Destructionator XIII wrote:This calculation is flawed, but you can see why because I showed my work. Where did you get your number? It is surely similarly flawed, but we can't tell why or how, since you didn't show your work.)
I made a point early that I was not arguing the efficacy of helium-3 mining, and I should have stuck to it because frankly nobody knows how much either helium-3 or orbital solar power will cost because nobody has come within 100 miles of doing either, and I am in danger of my mouth outrunning my knowledge again.
My original argument was that Titan was a suitable, and some would say preferable, location for mining operations in the Saturnian system should those operations be pursued.
The figure I quoted was an estimate by Robert Zubrin in his book Entering Space, and I did neglect to include the calculations for that figure. I’ll be happy to show Dr. Zubrin’s work should the argument below not satisfy you that even setting aside launch costs, orbital generated/ground beamed solar power doesn’t make much sense.
Again, I am not arguing we ought to go to Saturn to mine helium-3 (though it is my belief we will do so), but rather that should we do so we are likely to locate the primary base of operations on a natural body. Doing so provides the base with abundant local resources with which to construct and resupply their operations, reduces their radiation exposure by half (by virtue of the massive radiation shield under their feet), and offers similar protection for meteor impacts.
Locating such a base on a body with an atmosphere offers additional resources in more easily accessed forms, eased resupply and travel to the base through the use of aerobraking, and additional meteor and radiation protection. Any atmosphere of any appreciable density also offers the chance to reduce or eliminate the pressure differential which eases construction and maintenance costs, and provide a freely acquirable fuel for atmospheric transportation.
Titan offers abundant local resources, appreciable gravity, a dense atmosphere to ease travel and construction, along with side benefits such as ease of power generation (a nuclear reactor could be set out in the open air with minimal active cooling, or more directly Stirling engines could be used that make use of the necessary temperature differential between the interior of the habitat and the exterior environment) and an ideal location for any industry or research facility requiring a low temperature environment.
3) Because the argument was not about us sending manned missions to Saturn, but about what the focus of such missions would be. Helium-3 is a natural choice for an exportable resource for the reasons outlined above.
And never going to happen, since solar from Earth orbit outcompetes it.
That is a separate argument than where the focus of manned colonization of the Saturnian system will be.
Aerobraking
You don't need to build on the body to use its atmosphere.
No, but the material must come from somewhere to build the facility. You can bring it with you, get it from somewhere nearby, or get it where you are. If you bring it with you it will cost more and take longer, if you get it from somewhere nearby why aren’t you just building there in the first place if that is where the resources are?
Equalized Pressure Construction
Titan's atmospheric pressure is about 1.4 atm. You'd experience that about 12 feet underwater, for comparison purposes. At that depth, people experience pain in their ears and lungs, and it can cause serious damage to some.
That's not the kind of place I'd want to live.
I don’t know what situation you are referencing. Are these free divers holding their breath, scuba divers, saturation divers, some fool with a snorkel?
The main problem with scuba diving is not going down, it’s coming up. Saturation diving takes care of that since you’re living at the same pressure inside as you are when working outside, there is no decompression necessary until you return to the lower pressure environment of the surface. It would likely be necessary for workers to exit the habitat from time to time to effect repairs. If the entire habitat was maintained at a standard lower pressure those workers would have to operate in similar ways to how scuba divers do: pressurize to the outside pressure, work, then depressurize back to the inside pressure. The time spent in the airlock is time consuming and prevents you from effecting emergency repairs, and there are severe risks involved with repeated pressurizing/depressurizing cycles. For the EVA workers at least it would preferable to avoid repeated decompression cycles.
Saturation divers operate for weeks at a time at depths of ranging from 60 to 500 feet of sea water (
http://www.s297830378.onlinehome.us/usn/Chap15.pdf), surely 12 feet can’t be that big a problem? The biggest side-effect is
Avascular necrosis although it is yet unknown exactly what causes this and what risk factors are associated with it.
In fact the only personnel likely not to be pressurized to Titan pressure would be the pilots of the NTR shuttles (if those shuttles were in fact manned), since it makes sense as they are often in space to acclimate them for space travel, which is to say with the lowest operating pressure possible.
You can build the habitats cheaper than space stations or vacuum environments because you can build them lighter if you equalize the interior pressure to the outside environment.
Yeah, try again.
