Wednesday, May 25, 2011

The Moon Turns Fifty

Saguaro Moon
Thanks to the history of the early 1960s a lot of golden anniversaries of space milestones are coming up, and a couple of posts at the Atlantic magazine website called one to my attention.

Fifty years ago today, JFK declared that the US would reach the Moon within a decade, thus launching the Apollo program. Forty years after the deadline he set we are still living in its shadow. The two Atlantic pieces reflect, for the most part, one on JFK's decision, the other on its technological consequences.

Going to the Moon was, in some important sense, a stunt. Recently released tapes, as reported in the first linked piece, evidently shown JFK's own subsequent misgivings - mainly, it seems, about the cost, and the lack of dramatic progress as he looked toward the 1964 election. He mulls pitching a military use for space: not on the actual merits, but as a way to make it more politically acceptable.

This is not especially helpful to my own position in a recent post. (But it does not really challenge the core argument about public initiatives. YM, of course, MV.)

The other linked article deals with the path not taken, though I disagree with the author's interpretation of that path. NASA evolved as a vastly ramped up version of a previous agency, NACA, which dealt with aviation, and the idea of flying into orbit was well established in the rocketpunk era. It is certainly elegant; the problem is that it is extremely difficult.

Even 'conventional' ramjets overheat much past Mach 5, and while scramjets have now been successfully flight tested, these tests were enormously expensive, and tested only small scramjets operating for a few seconds. Given that high speed flight has been around even longer than orbital space travel, this does not encourage much confidence in flying to orbit as a practical technology. The Atlantic author sort of glides past that issue, but while you can glide back from orbit you have to get up there under power.

If my remarks here seem to contradict things I have said previously on this blog, it is because my feelings on the subject are in fact contradictory. A reusable two-stage orbital vehicle is, I would guess, technically viable. Perhaps, on a smaller scale, a three-stage vehicle with the first stage (or 'zeroth') stage based on jet transport technology.

But it is by no means clear that such a vehicle, if built, would make orbital spaceflight dramatically cheaper than the way we get there now. Or perhaps even cheaper at all. The problem is that any such reusable orbiter must have added weights and complexity in order to return for re-use, thus a reduced payload relative to its overall size, cost, and complexity. The savings from re-use may not be enough. Almost certainly they are not enough at the current tempo of space missions.

This is where I am supposed to neatly wrap things up and tie them in a bow. But since my views are complex and contradictory, I can only throw the question out for further discussion.


So discuss.




The image of a moonrise above Arizona saguaro comes, as so often, from Astronomy Picture Of the Day.

And a bit more honest plugola: Pending my setting up a proper permanent sidebar link, etc., a few more posts of mine are up at IBM Infoboom:

Business Analytics: Avoiding Too Much Information
The Open Virtualization Alliance: Virtual Storage Goes Open Source
LinkedIn IPO Sizzles: Business Social Media Are Cooking
Click love is very much appreciated!

93 comments:

Anonymous said...

(SA Phil)

From that other recent thread - I Like the Zeroth Stage Aircraft Concept.

I imagine a super-lifter with about 500,000 pounds of "cargo" capacity.

In good old 50's sci-fi style I would use a Nuclear/Electric power plant with impellers/props designed to reach high altitude.

Thucydides said...

Or you can go JP aerospace and do it with huge airships. Frankly, while I find things with moving parts endlessly fascinating (Stirling engines and opposed piston engines are particular favorites of mine), the rational part of my brain recognizes that things with the fewest moving parts are inherently cheaper and more reliable.

Laser thermal launchers are in that category, since everything is literally done with mirrors (some of the more complex Liek Myrabo "lightcraft" ideas excepted), and of all the ideas out there this seems to be the most scalable and cost effective. If the laser is ablating material stuck to the spacecraft itself, then the idea can be done anywhere in the solar system so long as there is a launch laser available.

This means launching to LEO, accelerating to the Moon, decelerating into lunar orbit and landing and launching back to Earth *could* be done without expending any propellant at all, or needing an on board power supply or energy source beyond what is needed for attitude adjustment and keeping the cargo and passengers in one piece. Getting the laser and associated sensors, tracking equipment and mirrors to the Moon is an interesting exercise.

Aaron Lee said...

I suppose on a very superficial level, spaceship one provided an inital flight+rocket TSTO in the same way that guy with wings on his back jumping off a castle tower provided a foundation for aerodynamic flight.

I honestly put my marbles on spaceX trying reusable craft in a serious way if their henry ford economy of mass production thing pulls through via falcon heavy lifts. Then again maybe non-sequitur.

Also I'ce just sort of noticed, but pver time it seems you've generally gone from high-minded fundamentals (manned fighter versus giant laser, fighter looses) to tackling specific modern issues (how to make orbit on a working class budget.) Right fine transition. Good go keeping it fresh.

Tony said...

I look at this as primarily an economics question. And, in pure economic terms, all market participants are being satisfied. The people with valid space applications can generate the cash flow to pay for space access, and the people who can provide space access make enough money to stay in business. The demand for space access would have to change radically for any of the megastructural launch solutions to be impemented. Where that demand is going to come from is not at all clear, highly speculative, and often relies on special pleading of the "if you build it, they will come" type.

But the real question is: come for what? What in spce is going to actually generate that demand? There's plenty of stuff in space for people living in space. But there's very little there worth the cost to people on Earth, even at space access prices reduced by an order of magnitude per kg of payload.

Byron said...

I think that reusability is a bad solution at the moment. Stuff should only be reusable if it's coming back anyway. A crew capsule, similar to the HL-20? Yes. It has to come back. A first stage? Maybe. It's coming back down, but I don't know how much of a penalty reusability will be. The upper stage? Not a chance. Bringing it back down in one piece is going to be really hard, and the mass and cost penalties won't be worth it. Most of it's just metal, anyway. If you could separate the engines from everything else and bring them back, that might work, but given our experience with the SSME's that might not be economical either.

Anonymous said...

(SA Phil)

Wouldnt the preferable long Space Industry system involve only putting people in space?

Everything else would be produced off planet.

Even if you had some product you wanted to bring back to earth you would ideally use a landing system manufactred in Space.

Tony said...

SA Phil:

"Wouldnt the preferable long Space Industry system involve only putting people in space?

Everything else would be produced off planet.

Even if you had some product you wanted to bring back to earth you would ideally use a landing system manufactred in Space."


But one has to answer the question: why put people in space in the first place? The only answers that have stood up to rational scrutiny have been scientific exploration (which we're already doing) and distribution of the human genome for long term species survival (which is a project so altruistic that even if it passes conceptual muster is probably too impractical to be undertaken).

Anonymous said...

(SA Phil)

Its easier to answer that for the "far future" than the near or "mid-future".

Far future its easy, because it is something to do.

Almost all our technical challenges would have been met and its just the next place to go.

----------
Mid future you would need a situation where you can make something better (cheaper, at all, w/e) in space than you can on Earth.

Once you are in Space already your increased presense there could snowball into a driver to want an even larger presense and so on.

Tony said...

SA Phil:

"Far future its easy, because it is something to do.

Almost all our technical challenges would have been met and its just the next place to go."


Except for adventurers, it still has to have a practical utility, or nobody will pay. That's a dynamic that's valid as far into the future as you care to look. And we may never solve all or even most of our technical problems. It is well within the realm of possibility that we're already experiencing the last great surge in learning fundamental knowledge.

"Mid future you would need a situation where you can make something better (cheaper, at all, w/e) in space than you can on Earth."

