Hello, gentle dopers. I’m writing a science fiction story about prospecting in the asteroid belt. My research into the “vermin of the skies” has been quite interesting. But my knowledge of orbital mechanics is quite limited. That’s where the many huge throbbing brains on this board come in.
My prospectors are setting out from Mars (more accurately, Diemos), checking out a few promising-looking asteroids before setting up shop and extracting precious metals from a choice hunk of rock. Then, with a hold full of gold (or perhaps some other, more precious mineral or metal), they return to Mars rich men and women.
That’s the plan, anyway. Of course it doesn’t work out quite that way, but therein lies the story, eh?
I was thinking a total travel time of about 10 months. Is that possible? Reasonable? Does anyone know of an online resource that would help me caculate orbits? I want to set this about 150 years in the future. No warp drives or anything like that, but a fusion-powered reaction drive that you could refuel by exploiting a passing comet or asteroid is perfectly legit.
Any help with or comments on the design of my prospecting ship and the navigation thereof would be greatly appreciated!
I don’t know anything about this but here is a page on orbital mechanics that might give you a kickstart.
One other thing…realize that most trips in space require a decceleration as much as an acceleration phase. That is…you may spend three months picking up speed but you’ll then need three months to slow down again (loosely speaking…how fast the object is moving that you are trying to match speeds with at the end of your journey may affect this).
Orbital mechanics would be useful, but you also have to fill in some blanks. What kind of thrust can
your hypothetical fusion drive produce? How long can it keep it up? What payload are you talking?
Are you going to ship raw ore or smelt the metal in place? If the first option, you might just strap a
booster to a hunk of asteroid. If the second, you might use a mass accelerator to launch the processed goods back to
civilization. In either case, chunks of rock or metal don’t need to eat or breath, so they can be launched back
slowly on an energy-saving trajectory while the crew might prefer a powered trajectory so they can get back to
the fleshpots of Mars in a hurry.
If fuel and propellant are expensive, and you are carrying non-perishable cargo (which you are), the most energy-efficient orbit is an elliptical orbit which is tangent to both orbits (i.e. orbit of the starting point and orbit of the destination). The period of this transfer orbit would be somewhere between the orbital period of the start point and destination. So travel time would be half of that.
If you have a fusion reactor, I guess energy would be cheap. I’m not so sure about propellant, but if the drive has a huge specific impulse (efficiency) that may be cheap too. In that case you can shorten the travel time as much as you want to, limited only by relativity.
By the way, do you think asteroid mining makes sense if you want material to use on a planet? I’d think it’s easier to mine the planet. In most science fiction, asteroid mining is only used to supply a space-based industry because it’s cheaper than bringing up material from a planet.
A hold full of iron, magnesium, or nickle isn’t going to make anyone rich. I suppose some of those organic compounds that are found in trace amounts could be interesting, but how are you expecting to process millions of tons of raw material in space from inside your one spaceship?
Normally, one talks of mining asteroids for iron, but the surface soil of Mars is basically iron ore, so iron wouldn’t be an economical choice. I’d go with nickel: It’s not as glamorous as gold, but there’s plenty to be found in the asteroid belt, and a large enough quantity of any metal can be valuable.
To clarify what scr4 said, an economy orbit would be half a period one way, and Mars has a two-year year (asteroids would be somewhat more), so for a round trip, you’re talking at least two years. Your practical upper limit on speed would probably be that you don’t want an acceleration higher than one g, but a one-g round trip would only take somewhere in the vicinity of a few days, so with the right choice of engines, you could have a ten-month round trip. If I’m feeling really bored later today, I might try to calculate the acceleration needed to make a 10-month asteroid run, but don’t count on it.
