Wednesday, August 10, 2011

Destination: Mars

ESA Mars Lander
The first human interplanetary mission will, more likely than not, go to the Red Planet. Apart from the Moon it is the easiest major body in the Solar System for us to reach. Its surface bears evidence of rivers and seas, and liquid water may still occasionally flow there. The similarity of its landscapes to the American Southwest is an illusion, but it remains a candidate for life, and its chief rivals - Europa and Titan - are far more distant and hard to reach.

A single image (of an artifact, for example) could of course change all this. But for now at least, Mars is the likely first place to go.


I am not concerned with pure stunt missions, whether by some multi-billionaire or an emergent great power. For this discussion I presume that a human mission to Mars is intended to explore Mars. Yes, other motivations will surely be in the background, involving the usual suspects. But the more serious the exploratory intent, the more likely that going to Mars will lead to further developments rather than end up as a costly one-off.

This does not mean that every individual mission must 'do science.' The engineering demands of safe human interplanetary travel justify what amount to shakedown missions, say, a manned flyby that does nothing but demonstrate our ability to perform the transfer mission. But the program as a whole should be aimed at advancing our knowledge of Mars.


The model here is not Apollo but the robotic deep space program, which in spite of some embarrassing failures (feet/second != meters/second), has in all been a profound success.

A first implication is that a human mission will be undertaken only when robotic missions reach diminishing returns. It is no doubt true that a geologist with a hammer could learn more about Mars in a day than our rovers have learned over years. But the cost of sending that geologist would be very much greater than the next few rovers. And human missions are subject to some constraints, such as landing where it is safe to land.


My instinct in thinking about a Mars program is to proceed cautiously and incrementally - unmanned tests of the vehicle, then a human flyby, then orbit without landing, and only then a full-on landing. I am not sure that each of these stage is strictly necessary, and there are alternate possibilities, such as a visit to a NEO, that would similarly exercise spacecraft and procedures.

And some of these missions - notably, orbiting without landing - might be able to 'do science' on an important and relevant scale. In particular, a crew on Mars orbit can operate surface vehicles and manipulators remotely, but without significant light lag - like steering a minisub from the surface, not steering a rover from Pasadena.

This is as good a place as any to note that 'going to Mars' combines at least two very distinct space missions: the deep space journey to Mars orbit and back, lasting at least months and perhaps most of two years; and landing on Mars, working there for weeks, and lifting back off to Mars orbit. This in itself is reason to test the Mars orbital capability before the surface landing.

Mars Direct argues in effect for a very different functional division - in effect a one way trip to the surface of Mars, then use of a second pre-positioned (and pre-fueled) spacecraft for the trip back. This feels cut-rate and precarious to me, not least because Zubrin is so much like a real estate promoter, not quite trustworthy on principle.

To be sure, there's no reason this architecture couldn't be tested in an unmanned mission, but I also have doubts about packing the hab elements into form factors suited to Mars landing and liftoff. It seems like awfully cramped crew quarters for such a long mission, or else a much larger cabin than you need to carry the crew and some rock samples from the surface to Mars orbit.

In any case, as longtime readers know, I have bias in favor of fast human travel using high ISP propulsion - most likely solar electric, though perhaps nuclear electric - for getting to Mars orbit and back. Faster travel means less exposure to radiation and weightlessness, the main health hazards of prolonged spaceflight.

Solar electric has now been successfully flight tested by the Dawn mission. A fast (~3 month) trip to Mars requires a much higher drive power/mass ratio, which may not be attainable. But solar electric space propulsion is far from technical maturity, and it may well be able to approach the 1 kg/kW standard for fast travel. .

Electric drive pretty much precludes the Mars Direct approach anyway, since an electric spacecraft is ill-suited to aerobraking, and doesn't need it. The surface components of the mission can be sent separately - a Hohmann transfer is fine, since the crew isn't aboard until the Mars landing.




Discuss.


The image, from a European proposal for Mars exploration, is recycled from an earlier post on interplanetary exploration.

249 comments:

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Damien Sullivan said...

