The Ferry to Hogwarts
Reality 1, whimsy 0 ...Alas there seems to be no ferry service to anywhere from this pier, though a block away is the ferry to one of San Francisco's most famously dubious tourist attractions, Alcatraz. (Possibly relevant note: The gap in my posting here was due to a stubborn head cold, not incarceration.)
Nor is there any profound justification for posting this image, beyond the general Rule of Cool. But it provides a handy segue to an ongoing topic of this blog, the somewhat uneasy boundary line between Realism [TM] and Romance.
Such border disputes are by no means confined to outer space, but space is a particularly productive environment for them, because the whole idea of going into space for any reason is essentially and profoundly Romantic. Yes, comsats, weathersats, and various other things we have sent into space have their practical uses, but it seems awfully unlikely that strictly practical people would ever have come up with them, given how absurdly difficult and costly space travel is.
Yes, before space travel there was military rocketry. But - setting aside the question of in what sense our blowing each other up qualifies as practical - the established or foreseeable roles of military rocketry in the early 20th century did not point toward space boosters. Practical military rockets like the Katyusha were essentially self propelled shells, more expensive and less accurate than standard shells, but able to be fired from cheap, lightweight launchers instead of heavy, expensive artillery rifles.
The V-2 was, in the pre-atomic age, a supremely impractical weapon: an expensive and inaccurate way to lob a shell not all that much farther than the longest-ranged guns of the time could achieve. No one would have come up with such an idea on purely military grounds. I'll guess that Versailles restrictions played a role in making the German army interested in alternatives to conventional artillery, but it was the first generation of space geeks, not military specialists, that put long-range rocketry into play.
Yes, nuclear warheads made ICBMs all too practical, but it is no accident that the first generation of ICBMs, both US and Soviet, turned out to be much more suitable as space boosters than as weapons.
Space travel is, like the image above, ultimately all about the Rule of Cool, AKA Romance. This has significant implications. As strong as are the practical reasons for not spending zillions on it, these reasons have not, so far, succeeded in making the whole silly thing go away. Unless post industrial civilization removes itself from the social selection options, it will probably not go away in the midfuture, either.
A comparison can be made here to other Zeerust-era future techs, such as the SST. Supersonic aircraft are also inherently cool, but not that cool. So, not only do SSTs fail to offer enough merely practical benefits to pay for their development cost, they also fail to offer enough coolness to overcome that limitation.
I suspect that people will walk on Mars before airline passengers (again) travel at supersonic speeds.
It may be somewhere between paradoxical and hypocritical for me to turn around and argue this point, considering how much time I spend here beating up on popular space tropes. But I beat up on the PSTs so you won't have to. Romance, in and of itself, need not apologize to realism for anything, but the minor sub-branch of Romance that decks itself out as hard SF has a certain obligation to fake it convincingly, including space futures that sustain at least the illusion that they were invented in this century.
The image was snagged from Google Maps. And here is a genuine example of mysterious British transportation signage. Can anyone here elucidate the meaning?
262 comments:
«Oldest ‹Older 201 – 262 of 262Thucydides:
"Scaling has the potential to send objects into orbit (see the sad history of Gerald Bull), so in an alternate universe without WWI and the Treaty of Versailles, immense guns might be sending small satellites into orbit today..."
Even if you use a big gun to send stuff up, you still need to fire a rocket engine while in orbit in order to circularize it. Otherwise you'll end up in an elliptic orbit and come back down as hard as you went up.
Nevermind how rough the sudden acceleration of being fired from a gun would be on your cargo, and let's not even think about passengers...
I never said that small rocket engines to circularize orbits would not be required, what *could have been* was a future where there was no need or desire to build big rocket engines, ICBMs and man carrying rockets. No Treaty of Versailles means no restrictions on artillery, hence no need to look for alternatives...
In *this* future, there would be little need to miniaturize nuclear weapons, since large bombers would be the means of carrying firepower beyond the range of guns. One reason the XB-35 and XB 49 Flying Wing bombers never reached production status was the bomb bay was not big enough to carry the giant sized nuclear and thermonuclear bombs of the late 1940-early 1950 period.
Ferrell:
"Tony: you are, of course, entitled to your opinion, just as I am. Your analogy with the turkey is interesting, and I have heard it before, but it is flawed; I have access to information from various other sources that the turkey didn't have; likewise, your "faith" in the rapidly approaching limits to knowledge is equially faulty; you have no basis other than faith in your position. I 'know' that that statement will bring a rebuttal from you, but that is my opinion and you can disagree with it, but unless you can show me concrete proof that you are right, I don't see any reason to change my opinion."
If I had actually professed a faith in running into the limits of knowledge sooner rather than later, you would have a point. But all I have said is that it's a real possibility. Denying the possibility based on nothing but past experience is what takes an act of faith.
Spaeking of which, what information do you have that the turkey doesn't? You -- all of us -- like the turkey, are inside the process. You -- all of us -- like the turkey, can't know anything but what past experience tells us. And that means nobody -- not the turkey, not us -- can know when our experience will cease to be valid, until it in fact does. It could be sooner, it could be later. But it will happen.
