons of the stuff!)

I have never been a real big fan of antimatter--because even if we do perfect a storage system the material is still incredibly explosive. A mere half-gram of Antihydrogen, when annhilated, would yield the energy equivalent of the Fat Man atomic bomb--about 21000 tons of TNT equivelent. A half-kilogram (a little over a pound) would create an explosion of about 21 Megatons, or a little larger than the Castle-Bravo test in the South pacific in the 1950's. Even if the safe storage of antimatter can be solved, there is still the probelm of creating it.

Currently antimatter is thought to be only created in high-energy collisions. It takes a powerful particle accelerator to create antimatter. Unfortunately, the reaction products end up moving pretty fast. The act of slowing them down again and cooling them can only be done by collisions. Bingo, guess what the antimatter must collide with? Matter--poof. Gone!

Only about 1 particle in a billion gets slowed sufficiently to be trapped before it is annhiliated. You see the efficiency problem right there?

Interestingly enough, there could be a way to get the energy out of the matter without actually using antimatter to do it.

Stephen Hawking in the early seventies proposed that Black Holes may undergo 'evaporation' by the direct application of the Second Law of Thermodynamics combined with Quantum Theory to the black holes event horizon. The results are startling--the event horizon causes charge seperation of individual virtual particles. The black hole sometimes swallows one virtual particle of a pair, preventing the other virtual partner from vanishing. The result--the virtual particle is promoted and becomes 'real' and can escape. What is really fascinating--not only does the black hole lose mass in this way--but it should produce an equal amount of matter and antimatter particles! The virtual pairs are oriented randomly, so an equal number of matter-pairs as antimatter-pairs gets swallowed. Thus forcing the black hole to emit an equal quantity of matter and antimatter particles.

Now the rate at which mass is lost is inversely proportional to the surface area (which in thermodynamics is a measure of the entropy of the black hole) as the hole shrinks, its radius decreases directly with its mass, but its surface area decreases with the square of the radius. Anyways, the process is decidedly nonlinear. The hole will shrink, it's blackbody temperature rises, and the amount of power emitted by the particle flux increases. Eventually, for a naturally formed black hole, the last million tons or so of mass will flash away in a last burst of radiation rivaling our sun's output for a brief instant. The point is, because of Hawking evaporation, if a tiny black hole could be created, it won't last very long, and it converts most of itself into radiant energy. A milligram black hole would yield the energy equivelent of about 21 tons of TNT--this is about the energy equivalent of a full tanker truck of gasoline!

If it were possible to create a really tiny black hole, say perhaps by plucking one out of the quantum vacuum by using a powerful heavy ion collision (there is an accelerator at CERN in Geneva, Switzerland--the Heavy Ion Collider that might just have enough energy to do the job.) If we can arrange to feed this hole, say about fifty micrograms of mass before it explodes--then we would be talking about the energy equivalent of about .1 tons of TNT, or about 200 lb (near 100 Kg.) By creating only one of these each second, the resultant blasts (contained within a blast-heat-and-radiation resistant casing such as a three foot thick shell of stainless steel about 40 feet across) could have the makings of a power plant. Infact, just the energetics suggest that such a plant would be quite capable of generating 1000MW electricity at the grid.

By feeding the holes more, or creating them more often, such a setup could ramp up power production to just about any desired energy production level. It could even be possible to use the evaporating micro black holes to heat a working fluid such as water (for really big ocean launched rockets!) or even lunar regolith (interplanetary cruise ships, anyone?)

Granted there are a lot of 'ifs' here. But 'ifs' are worth exploring, for if we didn't, we wouldn't even have computers or the internet, or thousands of other products we take for granted every day!

Date: Sep 19, 2004

Interesting post GoogleNaut !