What exactly is mystifying about this concept? Would it help if I illustrate it? First let’s build an air-tight tent in a vaccum. Let’s assume it has 1atm of internal pressure:
Exterior | Interior
0 atm | 1 atm
There is 1 atm of force exerted on the habitat shell. I must engineer the habitat to prevent that from happening. That’s fine if I’m using something with good tensile strength like steel or tent material, but if I’m using bricks I’m out of luck. To counteract the pressure difference in this instance the easiest thing to do would be to cover the habitat with something. It is true that in space you can make things surprisingly thin, but not as thin as it could be if the pressure were equalized.
Exterior | Interior
1 atm | 1 atm
Now there is no pressure difference, so our tent need only support its own weight and not that weight plus the pressure trying to get out. If our atmosphere were higher outside, we could equalize the pressure once more.
Exterior | Interior
1.5 atm | 1.5 atm
Now we’re on Titan, and again our structures need only support their own weight. This benefits us if we build using brick, since it is excellent in compression but sucky if under tension. Since Titan has some nasty stuff in its atmosphere, we might take out a safety margin by over-pressurizing the habitat slightly, any pressure differential will do.
Exterior | Interior
1.5 atm | 1.55 atm
Now if there are any leaks the hydrogen cyanide can’t get in or if it is a high wind day will at least come in slower. Again I can cover the habitat to compensate for the additional pressure. Now let’s look at a higher pressure outside.
Exterior | Interior
1.5 atm | 1 atm
This would seem ideal for building with brick, and it is. The exterior pressure compresses the structure nicely and might not even need to be covered. But there are drawbacks if the exterior environment is one like Titan’s with nasty stuff in it, so any small leak is going to bring in hydrogen cyanide and methane into our explosive oxygen environment. Then there is the added time and danger of pressurizing/depressurizing should you ever need to leave the habitat and work outside.
You may want to over-pressurize any structures on Titan slightly to prevent inflow of Hydrogen-Cyanide, but the cost savings still make it useful.
Oh man, yeah, let's crank up the internal pressure even more! My poor ear drums are hurting already
Cover your nose and swallow. Again, the pressure differential need not be great to be effective.
Do you know of another rocket engine into which you can dump pretty much any abundant gas and achieve sufficient thrust without an oxidizer?
You haven't shown that the nuclear rocket can provide adequate thrust either. But I'm curious, why not use an oxidizer? You can't just dismiss an option without giving some reason why.
I’m sorry, I thought most were aware of Atomic Rocket’s
most excellent engine list
You can use an oxidizer in your NTR if you wish, but it is not necessary, and LOX is heavy, rare stuff compared to hydrogen and most other propellants so often it is detrimental to bring it along when you don’t have to. There’s a design called the LANTR: Lox-Augmented Nuclear Thermal Rocket (It’s in the link too), which is essentially an NTR with a LOX tank and some pipes running to the exhaust nozzle. I mentioned it before in fact. The downside to this is that while dumping the LOX into the nozzle increases your thrust (force) it decreases your exhaust velocity (acceleration), so it’s good for takeoffs but not necessarily cruising.
Did you examine the downsides of using hydrogen? What about its lower density - how will that affect the mass of your tanks? Will hydrogen propellant provide sufficient thrust for the mission?
See above. A little hydrogen goes a long way. The biggest downside is storage, but not mass. Hydrogen is so small it will leak out of the tanks through the holes in between the tank’s own molecules, so it can’t be stored indefinitely, which is one reason you don’t often see it in deep space missions that have a lot of time between burns.
All you are showing there is that they aren't useful for liftoff, not that they are excellent once you get off Earth.
Did you consider electric or chemical rockets? Why did you decide against them?
I’ll copy from AR’s list to save people clicking back and forth. The maximum theoretical (not practical) limit for a chemical rocket (h
2 and O
2) is
Exhaust Velocity (km/s) | Thrust (Newtons)
4.5 | 1,669,000
The same theoretical maximum figures for a solid NTR are
Exhaust Velocity (km/s) | Thrust (Newtons)
12 | 7,000,000
Theoretical in this case means we lack the engineering to prevent these two drives from vaporizing themselves in the process.
You’ll need to be more specific what sort of electric drive? Solar Moth, Ion, VASMIR? Those all lose to NTR, and two of them would probably require a nuclear reactor or comparable power source to be viable. Solar Moth is nice because the engine mass is so small, which makes for a nice backup drive. Now if you want to look at practical, currently buildable NTRs, I’ve already posted the acceleration figures for various fuel mixes in a NERVA (1960’s technology) solid NTR engine, and those same values are also at AR. The thrust figures are all about 49,000 Newtons regardless of the propellant used, according to AR.