See above. economics doesn't stop working just because you're beyond some arbitrary point in the future.

"Once you are in Space already your increased presense there could snowball into a driver to want an even larger presense and so on."

But the question is: why be in space with people to begin with? One has to answer that before one can speculate about snowballs and mcguffinites.

David said...

How about using an inductrack for acceleration for a two stage ship. The first stage is an airbreather/hybrid rocket, the second stage is your payload insertion stage. The first stage is recoverable, landing jst like a conventional aircraft. The payload insertion hardware is expendable. Maybe even use an off the shelf Centaur upperstage? With current technology, the inductrack is fairly easy to build and just need to get the rocket up to 500 mph, then the hybrid rocket has to just get up to Mach 5 then switch to full rocket mode. The upper stage then handles the delta v for orbital insertion.

It seems to me though that the biggest problem is overcoming the "Why are we doing this?" People in general, as I have stated in the past, are really caught in the "looking down" or "looking inward". The stars are too far away for people to care about. Our world is so caught up in our tribalism and unwilling to embrace the need to look into the deep black.

Gene Cernan, the last man on the moon, is getting a reputation for being a bit of a curmdgeon, because we haven't been back to the moon since 1972. We have lost our way. I come from a state where almost a thrid of our 3rd graders cannot pass the minimum skills tests in reading and math. We have 40 percent of our high schoolers dropping out. But they know who won American Idol. Our priorities are skewed. Instead of building ourselves up, we are tearing ourselves down.

50 years ago, men and women of vision pointed at our satillite, and said we can go there, and come back. They invented our world, with slide rules, mechanical pencils,and graph paper. People forget just how big a change it all was. We stand on the shoulders of giants, but we are handicapped by our myopea.

Anonymous said...

Tony,

See above. economics doesn't stop working just because you're beyond some arbitrary point in the future.

=====
Don't they?

What happens when you reach a point that you have enough excess wealth that you can pay for it with pocket change.

Energy = Wealth basically.

Technology can change the Energy dynamic.

(SA Phil)

Tony said...

David:

"It seems to me though that the biggest problem is overcoming the "Why are we doing this?" People in general, as I have stated in the past, are really caught in the "looking down" or "looking inward". The stars are too far away for people to care about. Our world is so caught up in our tribalism and unwilling to embrace the need to look into the deep black."

There is no need, and there really is no introversion. Space is either boring, boring, boring, because it's something for communication company nerds to worry about, or it's out there beyond almost everyobdy's lifespan, so why worry about it? We went, we saw, and we found out there really wasn't that much to it except massive expense and little return beyond basic knowledge.

"Gene Cernan, the last man on the moon, is getting a reputation for being a bit of a curmdgeon, because we haven't been back to the moon since 1972. We have lost our way. I come from a state where almost a thrid of our 3rd graders cannot pass the minimum skills tests in reading and math. We have 40 percent of our high schoolers dropping out. But they know who won American Idol. Our priorities are skewed. Instead of building ourselves up, we are tearing ourselves down."

I've met Gene Cernan. (Which isn't saying much, because a lot of people have.) He struck me as more interested in manned spaceflight for philosophical reasons than for practical ones. Well, we're past philosophy being a part of spaceflight policy. We were long past it in 1972, when Cernan was on the Moon. It's got to have practical utility, or it's not of any real interest, no matter how well or poorly our kids are educated.

"50 years ago, men and women of vision pointed at our satillite, and said we can go there, and come back. They invented our world, with slide rules, mechanical pencils,and graph paper. People forget just how big a change it all was. We stand on the shoulders of giants, but we are handicapped by our myopea."

Mostly men, during the Apollo program. And the idea that they invented our world is a fable. It was a government program, and all of the hardware was built by established aviation contractors who used mostly off the shelf technologies, plus technologies developed for Cold War military programs. That includes computers, phenolics for heat shields, various other materials like Inconel. Even Tang wasn't invented for the astronauts -- it's just soemthing they liked to put in their drinking water.

And there was no visions involved. It was a simple matter of asking the question: what can we do that we can beat the Soviets at, and how long do we think it will take to do it. The answer were: land on the Moon, and before 1970. To the men who did it, it was an engineering challenge, not a grand adventure. They were way too busy for it to be anything else.

Tony said...

SA Phil:

"Don't they?

What happens when you reach a point that you have enough excess wealth that you can pay for it with pocket change.

Energy = Wealth basically.

Technology can change the Energy dynamic."


Special pleading -- technology may improve our energy future to the point of unprecedented levels of surplus. That's not the same thing as "can" or "will".

And if we've got all that surplus energy, there's no compelling existential reason to mess around in space. Everybody already has everything they need, while space is still expensive -- even if relatively less so -- dangerous, and uncomfortable. So why would anybody go, except for purposes of adventure or exploration?

Anonymous said...

Tony,

Special pleading -- technology may improve our energy future to the point of unprecedented levels of surplus. That's not the same thing as "can" or "will".

------------

I dont think it is special pleading. Its the basic assumption most futurists use when they look towards long term technological advancement.

We only use a small fraction fo the energy availible to us. When that changes, a lot of other things will change as a result.

(SA Phil)

Tony said...

SA Phil:

"I dont think it is special pleading. Its the basic assumption most futurists use when they look towards long term technological advancement.

We only use a small fraction fo the energy availible to us. When that changes, a lot of other things will change as a result."


It is certainly special pleading to invoke an energy-rich future as inevitable. You are relying on a favored condition without introducing evidence that it will ever exist. A non-special pleading statement would start with "if", not "when".

WRT futurists and futurism in general, one can't throw a dart into any page of any of their books or articles without hitting a special pleading -- I'm looking squarely at you Bob Zubrin, Marshall Savage, and Eric Drexler.

David said...

Tony, I will conceed that your view is technically correct. I will even go so far as to assign my comments as more of an emotional pleading.

I do have a question though. What is your solution to the question of "why"? We aren't going to go for any material reason, we aren't going to go to save the species, then what is our motivation? What would make it worthwile? Where is the vision, what will drive us out there?

Please understand, I just need to see where you are at in all of this. My motivation is preservation, I believe that this is the test that the dinosaurs never had the opportunity to take. This is the chance to make sure our species isn't taken out by an extinction level event. Space travel is just another phase in our evolution. We swung from branches, walked in savannahs, sailed on the seas, and flew through the air. Now we will cross those voids, and walk on distant worlds.

Or not?

Anonymous said...

=Milo=



Tony:

"So why would anybody go, except for purposes of adventure or exploration?"

I'll be very happy with a future that has affordable (non-robotic) adventure and exploration.

Towns may or may not spring up to support the researchers locally. If their infrastructure progresses enough, they can become sustainable habitats even after the scientists get bored.



David:

"I believe that this is the test that the dinosaurs never had the opportunity to take."

We have already surpassed the dinosaurs long, long ago, when we invented this thing called "language". Our ancestors also already managed to survive the meteor impact that did them in, if you'll recall.

Anonymous said...

So...no economic motivations? Then increase the scientific presence. Build research bases around the solar system, build a little fleet of resuply/recrew spacecraft to support those bases. Like I've said before, model it on the Antarctic research bases and their system of resupply. It may not be as dramatic as rocketpunk, but it may be all that we can muster for the time being. The longer we're out there, the more likely it is that permanant colonies will form...I wish that they will form before the 22nd century, but I doubt it.

Ferrell

Anonymous said...

