Originally published at: https://boingboing.net/2017/12/28/nasa-uses-450000-gallons-of-w.html
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The amount of systems needed to propel people and cargo into space is staggering.
Will we never just get into a space car and drive to the moon, Millennium Falcon style?
Damn you, Real Physics
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After the cover screencap, I think I must refer this thread to the “is it phallic” debate going on next door:
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It’s probably possible, but not in a rocket. The rocket equations and the propellants we have to work with are too limited and the physics of getting into orbit are just too demanding. That mostly goes for nuclear rockets as well, even if we were able to build one that wouldn’t unacceptably contaminate the launch site, which right now, we can’t. Elon Musk wants to believe that he can reduce the cost of getting into orbit by 100x, but I doubt it’s possible - the mechanical stresses and extreme conditions required of any earth to orbit rocket are just too extreme to ever allow us to make them as cheap as jet aircraft.
If we invested in (for example) a space elevator or a catapult launch system to get things into orbit, then yes, it’s conceivable that going into space could become a routine matter. The problem is that building something that makes going into space routine requires such a staggering investment that it only makes sense if you are needing to send massive amounts of cargo and people into space every single day – and it’s very hard to find a compelling non-bogus reason why it would be a wise use of resources to do that.
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Beanstalk type space elevators are probably impractical. Let’s say we figure out how to mass-produce long-chain carbon nanotubes. The beanstalk will be bombarded with micrometeorite impacts. It’s under such tension that as the polymerized bonds break, they whip back against themselves with incredible force, breaking more bonds. So it’s not enough to have a beanstalk that can support the relatively light elevator carriages. It also has to support a micrometeorite shield sheath as tall as it is, and it has to be indefinitely maintained along the entire length as it slowly pocks from impacts. The thinner the shield, the more vigilant the required maintenance.
Finally, if it breaks near the base from attack or atmospheric disturbance, the segment above the break just drifts into a higher orbit, but if it breaks higher up from attack or micrometeorites or space junk, the segment below the break whips against the ground. So they’re unstable and probably not feasible.
Moreover, they’re probably an inferior choice. Space elevators are static engineering, but space exploration typically works better with dynamic engineering (such as bi-elliptic and Hohmann transfers, Lissajous orbits, cycler orbits, ect…). Momentum exchange tethers (AKA rotovators) are vastly simpler to build than beanstalks and are scalable. Combined with high-altitude aircraft and/or linear motor catapults they could vastly reduce the required on-board reaction mass, allowing the use of solar and other energy sources to do things like trim the teather’s orbit and power the catapults.
Beanstalks are so last century. 
Disclaimer: I strongly doubt we will ever settle the heavens in these Earth-optimized sacks of watery meat, but we can and absolutely should continue exploring space and possibly sending robots for some resources we damage our home planet by extracting from the ground, such as metals. Therefore propulsion research is a legitimate interest to space science.
“Once you’re in orbit, you’re halfway to anywhere.” ~ Robert Heinlein
But the glass-is-half-empty side of that quote is that it takes as much effort to get into orbit as it does to go somewhere else.
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When I read about this during the shuttle program I was bummed out. Sleek powerful spaceship that would rattle apart without being doused with water.
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The Flying Brick wasn’t all that sleek.
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Hey I had one of those when I was a kid! Just fill it with water and pump it up, it could go way over the house!
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Yes… and as long as units of distance are mistaken for units of time.
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I didn’t remember those. Space elevators have always been an extremely out-there concept that requires material science that’s theoretically possible but not yet existing. The point stands - rotovators or elevators or hypersonic linear accelerators or something neither of us has thought to mention all stand to potentially reduce the cost of space travel to “jump in the Millennium Falcon and go” levels (reducing costs from a hundred million to a few hundred thousand per trip), but they all require huge amounts of traffic going to and from space to be practical and affordable.
Creating a spacefaring economy has always foundered on figuring out what things we need/want to do in space that will justify the extravagant cost of setting up the space infrastructure needed to make a spacefaring economy doable.
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It’s important to realize that the vastness of space means it’s a centuries long project even to step out into the rest of the solar system in great depth. I think we’ll be doing well if we get something even close to the launch pipeline I described going by the end of this century. Nowadays people want everything finished yesterday. Rome wasn’t built in a day. Space exploration is the work of generations and the economies involved take longer to reach than the tech.