Oh, and for comparison: the 3 Space Shuttle Main Engines together (and the SSMEs are amongst if not the most powerful rocket engines in existence) produce 4.4 km/s in exhaust velocity and 6,834,000 Newtons of force, so we’ve done pretty much all the engineering you can do on chemical rockets. They’re as good as they’re ever probably going to get as far as current engineering is concerned.
Really. Does it. Even in the depths of interstellar space or say beyond the orbit of Mars?
No, solar's effectiveness drops off out there (I'd probably want to beam in power from the inner system). But that's not what you said: you said "ideal for space-based power"
Yes because running an extension cord millions of miles long is more practical than making the power on board. I absolutely want you in charge of NASA.
How big a laser/microwave dish would you need on the power station? How large would the solar array/rectenna be on the receiving end? What happens when the craft goes into the shadow of a planet? How big would the batteries be on board? How much would it cost to construct your power station in orbit?
An artificial sun shines brightly wherever it is. It is a reliable, predictable, consistent source of power no matter your distance or orientation to the Sun.
Your reason for going to Saturn is to fetch this shit; you aren't fetching this shit because you are going to Saturn and need power for that trip.
To fetch more of this shit (there’s quite a bit on the moon, enough to last us a while, 10,000 TW-Years, again according to Dr. Zubrin), but again my original argument wasn’t about the why of mining Saturn, but the how.
A 1,000 MW SPS would be 5 square kilometers in size and weigh in at 41,000,000 kilograms.
Size is irrelevant. Weight is irrelevant.
MASS IS EVERYTHING. Especially when you’re launching from a world of unusually high gravity for its neighborhood.
But, what's your source for the mass? I've read papers with proposals getting down to 1/8 that, and you can also do very well with a solar thermal plant.
Entering Space, pgs. 70 to 74. Let’s look at orbital solar power stations beaming their power Earthside first in terms of how much more power they’ll actually make in orbit compared to ground based systems of the same size.
Advantage of placing solar panel above atmosphere = 1.5x
Advantage of solar tracking = 4x
Total Advantage, gross time-averaged = 6x
Power lost through microwave beaming (assuming optimistic efficiency of 50%) = -.5x
Current Advantage = 3x over ground based systems
Increased power generation if ground based systems employed solar-tracking = 4x
Net advantage of locating solar panels in space and beaming the power to the surface = .5x
So at best you get 50% more power Earthside if you located the panels in orbit than if you put them outside your house. If you want me to explain the cost calculations of actually launching such a monstrosity into orbit I can, they favor your scheme even less.
I think we can build an orbiting D-He3 power facility for a bit less than that, but then we wouldn’t have to build it in orbit at all if our goal was power for Earth.
You "think"? Do you have any reasoning here at all? I'm not asking for strict rigor and sources, just some reasoning why.
To produce 1,000 MW of power using D-He3 fusion requires 0.00285 grams of 3He-D fuel per second. A good rough estimate for how massive such a reactor would be is 1,200,000 kg, or 34 times less massive than a similarly capable solar power satellite (Source: Atomic Rocket, see link above). Even assuming the reactor is less efficient than estimated it has a wide margin to play with before Solar is more effective per kg.
It is equally laughable for powering bases beyond that distance or of any self-sustainable size.
i laugh at the idea that the sun powers the earth
it is patently ludicrous
Look at what I wrote. Did I say “Heat a planet”, did I say “make plants grow”? No, I said power a base. Until all of humanity runs off solar & wind power, the Earth is not “powered by the Sun” in any realistic sense.
Regardless of your mischaracterization, it is unlikely that we will use He3 as a power source until we start expanding into the greater solar system for other reasons; there is more than enough nuclear fuel and other local sources to supply our needs for the near term. But again, the why was not my original argument. I was not seeking to lock down a timeline under which man WILL be at Saturn mining helium-3 and exporting it, I was merely arguing that Titan was a fine location for a base from which to do so.
If solar power can’t be made cost-effective here on Earth where we don’t have to spend the extra $40,000 per kg it takes to put something in GEO, how is it going to be profitable to do the same thing in space?
Do you know
why it doesn't perform well on Earth? Would those factors apply in space?
See above.
Also, do you know why the cost to launch something is that high? Do those reasons still need to apply in the future?
There is an actual limit as to how cheaply something can be launched using chemical means. That limit is the price and weight of the propellant. To launch something heavier (yes, weight is important here) you need more propellant. To carry more propellant you need to carry more propellant and to carry that you need more propellant, etc.
In other words the less you launch the better.
What about getting the materials to build the power satellites from space instead of launching them from Earth? Did you consider that as an alternative to launching them all? Why dismiss it?