(SA Phil)

Okay Mr arbiter of the future .. how do you see our energy future?

Do you suggest we can continue to thrive as a species on the thimbleful we now harness?

Anonymous said...

=Milo=



SA Phil:

What we want is irrelevant. If we need more energy for our civilization to prosper but significantly better energy technology than we already have is scientifically impossible, then it sucks to be us. If energy technology significantly better than we already have is scientifically plausible, then we will eventually develop it, regardless of whether it's a necessity or just a convenience.

Anonymous said...

Milo,

What we want is irrelevant. If we need more energy for our civilization to prosper but significantly better energy technology than we already have is scientifically impossible ...

=======
But it isn't. We just don't want to pay for it.

The sun bombards the earth with something like millions of times the energy we actually use every year (I forget the exact figure)

There is no reason to suspect we wont be able to harness far more energy than we can today.

And there is of course a lot more energy available in space, the Earth isn't very big compared to the scale of the Solar System

(SA Phil)

Anonymous said...

=Milo=


Short of building a Dyson sphere, there is not that much more energy in space. Earth has the single largest cross-section of any piece of celestial real estate, and most other rocks are pretty far away from the sun. Covering every available surface in the solar system with solar panels will give us less than an order of magnitude more power than covering every available surface on Earth. And don't forget all the energy it takes to get there in the first place.

The one MacGuffinite that might make a difference energy-wise is gas giant helium-3, and now we're not talking about solar power anymore.

Anyway, I wasn't saying that we won't, more than likely, have more energy in the future. However it isn't a guarantee, and I was saying that your rationale ("Do you suggest we can continue to thrive as a species on the thimbleful we now harness?") was stupid.

Thucydides said...

In my pessimistic moments, I can picture some radical breakthrough solid state technology that would allow mankind to capture a large fraction of the solar energy, making everyone fat and happy with no reason or desire to leave Earth. (The total solar energy budget of the Earth is 174 Petawatts, which is a lot of freaking power). Be careful what you wish for.

Religious or ideological motivations may be dampened at the moment, but there is no real reason to suppose this will always be the case (or will be the case for non western powers which go into space). Vast sums of money and resources were raised to send colonies to the New World in search of gold; only the Spanish really succeeded at the cost of wild monetary inflation and eventual military overstreach and exhaustion. Spain had become a decidedly third rate power by the time of the Seven years war.

The French failed mostly because they tried to retain an essentially feudal social organization in New France and were unable to take full advantage of the opportunities, while other powers like the Netherlands didn't commit enough resources to expand. Only England had the combination of resources, talent and a social model which rewarded hard work and initiative to rapidly expand and thrive.

So the motivation may be something other than what we would consider rational, and even economic models might be temporarily bypassed as resources are poured in to achieve the Transcendent goal. Such people would suitably reword "Jerusalem" as their anthem:

Jerusalem
William Blake

And did those feet in ancient time,
Walk upon England's mountains green:
And was the holy Lamb of God,
On England's pleasant pastures seen!
And did the Countenance Divine,
Shine forth upon our clouded hills?
And was Jerusalem builded here,
Among these dark Satanic Mills?

Bring me my Bow of burning gold;
Bring me my Arrows of desire:
Bring me my Spear: O clouds unfold:
Bring me my Chariot of fire!
I will not cease from Mental Fight,
Nor Shall my sword sleep in my hand:
Till we have built Jerusalem,
In England's green & pleasant Land.

Go forth and build Jerusalem!

Rick said...

I'll add a link to a piece I wrote here a couple of years ago, for those who haven't yet stumbled across it: A Solar System For This Century.

It still pretty much sums up what I expect in the PMF, as distinct from demi-operatic settings more suited to, well, space opera.

Geoffrey S H said...

"Everybody already has everything they need."

"There is always something more to be had- and I'm saying that without any reference to whether colonies are possible or not. Even the most privelidged member of society goes without something a poorer member from the future might have.
WRT futurists and futurism in general, one can't throw a dart into any page of any of their books or articles without hitting a special pleading -- I'm looking squarely at you Bob Zubrin, Marshall Savage, and Eric Drexler."

Less space-concerned and more terrestrial based speculation sometimes is sort-of correct however.

Geoffrey S H said...

Huh? That was odd.

"Everybody already has everything they need."

There is always something more to be had- and I'm saying that without any reference to whether colonies are possible or not. Even the most privelidged member of society goes without something a poorer member from the future might have.


"WRT futurists and futurism in general, one can't throw a dart into any page of any of their books or articles without hitting a special pleading -- I'm looking squarely at you Bob Zubrin, Marshall Savage, and Eric Drexler."

Less space-concerned and more terrestrial based speculation sometimes is sort-of correct however.

Tony said...

David:

"Please understand, I just need to see where you are at in all of this. My motivation is preservation, I believe that this is the test that the dinosaurs never had the opportunity to take. This is the chance to make sure our species isn't taken out by an extinction level event. Space travel is just another phase in our evolution. We swung from branches, walked in savannahs, sailed on the seas, and flew through the air. Now we will cross those voids, and walk on distant worlds.

Or not?"


Where I am is that we have to be realistic about motivations and resources to match those motivations. Humans explore, but we don't always go and live where we have explored.

Antarctica has been mentioned. Well, I used to work with a guy who was a navigator on a USN C-130 that resupplied the South Pole station during the southern hemisphere summer. They ran that whole operation with four aircraft at realtively little cost to the US taxpayer. It was probably written off as a prestige expense.

People want to think space is like that, but it's not. It's incredbily expensive and it's going to remain that way. So it's going to be a major budget item, and require major budget item justifications. I really just don't see what is to be done, other than hope for a breakthrough in the cost of space access and otherwise just live with the reality that we have.

Tony said...

SA Phil:

"Okay Mr arbiter of the future .. how do you see our energy future?

Do you suggest we can continue to thrive as a species on the thimbleful we now harness?"


I'm not the arbiter of anything. I'm just advocating a realistic worldview. All I'm suggesting is that we may have to get by on what we've already got, because we may not find anything better in the real world, no matter what Promethean powers we imagine for ourselves in our daydreams.

Byron said...

Tony:
Do try to remember that most of us (myself included) didn't come here to be serious futurists. We came because we wanted more realism in our giant space battles. This is the core of the whole argument over economics.

Tony said...

Byron:

"Do try to remember that most of us (myself included) didn't come here to be serious futurists. We came because we wanted more realism in our giant space battles. This is the core of the whole argument over economics."

I do remember that. That's why when I bring up economics on space battles threads it's in the context of how it affects strategy and technology in general, not whether or not space battles can happen. For example, if you assume the consensus PMF toolkit, you can have space battles, but only in planetary orbital space and only between forces of Earth powers; no Mars Republic vs the UN.

But this thread is specifically about the economics of spaceflight in the real world. So that's the approach I'm taking, here, on this thread.

Anonymous said...

Tony,

no matter what Promethean powers we imagine for ourselves in our daydreams.

------------
Something will need to change in how we get Energy.

Thats a given. Oil/Coal/etc will not last forever.

Its seems reasonable to speculate the amount of energy availible per person will go up.

We wont need the divine intervention of a mythical greek titan.

Tony said...

SA Phil:

"Something will need to change in how we get Energy.

Thats a given. Oil/Coal/etc will not last forever.

Its seems reasonable to speculate the amount of energy availible per person will go up.

We wont need the divine intervention of a mythical greek titan."