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I probably still have mine somewhere in the basement. You can’t get them anymore (because shoot your eye out).
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From Earth, yep, probably so.
OTOH, from the Moon?
Turns out a lunar beanstalk could be built from the lunar surface to the Earth-Moon L1 or L2 LaGrange Points, using existing materials and technology. No magic carbon nanotubes needed. (-;
Because the Moon is tidally locked to the Earth, the Earth-Moon LaGrange Points are, conveniently, also “luna-synchronous.” Typically, the cable would run from near the lunar equator to the L1 or L2 point, but one could also be built very close to the poles.
The lunar poles have water, and peaks with “eternal sunlight” for constant high-intensity solar power.
The cable could also function as a supply pipe, exporting water (or hydrogen/oxygen produced from water) for use in deep space.
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Water curtains can also be used to oxidize metal vapors in rocket exhausts, rendering them less dangerous to humans, but this isn’t a factor in public launches.
The launch infrastructure for big rockets, like the Saturn V for example, includes channels to direct hot gasses and landscaping to direct shock waves, so the large storage tanks near the pads won’t be punctured or shattered every time you light the match.
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If it was a real Orion, I think they’d need more water.
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Sorry, the amount of solar power delivered by those eternally lit peaks will not provide a significant amount of power.
Those eternally sunlit areas comprise in total, “a few football fields”.
Some figures:
- On earth, one hectare of solar panels delivers a bit less than 1 gigawatt per year of solar power. That’s the average for all solar installations in the US, most of which are in the desert Southwest.
- in space, you get about 3x as much solar power per area as a dry sunny desert on earth.
One gigawatt hour per year equals 114kw per hour, if i did my math right. So if “a few football fields” constitutes 10 hectares, and we totally blanket those areas with solar panels, we will get 114x10x3 = around 3,500 kilowatts per hour.
That’s a lot for powering battery operated robot rovers and it might be enough for keeping the lights on in a small manned research station. It’s a pittance for any kind of large scale industrial use.
PS: It’s totally possible to power a polar lunar mining base, without messing around with those eternally sunlit peaks. Run power lines from the pole to 3 solar power installations a hundred or so Km from the pole, equally separated in longitude. At least one power station will always be in sunlight, and you can build as many thousands of hectares of solar panels as you need to power your mining operation.
eta: added citation links.
eta2: Some examples of energy demands that a Lunar ice-mining operation might have:
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Heat of fusion of ice is 334 mj per tonne, about 93 kw, but we’ll be heating mixed ice-rock, if we’re very lucky and the ore we mine is around 50% ice, and allowing for distillation, pumping, and filtering, we’re looking at about 200 kw to melt and extract a ton of water from the “ore.”
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If we’re using it for rocket fuel, then we need 50kw to perform electrolysis on 9kg of water, producing 1kg of hydrogen. Our 10 hectares of solar panels produce only 84,000 kwh per day, so at the very maximum, we can produce 1.6 tonnes of hydrogen per day.
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Liquification of hydrogen takes 10kw/kg, or 10,000 kw/tonne. At an absolute maximum, we can turn 8.4 tons of hydrogen into LH2 per day.
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The Atomic Rockets site includes figures for an earth orbit to lunar orbit nuclear powered cargo/passenger transport, which, if I read the tables correctly, would require 40 tonnes of LH2 per round trip. It would take 24 days to produce that much hydrogen from water and another 5 days to turn it into LH2, so we’re looking at a maximum of 1 cargo ship per month being fueled by our mining station if we just use the power from the eternally sunlit areas at the pole.
PPS, I tried to calculate the energy required for the actual mining operation, but the figures I found were in liters of diesel per day, and figuring the conversion to electric vehicles defeated me, especially since most of the numbers I found were relevant for cars and I don’t know how well they would apply to heavy earth moving equipment. For those braver than I, An open pit mine on earth processing 10,000 tonnes of ore and rock per day uses 4,751 liters of diesel fuel per day (they also need 3 tonnes of explosives per day).
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I think it was Tim Allen who said, “I remember when toys could kill a kid!”
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