Thucydides:
"Even if Tony is right about us being close to finding the limits of knowledge, there is still immense room to work."
Just to reiterate, I'm not saying we are close to the limits of fundamental knowledge. I'm saying that it's a possibility that we are.
As for the roads not taken argument, there is one has to remember that there must be an application, and that a complex technology needs more than an observed effect in order to work. Hero's aeolipile was a curiosity that couldn't be turned into an engine because all of the things that go into an efficient heat engine hadn't been invented yet, from basic materials technology to even the basic understanding of thermodynamic cycles thatNewcomen and Watt had. Also, there just wasn't a perceived application -- everything that people wanted to do was already being done by people and/or animals.
Nowdays we systematically investigate curiosities and figure out how they can be incorporated in our technological toolbox. On top of that, we have an application for improved propulsion or new propulsion principles. If one could achieve orbit for a few dollars a kilo, or even a thousand, there would be plenty of people to jump on that.
Thucydides:
"In *this* future, there would be little need to miniaturize nuclear weapons, since large bombers would be the means of carrying firepower beyond the range of guns."
Bombers are more vulnerable to interception than missiles.
Tony:
"Just to reiterate, I'm not saying we are close to the limits of fundamental knowledge. I'm saying that it's a possibility that we are."
I don't care what's possible. A very large number of things are possible. What do you think is likely?
Tony: one, you should be more clear about whether you are speaking of possibilities or are making a declaritive statement;
two, the turkey in your example is in a state of isolation; he can only know what he has personally experianced; we, however, can look at the experiances of other, discuss the possibilities with others in our situation, we can even make inquiries of the Farmer (if not directly, then indirectly). The example of the turkey is commonly used in basic philosophy classes to spark debate, and then teach logical fallicies; Only if the turkey is totally isolated from all forms of information, except what he can only, directly observe for himself, can your example be valid; that you cannot logically expect to be so isolated will invalidate it in the real world.
While the world might end at any time, it is not reasonable to belive that it will, without compeling evidence; in the absences of such evidence, then it is more reasonable to belive that the end is not near.
Again, my opinion is, seeing no evidence to the contrary, that we are nowhere near the limits of knowledge.
If anyone disagrees with that, then that is your opinion and you are welcome to it. Just don't try to change my opinion unless you have some very compelling arguements, and I haven't seen any so far.
Anyway, back to what (I think) was the original topic of this thread; the main stumbling block to expanded space travel (in my opinion), is the cost of launch vehicles. This includes the cost of building the launch vehicle, the cost of developing it, the cost of the payload (including insurance), the cost of operating the payload vs its profit generation, the overhead costs of operating the launch facility and the buarucracy assosiated with it. If any of those costs could be significantly decreased, or if smaller saving in most (if not all) those areas could be realized, then the cost of missions could be lowered. Even just lowering the cost of 'doing business' could have a significant cost savings; as useful as the buarucracy is, it is very costly and generates a lot of excess costs. Some commentators have overlooked the massive impact of these buarucratic costs have on not just space launch, but any other commercial endevor; while you cannot do away completely with the buarucracy, you can limit it so its costs don't artificially inflate the cost of your product (space launch). That there is a de facto government monopoly on spacelaunch, it is no wonder that costs are much the same as they were back in the 1960's. Maybe we should reduce the costs of overhead, before we conclude that the current cost of launching chemical rockets will always be what they are now.
Ferrell
Ferrell:
The average turkey is not smart enough to talk to farmers, read calenders, or look anything up on the internet. Therefore, within the knowledge that the turkey knows how to access, there is no way to realize that tomorrow is Thanksgiving.
Humans are smarter than turkeys (or so I heard) and have more ways to learn things through indirect observation, but we still have to observe something - to learn something from a book, you must observe a book that was written by someone who had observed the thing being taught (possibly with some additional links in between). There are limits to what we can observe, and so there is a possibility for something unexpected in what we have failed to observe.
Ferrell:
"Tony: one, you should be more clear about whether you are speaking of possibilities or are making a declaritive statement;"
"We may be closer to knowing all of the physical laws and their manipulations than many think...We wouldn't like that. But we have to take that into account."
"Hopefully we're not close to there yet. But we may be."
"One can hope for much more left to explore; One can't know it."
I'm not sure how much clearer I could have made it that I was addressing possibilities, not certainties.
"two, the turkey in your example is in a state of isolation..."
As are we. Just because you have the whole of human experience to learn from, it still can't teach you what the depth or extent of the process actually is. All it can teach you that the limits haven't been reached yet. But it can't teach you whether the limits are far in the future, or just around the corner.
"Again, my opinion is, seeing no evidence to the contrary, that we are nowhere near the limits of knowledge."
And again, like the turkey, you know only the history of the process, not its design. Without knowledge of the design, you have no data on which to base any conclusions about how the process will proceed in the future.