It would be convenient for the continuation of civilization as we know it if the amount of energy per person went up. But it's not at all reasonable to speculate that it necessarily will. Once again you're engaging in special pleading by asserting that a desirable condition is the only possible one.

Anonymous said...

(SA Phil)

How is it not reasonable to speculate it will go up?

It certainly it is at a minimum just as reasonable as it would be to speculate it will go down.

Tony said...

SA Phil:

"How is it not reasonable to speculate it will go up?

It certainly it is at a minimum just as reasonable as it would be to speculate it will go down."


It's reasonable to speculate about what might happen if per capita energy generation increases. It's not reasonable to assert that such a thing will necessarily happen.

It's like playing poker with two aces in your hand. You can speculate to yourself about how your betting behavior will be modified if you draw a third ace. But just because you think you know what you would do, that doesn't mean you actually are going to draw that card.

Anonymous said...

(SA Phil)

.. all rightie then ..

So speculating that the enrgy per person goes up because of technology ..

And speculating that this energy availibility will translate into higher wealth (Rickover stated that, you rode around in his cruiser - so I assume I am okay speculating that)

As a result of this abudant wealth -- the affordability equation could change, thus making it more likely there will be more things in space.

If the danger aspect is the concern - that is off course avoidable, just dont send any people.

Tony said...

SA Phil:

"So speculating that the enrgy per person goes up because of technology ..

And speculating that this energy availibility will translate into higher wealth (Rickover stated that, you rode around in his cruiser - so I assume I am okay speculating that)

As a result of this abudant wealth -- the affordability equation could change, thus making it more likely there will be more things in space."


Stated that way, I would agree that that is entirely plausible.

But I still don't think that space will become particularly heavily populated anytime in the next several hundred years, because even with cheap space access, there won't be that much to do in space. Since we're predicating things on higher per capita energy, to the point of significant surplus, we're not going to go into the solar power satellite business. Presumably minerals aren't going to be in short supply either, so asteroid mining isn't going to take off. All that's left is scientific exploration and adventuring. That doesn't take a lot of people.

Anonymous said...

(SA Phil)

Yes possibly so - which is why I speculated on the far future for the big energy surplus.

Although I am hopeful this effort into renewable energies does improve our lot some in the near future.

And of course I am a big advocate of nuclear power -- but hysteria has won out on that one for now.

jollyreaper said...
This comment has been removed by the author.
jollyreaper said...

Putting aside scifi speculation and being realistic, I see two ways we're getting up there: national prestige project and tech falling to the point that quixotic billionaires can do it for the hell of it.

We got to the moon as a national prestige project aimed squarely at pissing in the Bear's eye. Because there was no further bonus seen, we gave up on it.

Potential McGuffinite hasn't panned out and I don't even know if the solar power sat argument still holds up. Even if it did, we could probably handle most construction from the ground via telepresence. We could have gigatons of hardware on orbit and only a minimal human staff. Hardly cities in space.

I think America's era of big ideas is over. The 2008 Olympics, that was totally a prestige project. Just look at that extravagantly over-produced opening ceremony. If China does build a moon base like they plan, it's a prestige project. And because of that, I have my doubts as to it being self-sustaining. Either they're going to half-ass it as a flag-planting mission that's less capable than our Antarctic base and they abandon it in a few years or they make a self-perpetuating Chinese colony a point of national pride and then maybe we'll get one.

If that doesn't work, all that's left is hoping the billionaires decide to make it happen. All is possible with playboys and unlimited cash.

Anonymous said...

(SA Phil)

Oddly - Star Trek First Contact had a bit of a physiological mcguffanite the world was wrecked in a nuclear war .. so they went into space to look towards something better.

(in a sense)

============

As to China .. I think they are the next big bubble that will burst.

Thucydides said...

Tony is correct about speculation. While it is reasonable to speculate about a positive outcome, it is equally reasonable to speculate about a negative outcome.

After all, there is no reason to suppose that post hydrocarbon futures could not be strangled through stifling of new technologies by regulations and taxes, choosing to invest resources in the "wrong" technologies or perhaps the failure of technologies being touted, or consumed by wars for the remaining resources. Then the future will resemble "The Road Warrior" rather than "2001", and Rocketpunk (and the Internet, for that matter) will be a fading memory.

To be blunt, most renewable or Green technologies are not viable except as niche providers, and the costs of adopting them on a large scale are horrendous (see Spain or Ontario for concrete examples of how adopting large scale Green energy have cratered the budgets and stifled economic growth). Nuclear energy seems destined to remain in the PR dustbin for now, and the only way I could see some changes is by "stealth" adoption of micro nuclear technologies like the proposed 40 MW Thorium salt reactors buried in out of the way places near industrial parks without any fanfare at all.

Steven Den Beste once wrote an essay about the need for replacement energy technologies to be massively scalable (being able to raise plants with outputs in the Megawatt to Gigawatt range) as being the only practical way to power modern economies; his choices were "core tap" (really deep geothermal wells), SPS, Nuclear Fusion and the direct conversion of matter to energy. Note he was rather sceptical or at least not very hopeful about the last three choices.

http://www.denbeste.nu/cd_log_entries/2002/09/Obscureenergysources.shtml

So while an energy rich future is something to be devoutly hoped for, the practical issues may be more than can be overcome. If I was to place a bet, I'd say the best payoff would come from tweaking everything to increase efficiency and reduce energy losses as much as possible in the short to mid term.

David said...

If we are deciding to be very real here, then we might just as well expect to break out our spikey leather outfits. Consider the following: 1. according to recent research, 1 in 6 children in the USA, are being diagnosed with some sort of developmental disability. 2. we have consistently graduated fewer technical professionals than are retiring. 3. We have more high school dropouts, who ae cumulatively less educated, then at any time previous to WW2

What does that leave us with? Less actual brain power to be dedicated to solving problems. Have you ever watched an episode of "How It's Made"? It is a fascinating show, describing how the simplest items from our day to day, are actually involved in extraordiarly complex processes. These processes require energy. Not just the type that comes from a wal outlet, but the intellectual prowess to build, maintain and develop the infrastructure to use it.

It seems to me that if we cannot answer the energy problem, the "Road Warrior" scenario would be the best possible case. The Amish would be considered "advanced" compared with what the "new reality" would be. We're looking at stone knives and bearskins, and a lot of death and disease.

H.G. Wells said it best in "The Shape of Things to Come", "...Either the stars, or nothing." Either we grow out of this, or we collapse. Maybe not all at once, but it will happen. We will stagnate, burn up our resources, and by the time we realize that we have depleated our coffers, it will be too late to do anything about it.

Damn shame really.

Anonymous said...

Thucydides said...

see Spain or Ontario for concrete examples of how adopting large scale Green energy have cratered the budgets and stifled economic growth

===============

The entire global solar industry was less than $100 billion last year. It is just not big enough to have bankrupted any large countries yet.

Spain's GDP >1 Trillion
Ontario's GDP >575 Billion

Whatever incentives they may have had might have been poor choices, but cratering their budgets? Stifled economic growth? Seems hyperbolic.

I'd venture it more likely the causes of their woes are the same causes as everyone else's woes in our current global economic climate.

(SA Phil)

Thucydides said...

In the specific case of Ontario, electricity prices have risen 150% to pay for such initiatives as MicroFIT, which obliges the utility to pay $.80 a KW/hr for solar electricity, while the wholesale rate is closer to $.08. Similar "incentives" apply to wind generating farms. The steep climb in electricity prices affects the manufacturing and retail sectors, while taxes rise to pay for this.