I think it's guaranteed that there's new physics to be discovered. The fundamental incompatibility of QM and GR proves that, as do things like dark matter and dark energy. There are phenomena we can observe but not explain; QED.

Whether those new physics will be discovered at all soon, and whether they'll be relevant to space access, are entirely different matters. It'd be nice if near-term discovery of the Higgs boson led to antigravity or inertialess drives, but it's quite possible that we don't learn what we need to for centuries or millennia, and that what we learn does nothing for getting off Earth. So new physics in principle, but not to be counted on or expected on any time table.

Anonymous said...

Tony said:"Thousands of people in a small town, huh? Okay...I live in a samll town in a desert with a few thousand people. It couldn't survive if it wasn't on a major interstate route to bring it everything it needs from all throughout the 21st Century Western industrial base. Please forgive me if I think you're not thinking this through."

Tony, how does this dying little town you live in resimble my hypothedical Lunar base/colony? The Lunar town must grow all it's own food, produce all it's own air, water, and power; it must mine its own minerals and manufacture as much of its own needs as it can; only those things that it phyiscally cannot produce must come from Earth. That's the whole point of the place; it cannot be like the town you live in where for a small potion of the residents' income they can import literally everything. On Luna, everything you ship in from Earth will cost a barge-load of money and must be absolutely esentual to survival to be worth it. Life in your town is comfortable; life on Luna will be rather sparse in contrast; leaving your town (for a day trip, visiting family, or moving away permantely) is relatively simple, easy, and cheap; doing any of those things on Luna are major undertakings, both expensive and even risky.
Yes, I do beleive that several thousands of people living on a Lunar base could achieve 80-90% self-sufficency; it wouldn't be easy or cheap, but I don't see anything to change that opinion; if you said that hundreds of people in that Lunar base would not be enough to sustain it or be enough to provide a workforce sufficent to produce even a single export produce, then I would agree with you. It seems that you and I simply think the minimum size of a self-sustainable base that can produce a viable product is different; you think it is closer to a million and I believe that it is in the thousands. We might need an experiment to see who's right.

Ferrell

Tony said...

Ferrell:

"Tony, how does this dying little town you live in resimble my hypothedical Lunar base/colony?"

People can live in the thousands and tens of thousands in remote places on Earth relatively easily, precisely because access to the outside world's resources is so convenient. On the Moon, as you yorselv quite properly point out, a community has to to as much as possible for itself, and even then it will be subsistence level living for years, perhaps decades.

A few real problems come along awith that:

1. The infrastructure investment will be huge, even for subsistence farming, chemical, and energy production. And then you have to ship up the actual industrial tools and supplies for whatever the ultimat object of the exercise is. The question then becomes what is this mine/factory/whatever supposed to produce that couldn't be produced more economically on Earth, all real costs considered?

2. Who would you find to work in this environment that would be competent not only to run the shop, but survive at all?

3. How long are you really willing to wait for all of your stellar performers to get their subsistence economy going, get the shop running, and then, finally, start turning out more than token amounts of product?

"It seems that you and I simply think the minimum size of a self-sustainable base that can produce a viable product is different; you think it is closer to a million and I believe that it is in the thousands. We might need an experiment to see who's right."

You're missing the point. Whatever the size of a viable community, that's the size. I'm just pointing out that justifying the investment in even a few thousand people, in a really viable enterprise, is highly problematic at the board room level, even before a single bit of metal is bent. The costs are so great that the first question a money man would put you is: "How is any of this more cost and effort efficient than just building finished products on Earth and launching them to wherever they need to go?"

Anonymous said...

Tony, I do believe the original question was about political reasons for placing a rocket factory (and by extrapolation, the base that supports it), on the moon due to enviornmentalists' and others objections to launching nuclear reactors from Earth. If I understand you correctly, your arguments are that it costs too much, it takes too many people, you have to ship too much stuff, and that it takes too long before it makes a profit; did I miss anything? Like not finding enough people qualified to go there and make a go of it?