Regarding you statement, "A mere half-gram of Antihydrogen, when annhilated, would yield the energy equivalent of the Fat Man atomic bomb--about 21000 tons of TNT equivelent. A half-kilogram (a little over a pound) would create an explosion of about 21 Megatons, or a little larger than the Castle-Bravo test in the South pacific in the 1950's."

....I would merely qualify that by saying that the enormous energy equivalence is a misleading comparison to the nuke bomb explosions : except for the immediate vicinity of the annihilation, where charged pions are produced for a brief moment prior to their decay, all the energy ends up as gamma rays. Therefore, an antimatter-version of an aerial shot like Fat Man or even a tower shot like Castle-Bravo would produce a tiny fraction of the explosive effect of their fission/fusion cousins. Antimatter bombs would in fact be the (near-) perfect radiation weapons - not unlike the pure-fusion neutron bomb (which itself could be realised using antimatter triggers).

Long-term storage of the antihydrogen is feasible, using the principle of quantum-mechanical barrier repulsion, with a cryogenic container lined with frozen nitrogen maintained in the 2p0 ground state, at a temperature below 0.03 K. (Ref.: Zito, R.R., "The Cryogenic Confinement of Antiprotons for Space Propulsion Systems," JBIS vol. 35, pp. 414-421, 1982, and "Chain Reactions in a Hydrogen-Antiproton Pile," vol. 36, pp. 308-310, 1983.).

Recent developments in solid-state refrigeration devices may permit antimatter storage in very compact packages.

It appears that science-fiction writers have foreseen such technology -- as for example in the old Star Trek TV series episode in which Kirk's landing party fends off attack using a small mortar, lobbing radiation grenades....

Date: Sep 19, 2004

Interesting--I didn't know about the frozen nitrogen method: it seems almost unbelievable that it could work. Maybe there is hope yet for antihydrogen after all...

As for an antimatter annihilation explosion: I can only surmise that the predominant annihilation products (pions for anti-hydrogen, gamma-rays for positrons...) would decay very quickly by cascade showers to potent gamma-rays. The resulting gamma-ray flash would penetrate a medium such as air much farther than x-rays, so perhaps you are right Jaro. It would take a lot more antimatter to create blast effects. A nuclear fireball will induce a lot of x-rays, which are readily absorbed by the surrounding air for thousands of feet. This is the origin of the brightly luminous 'fireball' associated with high-yield atmospheric nuclear explosions. A near surface shot with antimatter I would imagine would still induce surface ablation and near surface superheating of the air resulting in the catastrophic supersonic blast waves seen in tests such as the Grable shot (the nuclear cannon: Atomic Annie...) As for induced radioactivity and fallout from an antimatter shot...I don't know. My guess is that there would be some induced radioactivity, but not much. I would imagine that most if not all radioactivity associated with antimatter shots would be created by photonuclear effects: ejection or spalling of neutrons from nuclei clobbered by high energy gamma-rays. Possibly some radioactivity could be induced by fusion reactions in the casing or by photofission...but I'd guess that these sources could be small.

It could be possible to create a 'psuedotamper' around the antimatter-matter primary made of a high-Z material such as lead or tungsten which would tend to scatter and 'downshift' the energies of the gamma-ray/pion annihilation flash creating a hot x-ray emitting fireball. This would tend to create more blast by the more 'conventional' thermal x-ray transfer mechanisms associated with nuclear weapons. However, this has next to nothing to do with propulsive applications (other than Orion of course...)

Date: Sep 19, 2004

RE: Solar Power at 0.1au

Date: Sep 20, 2004

RE: Collecting Solar Power at 0.1au

Date: Sep 30, 2004

This is all very good. But we need to get behind Heavy-Lift first, for everything else to follow.

Date: Oct 2, 2004

quote:
Originally posted by: publiusr
"This is all very good. But we need to get behind Heavy-Lift first, for everything else to follow."

Smart post 'publiusr', make NS members write this quote 100 times on the "Blackboard" !