"If anyone disagrees with that, then that is your opinion and you are welcome to it. Just don't try to change my opinion unless you have some very compelling arguements, and I haven't seen any so far."
You are perfectly entitled to your opinion. I'm just pointing out that it's not based on any hard data. You could be right, you could be wrong, but you have no basis to say whether you are right or wrong at this moment, only a personal preference for a certain outcome.
"Even just lowering the cost of 'doing business' could have a significant cost savings; as useful as the buarucracy is, it is very costly and generates a lot of excess costs. Some commentators have overlooked the massive impact of these buarucratic costs have on not just space launch, but any other commercial endevor; while you cannot do away completely with the buarucracy, you can limit it so its costs don't artificially inflate the cost of your product (space launch). That there is a de facto government monopoly on spacelaunch, it is no wonder that costs are much the same as they were back in the 1960's. Maybe we should reduce the costs of overhead, before we conclude that the current cost of launching chemical rockets will always be what they are now."
I'm game -- what part of the "bureaucracy" is unnecessary and how can it be removed without increasing risk (and ultimately cost)?
I know this has raised some hackles in the past, but Bob Zubrin did calculations based on his experiences in the Aerospace industry to suggest that Mars Direct cold have been done for @ $5 billion dollars in the 1990's. This is a far cry from the $30+ billion he suggested it would cost as a NASA program.
The removal of bureaucracy not only takes away vast amounts of overhead which mostly seems to exist to cover someone's a**, but would also reduce costs by reducing the time delays in moving projects forward and cutting down the time value cost of money. After a while, the cost of tying up money and resources exceeds the return from more mundane investments.
There would be a certain increase in risk, but like most things, we would have to try and get a sense of the risk/reward ratio of doing so.
The low-hanging fruit is a very good point. We're not seeing a creation of "big name" scientists as much these days because it's harder for one person to make amazing, ground-breaking contributions that get names put on fundamental laws and used as units of measure.
However, we're also seeing the immense empowering of the individual. While not everyone gets a multi-billion dollar particle accelerator to play with, personal access to computing power is unbelievable. I can build my own personal machine and have the kind of number-crunching power that would have cost millions back in the day. And we're seeing examples of empowered individuals like that recent story of the guy finding a thousand archaeological sites in Saudi Arabia just by looking at the satellite imagery.
The history of science has seen a TON of duplication of basic science in new fields because of poor publication of findings. With the internet and search engines, it becomes trivial for people working in obscure fields to find each other, collaborate, and disseminate their findings.
So in some ways, this may be like the situation with computer processors. Skeptics said there's a finite limit to the speed increases that can be made with microchips, fundamental limitations of physics. They're correct. So the designers throw in multiple cores and try to run multiple threads in parallel. It's still a speed increase but now it becomes a bit more of a chore to write software to take advantage of that speed.
One last thought -- the data's expensive to gather but it takes eyeballs to make sense of the data. And that's where the enthusiastic amateur can still make real contributions. Because once the data's in, it still comes down to someone sitting at a desk and fiddling about on a computer to put it all together. There's only so many grad students out there for a given discipline but just look at the world of amateur astronomers. Most of the comet discoveries go to them. They have the time, they have the interest, and the professionals are looking at different things with the expensive equipment. There's room for both and it's mutually beneficial.
Thucydides:
"The removal of bureaucracy not only takes away vast amounts of overhead which mostly seems to exist to cover someone's a**, but would also reduce costs by reducing the time delays in moving projects forward and cutting down the time value cost of money. After a while, the cost of tying up money and resources exceeds the return from more mundane investments.
There would be a certain increase in risk, but like most things, we would have to try and get a sense of the risk/reward ratio of doing so."
What you're missing is that all that covering of backsides is necessary for anything to get done, because the risk is so high and the investment so great. Take the Challenger incident, for example. The decisionmaking process was skewed by politics, but the pre-flight review process was validated in that it did raise real safety issues to the level where decisions needed to be made. It wasn't just another layer of bureaucracy.
Or, to take a more recent example, during preparations for the most recent SpaceX Dragon flight, cracks were discovered in the second stage engine bell. SpaceX sent out a tech rep who shaved off the portions with the crack and certified the engine ready for flight, all in about 48 hours. That could be done by a startup company working a flight test program. When SpaceX gets real business, with payloads they can't afford to lose, they will be much more risk averse and take a lot greater care with how they proceed through any technical issues. Quality control on the factory floor will also get more extensive and expensive.
This is what people don't seem to get. With the current technology, the irreducible costs are so high that layers of checks and balances are needed to protect such huge investments.
Milo:
"There are limits to what we can observe, and so there is a possibility for something unexpected in what we have failed to observe."
+10
The size and shape of the knowledge base we have yet to discover is one of those things that logicians cal a "known unknown" -- we know that there is probably more out there, but we don't know how much.
Tony: you do know that you have successfully argued for my position? Thank-you for agreeing with me!