The Spanish situation is somewhat similar, diverting resources away from productive sectors of the economy, and by some estimates costing the economy 2.2 jobs for every "green" job created. Once the subsidies are lifted, the "green" job goes as well; net loss = 3.2 jobs, and the Spanish economy isn't strong enough to fill the void (after all, Spain is the largest of the PIIGS).

This is an example of resources getting invested in the "wrong" technologies. Wind and solar cannot scale without vast subsidies using current technologies, subsidies which taxpayers simply cannot afford and that crowd out alternatives which may be more appropriate.

Low cost and scalable ideas are needed instead. Since this is the Rocketpunk, I'll advocate for "Server Sky" http://server-sky.com/. This idea is low cost and scalable, and the energy generating capacity can build up in a linear fashion rather than waiting for large chunks of capability to be built i the form of traditional SPS units.

Thucydides said...

Next Big Future offers up another maglev launch proposal. The short track for launching cargo seems "doable", while the gen two system seems too good to be true in terms of technical ability and time line:

http://nextbigfuture.com/2011/05/startram-launch-system.html

Using the ISS itself as a spaceship is also discussed; this has more plausibility, but would require so much refitting that it would make more sense to just haul up ISS2 and strap the engines to that:

http://nextbigfuture.com/2011/05/using-iss-for-human-exploration-beyond.html

Anonymous said...

David wrote among other things:
"50 years ago, men and women of vision pointed at our satillite, and said we can go there, and come back. They invented our world, with slide rules, mechanical pencils,and graph paper."
65 years ago, public spending had just turned the USA into #1 and killed off the Depression. You had high taxes, the GI bill and higher education went mainstream.
From 65 to 40 years ago, you had a real average hourly wage that rose with productivity. Since then you've had rising profits and unemployment. The cost/benefit of academic achievement isn't what it used to be.
Now taxes are evil while cost-cutting, outsourcing and ROI are where it's at. So speculation is called investment and consequences are someone else's problem.
This situation was brought about by people who went through college and got good grades at many pointless tests, not by academic underachievers.

Note that cheap electronic gadjetry and software gets better every year in spite of the lack of slide rules and moral values. People can afford to waste money on that stuff. Medical technology has been advancing steadily as well. People will go to great extents to pay for that. But space? You need a surplus recognized as such to pay for that.

Tony wrote:
"distribution of the human genome for long term species survival (which is a project so altruistic that even if it passes conceptual muster is probably too impractical to be undertaken)."
Not that I disagree but after being subjected to sociobiology for so long it makes me smile to see the distribution of genes framed as altruistic.

-Horselover Fat

Tony said...

Re: Horselover Fat

The high taxes 65 years ago were instiuted to pay off a war debt incurred by voluntary subscription to government debt instruments. All high taxes today would pay off is massive overspending to buy votes. They may inevitably become necessary to pay off those debts, but let's not kid ourselves about the nobility of high taxes per se.

WRT sociobiology, interplanetary or interstellar distirbution of the human genome is a highly complex behavior. It has nothing to do with genetically linked behaviors that are used to illustrate the sociobiological argument.

Thucydides said...

One of the issues is the ability to get into orbit cheaply. While from a physics point of view this might be always be quite difficult (you have to accelerate the mass to orbital velocity, after all), from an economics POV this might become quite cheap in the near future (Really near future, like two to four years from now), given the sudden abundance of hydrocarbon energy that seems to have become available due to technical and economic advances.

http://www.salon.com/news/politics/war_room/2011/05/31/linbd_fossil_fuels/index.html

http://pajamasmedia.com/tatler/2011/06/04/arabian-alchemy-shell-makes-black-gold-in-qatar/?print=1

Cheap hydrocarbons are not a direct driver (fuel for spacecraft is a very small component of the cost of launch anyway), but cheap energy powers a rapidly growing economy, which will have the extra wealth to indulge in space travel and devote resources to alternative approaches that *could* drive down costs and drive up demand in a positive feedback loop.

Of course the grown ups also need to use the new wealth to pay down past debts and deal with current issues like infrastructure, but even after these issues are being taken care of, new wealth should still be available for space.

Anonymous said...

(SA Phil)

So back on the Nuclear Spaceplane Idea, I have been doing a little thinking.

Ideally you need a lightweight reactor that runs very hot. I am envisioning a sort of closed cycle/ Nuclear Flashlight system.

The reactor uses plutonium to take advantage of the lower critical mass requirements. The Reactor would be built of tungsten, Carbon/Graphite and Quartz, "Liquid" core essentially.

It would be shaped like a roll of papertowels with the "cardboard" being the quartz containment vessel and the "paper" being a honeycomb radiator of carbon.

The inner core could be "cooled" with Helium but as much of the cooling as possible would be done by air-cooling the radiator.

This allows me to heat large quantities of air without irradiating it. This heated air would be my reaction mass. Basically a nuke thermal Ram/Scramjet.

Thus the spaceplane takes off at a shallow angle, going against the planet's rotation, Maximizing travel time where I can use the atmosphere as reaction mass. As the air become rarified you would pump in another reaction mass (hydrogen, helium, nitrogen, something) and use that to finish the ascent.

The advantage over chemical rockets comes in by utilizing reaction mass that you dont have to carry with you. Which also helps during landings. And your fuel would last months/years.

Thucydides said...

You will need some way to get started, since any sort of ramjet has zero thrust at zero velocity.

As well, I don't think many people will be very keen on nuclear lightbulbs in the atmosphere for lots of reasons (some of which were brought up in previous posts). Even in the real world, Nuclear lightbulbs were eventually dropped due to issues like the fragile nature of the quartz containment vessel (including the changing optical properties as the temperature changed and the issue of the quartz crazing or cracking at high temperatures).

Frankly, megastructures and mega engineering projects like Lofstrom loops have a better chance of getting funding and acceptance than nuclear fission engines of any sort in the atmosphere.

Anonymous said...

(SA Phil)

To get it started you could use the same propellant type you use for the final push to orbit.

===================
I don't think there really was much development work done on nuclear flashlights -- I think instead solid core rockets had some work on them and then interest in Nuclear Thermal Rockets waned with general interest in Nuclear Power.

I think the flashlights were just on the concept drawing board stage, so I am unsure how people would find actual weaknesses in the design.

Of course there is no end to supposed "engineers" who make decisions on feasibility with very little math or data involved. So I suppose it is possible people judged the designs even at that embryonic stage.

I think it helps to remember that the current hysteria regarding Nuclear Fission is not actually based on scientific or engineering realities.

Thucydides said...

Nuclear light bulb R&D from the 1960's:

http://atomicrockets.posterous.com/nuclear-lightbulb-part-3

Nuclear Lightbulb, Part 3
To continue…

Even with the neon buffer layer, a simple glass wall would not be sufficient to withstand the harsh environment. As well as simply being in contact with 2000 R neon gas, the transparent wall would also have a vast sleet of radiation passing through it… infra-red, gamma rays, neutrons, the whole spectrum. Once again there was the problem that no transparent material would possibly be able to survive the environment. Even the most optically transparent material will absorb some of the radiation passing through it… and this absorbed energy will be converted directly to heat. It would not take very long at all for the clearest substance to get incredibly hot… which, of course, was the goal with the hydrogen propellant. What was desired for the propellant was manifestly not desired for the structure.