I've already acknowledged that it would take a huge amount of money to create it; I've already stated that the whole point would be to become as self-sufficent as possible, due to the enormous cost of shipping anything; anyone who plans such an enterprise would anticipate the build up and start-up costs, as well as the lag between breaking ground and shipping the first article. I think that you would be surprised by the number of people both qualified and willing to participate in such a grand experiment; you have to realize that the factory is only one component of a whole town dedicated to researching the best methods and uses of an off-world base.
I agree that it would cost a barge-load of money to establish it, but I do think that it can be made self-sufficent; whether it takes a couple of decades or the better part of this century, I do think that the experiment should be conducted. It would generate huge amounts of data about how to survive on other worlds, it would generate unknown amounts of data about the various activities conducted by the residents of the base, and it would show us what not to do (always a major consideration), and in the end it would give us a practical knowledge of living on another world for extended periods of time; succeed or fail, we will only gain this knowledge by doing it, not by finding excuses for not doing it.

Ferrell

Anonymous said...

Oh, and by the way, what makes you think that private industry and not a government agency would undertake this enterprise?

Ferrell

Rick said...

On the pace of development, see the post I linked at the end of this one. The time scale of space is largely the money scale of space.

It is an enormous investment, and under most conditions it will be made gradually, though perhaps with occasional bursts of enthusiasm and greater spending.

Jim Baerrg said...

Monte Davis:
"Less radioactive, but a much greater mass. And while space RTG material these days is typically in tough little pellets (sintered/ceramic?), would the fuel elements for a space-only NTR be as tough in the event of a Rapid Unscheduled Disassembly Event during the ground-to-orbit leg?"

You probably have a valid point for NTRs designed to output GWs for a few minutes to hours, out of something massing a few tens of tons.

I was thinking more of reactors designed to put out about a MW for years from a device massing less than a ton. The latter could have its fuel in tough little pellets. The reactor would be the sort of thing that would be useful for powering an ion drive craft to the outer solar system or keeping a moonbase running through the lunar night.

BTW I was googling 'Nuclear Thermal Rocket' & 'Space Nuclear Reactor' to make sure the sizes were roughly right.

Monte Davis said...

Damien: I think it's guaranteed that there's new physics to be discovered...
but not to be counted on or expected on any time table.


What you said. I suspect that on a centuries-to-millennia time scale, we've been "spoiled" by our success in stair-stepping from muscle power to combustion of wood, then fossil fuels -- a fine (if not ultimately scaleable or sustainable) tango between increasing energy density and increasing power.

A moment ago (on that scale) we raised our game from chemical (aka electromagnetic) bonds to the strong nuclear force -- in principle, a million times denser. Trouble is, the EM bonds in boring old condensed matter limit reactors to a few thousand K, just as they do for chemically-fired power plants and rocket engines. So in order to really use that 10^6 increase in energy density, you need magnetic/inertial confinement -- or else Orion-style nuclear pulse ("I don't care how much is wasted, I'm still getting a hell of a lot more kick per kg than chemicals will ever give.")

My dark suspicion is that even if the Higgs or whatever were to offer sill higher energy density, it's likely to need even bigger, heavier, more complex and more expensive surroundings than controlled fission does.

Monte Davis said...

Jim Baerrg: I was thinking more of reactors designed to put out about a MW for years from a device massing less than a ton...

Agreed. There's certainly a large trade space worth exploring between existing RTGs and high-power NT rockets.

Tony said...

Re: Ferrell

For you it's a philosophical argument. For me it's a political, technical, and economic one. I just don't see the resources coming available for a massive, big bang enterprise of the type you're suggesting. I see it as being so expensive that no realistic motivation would suffice -- not even radiological safety concerns. Somebody -- and enough somebodies -- would always be able to point out that there is a cheaper way to do it, even at the cost of shipping up ten ton reactors inside 90 ton lead casings.

In fact, if you figured you'd need 100,000 tons of initial infrastructure to start a Moonbase, you're looking at 1,000 100 ton class super heavy launch vehicles. For one tenth the effort, you could put 100 reactors in space, configured for safety as described above.