You cannot suck silicon metal out of space, you have to go someone and find it. The Moon has plenty of silicon, but it is locked up in silicon dioxide, which requires heating it with carbon (which the Moon lacks) to separate it into silicon metal useful for making solar panels. So the Moon is out because the cost of importing the carbon eliminates the benefits of exporting the silicon. A lack of atmosphere also means you will be forced to expend additional deltaV to slow your freighters down for Trans Lunar Injection.
Mars is a better place to make silicon. Plenty of carbon and silicon dioxide and an atmosphere to reduce propellant costs, along with the ability to manufacture all your propellant there for the return trip means it might be economically viable to make solar panels and ship them back to Earth. The problem is what to do when you get them there. If you locate them in orbit you must expend propellant again (you can aerobrake them to accomplish TEI but you’ll need propellant to bring your freighter to the construction site accurately) And once you get up and running the most you’ll possibly get is a 50% bonus for putting the solar power in orbit.
Just deorbiting the solar panels and building them where you need them would likely more than pay for the additional aeroshielding and reduced power generation in saved maintenance and servicing (your solar power satellite can only get that extra 50% by tracking the sun, and it can only do that by either moving the entire satellite or moving just the panels, requiring motors, gyroscopes, and/or propellant, all of which will need to be serviced in some manner)
Prove it. Name another system that we could build with current technology that would allow you to achieve 10% or greater or C.
Laser beams. The power generation apparatus is left behind, and the spacecraft only worries about using the result.
What happens if the spacecraft moves behind a planet? What happens if your laser moves behind a planet? How much power will be lost for every extra light year? How big is the laser? How big is the mirror? What happens if the laser breaks? What if the spacecraft needs to change direction? How much power will it take? How do you generate that power?
And biggest of all perhaps, when it comes time to slow down so you don’t fling past your destination at an appreciable fraction of C, how will you do that if there is no laser station ready to go on the other end? I know a possible answer, but I doubt you do.
so why would we trade a small, fast, easier to use process for a larger, slower, and more difficult process.
Probably the same reason why we'd trade fission for H-3...
Well no because you see you actually make more power with fusion that fission, just look at A-bombs vs. H-Bombs. P-P actually produces power slower, also known as less powerfully. It just seems like a lot because the Sun is fucking huge.
Because there is simply not enough on Earth or within the inner solar system to sustain an interplanetary or interstellar civilization.
What's your reasoning behind this? How the damn much hydrogen does your civilization need?
That would depend entirely on how fast my civilization is growing, what my civilizations population is, how many spacecraft I have, how much power I need, etc. What matters is the amount of hydrogen available on Earth (even if you harvested all the oceans to get it) is inconsequential compared to the amount available in the outer solar system.
Because it is worth $1 million a kilogram. Deuterium is common dirt in comparison
Item A is obscenely expensive. Item B is common dirt in comparison. Both items A and B do the same thing.
They do not do the same thing, Item A is makes more power, more efficiently, and does so cleanly.
Let me tell you the real reason why airports and seaports are on the ground: that's where the people are. Sure, you could build an artificial island and dock your ship to it, but why would you? There's no passengers to pick up. No relatives living there to visit. No markets to whom to sell your cargo.
Does this apply when building on Titan vs building in Saturn orbit? (tip: no)
I wish to build a pyramid of limestone blocks. Do I build it next to the quarry, or on top of a mountain?
To build your Saturn station you need building materials. Since you’re building in a vacuum you’ll need material with good tensile strength, which means metals. You have to go somewhere to get that material because it isn’t sitting around at your construction site in nice piles. So you have to build a distant base to harvest the material first, which means you need to build a mining base, which takes material, etc. Or you can bring the whole damn block to you, waste material and all, which will cost even more propellant to effect a change in deltaV, and so on.
What you need to find is a nice place to build your operations base with abundant and effective local building material. That is Titan. It’s your quarry. You may well have to go elsewhere to get some materials, but because you can just throw them into a nice dense atmosphere to slow them down, and because you need only tank up on propellant to leave Titan it looks pretty attractive. Of course you’ll build a few stations in Saturn orbit for things whose final destination is not Titan, like the helium-3, but you’ll house your people and supplies on Titan because it is cheaper to get them there and house them.
In both cases the house at the bottom of the hill is easier to build. The same holds true for a base on a planetary body vs one on orbit.
You're actually somewhat right. Avoiding a gravity gradient does make things easier.
Now, do you see why this reasoning favors building in orbit over building on a moon?
Certainly, if I ever planned to lift my giant, heavy brick-built base into orbit, or bringing the helium-3 down to Titan before sending it back to the inner solar system, but I don’t plan to do either. Titan is not the export platform, it is the support platform. It need not be equally easy to get things out of it as getting things down to it.