So the transparent walls were to be made not out of monolithic sheets, but thin-walled tubes. High-purity fused silica was the baselined material of choice. Thought was given to single-crystal beryllium oxide and synthetic quartz as materials, as they had better transparency in the ultraviolet, but production of the required tubes using these materials was undemonstrated. To cool the tubes, hydrogen gas would be pumped through.

The cylindrical walls were built in three 120-degree radial segments. At the end of each segment was a manifold for injection or extraction of the hydrogen coolant, so the hydrogen did not travel very far around the circumference of the cylinder. This assured that the hydrogen did not have time to heat up to much, and that the silica glass would be maintained at a reasonably constant temperature of between 800 and 1100 Celcius (yes, the reports have units all over the place). Corning Type 7940 and General Electric Type 151 fused silicas typically had a purity of SiO2 of 99.997 percent, with Al2O3 being the primary impurity. Purity was essential… the greater the purity, the greater the transparency.

Since this was the late 1960’s, United Aircraft actually ran a number of physical experiments to demonstrate the feasibility of their designs and materials, rather than a series of colorful computer simulations. As operating a uranium plasma reaction was somewhat beyond the scope and funding of their contract with NASA, they instead used a 1.2 megawatt RF induction heater to generate an argon plasma of about 15,000 R in a subscale “reactor.” The subscale test setup used both axial tubes (with wall thicknesses down to 0.005inches) and circumferential tubes potted into the manifold with RTV silicone.

——————–

In the tests, water rather than hydrogen was used as the coolant.

Test results were generally encouraging, but a number of issues were discovered. One of the more odd things that was noted in this and other testing was that the color of the glass tubes was a variable during the course of nuclear engine operation. Radiation damage to the glass would cause the glass to gradually become blue, then purple, then black. This is, of course, fatal to not only the functioning of the engine, but the survivability of the glass. Any amount of coloring would cause massive increase in radiation absorbtion, resulting in rapid overheating and structural failure. But over 800 Celcius, the glass would thermally anneal… which would wipe out the coloration and restore transparency. Thus the need to keep the glass operating at a minimum of 800 C. But above 1100 C, devitrification of the glass would occur… it would continue to be perfectly servicable clear glass, but once it began to cool down after engine shutdown the surface of the glass would turn milky white due to a myriad of microscopic surface cracks. This would cause the glass to overheat if the engine was restarted. And thus the need to make sure that the glass did not rise above 1100 C.

Anonymous said...

(SA Phil)

Ahh interesting

So basically they could neither make the actual reactor, nor replicate the desired containment vessel..

So they approximated both and the results were not what they had hoped for ...

A lot more work than I surmised, but not exactly proof the concept is unfeasible.

Thucydides said...

More like the desired containment vessel was unable to perform in the desired manner. Limiting the temperature to under 1100 degrees certainly sets an upper limit to the performance of the nuclear light bulb engine.

Anonymous said...

(SA Phil)

It did not look like the containment vessel was what they actually wanted .. So I don't see how it follows it was the desired one.

More like it was the one they were able to build at the time.

How hot do the solid NTRs run?

Thucydides said...

The containment vessel was wat was possible using the laws of physics. The optical qualities of several materials was considered, and the one material which also had the required mechanical properties was chosen. Everything else is (as it were) history.

The only way a Nuclear Light Bulb can exceed the performance of a conventional NTR (Which is usually core limited to under 2000 degrees before melting) is if the reaction mass can efficiently couple with the energetic radiation pouring out of the light bulb, particularly the in the UV spectrum. I am not clear if Hydrogen couples well with UV radiation, but perhaps someone can comment.

If you go to the link, you will see there was a lot of detailed work on nuclear light bulbs, most of which makes me feel this is a case where the practical issues outweigh most of the benefits. Each of the quartz light bulbs contained a uranium plasma at @500 atmospheres, required a hurricane force Neon coolent flow to keep the plasma rotating in the vortex and had to be strictly temperature limited, if fueled by UF6, had Fluorine gas circulating at a temperature approaching 1000 degrees...

At this point it would probably be much simpler to look towards unconventional Fusion reactors such as MTF, Dense Plasma, IEC and so on to find a compact, high performance nuclear engine.

Anonymous said...

Blogger Thucydides said...

The containment vessel was wat was possible using the laws of physics. The optical qualities of several materials was considered, and the one material which also had the required mechanical properties was chosen. Everything else is (as it were) history.
=====================

You are editorializing here. It was instead an approximated "laws of physics"


(SA Phil)

Anonymous said...

(SA Phil)

Basically in your quoted text they used thin synthetic quartz cooled by hydrogen which could not withstand the temperature

The concept is to use quartz that can withstand the temperature.

Thus it is an approximation.

It is entirely possible that the manufacture of a viable quartz containment vessel is not feasible using year 2200 tech much like it was not using 1960's tech.

But that wasn't what the text said. It instead highlighted the issues inherent with the synthetic quartz system they did use.

(SA Phil)

Tony said...

Quartz melts at ~1700 C. That's significantly higher than the 1500 C usually quoted as the high end for steel. But the operating temperatures for actual rockets are much higher. Kerosene burning in oxygen, for example, combusts at more than 3300 C. According to various sources on the net, NERVA type engines were expected to run at remass temperatures of as much as 3000 C. So the effectiveness of the cooling system is the real question. While fused natural quarts might have been marginally better than fused silica in basic material properties, it wouldn't be significantly so. I think the nuclear lightbulb experiments with fused silica hardware were sufficient to demonstrate that there were too many hassles, particularly a requirement for too fine a control of hardware temperature.

Rick said...

Chemfuel rocket engines use propellant flow as coolant, but therein lies the rub - the propellant flow is what we are trying to reduce.

Tony said...

Rick:

"Chemfuel rocket engines use propellant flow as coolant, but therein lies the rub - the propellant flow is what we are trying to reduce."

All nuclear designs that I an aware of use remass flow for regenerative cooling. The nuclear light bulb was different in that the propellant heating and engine cooling are combined into a single step.

Thucydides said...

It occurs to me there is a way of having a fusion "Nuclear Light Bulb".

Most proposals for aneutronic fusion have a sticking point of excess bremsstrahlung losses. If the containment vessel is reasonably transparent to bremsstrahlung radiation then the remass can flow past the vessel and absorb the radiation.

This requires a vessel that is strong enough to contain a high quality vacuum for the reaction to take place, transparent to hard x-ray radiation and able to resist erosion of the remass flow. the remass needs to couple well with the x-ray radiation as well. Still quite the set of requirments...

Tony said...

Bremsstrahlung radiation quenches the reaction, making it useless as a heat source over any practical length of time.

Rick said...

All nuclear designs that I an aware of use remass flow for regenerative cooling.

Nuke thermal, at any rate. Nuclear electric is an entirely different beast. Or really, two separate beasts - an electric thruster doesn't care what its power source is, and a power reactor doesn't care where the juice is going.

Tony said...

Rick:

"Nuke thermal, at any rate. Nuclear electric is an entirely different beast. Or really, two separate beasts - an electric thruster doesn't care what its power source is, and a power reactor doesn't care where the juice is going."

The other way to look at that is that the actual rocket in a nuclear-electric setup isn't nuclear at all, and thus outside of the scope of the conversation.

Rick said...

True that nuclear engines, in a strict sense, imply nuke thermal.

In principle you can have a high end fission engine with magnetic containment - thus an electric drive with an internal energy source. I think mini-mag Orion fits this bill. Where it falls on the practical scale I don't know, but I assume there are ... challenges.