And before you say those are straw man numbers, I could easily see 100,000 tons being too little for a community of thousands with their own mostly self-contained life support. 100,000 tons is the displacement of a Nimitz class aircraft carrier. Now, of course you'd use lighter materials for a lot of things in space, but you also have to recognize that there's so much more to do. An aircraft carrir is far from self-sufficient.

Also, I don't think one would get all that many qualified volunteers to participate in such a project. To you it's a grand adventure. People actually qualified to do such things are successful and happy on Earth. Sure, there are highly qualified people willing to be astronauts and risk their lives to fly in space. But they get to come home after the mission, kiss their dogs and kick their wives. You want the same type of people to go live on the Moon at least for a significant portion of their professional lives, if not for the rest of their lives. I don't think you can really criticise me or anybody else for being more than a little bit skeptical.

BTW, you think I'm suggesting a private enterprize operation simply because I used the expression "board room"? You're being far too literal. I simply meant the level of policy at which projects are approved or not.

Anonymous said...

Well, Tony, if you don't think the experiment worth it, don't participate :> Seriously, this just shows the huge problems that need to be overcome before such a "grand experiment" could even get started. All of Tony's objections would have to be overcome/addressed before the first rocket launch; funding, planning, organization, clear statement of goals, and personel issues would all need to be dealt with before it could be placed before the powers-that-be who hold the purse strings for their blessing. That would be the toughist part of the whole project, in my opinion.

Ferrell

Tony said...

Tony:

"Well, Tony, if you don't think the experiment worth it, don't participate :> Seriously, this just shows the huge problems that need to be overcome before such a "grand experiment" could even get started. All of Tony's objections would have to be overcome/addressed before the first rocket launch; funding, planning, organization, clear statement of goals, and personel issues would all need to be dealt with before it could be placed before the powers-that-be who hold the purse strings for their blessing. That would be the toughist part of the whole project, in my opinion."

Wow.

Thucydides said...

Sidestepping some of the arguments, here is a piece from Centauri Dreams which talks about world ships. Now Island Three colonies, NEO's and even very large Earth-Mars Cyclers could be considered "prototypes" (since they are the self contained ecosystems but lack propulsion systems capable of long distance voyages).

Much of this is very speculative, but an interesting view of a possible PMF as well. Some arguments about the minimum size of viable colonies or the desire of the space civilization to live in engineered colonies rather than planets have been hashed out here before as well:

http://www.centauri-dreams.org/?p=19423

Tony said...

Re: Thucydides

Mars cyclers would hardly be self contained. Their purpose is to save on hab mass for subsequent missions, not consumables.

Thucydides said...

Large cyclers will probably have some sort of semi closed ecosystem because there is plenty of room for the greenhouse and ecosystem parts and plenty of time for the crew to tend to it. It may even "grow" over time if the cycler is long lived, with maybe a little garden patch or fish tank that a crew member brings aboard and gradually expanding from there.

I would see that process as being more for the comfort and mental well being of the crew than a hard requirment for the mission in a cycler.

Tony said...

A Mars cycler is going to be unmanned most of the time. One typical trajectory design has a cycler occupied for only twelve months out of every twenty six -- six going up and six going down. After the first Mars encounter, it's basically for a full year -- six months coming down and six going up, presumably with a different crew on each leg. The spacecraft would be unoccupied for 14 month duration of the "escalator" portion of the orbit beyond Mars. (Enumerating the good engineering reasons for this is an exercise left for the student.)

So significant amounts of onboard gardening would be hard to support. Plants couldn't be left untended. They would have to be started by the upbound crew for Earth-supplied resources. After six months they would have to be terminated and the waste products dealt with, so that they didn't cause problems on the escalator section of the orbit.

It would probably be worthwhile to give the crews some seed and other supplies to grow some flowers and maybe a few tomatoes/grapes/etc. Certainly both the up and down crews could do this, since seeds aren't too massive and will keep for a couple of years, as will simple garden nutrients.

Jim Baerg said...