As far as reducing overhead, perhaps reducing the number of levels of supervisors and levels of review would help; also, (and I'm sure there are seveal who will disagree) dropping the "no failure" philosophy and replacing it with a "best cost-risk ratio" type would help as well. As they say, "perfect is the enemy of good".
Ferrell
Ferrell:
"Tony: you do know that you have successfully argued for my position? Thank-you for agreeing with me!"
Really? How does one extract certainty from uncertainty?
Tony: you havfe purposely missunderstood what I have said; the turkey in your example cannot have certainty in anything whatsoever (that was never an issue except that you insisted it was even though I didn't), however, there is a 364 to 1 chance that the next day will not be significantly different than the day before; there is only a 1 to 364 chance that it will be signifacantly different, with anequial chance of that difference being good or bad, a reasonable person (or turkey) would literally wager his life that thing would most likely be the same the next day and so dismiss any possibility of a significant difference due to it being too small to worry about. Only a neurotic turkey that took a perverse pleasure in worrying over such negative things would fixate on such a remote possibility. Because you insisted on the turkey only being able to know anything by direct observstion, then it is only reasonable that he expect that things continue on the way they have been; you cannot insist on an example where that is the logical outcome and then insist that I contimplate a possibility that lies outside the perameters that you yourself insisted on! So, you have actually argueed for my position! Again, thank you...
Ferrell
Re: Ferrell
Siiigh...
Your side trip into figuring odds is totally irrelevant to the question. Neither you, nor the turkey, knows what the statistical universe looks like. The turkey doesn't know what the total number of days in a table bird's life normally is. You don't know the total amount of discoverable fundamental knowledge.
And here's where you get in trouble figuring odds. The odds of the turkey getting whacked tommorrow are not constant. They're effectively zero at the beginning of the turkey's life, both for statistical and practical reasons. As the turkey gets older, the odds increase with each day, since the number of days in the turkey's life is decreasing. (Yes, I know this is simplistic, since things like time of year a bird is born and seasonal demand figure into the real world.) But the turkey doesn't know this. All the turkey knows is that the previous 1000 days have been the same. Based on the information he has, the turkey could reasonably figure that tomorrow will be the same as the next day. But we know the turkey doesn't have all of the information, and therefore his calculations are baseless.
The same goes for you asserting that there is still enough knowledge left to discover to fuel whatever technological future you desire. You know that humans have kept discovering knowledge over time. With that data, you can say to yourself, well, we'll just keep following the trend. But that's mistaken. There's only so much fundamental knowledge that can be discovered -- only so far down in scale we can probe, only so far out we can observe, and only so many degrees of freedom to explore. We may not have hit the limits yet, but the limits are there. So, with every new discovery, the odds of hitting the limits increase, because the amount of knowledge left to learn decreases. They do not remain constant.
That's the abstract statistical argument. The practical argument is that we have reason to believe there's more to know, but we don't know how much more. Let the amount of knowledge necessary to achieve Ferrell's desires be represented by the quantity x (in some dimensionless unit that can measure knowledge). Then the only thing we can say with with certainty is that the magnitude of the knowledge left to be discovered is some multiple of x. Now, here's the important part: with the data available to us, we can't say what that multiple is. It may be 1. It may be > 1. It may be < 1. While you may feel free to assert that the multiple is at least 1, you have no data to support that. All you have is a personal preference that it be so.
I'd suggest giving this particular subthread a rest - at this point I think it is pretty much grinding gears.
Anyway, so maybe a Solar Sail would need a 'keel'; since there are two components to solar radiation; light and plasma. The sail uses the light and a magnetic field would act as a 'keel'; not only would it provide another layer of radiation protection, it would interact with the solar wind and (hopefully) act as an analogue to a keel.
Ferrell
As usual there is a hitch - the solar wind is also moving outward from the Sun, and at a good clip, so any interaction probably (??) tends to push you outward as well. Good if you are outward bound, not so good if you're inward bound, or outbound and trying to slow down.
The good old fashioned aether would have been helpful here, but alas ...
When all is said and done, though, deep space travel at decent speed should be attainable without need of magitech, at costs that aren't that outrageous by space standards. As always it is orbit lift that remains the real bottleneck.
Ferrell
There is quite a bit of commentary in "The Unspecified Drive" WRT sails. For tacking and other directional changes, the Sun's gravity is the "keel", and the sail gets around by adjusting the thrust vector in relation to the Sun's gravitational field and your direction of orbit.
Hmmm...Solar Sail tech seems to have many distinct possibilities. Perhaps there will be an "Age of Sail" ala Rocketpunk in the midfuture. Well, maybe a Solar Sail option; a space transport company, scientific exploration agency, or private foundation of the midfuture could have a wide range of options as regards to busses, propulsion, payload housings, and control units to assemble manned or unmanned ships either for temporary (single-voyage) or semipermanante use. Whatever is the most economical for that paticular mission. I, personnally, don't see that until the mid to late 21st century at the very earlist.