Tony said...

Rick:

"In principle you can have a high end fission engine with magnetic containment - thus an electric drive with an internal energy source. I think mini-mag Orion fits this bill. Where it falls on the practical scale I don't know, but I assume there are ... challenges."

A fission fragment rocket would inherrently be an electric rocket. The prolems with mini-mag Orion are the same problems that all inertial confine ment fusion have, slightly relaxed by no inherrent requirement to generate a self-sustaining amount of electrical power. (The whole point is to get thrust, even if you have to have a supplementary power reactor to do it.)

Anonymous said...

As an interplanetary propulsion engine, fission-fragment does have some good points; compact, very high energy density, long duration, very high ISP, and you can use it to generate electricity;on the down side, it has a radioactive exhast and is hard to throtle. Oh, that and some people freak out even when you just say it's name...:}

Ferrell

Anonymous said...

=Milo=



Ferrell:

"very high ISP"

Exactly, that's the problem. It has way more than you need, and not enough thrust to actually make use of it.

You would need to augment the fission-fragment exhaust with extra propellant, driving up thrust and down exhaust velocity, to have an engine that's useful for anything short of (still really slow, but slightly less so) interstellar travel.

Rick said...

This is generally true of very high-end nuclear drives, including fusion.

Thucydides said...

Several odd ball ideas for getting into orbit exist, including air to air refueling of the rocketplane (Blackhorse) and a rather incredible idea of playing "crack the whip" with a tow cable from a large transport aircraft to the small orbital vehicle being towed behind.

While I would not want to be the pilot or passenger on a vehicle being swung at supersonic speeds on the end of a tow cable, Blackhorse does have the merit of being based on known and current technology; the only thing different between Blackhorse and refueling an F-16 is you would be pumping H2O2 oxidizer into the receiving craft rather than fuel, so your rocketplane does not have to carry the weight of the oxidizer from liftoff to orbit.

Tony said...

WRT high Isp vs high impulse, I think people are getting all wrapped up in what a single engine can do, rather than taking the problem piecewise like aerospace engineers do. A standard two stage launch vehicle, for example, has a first stage optimized for high impulse but relatively low efficiency, so that it can get the rest of the stack above the sensible atmosphere. The second stage is lower impulse but relatively high efficiency, and does all of the work to get the payload up to orbital velocity.

For a high Isp electric drive, one doesn't need to have a gearbox like VASIMR. One might just use a chemical kick stage to raise the interplanetary craft's apogee, then a series of perigee maneuvers to achieve escape in an acceptable short amount of time.

Anonymous said...

=Milo=



Yes, but an engine with overly high exhaust velocity and overly low thrust will be ineffective at both stages. Sure, different roles require different thrust/exhaust balances, but the 10000 km/s exhaust velocity quoted for fission-fragment rockets is overkill for practically any application (short of a torch, which the fission-fragment rocket isn't). To make use of 10000 km/s you pretty much need a 1 gee brachistochrone trip to the outer solar system!

Tony said...

Milo:

"Yes, but an engine with overly high exhaust velocity and overly low thrust will be ineffective at both stages. Sure, different roles require different thrust/exhaust balances, but the 10000 km/s exhaust velocity quoted for fission-fragment rockets is overkill for practically any application (short of a torch, which the fission-fragment rocket isn't). To make use of 10000 km/s you pretty much need a 1 gee brachistochrone trip to the outer solar system!"

I'm not seeing your point. Or maybe I should say i am seeing it, but see the "problem" as a feature, not a bug. Much like ion engines -- in fact just like them, because a fission fragment rocket is a species of ion thruster -- the figure of merit is not how much thrust a single unit delivers, but how many units can be reasonably run in parallel, and how much thrust that gives. For solar or nuclear electric, the limiting factor is how much does the power plant mass. The thrusters themselves are a constant mass per Newton of thrust. For fission fragment rockets, the thrusters are also constant mass per Newton of thrust (or should be, within a fairly tight range). But they have no external power plant beyond the marginal amount needed for control and spinning the fuel plates.

Thucydides said...

High ISP is desired for "fuel economy", since the amount of remass you need to carry with you (and accelerate and decelerate during the voyage) is minimized.

Even doubling the effective ISP from a chemical rocket (ISP @ 400 using H2 and O2) and a NERVA rocket (proven ISP in ground tests @ 800 seconds) makes a dramatic difference in the amount of cargo you can carry in the same sized spacecraft, since you have pretty much halved the amount of remass needed. Even higher ISPs just carry the equation farther, all else being equal.

All else isn't equal, alas. Pushing NERVA to an ISP of 1200 seconds is possible in theory, but requires materials capable of operating in a much higher temperature environment, and probably much more mass.

Theoretical fusion drives with ISP's of 1,000,000 seconds require magnetic nozzels, radiators and probably a high degree of sheilding against neutron radiation (if using "conventionsl" fusion) or some magitech means of running athermal plasmas and supressing bremsstrahlung radiation if you want aneutronic fusion.

Still, the use of high ISP drives allows you to carry much more stuff both as an absolute measure and as a fraction of your total mass sent to the target.

Anonymous said...

=Milo=



Tony:

"Much like ion engines -- in fact just like them, because a fission fragment rocket is a species of ion thruster -- the figure of merit is not how much thrust a single unit delivers, but how many units can be reasonably run in parallel, and how much thrust that gives."

Well, yeah. The important factor for an engine type (rather than a specific engine installed on a specific ship) is thrust-per-weight, not plain thrust. The same principle still applies.

All I'm saying is fission-fragment rockets have a thrust-to-weight ratio too low for most applications. Show me evidence to the contrary and I'll back down. But everything I've read about them says that fission-fragment rockets have very low thrust-to-weight.



Thucydides:

"Even doubling the effective ISP from a chemical rocket"

Yes, doubling the exhaust velocity of a chemical rocket is very useful. That's because there's an optimum range of exhaust velocities (with the exact value depending on your intended application and how much acceleration you're capable of), with chemical engines being rather on the side of "too low", and unseeded fission-fragment engines being far on the side of "too high".

Tony said...

Milo:

"Well, yeah. The important factor for an engine type (rather than a specific engine installed on a specific ship) is thrust-per-weight, not plain thrust. The same principle still applies.

All I'm saying is fission-fragment rockets have a thrust-to-weight ratio too low for most applications. Show me evidence to the contrary and I'll back down. But everything I've read about them says that fission-fragment rockets have very low thrust-to-weight."


There's no evidence to the contrary, because nobody's ever built a flight qualified example and actually tested its performance. But all electric rockets are very low thrust, so in the case of any of them, usefulness is determined by vehicle configuration and mission architecture. If you put enough of them together, and if their weight plus the weight of any necessary power supply is not too much, then they can provide useful amounts of thrust. In principle it's the same thing as chemical rockets or nuclear-thermal, with electrical power supply mass replacing propellant mass as a critical factor.

Anonymous said...

Milo, think of chemical rockets as sprinters and electric rockets as marathoners. Chemical rockets want to expend all their propellant as quickly and violently (but controlled) as possible; electric rockets want to throw their propellant as fast and miserly as possible. The faster the exhast, the better the 'fuel milage' of the rocket is.

Ferrell

Anonymous said...

=Milo=



Ferrell:

"Milo, think of chemical rockets as sprinters and electric rockets as marathoners."

Isn't that exactly what I've been saying?

Chemical rockets are better over short distances (like Earth-Luna or between gas giant moons), electric rockets are better over long distances (interplanetary).