Re: Nuclear reactors in space.

http://news.yahoo.com/suitcase-size-nuclear-power-plants-may-revolutionize-space-210400915.html;_ylt=A2KLPyX9C1xOS0kA9QES.MwF;_ylu=X3oDMTM1czRnYnUzBHBrZwM0YTBhOTQ0NC0xZTQzLTNjMWItODNjMC1lOWI4OGQ2OWZkYzEEcG9zAzEEc2VjA3RvcF9zdG9yeQR2ZXIDYjkyOWYxMzAtZDI4Mi0x

or

http://www.innovationnewsdaily.com/minature-nuclear-reactor-mars-moon-nasa-2221/

Too bad there is no link to a technical paper or mention of precise masses or dimensions rather than 'suitcase size'.

Presumably that size leaves out any shielding, but for a moonbase the shielding would be regolith piled around the reactor, & for a space probe the shielding would only be on one side.

Tony said...

Jim Baerg:

"Re: Nuclear reactors in space.

...

Too bad there is no link to a technical paper or mention of precise masses or dimensions rather than 'suitcase size'.

Presumably that size leaves out any shielding, but for a moonbase the shielding would be regolith piled around the reactor, & for a space probe the shielding would only be on one side."


I think the suitcase is probably more like a steamer trunk. The "backpack" nuke was about the size of a ten gallon container, after all. Still, at 40kw, if it was suitcase size, it would be in the vicinity of the magic number. Then you wouldn't worry so much about uses for a static site, but weather it was scalable for propulsion use.

Anonymous said...

Tony said:" think the suitcase is probably more like a steamer trunk. The "backpack" nuke was about the size of a ten gallon container, after all. Still, at 40kw, if it was suitcase size, it would be in the vicinity of the magic number. Then you wouldn't worry so much about uses for a static site, but weather it was scalable for propulsion use."

I'd think it might be fesable to 'stack' or 'cluster' those suitcase-sized reactors if they weren't scalable; that way, you could customize your propolsion unit for each mission; also, if a reactor malfunctioned, it wouldn't necesarilly be catastrophic to the mission.

Ferrell

Tony said...

Ferrell:

"I'd think it might be fesable to 'stack' or 'cluster' those suitcase-sized reactors if they weren't scalable; that way, you could customize your propolsion unit for each mission; also, if a reactor malfunctioned, it wouldn't necesarilly be catastrophic to the mission."

I think that depends very much on how much irreducible redundant overhead mass you have in each reactor module. Numerous complete systems add to complexity and increase the possibility of failure, even if any given failure has less chance to be catastrophic. Packing them closely may lead to reactors interfering with each other through stray neutrons. Those are scalability issues as much as anything that might pop up in physically scaling up a single reactor.

Anonymous said...

Tony said:"Packing them closely may lead to reactors interfering with each other through stray neutrons."

True; however you can place individual reactors at different points on the ship. The trick would be to balance power production with the extra mass of multiple radiation shields.

Ferrell

Tony said...

Ferrell:

"True; however you can place individual reactors at different points on the ship. The trick would be to balance power production with the extra mass of multiple radiation shields."

The problem is indeed the shielding. You'd hit diminishing returns pretty quickly having to individually shield multiple reactors. Also, distributing the reactors around the ship complexifies and extends the shielding requirements. One can't just shield in the direction of the crew cabin. One has to shield in all directions towards ship components, in order to protect against neutron embrittlement and the buildup of Wigner energy.

Thucydides said...

If the purpose is to provide energy to the ships drive, then scattering the reactors all over the place seems counterproductive. The mass budget would be shot not by the reactors or their shielding (although that would be an issue), but the multiple sets of power conversion machinery. The ship would be a plumbing nightmare (just the radiator circuits alone would be a massive headache).

The paper indicated the suitcase sized reactor could provide the amount of power typically consumed by about 8 American houses, which isn't that much compared to the gigawatts of energy needed to provide an electric drive with enough juice to move a big manned spacecaft with the sort of speed we want. Going NTR reduces the amount of mass (no power conversion equipment), but at the cost of ISP.

Anonymous said...

