New Nasa Spaceflight On pB11

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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MSimon
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New Nasa Spaceflight On pB11

Post by MSimon »

Engineering is the art of making what you want from what you can get at a profit.

Tom Ligon
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Post by Tom Ligon »

Fun! I had not been there in a while and just had to post. There's a paper addressing the problem on Askmar, of course.

choff
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Post by choff »

The downside to the ramscoop is its huge. If you want to travel to the stars, why not have unmanned ships run by intellegent computers make the long term trip and drop off tanks of fuel along the path. Then send the humans in a ship thats just fusion engine with small fuel collectors and habitat. The dropped off tanks of fuel are signalled in advance to dump fuel just as the manned ship approaches. Get the manned ship to near light speed fast, decelerate at the other end fast, repeat on the return trip. The only downer is you have to wait a few hundred years for the machines to get the trip ready.
CHoff

Tom Ligon
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Post by Tom Ligon »

Choff,

The problem with that scheme is that the business model just sucks. The Spanish would not have explored the New World if the trips took three hundred years. We're having trouble convincing people to go back to the Moon, go to Mars, explore the asteroids, where at least the discoveries get back to us in weeks to years.

Faced with an exploration lasting centuries, what are the odds you would develop better propulsion and pass the explorers before they were halfway to their destination? Probably the trip would be put off indefinitely.

Dr. Bussard liked fast cars, fast sailboats, and fast rockets. However, he thought the interstellar ramjet would take 200 years to develop. It is an attractive bit of SF for now, with plenty of more attainable SF between now and the possible then.

kurt9
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Post by kurt9 »

I posted some comments about the nature of space colonization and interstellar travel on the Tau Zero website (Centauri Dreams) a few days ago that got me into hot water. I stated that if we do not get any kind of physics breakthrough (FTL, wormhole. etc.) that the O'neill scenario for the human settlement of our own solar system was our future in space for the next 200 years or so, and that we would not attempt to go to the stars until significant settlement of our own solar system had occurred. For some reason, some of them seemed to get upset about this. However, I stand by this point.

The distances involved, the technology necessary, and the lack of Earth-like planets ensures that O'neill type space settlement will be a prerequisite for any kind of interstellar travel. Any kind of interstellar space craft will require the same kind of biospheric and other technologies that would comprise an O'neill habitat. Also, because there are so few Earth-like worlds, resources in the target solar system are more likely to be used to build O'neill style habitats than to be used for planetary surface settlements. Also, nanostructured materials such as fullerines make possible construction of habitats far larger than those envisioned by O'neill in the 1970's.

It also seems to me that any "early" possibility of interstellar travel could only result from successful development of speculative physics ideas (Heim theory, Mach-Lorentz thrusters, wormhole technologies) and not on anything else. This suggests that moderate funding of some of these schemes may be reasonable.

CaptainBeowulf
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Post by CaptainBeowulf »

Kurt, I agree with you to some extent there. If rockets remain the only viable technology, humans won't leave the solar system for centuries, probably until it's basically all colonized. There may be some robotic probes sent out... but more likely super-space telescopes will be deployed at the edge of the solar system.

Think about the types of telescopes people have mooted launching on an Ares-V type vehicle, and putting at a Lagrange point. If they work out, they would be orders of magnitude more powerful than Hubble (or the equivalents for infrared etc.). An even larger system parked out at the solar system edge would be orders of magnitude beyond that. You might be able to work out the atmospheric composition etc. of planets around other stars with such a system.

My guess is that some sort of propellantless "spacedrive" breakthrough is needed to get us moving any sooner. Heim theory doesn't seem quite right (it's certainly not popular with physicists), but it may not be entirely wrong. There are a number of theories along a similar vein. Tajmar's gravity modification experiments are also interesting. I maintain a faint hope that an FTL loophole may be found - either transiting through "rolled up" higher dimensions in "hyperspace" (ie. 5th-12th dimensions), finding a way to deform the space-time fabric, or finding powerful enough "negative energy" to hold open wormholes. But all such methods may well prove impossible.

However, the old age of exploration ships did often take years to make their long and dangerous journeys. Heim/Tajmar type may lead to a gravity drive. If spacetime does have some sort of "fabric" or "ether", it may be possible to create a "vacuum propeller" which pushes against that through gravitomagnetism. The resulting effect might look similar to Alcubierre's "warp drive". On the other hand, it may render a repulsive gravitational force - "antigravity". If it works that way, you may be able to accelerate by swinging in as near to the sun as you dare (big gravity well) and then switching the repulsive drive on full force, causing you to be ejected from the solar system. You would slow down at the other end by skimming the target star's gravity well and again using the repulsive effect against it - sort of like a gravitational drive version of aerobraking.

If such gravitomagnetic drives are possible, the gravity effect may be powerful enough to get you close to the speed of light. In that case, a trip to somewhere like Tau Ceti or Epsilon Eridani, about 10-12 light years away, might be accomplished in 10-15 years. The astronauts onboard the ship would experience anywhere from weeks to a couple of years of time passage during the trip. From the traveller's perspective, it's certainly possible, while for the people on earth, a trip could return samples etc. within 30 to 40 years.

Gravity control would have other benefits. These include a ship-internal gravity field separate from outside fields and inertial changes - an "inertial dampener". Acceleration/deceleration could be arbitrarily quick. Also, AG would eliminate the problems of calcium and muscle mass loss for the astronauts. If the gravitomagnetic effect is powerful enough, the ship could also be quite heavy. Rather than being a brittle eggshell like many of our current ideas, it would be compact for its mass and heavily armored. This would be better than some flimsy structure with rotating sections, ramscoops, etc.