Ferrell
Thucydides:
"There is quite a bit of commentary in 'The Unspecified Drive' WRT sails. For tacking and other directional changes, the Sun's gravity is the 'keel', and the sail gets around by adjusting the thrust vector in relation to the Sun's gravitational field and your direction of orbit."
Once again, you can't "tack" a solar sail. You can rotae your thrust vector through almost 180 degrees, but it's still a thrust vector that applies in the same way any reaction drive does.
Tony, without getting into a flame war, 'tacking' is a technique for sailing into the wind; it involves thrust, no matter what direction you are going, and discribes a way of using that thrust to achive a specific action. "Tacking" is discribing a technique, an action, the difference between using 'tacking' on the sea and in space is somewhat different from one another, but you can use the same term to discribe a simular outcome. Again, I have no intention of getting into a flaming war, but I do think that you can use the same term to discribe simular outcomes in different enviornments.
Ferrell
I don't think the term 'tacking' is problematic. I agree, and from his comment Tony also agrees, that a solar sail can be angled to vector thrust across nearly 180 degrees. But not, so far as I can see more than 180 degrees, which would be needed to 'sail to windward,' i.e. sunward.
A solar sail can 'tack' against its orbital velocity, then take in sail and fall into a closer orbit, but inward speed is limited to falling speed. I don't see a way around this limitation.
I have a table of solar sail missions (I'll have to look up the reference again; poor note taking on my part), which provided some very interesting numbers.
Using the assumptions that:
a. Acceleration is 1mm/s^2
b. You start from Earth and do an infalling manouevre sunwards to gain velocity, and
c. The cargo detaches from the sail and aerobrakes at the destination
You get very fast transit times.
Earth to Mars is 4 months, somewhat faster than Mars Direct or NERVA (the sail in this case can come back to Earth after a two year flight, to be refurbished and reused)
Jupiter: 2.03 years
Saturn: 3.29 years
Uranus: 5.79 years
Neptune: 8.48 years
While this is only 1/2 the loaf, these times are practical for cargo drones and even manned missions out to Jupiter or Saturn. Very massive and complex systems will be needed to get much lower transit times, or reasonable round trips.
Thucydides:
"Using the assumptions that:
a. Acceleration is 1mm/s^2"
Wait, what? The acceleration of solar sails depends on how far you are from the sun, and whether you're trying to accelerate straight outwards or "tack" at an angle.
Any model that assumes constant acceleration cannot reasonably be taken to depict solar sails in anything even resembling accuracy - you just have a garden-variety reactionless drive.
Re: "tacking" solar sails
Tacking is the action of coming across the wind to an alternate course while beating a boat upwind. As mentioned, it takes a keel or center/lee board working in the water to do this.
In sailing terms a solar sail simply can't beat against the direction of the wind. It has no medium to gain purchase against and convert the momentum of the incoming wind to a near reciprocal direction. So talking about tacking isn't even wrong, it's irrelevant. A solar sail can't even reach (sail nearly perpendicular to the wind, which also requires a waterplane). All a solar sail can do, really, is run before the wind.
Now, I understand where the desire to use the term "tack" comes from. It is meant to refer to the action of thrusting against orbital motion. But orbits aren't winds. They're more like currents. (An inexact analogy, I know, but it serves.) So wat a solar sail is really doing, when thrusting up-orbit, is breasting the current, not tacking.
Thucydides:
"Using the assumptions that:
a. Acceleration is 1mm/s^2
b. You start from Earth and do an infalling manouevre sunwards to gain velocity, and
c. The cargo detaches from the sail and aerobrakes at the destination
You get very fast transit times.
Earth to Mars is 4 months..."
At 1mm/sec^2, it takes 345 days to fully cancel Earth's orbital velocity. Now you would of course start falling long before then, and gain some help from increased solar flux, but I doubt one could go all the way downhill to perihelion, and all the way back up to Mars, including orbit matching maneuvers, in four months. Remember, trajectories that use close approaches to the Sun are generally meant to reach solar escape velocity, not achieve planetary orbits.
I think we'll have to see a link to the full source (no abstracts, please).
Tony; so if 'tacking' isn't an acceptable term, then what term would you use to discribe a Solar Sail manouver to reach a destination closer to the Sun? I'm curious to know.
Ferrell
Ferrell:
"Tony; so if 'tacking' isn't an acceptable term, then what term would you use to discribe a Solar Sail manouver to reach a destination closer to the Sun? I'm curious to know."
Lowering orbital altitude.
Info comes from the book: Space sailing by Jerome L. Wright. http://www.amazon.com/Space-Sailing-Jerome-Wright/dp/288124842X
I'll have to go to the library and look up that table again (perhaps I made a transcription error in the acceleration figures)
Thucydides:
"Info comes from the book: Space sailing by Jerome L. Wright."