So what about having multiple reactors situated on booms; each boom has it's own shadow shield and one set of energy conversion equipment. Depending on the mission, you could have one, two, three, or four booms (if one boom, you'd most likely need to counter-balance it with something, like a hab module on the end of a paired boom); the number and arrangement of the mini-reactors on each boom would have to be carefully planned so as to minimize interferance by the radiation flux of the other reactors. It seems that the proper design would alleveate many of those design concerns and I'm sure that qualified engineers would be the ones designing such a craft.

Anyway, it may well be that the first mission to Mars would be sponsored by a bunch of big corporations; Instead of a national flag, a big billboard with the logos of all the sponsers and a "Coming soon" sign would be left on the surface of the red planet.

Ferrell

Thucydides said...

I don't really see the point of multiple small reactors given the need to provide energy in the Gigawatt range for either electric or NTR drives. Perhaps I am missing something in your argument.

By analogy, modern nuclear submarines only use one powerful reactor rather than a bunch of smaller ones, the few exceptions that I know of use two reactors due to the space limitations in the hull. A spaceship in free space would not have that sort of limitation.

Another useful analogy might be to compare steam powered ships to modern counterparts using diesel or turbine powerplants. Raising steam from multiple boilers and ensuring the proper amount of steam is available (on top of managing multiple steam expansion engines) adds many levels of complexity compared to using IC engines.

Anonymous said...

If I remember correctly, the argument was started by wondering about the scalability of these little reactors; if they can't be scaled up, then you have to get creative with them; if they can be scaled up, then it's all moot.

Ferrell

Tony said...

Ferrell:

"If I remember correctly, the argument was started by wondering about the scalability of these little reactors; if they can't be scaled up, then you have to get creative with them; if they can be scaled up, then it's all moot."

The problem is that if the reactors can't be scaled, that doesn't necessarily mean there's a workaround.

Anonymous said...

Tony said:"The problem is that if the reactors can't be scaled, that doesn't necessarily mean there's a workaround."

It also doesn't mean that there aren't workarounds...we just need to find out before we build the things.

Maybe instead of worrying about drives (we seem to be able to send stuff to Mars already), maybe we should try to come up with better shielding and life support. That, in my opinion, would go a long ways toward creating a reliable interplanetary transport.

Ferrell

Thucydides said...

We can send small packages to Mars, but large ships suitable for human explorers and all their kit is beyond most current technology.

The "classic" NTR missions from the 1970's had three stage NERVA engined ships assembled in LEO (with three parallel stages to boost the ship out of LEO) to send a bulked up Apollo mission to Mars. I'm sure the astronauts wold have been very keen being stuck in a can for six months one way...

For another historical analogy. we are planning to go the way of the Franklin expedition, carrying everything into a hostile environment in very marginal ships. We can hope the outcome is not repeated.

Anonymous said...

=Milo=



I looked up the Franklin expedition (to the Arctic), and note that the same ships had previously taken part in the successful Ross expedition (to the Antarctic), which carried the same amount of crew.

Tony said...

Tony:

"It also doesn't mean that there aren't workarounds...we just need to find out before we build the things."

Actually, there very rarely are workarounds. Brute forcing scalability issues just doesn't work, because complexity and geometry issues make the thing unworkable. It turns out that you just need bigger boilers for bigger ships and bigger engines for bigger jets. I can't see anything fundamentally different about nuclear reactor technology that would break that principle.

Anonymous said...

Well, since no one knows yet if these little reactors are viable or not, much less if they are scalable, then perhaps we should wait until we have a little more data about them before we try to make intelligent arguments regarding them.

On another note, I do think that developing better shielding and life support technology would allow longer trips with exsiting technology; it should spur space propulsion technology advancement to make fuller use of the extended ability of spacecraft crews to spend in space.

Ferrell

Thucydides said...

Ferrell

The evidence does not seem to support you. NERVA engines were considered fight ready before the program was cancelled, and these were quite powerful engines in very compact packages (say the size of a minivan) that could generate GW of thermal energy. Despite this, only a very marginal expedition to Mars was possible using the technology; a six man bulked up Apollo mission.