Date: Oct 10, 2004

Agreed, we need an HLLV. However no HLLV will materialize unless there is a long term government/industry commitment to a large scale space project. Furthermore, there will be no long term development project for an HLLV because there currently isn't any use for one. It's a vicious cycle.

Only a concerted, multiprong effort requiring simultaneous development of HLLV and advanced man rated systems, coupled with a long term commitment by an international consortium of countries and companies can do the job. Such an effort will take decades and likely cost trillions of dollars!

However, what people fail to realize is that money is spent here on Earth. It buys groceries and houses; pays for college tuitions; pays taxes; creates new jobs and technologies and stimulates growth in the economy. Eventally all sectors of the economy will benefit which is a good thing--and is much better in the long run than spending the absolutely astronomical sums of money that the US of A currently spends on Social Services [I'm not saying that these programs don't have their place--only that ultimately stimulating growth in the economy is the only way to pay for them. Otherwise, eventually the expense of Social Services will grown beyong the Governments (and tax payers) ability to pay...] It is a far better thing to spend the money increasing productivity instead of spending vast sums on something with little or no return at all.

Date: Oct 10, 2004

Sorry, but I totally disagree with the above. It's far better to spend money on a space activity at least the Public sees what the 'score' is - failure or success in space. Where is there that kind of closure in perpetual bogus failed government social programs or private business dealings where white collar criminal CEO's pocket billions from hard working taxpayer or investor money?

Government should remove NASA budget from VA housing appropriations. Social programs that work found public money because they demonstrated the 'real' need. Space money in the past also found money because of the 'obvious' tech benefits for doing so also worked in space.

Why U.S. government changed its tactics to farm low expectations?

HLLV is not a 'vicious cycle'. It's either built or its not. Spaceshipone flew because there was finally a Will and the necessary funds to accomplish the job- very simple.

Our kids stand a better chance at real jobs in activity where robotic and human colonialization of our Solar sSstem works toward reality in space.

Date: Oct 10, 2004

That was essentially my point. Agreed with your observation that the HLLV project is either done or it is not. All it takes is a will to do it--applications will falow when the machine is built (unless of course this is no fallow up funding.)

As far as the social programs go--I am concerned that the future economy will not be able to grow enough to support the level of growth that social spending is achieving. Just in the last few years spending on Social Services topped $550 billion, while Defense spending (the second largest sector of the federal budget) was only about $400 billion. Agreed that some programs do work--but many do not. And worse, they don't necessarily achieve economic growth. This is where my concern lies, the majority of federal spending is not on things that improve productivity. Eventually the parasitic aspects of federal spending will achieve a level at which it is no longer sustainable.

This is one reason why I think it is important to increase our space activities. It promotes economic growth in high-value technology sectors. It tends to generate new technologies which generally have great economic potential. Further, a commitment to a large scale, long term project such as lunar or near earth asteroid mining, or construction of solar power satellites can give us (if successful) important resources such as energy, platinum group metals (useful in making fuel cells for automobiles,) as well as giving us a global and near earth space transportation infrastructure. All of these things combined should promote a healthier global economy.

Furthermore, in an effort to 'hedge our bets,' I would like to see U.S. investment in nearer term energy solutions, such as the High Temperature Gas Cooled Pebble Bed Reactor. The Chinese are investing heavily in this technology with a 'cookie cutter' construction philosphy--build many plants off one standard design. We can alleviate much of our petroleum consumption concerns by suitable applications of nuclear energy in the near term and possibly solar power sattelites in long term. Perhaps another more practical technolgy may develop--we'll just have to keep doing R&D.

I am not opposed to an HLLV program, quite the contrary. I just want to see a space program wherein the machine will actually be used. The Space Shuttle was a great first attempt at a reusable space craft--but we have done little to replace it with a safer second generation space plane. We finally have a space station--but it is an order of magnitude more espensive that it ought to be and it is in the wrong orbit (51 degree inclination) to be really useful. For the amount of money that the US spent on the space station, I always imagined that we would have something more akin to the double wheel station in Arthur Clarke's and Stanley Kubrick's "2001: A Space Odyssey."