You are probably referring to this:
http://books.google.com/books?id=KH5jTAzVw5MC&lpg=PP1&ots=0OvV4C1oux&dq=space%20sailing%20jerome%20wright&pg=PA20#v=onepage&q&f=false
Note that the 131 day transfer relies on a 20 ton payload with aerobraking. A large portion ofthat payload will be eaten up by the aerobrake and whatever soft landing technology is involved. Of course, the calculations are based on conservative estimates of sail material strength and density. But there are physical limits to everything. Sails can only be made so light. And the lighter sails can only be constructed at and operated from one of the Lagrange points, so the cost of the necessary infrastructure has to be considered.
Sails like everything else have limitations, but if you can get your payload to Mars etc without hauling the fuel, huge power reactor etc. then you are still ahead of the game.
Tony: "Lowering Orbital Altitude"? that is as unweldly as it is acurate; perhaps the others could help come up with a handier term?
Ferrell
Thucydides:
"Sails like everything else have limitations, but if you can get your payload to Mars etc without hauling the fuel, huge power reactor etc. then you are still ahead of the game."
If you go orbit to orbit with nuclear electric propulsion, the reactor is reusable -- probably for five or six round trips in the context of Mars. And the reaction mass isn't all that massive with high Isp drives. Sails may serve in niches, but they're not going to be the Ford pickup trucks of space.
Ferrell:
"Tony: 'Lowering Orbital Altitude'? that is as unweldly as it is acurate; perhaps the others could help come up with a handier term?"
Okay, "ascend" and "descend" (in terminology WRT the Sun and solar orbits).
I'll admit some bias in favor of nuke electric drive - for all its failings it has lots of performance potential and minimal magitech - and a bit of bias against techs like sails. (No magitech, but substantial tech challenges and severely constrained performance.)
That said, there probably will be no one Ford pickup of space. I don't think solar sails are practical for human transport, but they could turn out to be an effective way to deliver payloads especially to the outer planets.
Actually, if the niche is carrying assorted cargos, sails will be the pickup trucks, while VASMIR or other nuclear drives will be the the minivans of space.
(I suppose we could use other analogies like container ship/QEII or C-130/737, according to taste)
Thucydides:
"Actually, if the niche is carrying assorted cargos, sails will be the pickup trucks, while VASMIR or other nuclear drives will be the the minivans of space."
That greatly depends if the cargoes are time sensitive or not. Sails are technically elegant, and possibly romantic, but they have travel time and consequent cargo exposure issues (if you don't assume speculative sail technology).
Goods in space are probably going to last pretty long - hard vacuum isn't a highly contaminated environment, and things like asteroid minerals or helium-3 aren't known for decaying much anyway. The big exception is live cargo, which will have to be handled similarly to passengers (and carried on similarly fast ships), even if farm animals aren't quite as likely to file a customer dissatisfaction form.
A bigger issue as far as time goes is dealing with fickle markets, and making sure that the goods which are currently in demand on another planet will still be in demand when your shipment arrives.
Tony said:"Okay, "ascend" and "descend" (in terminology WRT the Sun and solar orbits)."
Yeah, those sound better; however, what do you think of the terms "spiral" and "despiral" since they discribe the orbital motion of the sail? (spiral out to a higher orbit; despiral in to a lower orbit; its logical, but doesn't have to be reasonable)
Ferrell
I'm wondering why solar sails have not been combined with other forms of propulsion.
One concept I can think of is having a solar sail carry a nuc-electric drive, or fission fragment depending on mass an Isp.
The solar sail, after a sundive, gets up to speed very quickly, then the nuc-electric drive provides maneuvers, deceleration or even the possibility of magsailing further beyond.
Another one is the fission frag sail+solar sail. It HAS been mentioned, but I wonder if we can balance the solar sail and the fission frag sail to have a sundive followed by a very gentle deceleration from the frag sail, mounted on the opposite side. When the outbound velocity is killed off and the orbital velocity increased to match destination planet speeds, the fission sail is 'scraped' off from its fissile fuel and that powder is fed into a lower Isp, higher output nuclear drive.
These combo's would give the best of both worlds if we manage to overcome the engineering issues.
Since the solar sail needs very limited infrastructure or support, I pegged it as being the least expensive and most versatile of the various forms of propulsion available, hence their analogy comparison to pickup trucks etc. Maybe they will be the tramp steamers of space, able to carry insensitive cargo on spec. without incurring vast costs on the operators.
The relatively low costs even allow for a sort of disposable transport system, accelerating outwards from the Sun and cutting the cargo free from the sail to aerobrake or use some sort of on board propulsion system (which is much smaller and simpler than any drive that has to accelerate and decelerate the cargo).
While not exactly bush pilots in Spaaaaace, this is a niche that will attract a lot of attention and investment.
Ferrell:
"Yeah, those sound better; however, what do you think of the terms "spiral" and "despiral" since they discribe the orbital motion of the sail? (spiral out to a higher orbit; despiral in to a lower orbit; its logical, but doesn't have to be reasonable)"
"Spiral" works for both directions. "Despiral" has the sense of unwinding a spiral, which is manifestly not what is happening. I would agree with "upspiral" and "downspiral" (once again, this is solar-relative terminology). But those only apply to relatively low energy trajectories. When talking about very lightly loaded sails using fast trajectories, we're still left with "ascend" and "descend" as the most technically correct terms. So, choice of terminology will either be dependent on trajectory design (low energy => "upspiral"/"downspiral"; high energy => "ascend"/"descend"), or rely on the most broadly correct terms ("ascend"/"descend" in all cases).