I can build the base on the ground with cheap, heavy bricks, something I can’t do in orbit because weight is the deciding factor in any orbital operation (If that needs explaining it is because given two materials that do the same job but one weighs half as much, you will always pick the lighter one because your biggest cost is lifting weight to orbit)
No, no, no.
First off, weight doesn't matter in orbit. It does for the launch, but not in orbit.
Mass doesn't matter either (what's the difference between mass and weight?), if you aren't going to be changing orbits. (Quiz: why didn't I say "not going to be
moving"?)
If you build stuff out of materials already in orbit, the mass isn't terribly important. It most certainly isn't going to be the biggest cost.
First of all, fuck you and your condescension and patronizing tone.
Secondly, where and what are these fabled materials just sitting in orbit ready to be turned into a massive space station. How will you transport them from their disparate orbits to your construction yard? How will you power the machines needed to assembly it all? Where will you get the oxygen and other materials needed to supply your station residents and craft? How will you grow the food? These are all things you can accomplish on Titan relatively easily compared to an Saturn orbiting station.
Titan has many resources we’ll be glad to take advantage of, gravity, dense atmosphere,
These are hurdles, not advantages. I already discussed the atmosphere. The gravity is also a bad thing - enough to make travel non-trivial (climbing the mountain), but not enough to be Earth like; its gravity is less than our own moon's.
It is not currently know what long term effects living in lunar gravity would have on people's bodies.
Valeri Polyakov, First mission duration (zero-g), 240 days, 22 hours, 34 minutes. Second Mission Duration (zero-g), 437 days, 17 hours, 58 minutes.
If simple exercise can prevent him from collapsing under his own weight on return to Earth I see no reason to believe it could not do the same for any Titan miners. That is of course assuming they ever want to return to Earth.
It is possible that Titan living would have all the disadvantages of gravity, with very few of the advantages.
There have been to my knowledge no lasting medical effects to astronaut’s bodies linked to a lack of gravity upon their return to normal gravity, provided they exercise regularly while in orbit. The earliest astronauts did not have the space to exercise effectively in their small craft, but things have progressed quite a bit since the early days of Soyuz and Apollo.
In terms of resupply it is far easier to go outside and dig up a little soil than support an expedition to another natural body to get what you need and bring it back to your station.
Make the materials come to you; capture an asteroid, for example, and build around it.
You cannot do so for free. How much waste material are you prepared to move to supply your base?
I’m assuming for the initial construction you mean to use a metal rich main-belt asteroid. Putting aside that by the time travel to Saturn for helium-3 mining becomes desirable (i.e. when the Lunar helium-3 reserves approach the point of diminishing returns) humanity will likely have claimed and built substantial mining complexes on the most attractive asteroids, or mined some of them out, how will you transport the asteroid? How much deltaV will that require? How long will it take? When you get it there How will you power the machines needed to assembly your base? Where will you get the oxygen and other materials needed to supply your station residents and craft? How will you grow the food?
Because a D-He3 engine has an exhaust velocity of 7,840 km/s and a weight of about 1,200 tons.
Pardon the colloquialism, I think you know I meant mass. The point was that such an engine requires less material (in terms of both the actual mass of the engine and the mass of the propellant) than other designs per km/s of acceleration.
Any civilization using such a method of propulsion has cracked cheap surface-to-orbit rocketry.
Non-sequitur; one development doesn't need to have anything to do with the other.
A minor note: cheap does not mean free in this instance, but merely as efficient, inexpensive, and practicable as is theoretically possible.
The point was that a civilization contemplating interstellar travel via a D-He3 fusion drive is unlikely to be concerned with the minor cost in lifting a small amount of mining equipment from Titan orbit to Saturn orbit and back. It’s like caring about the effort required to put the pump nozzle into your gas tank when that same gas will allow your car to drive 300 miles before refueling. And as mentioned before the exportable helium-3 in this particular scenario would never be taken to Titan’s surface.
And even if we’re just talking about He3 for power generation Earthside the value of He3 justifies it.
So you dismiss space solar due to the cost of getting the materials to orbit, but now dismiss the cost of getting to orbit as being a solved problem? This is inconsistent.[/quote] Silicon weighs more than helium for a start. There’s also the benefit that a He3 tanker using a D-He3 drive would be carrying propellant and cargo in equal measures, and can trade speed for amount of cargo delivered directly. A silicon freighter cannot do so as effectively.
I have other reasons for dismissing orbital solar power as well, which are outlined above.