Date: Oct 11, 2004

I quite agree with googlenaut now...

From the bottom: A wheel space station seems the best ticket for design to provide the necessary micro gravity to assist in human health in space-no question. Could it be done affordable now...Yes, 'cause it can always be recycled for that purpose. There are bright plans by companies, engineers and scientists that have already spent time and money to work on real methods in providing human transportation in bridging the Solar System. As of today I don't see efforts at building HLLV. Without it 'half hearted' space activity will continue to be the order.

In the area of nuclear power plant technology there is also a great number of experimental nuke power plants and some have shown to be very efficient, safe and secure. Again, bright plans by companies, engineers and scientists the world over that have already spent time and money to work these fusion, fission systems. Where are these systems of scale replacing older N power plants with the necessary MW to power affordable electricity to American cites reducing dioxide emissions and dependence on foreign oil?

Again it simple, media and politicos spend more energy blowing 'hot air' on the issue of real bread and butter issues that effects the U.S. public's pocket book. Sorry went off topic here. My brain is saturated with so many promises spun by current U.S. political debate.

Date: Oct 11, 2004

From the bottom: A wheel space station seems the best ticket for design to provide the necessary micro gravity to assist in human health in space-no question. Could it be done affordable now...Yes, 'cause it can always be recycled for that purpose.

Hmm.... I have my reservations as to whether or not a wheel station is feasible today. Such a design significatly complicates construction and assembly. Especially when you take the difficulties astronauts have with current suits into account. (I honestly think NASA needs to spend a little more research time on skin-suits.)

However, a good compromise can be achieved. If you build a station out of large spokes revolving around a simple lattice-work, you could achieve much of the "snap-together" simplicity of today's station components and add partial gravity via spin. Even 1/10th gravity could make a space workshop much more feasible.

As for needing HLLV first, I actually think the biggest thing holding us back is inexpensive man-rated vehicles. If we could built something that could put ~5-10 people into LEO, allow them to dock with our space-station, and bring back the same number of people for a few million dollars or less, then the *need* for larger stations would begin appearing. I've been over this problem in my head a few thousand times and I can only see one way to make the craft truly inexpensive. It *must* be a nuclear thermal craft. With an NTR, the craft can breath oxygen and only kick in hydrogen stores toward the upper atmosphere. A similar oxygen scoop might even be useful for retro-manuevers (although that's actually one of the easier parts of the journey).

That being said, Bigelow is showing us all up. His inflatable space-station means that there would be almost no need for HHLV vehicles in the near future. In fact, his design means that a "wheel" shaped station might even be launched and simply inflated in place. Yay for progress.

Date: Oct 11, 2004

I am not entirely convinced about the inflatable modules. True, they offer significant advantages in weight savings, and true they could be made to be very strong. But I am more concerned with micrometeoroid imacts and for interplanetary travel, radiation shielding. I suppose this could be mitigated by using water--frozen as ice in bags or blocks--and stacking them around the habitation modules. Using a metal based superstructure might improve things a bit--but you still will need shielding. So perhaps my concerns are unfounded. Perhaps inflatable modules could work.

The wheel space station idea was just to illustrate the point that for the amount of money that we spent on the space station that we have, I think we could have had something far more useful: an orbital laboratory, construction yard, and deep space launch point for future space missions. A real space base--not just a station. Unfortunately with all of the Congressional budget wrangling over the decades--all of these useful qualities seem to have been lost. And a lesson to any Congressmen who happen to read this--Not One Nickel of Money Was Saved in the Re Designs!

There comes a point when a good design is achieved--then build it. Don't waste more time and money redesigning the thing to death. Of course that was what the real purpose of the redesign was--to waste enough effort to kill it outright.

O.K. enough complaining by me!