Thucydides:
"Since the solar sail needs very limited infrastructure or support, I pegged it as being the least expensive and most versatile of the various forms of propulsion available..."
I don't comprehend this assertion. If the sails are made on the ground, they rely on just as much infrastructure as a rocket. The relationship between rocket size and plant size is not linear -- larger rockets take up more floorspace and have special transportation requirements, but you make fewer of them. Fuel is just industrial chemicals. The infrastructure for them already exists. If sails have to be manufactured in space, then you have to lift the manufacturing infrastructure up into space, supply it with materials, move workers up and down, supply them, etc.
"The relatively low costs even allow for a sort of disposable transport system..."
Aside from the fact that nobody has actually established that the cost would be significantly lower, there's no reason to throw away a sail just because the payload aerobrakes. Once the payload is released, if the sail isn't going too fast one can always reshape the orbit to bring the sail back to Earth or wherever for reuse.
Tony: "upspiral" and "downspiral" do sound better. If solar sails do come into common use, I susspect that most of their missions would be low energy ones.
Ferrell
Ferrell:
"Tony: "upspiral" and "downspiral" do sound better. If solar sails do come into common use, I susspect that most of their missions would be low energy ones."
Agreed. But I wouldn't rule out the possibility of lightly loaded, fast trajectory sails for some applications (though I can't imagine what they would be, at this point).
Anyone else thinking that moving up and further down the spiral might sound a little too Trent Reznor?
"Anyone else thinking that moving up and further down the spiral might sound a little too Trent Reznor?"
Man, I haven't listened to that CD in ages. I guess I've been too happy lately ... :)
"'Lowering Orbital Altitude'? that is as unweldly as it is acurate; perhaps the others could help come up with a handier term?"
How about just "sailing in" vs. "sailing out"?
Maaan, everyone is out to expose my pop culture ignorance lately! Even Wikipedia left me clueless about the connection of Trent Reznor / Nine Inch Nails to moving up or down the spiral.
For solar directions, why not simply inbound or outbound, applicable to any mode of propulsion?
Rick:
"Maaan, everyone is out to expose my pop culture ignorance lately! Even Wikipedia left me clueless about the connection of Trent Reznor / Nine Inch Nails to moving up or down the spiral."
The Downward Spiral
"For solar directions, why not simply inbound or outbound, applicable to any mode of propulsion?"
I like "upgrade" and "downgrade".
Rick, if you haven't pinned it down yet, jollyreaper is referring to the CD The Downward Spiral by Nine Inch Nails.
Probably the best-known songs from that CD would be "Hurt" (later covered by Johnny Cash, and a dang fine job he did of it, too) and "Closer" (AKA "F*** You Like an Animal").
Wikipedia reminds me that there was a remix version of the CD called Further Down the Spiral.
(If you already knew all that and I misinterpreted your last comment, my apologies.)
The definitive version of "Hurt" was performed by Kermit the Frog. Moving and powerful.
http://www.youtube.com/watch?v=57ta7mkgrOU&feature=youtube_gdata_player
While I at least have heard of Nine Inch Nails (Johnny Cash, too), I know zilcho of the actual music mentioned.
Pathetic, I know ...
Upgrade and downgrade has a sort of nice space trucker vibe to it. Though the first, at least, sounds like someone modernized (or at least spiffed up) their ship.
"the fission sail is 'scraped' off from its fissile fuel and that powder is fed into a lower Isp, higher output nuclear drive."
No-body's replied to that here or on sfconsim-l. Maybe it's just stupid.
"cutting the cargo free from the sail to aerobrake or use some sort of on board propulsion system (which is much smaller and simpler than any drive that has to accelerate and decelerate the cargo)."
First-off, aerobraking is great but 200km/s aerobraking is not so good. Especially when there are not many candidates with both thick atmosphere and colony-attracting surface...wait...Except the obvious one.
Then there's the smaller engine onboard. I hit the problem of high velocity to kill, lower efficiency to work with leads to quite big onboard engines. Haven't done the maths, but nuc-electric is a good option if you sacrifice all form of payload...
"nce the payload is released, if the sail isn't going too fast one can always reshape the orbit to bring the sail back to Earth or wherever for reuse."
Or whatever can be a fission sail implemented on the opposite side. I just doubt that making an angle with your solar sail at Jupiter orbit leads to recuperation of sail before the next century. Light intensity is just too low. Except in the case where you can happily boost lightsails with massive lasers, and you can use that technology at destination, at a smaller scale, to decelerate the solar sail alone and let the cargo pod be recuperated by other means.
"Maaan, everyone is out to expose my pop culture ignorance lately!"
Okay, a heavy metal band popping up during a discussion on solar sails left me surprised too...