Even if a gravitomagnetic drive breakthrough happens in the foreseeable future (for example, Tajmar's work produces something unexpected by 2020), I wouldn't expect an interstellar mission any time soon. It would usher in several decades of the long-predicted colonization of the solar system. People would be building ships that could fly between Earth and Mars in a couple of weeks and stuff like that. You might actually see interplanetary ships which could lift off from Earth's surface and fly to the moon, Mars, and elsewhere. Also, you would probably see jetliners go the way of propeller planes. Initial commercial investment would be into stuff like atmospheric grav-drive "planes" which could carry 2000 passengers from L.A. to London in under an hour, etc. Still, I would be happy with that in my lifetime. I'm sure there is lots of fascinating stuff to find on the moon, Mars, Europa, and elsewhere.

BenTC
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Post by BenTC »

Tom, you mention "fuel mix has to be around 8 hydrogens to one Boron in order to minimize bremsstrahlung radiation." Can you expand on how that works?
In theory there is no difference between theory and practice, but in practice there is.

Art Carlson
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Post by Art Carlson »

BenTC wrote:Tom, you mention "fuel mix has to be around 8 hydrogens to one Boron in order to minimize bremsstrahlung radiation." Can you expand on how that works?
For given energy distributions and no impurities, the fusion power is proportional to n_p*n_B and the bremsstrahlung power is proportional to n_e^2*Z_eff with Z_eff = (n_p + Z^2 n_B) / n_e and Z = 5. Introducing r = n_p / n_B, we can write the ratio as [ n_p*n_B ] / [ n_e^2*(n_p + Z^2 n_B) / n_e ] = r / [ (r+Z) * (r+Z^2) ] .If we maximize this expression by setting the partial (logarithmic) derivative with respect to r equal to zero, we find that r = Z^3/2 = 11.18 is optimum.

Tom Ligon
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Post by Tom Ligon »

Yeah, what Art said. Increasing the ratio of hydrogen to boron reduces Z-effective, sorta-kinda the average atomic number. Bremsstrahlung becomes a factor at high atomic numbers, so this measure helps reduce it.

An EMC2 paper on Askmar.com goes into it in detail.

Even if you could run a Bussard Ramjet in pure fusion mode, I would expect you might use a RAIR (Ram Augmented Interstellar Ramjet) strategy when at a low fraction of the speed of light. Boosting reaction mass should increase acceleration.

djolds1
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Post by djolds1 »

Tom Ligon wrote:Dr. Bussard liked fast cars, fast sailboats, and fast rockets. However, he thought the interstellar ramjet would take 200 years to develop. It is an attractive bit of SF for now, with plenty of more attainable SF between now and the possible then.
Isn't the ramjet/RAIR of low utility for us because the Local Bubble has an unfortunately low density of interstellar gasses?
Vae Victis

Tom Ligon
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Post by Tom Ligon »

Lower utility, but not zero. The numbers I've seen say around 1/3 the presumed average density of interstellar gas. When you get right down to it, the interstellar medium is the next best thing to a perfect vacuum, zero density by all standards we can achieve here.

Within the Oort cloud it might not be so bad. Possibly we could use BFR-powered RAIRs for less than interstellar distances, perhaps long before we had practical interstellar ramjets.

In any case, the utility of interstellar hydrogen for propulsion gas is, at the moment, of use primarily to writers of science fiction.

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Post by MSimon »

Speaking of Science fiction.

This is kind of OT but there here is the first post by another SF author at a place I regularly post.

http://www.classicalvalues.com/archives ... s_tal.html
Engineering is the art of making what you want from what you can get at a profit.

choff
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Post by choff »

I still like my idea if only for a manned mission to the nearest star within the next 100 years. If Von Neumann intellegent computers/robots become available, you only have to send a small ship with one or two robots to the next star with enough fuel to decelerate rapidly on arrival. The robots use available resources to build more robots and fuel processing. The fuel is used to decelerate the manned vehicle when it arrives.
If you keep to small vehicles with minimal internal fuel, the time saved enroute and back accelerating and decelerating from light speed would make it reasonable nearest star and back within one human lifetime.
CHoff

choff
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Post by choff »

I still like my idea if only for a manned mission to the nearest star within the next 100 years. If Von Neumann intellegent computers/robots become available, you only have to send a small ship with one or two robots to the next star with enough fuel to decelerate rapidly on arrival. The robots use available resources to build more robots and fuel processing. The fuel is used to decelerate the manned vehicle when it arrives.
If you keep to small vehicles with minimal internal fuel, the time saved enroute and back accelerating and decelerating from light speed would make it reasonable nearest star and back within one human lifetime.
CHoff

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Post by 2edfe9 »

choff wrote:I still like my idea if only for a manned mission to the nearest star within the next 100 years. If Von Neumann intellegent computers/robots become available, you only have to send a small ship with one or two robots to the next star with enough fuel to decelerate rapidly on arrival. The robots use available resources to build more robots and fuel processing. The fuel is used to decelerate the manned vehicle when it arrives.
If you keep to small vehicles with minimal internal fuel, the time saved enroute and back accelerating and decelerating from light speed would make it reasonable nearest star and back within one human lifetime.
If we're going to be looking that far into the future, then you need to take into account progress in AI. In my opinion, some form of hard AI, either software-derived people or uploaded biological people will have emerged by the time we're ready to go interstellar. At that point, we can build very fast "Coke Can" rockets containing just enough computer power to host the crew, and an "ant colony" of small robots that they can use to get started building an industrial infrastructure when they reach their destination. My point is, the AI's will be the crew, not some sort of vanguard for humans. Sending "Canned Monkeys" after them would just be a waste of time and technically far more difficult.

Deep space will be owned by computers, not humans.
Patrick A

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