Thank you for reminding me of the Ross expedition; obviously leadership and preparation are very important as well. However, since the Franklin expedition was not as well planned or led, the minimum margin available was rapidly used up. Later expeditions learned to live off the land, greatly expanding their margin without expanding the ship or logistical support needed to carry out the expedition. (This partially explains my fascination with things like Solar Sails; you are harnessing the environment and minimizing the mass and energy needed to bring the important stuff to the destination).

Anonymous said...

Thucydide

Your example of the two polar expeditions is actually closer to the point I was trying to make; except for the whole starving and freezing to death, using the lessons of early expeditions to help guide the developement of later life support and radiation shielding. We have a lot of options with propulsion (either at hand, or on the drawing boards) but we are still worried about both adiqute shielding and effective life support for long term space travel; the experiances with the ISS have gone a long way to expand our knowledge, but we still have a ways to go.

Ferrell

Thucydides said...

Another compact fusion drive idea, this one uses aneutronic reactions (p-11B) which is so much better from many angles. So far as I understand the paper, this is a pulsed drive like ORION, only using high frequency pulses of relatively low power for thrust. Since it does not relay on self sustaining fusion reactions, it seems much more feasible than many other schemes.

Read about it here: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014263_2011014853.pdf

Tony said...

Thucydides:

"Another compact fusion drive idea, this one uses aneutronic reactions (p-11B) which is so much better from many angles."

Only if you totally ignore the fact that aneutronic fusion requires plasma confinement and sustainment orders of magnitude beyond even the most pessimistic assumptions about D-T fusion plasmas.

Thucydides said...

If I am reading the paper correctly, confinement isn't an issue since this reaction is not self sustaining. Each reaction is triggered by a burst of laser energy starting a "cascade" in the metal foil, releasing high energy protons which triggers a burst of fusion energy in the 11B fuel.

No magnetic confinement, no electrostatic fields, no magitech (that I can see), just an energetic reaction in the fuel releasing a stream of alpha particles which can be used for high ISP thrust or captured for electrical energy on board.

The apparatus to do this looks like it can be set up on a lab tabletop, so the testing to see if it really works and if it is scalable could be done quickly and easily compared to may of the other schemes being proposed.

Tony said...

Thucydides:

"If I am reading the paper correctly, confinement isn't an issue since this reaction is not self sustaining. Each reaction is triggered by a burst of laser energy starting a "cascade" in the metal foil, releasing high energy protons which triggers a burst of fusion energy in the 11B fuel.

No magnetic confinement, no electrostatic fields, no magitech (that I can see), just an energetic reaction in the fuel releasing a stream of alpha particles which can be used for high ISP thrust or captured for electrical energy on board.

The apparatus to do this looks like it can be set up on a lab tabletop, so the testing to see if it really works and if it is scalable could be done quickly and easily compared to may of the other schemes being proposed."


As described it's a novel means for generating highly energetic ions for propulsion purposes. It still requires electromagnetic fields to direct those ions out the rear end. And they have to be much stronger fields that you might find in a Hall effect or grid type thruster, because the ions are so much more energetic. YOu have to have external power for those fields and for the excitment lasers, control circuitry, ship's service circuits, etc.

In addition, considering the very low gain of the described reaction, I'm having trouble seeing that it could ever be a self-sustaining power source, much less one can generate utility power above it's own operating needs.

Anonymous said...

Tony, I think that the whole point of this drive is that you don't need to sustain a fusion reaction for the drive to work. It isn't designed to be self-sustaining or power generating; like a rocket, it is primarily for propulsion.

Ferrell

Tony said...

Ferrell:

"Tony, I think that the whole point of this drive is that you don't need to sustain a fusion reaction for the drive to work. It isn't designed to be self-sustaining or power generating; like a rocket, it is primarily for propulsion."

You should read the linked document. It makes very specific and unambiguous mention of electrical power generation. Also, if it was just about generating energetic ions, then it does require more poweful (and thus more power intensive) magnetic confinement to direct the exhaust. TANSTAAFL.

Anonymous said...