"But I wouldn't rule out the possibility of lightly loaded, fast trajectory sails for some applications (though I can't imagine what they would be, at this point)."
There's the obvious one -WARR- and the less obvious, niche economic applications. Secured transport? Large crypted data handling for your laserstar blueprints you don't want your neighbors hearing? Unobtainium express? Probes? Exploring the Oort cloud? Loads of applications, and once the sails become big enough, most if not every solar sail will be of this kind just to reduce transport times.
A space based sail "loom" might be large in size, but essentially a gossamer assembly of booms like the ISS truss for the machines to work from. A relatively small amount of material is actually required to make the sail (the most extreme is the 20 square mile Drexler sail which can be made from a block of aluminum the size of a classic VW "Bug"). More modest sails require less material and machinery. The machinery itself might resemble a simple roller to dispense sail materials, reinforcing strips and adhesive as it runs along a track. Without going into lots of details (most of which is as speculative as building a VASMIR space cruiser anyway) sail building seems to lend itself to simple semi automated and teleroperated construction.
Compare this to the amount of infrastructure required for a solar or nuclear electric drive, not to mention the large parts required to build the ship (even if large chunks are built on the ground, there will still be large building blocks to boost and assemble in orbit). This amount of effort and energy is needed for a different niche than sails.
Disposable or semi disposable lightsails are a possibility depending on the parameters you are trying to achieve. Rapid, one way delivery of cargo could use this route (and the sails may eventually come back, but only after a long flight time in the outer solar system. Even the fast Mars mission the sail takes 4 months the get to Mars but 2 years to return to Earth. If we assume a similar ratio then a sail to Neptune will return to Earth 48 years after launch. Better to build a new sail in the mean time).
If I am going to aerobrake cargos in the outer solar system, I will be aiming for the atmosphere of the gas giant planet for the initial brakeing sequence. If necessary, the cargo can go into an eliptical orbit and brake several more times to circularize and a tug from the local moon/colony can be sent to pick up the cargo pod when the brakeing sequence is finished. Once enough speed has been bled off, a modest on board motor might also do.
Thucydides:
"A space based sail "loom" might be large in size, but essentially a gossamer assembly of booms like the ISS truss for the machines to work from...
Compare this to the amount of infrastructure required for a solar or nuclear electric drive..."
Once again, I think you have seriously underestimated both the size and complexity of an operation capable of manufacturing low density sails.
I am trying to see how to fit plausible midfuture(tm) tech into a Rocketpunk Universe.
High performance spacecraft will require lots of time and resources regardless of the power plant, I think a one to one comparison still favours sails in terms of resources needed.
The "classic" 1mm/s^2 sail is actually aluminum and Mylar, based on the Halley's Comet proposal, so there is a tech basis that can be used today (1970's tech, really) while high performance Drexler sails will be the natural evolution.
Re: Thucydides
Rocketpunk IMO is about, well, rockets, even if they have more in common with an electric heater that a nuclear "jet" of the 1950s.
Even if we just want to talk about the plausible midfuture, sails might have niche applications, but only where resources, time constraints, and technological capabilities dictate that they do. I'm not trying to harsh your mellow, but sails, just like any other propulsion system, have infrastructure costs. If those infrastructure costs are too great, then it simply doesn't matter that sails are more efficient than rockets.
Like.....wow, man
Since this is speculation it is difficult to assign real costs to everything, but Rick estimated aerospace grade engineering costs something like $1,000,000/ton in an earlier post (correct me if I got the numbers wrong, but I think I'm in the ballpark).
So simply adding up masses of the various parts that make up a nuclear electric or VASMIR space cruiser (plus the costs of boosting the pieces into orbit) puts you behind the curve when compared to the masses of the sail and the loom.
There are niche markets where sails would be at a disadvantage over nuclear, and others where sails shine, so in a mature space economy, you will see various different systems in use.
So far as the term Rocketpunk is concerned, I am for the more inclusive definition where we mean lots of manned space activity without being too stuck on rockets. Besides, it sounds much cooler than "Sailpunk"...
Thucydides:
"Rick estimated aerospace grade engineering costs something like $1,000,000/ton in an earlier post"
Yes, but that's a rough estimate. Some components are going to cost more or less per ton than others. The price estimate is for the ship as a whole, taking into account likely ratios of expensive to cheap components. (Armor is pretty cheap per ton, since it's just dumb material, but you can't afford to have much of it without weighing your ship down.)
Sails in particular are going to be very expensive for their mass. (Or very light for their price, if you want to look at it that way.)
My $1 million/ton estimate is for complete vehicles, based on the present day cost of jetliners. So I'd expect a sailing rig, like other drive engines, to cost more.
Rocketpunk, as I originally conceived it, is SF with a retro 1950s vibe, especially as regards the space tech. But the usage is pretty loose, and I can see the argument that any non-magitech setting with extensive human space travel is rocketpunk-ish.
In any case, I'm pretty sure that solar sails were discussed in the midcentury era.
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