Rick said...

For a high Isp electric drive, one doesn't need to have a gearbox like VASIMR.

No, but at least in principle - and perhaps even in practice - a gearbox is not that hard to do.

I think Milo's point is that really high Isp - corresponding to exhaust velocities in the thousands of km/s - are poorly suited to interplanetary mission profiles. For these, within Realistic[TM] constraints, we want exhaust velocities in the range of about 30-300 km/s.

Tony said...

One has to ballance gearing vs staging. Gearing requires extra mass and complexity in a motor you can't dump overboard after the high gear has served its purpose. Staging can be done with a combination of very simple, high impulse kick motors and relatively simple (compared to a geared motor, like VASIMR) low impulse electric motors. It's not too hard to imagine -- especially since ion thrusters are flight demonstrated and VASIMR isn't -- that an operational advantage might be perceived in staging, at least for a while.

Thucydides said...

I don't see anything wrong or wrong headed about using high ISP drives in interplanetary space.

To quote a theoretical example, a hypothetical single stage ship mounting a "Polywell" fusion drive with an ISP in the million second range could travel from Earth to Mars in just 33 days with a 15-20% payload fraction.

Earth to Saturn would take two months (including a short coasting phase) and have a 14% payload fraction.

These examples were calculated by the late Dr Brussard as examples of the potential of the Polywell fusion concept. Now Polywell might not work, but any fusion drive capable of producing an exhaust beam with an ISP of 1,000,000 seconds will have very long legs in terms of getting around the Solar System.

Fusion drives of that sort might also have "gearing"; injecting streams of remass into the beam for higher thrust (but lower ISP).

Anonymous said...

=Milo=



Thucydides:

"To quote a theoretical example, a hypothetical single stage ship mounting a "Polywell" fusion drive with an ISP in the million second range could travel from Earth to Mars in just 33 days"

In order to build 10000 km/s delta-vee over the course of 33 days, you need an acceleration of 3.5 m/s/s, which is only slightly lower than the gravity of Mars. An engine which can produce Martian-level gravity for a month on end classifies as torch-level.

I realize that exhaust velocities and delta-vees are only equivalent if you have a mass ratio of e, but they'll at least fall within an order of magnitude of each other. If you have 60% payload/40% propellant, for example, then that cuts your delta-vee (and thus the needed acceleration for a trip of a constant length) only in half.

I didn't bother checking if your 10000 km/s, 33 day numbers are actually valid, because that doesn't matter. The point it that it is impossible for a 10000 km/s exhaust velocity rocket to be useful for anything short of years-long voyages, unless you have torch-level performance.


(And please, can we stop using the "specific impulse" measure and its annoying hidden 1 gee factor? There's no logic to even including that for rockets intended for outer-space usage rather than planetary take-off/landing on Earth.)


"Fusion drives of that sort might also have "gearing"; injecting streams of remass into the beam for higher thrust (but lower ISP)."

Yes please. That would actually make them useful.

I'd be happy with something that can do, oh, 300 km/s exhaust at 0.1 m/s/s ("centigee") acceleration.

Tony said...

Milo:

"And please, can we stop using the "specific impulse" measure and its annoying hidden 1 gee factor? There's no logic to even including that for rockets intended for outer-space usage rather than planetary take-off/landing on Earth."

Why? The pros use Isp all of the time, talking about anything from chemical solids to electrics. The g factor is just stuck in there so units can be cancelled out and the answer comes out as seconds of thrust per thrust equivalent weight of propellant. (Try saying that three times fast!) As long as you use the formula consistently, it's a constant of no engineering importance.

Rick said...

I have a bias in favor of exhaust velocity over Isp, precisely because it gives a direct comparison to ship delta v.

That said, the pros do use Isp, though it does not really play well with SI units, given that 'kg of thrust' or 'ton of thrust' seem to be nonstandard and deprecated. (Can you deprecate something never accepted in the first place?)

Tony said...

Rick:

"That said, the pros do use Isp, though it does not really play well with SI units, given that 'kg of thrust' or 'ton of thrust' seem to be nonstandard and deprecated. (Can you deprecate something never accepted in the first place?)"

They use Newtons for thrust in SI, with a slightly modified formula to make it come out in seconds. Specifically, Newtons are multiplied by 9.8066. The origin of that constant is left as an exercise for the student.

Tony said...

On a more practical note, the reason that gravity (literally) enters into the Isp equation is that all of the components are manufactured, tested, and assembled on the Earth. All of the masses are measured as weight in the Earth's gravity field.

Thucydides said...

An interesting proposal which does not need super power lasers or electron beams to initiate fusion. How well this would actually work would need to be seen, but if it does work, then high ISP drive is possible without massive external power supplies.

The end state seems to be in thrust the megawatt range if certain assumptions are correct.

http://nextbigfuture.com/2011/06/laser-enabled-megawatt-class-fusion.html

Anonymous said...

Thucydides; I read about this a day or two ago on Atomic Rockets website and it does seem as though (if it can be made to work) to be a viable engine for space travel; I don't see how (even with propellant dumping) it could be adapted for planetary launch, but getting from one world's orbit to another's orbit seems quite reasonable.

Ferrell

Thucydides said...

Sadly, the tech revolution that will get us cheap, reliable space access from Earth to LEO still isn't here. The only thing that isn't either a megastructure or megascale engineering that I can think of today is the advancement in material science. If very light but strong structures can be made of advanced composites, graphine or fullerine tubes, then the overall mass of the vehicle comes down, leading to lower requirements for engine power, fuel consumption and the mass of fuel and oxidizer needed to get to orbit in the first place, in a virtuous circle.

We are talking order of magnitude weight reduction here; a shuttle orbiter weighing in at 10 tons rather than 100, otherwise the effect would not be so pronounced.

If this sort of technology were possible, it would also have pretty profound effects in many other parts of the economy, transportation, construction, energy production and consumption and a host of other things as well.

Anonymous said...

Graphene, being discovered only about ten years ago, still has a lot of work to be done to develop manufacturing techniques and bring down the cost of large-scale production; fity years from now, we most likely will have our ten-ton shuttles, super light-weight-cars, high-tech practical airships, low-cost megastructures, and a 10001 other things that will benefet from extreme low mass-high-strength materials. We might have a revolution in space launch, but from a different direction then from what we usually picture it coming from.

Ferrell

Tony said...

Thucydides:

"If very light but strong structures can be made of advanced composites, graphine or fullerine tubes, then the overall mass of the vehicle comes down, leading to lower requirements for engine power, fuel consumption and the mass of fuel and oxidizer needed to get to orbit in the first place, in a virtuous circle."

Actually, that's not what would happen. Structure would be replaced by payload, but rockets would still be expendable, even if only single staged, and still have the same GLOW.

Thucydides said...

Upping the amount of payload is one possible direction to go if ultra strong materials can make order of magnitude weight reduction possible (although the cargo may also weigh an order of magnitude less as well), but there will be the option to take "ordinary" sized cargo and launch it on smaller, lighter and cheaper cargo rockets as well. This will be the sort of niche market that smaller rockets like the Delta or Falcon service today; there would be room for a Graphine "Falcon" as well as a Graphine "Falcon 9 Heavy" analogue.

While in theory material science advances might make SSTO possible (it is the only path besides magitech or mega engineering that seems to make SSTO possible) I make no claims for re usability in this or any segment of the market with ultra light material science, although I'm sure someone, somewhere will try hard to do so....