Tony, I'd read the article if the damned link would work; I obviously thought you two were still talking about the bi-foil laser pulse ignited fusion drive that we talked about earlier; that drive is not designed to be self-sustaining, and I did make the comment that you'd need an MHD on the output of the drive to get any power from it; as far as I can tell, you would either get electrical power or thrust from the thing, but not much of both or either.

If this drive (that I can't get the link to work), is not that fusion drive, then please accept my apologes.

Ferrell

Tony said...

Ferrell:

If this drive (that I can't get the link to work), is not that fusion drive, then please accept my apologes.

It is the drive, but the article has a bit wider scope than propulsion. You can get to it by highlighting and copying the link plus all the text after it, paste into a text editor, and select the actual url at the beginning of the string. It's a .pdf file, so you shouldn't have any trouble selecting just the url.

Tony said...

Or I could just give you the link raw:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014263_2011014853.pdf

Tony said...

Trying again:

http://ntrs.nasa.gov/archive/
nasa/casi.ntrs.nasa.gov/
20110014263_2011014853.pdf

(Remove the newline characters before you paste into your address bar.)

Anonymous said...

*sigh*

...Guys, this is how you do it.



=Milo=

Tony said...

Milo:

"*sigh*

...Guys, this is how you do it."


Sigh. I develop web applications for a living.



=Milo=

Thucydides said...

Sorry the link didn't seem to work for you, but I tried the various work arounds posted and they did work (for people interested in the article).

While the article does say you can use this method for electrical generation, it is only an incidental paragraph near the end, so I don't think the author is suggesting this is a dual mode system. If anyone were to consider this as a dual mode system, it would probably be "either/or"; using it for thrust or running it to generate electrical energy (although I don't see this as being able to generate excess power to run itself and the hotel power for the ship).

One last point; given the configuration in the diagrams, it seems to me that the beam of alpha particles would already be fairly focused coming out of the reaction chamber, which would allow for a smaller and lighter magnetic nozzel. Is this a correct observation, or am I missing something here?

Tony said...

Thucydides:

"While the article does say you can use this method for electrical generation, it is only an incidental paragraph near the end, so I don't think the author is suggesting this is a dual mode system..."

I don't recall that anyone said anything about dual modes. But the author does mention electrical power generation, and in more places than just the end:

"Thus energetic alpha particles
“exhaust “ momentum can be used directly to produce high ISP thrust and also offer possibility of
power conversion into electricity."

"Proton-triggered 11boron fuel (p-11B) offers the
potential for abundant ion kinetic energy for in-space vectored thrust applications as well
as for direct energy conversion in specialized direct electrical energy conversion plants."

"This
kinetic energy can be converted directly into electricity via conversion techniques based on
mature technology derived from other fields, such as microwave technology, resonance-tuned
rectennae which entails equipment that is more compact and potentially cheaper than that
involved in conventional thermal production of electricity."

"Energetic alpha particle 'exhaust'
momentum can be used directly to produce high ISP thrust and also offers the possibility
of direct power conversion into electricity."

"One last point; given the configuration in the diagrams, it seems to me that the beam of alpha particles would already be fairly focused coming out of the reaction chamber, which would allow for a smaller and lighter magnetic nozzel. Is this a correct observation, or am I missing something here?"

That diagram is a bit misleading. By their very nature, alpha particles are emitted at a wide variety of angles from the initial event. They have to be directed by an electromagnetic field if you want to focus their effect in a certain direction.

Anonymous said...

Ok, I finally got to the correct site, and you're right, it does go into much greater detail than the previous article I read. However, it didn't change my understanding of the basic device; you can use the thing to either generate thrust or power, and it isn't a self-sustaining reaction; turn off the laser and the reaction dies. I also don't see any mention of the power produced (the ion stream of Alpha particles) to be sufficent to power the thing; on the other hand, the laser does seem to be of overall low power and the magnetic nozzel just needs to be powerful enough to get the ion stream going in the general direction; that being said, it does seem to be a very PMF type of rocket engine...if it can be made to work as advertised. We should know in about ten years or so, one way or the other.

Ferrell

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