Well, the geochemistry involved does actually increase the amount of precious metals in iron meteorites above what’s found in planetary crusts. The abstract below (publically available on the indispensible Astrophysics Data System Abstract Server) is from a relevant paper. The paper itself, as I recall, was a bit dodgy on the economics of bringing that much stuff back, but it should be a starting point for a story…
From the Journal of Geophysical Research – Planets, vol. 99 1994, by Jeff Kargel
Abstract
Recent discoveries of near-Earth asteroids (NEAs) and chemical analyses of fragments of asteroids (meteorites) suggest that there may be a gold mine, literally, in
near-Earth space. Judged from meteorite analyses, two types of asteroids offer particularly bright prospects for recovery of large quantities of precious metals (defined as Au,
Pt, Ir, Os, Pd, Rh, and Ru), the ordinary LL chondrites, which contain 1.2-5.3% Fe-Ni metal containing 50-220 ppm of precious metals, and metallic asteroids, which consist
almost wholly of Fe-Ni phases and contain variable amounts of precious metals up to several hundred ppm. The pulverized regolith of LL chondrite asteroids could be
electromagnetically raked to separate the metallic grains. Suitable metallic asteroids could be processed in their entirety. Statistically, there should be approximately six metallic
NEAs larger than 1 km in diameter that contain over 100 ppm of precious metals. Successful recovery of 400,000 tons or more of precious metals contained in the smallest and
least rich of these metallic NEAs could yield products worth $5.1 trillion (US) at recent market prices.
I ask again, exactly what would be necessary to process 100 ppm (0.01% or 10,000 tons of asteroid to gain one ton) of precious metal in space? How much metal would have to be returned in order to finance a space mission? How would one go about returning 400,000 tons (800,000,000 pounds) of metal from space to wherever it is needed? How many ships, carriers, factories, staff? Is this scaleable down to a few prospectors and a spaceship?
Asteroid mining is potentially interesting. But it is not analogous to grizzled prospectors and their mules in Arizona.
As Exapno Mapcase pointed out, you will need to do a little infrastructure development.
As far as the OP goes, scr4 gave you an impressively concise description of a mathematical headache, but you have another problem.
This one:
[sup]emphasis mine[/sup]
Contrary to what George Lugas showed on screen, asteroid belts aren’t that dense (at least “ours” isn’t). You will need to establish some reasonable orbits and separations for your likely asteriods, and calculate a veritable crapload of tangent orbits. I say fudge it, it’s not a funding proposal.
Why not? Say we found a Mars colony 50 years from now. That leaves fifty years for some growth, and provides a very creditable explation for the pressing need for new wealth. You’re right about the moons. Deimos and Phobos are relatively dinky rocks, but that’s a good thing. Low escape velocity.
Gosh y’all! Thanks for the interesting and informative discussion.
As several of you have pointed out, the biggest hurdle in developing my story right now seems to be justifiying the economics of the expedition. Expano Mapcase is correct in his/her assertion that asteroid mining is quite different from the miner '49er, but I think the economic incentive to set off in a rickety old ship would be similar. How many prospectors actually hit the motherlode and got rich? How many found just enough gold dust to get them drunk in town for a couple of weeks and finance another expedition? How many disappeared into the desert and were never heard from again? And yet there were still plenty of volunteers.
However, Expanos’ point is well taken. It would be really hard. But one does not have to process the full 400,000 tons of platium, gold, etc. One could merely fill the hold of the ship with, say, 50 tons of platinum and gold. That’ll buy another load of propellant for another trip. Furthermore, if one is the first person to set foot on the asteroid, one would be able to claim the mineral rights, which would be worth a mint. Literally. But you have to return to Deimos Station with proof that you were actually there, right?
Or maybe in the future they have set the bar for mineral rights a little higher. How hard would it be to change the orbit of your average-sized asteroid to send it careening inward from the belt into the vicinity of Mars, where its resources could be more easily exploited? Would that be easier for a small crew to accomplish than, say, setting up a solar oven and refining out the good stuff on site?
Exgineer, I am aware of the low density of the asteroid belt. That’s why I was thinking ten months total trip time. But I could expand it to 18 months or two years, if need be. Could you get from average asteroid A to average asteroid B in two weeks?
Wouldn’t there also be a problem of bringing back more of a mineral than the market could bear and depressing the price? That is exactly the problem that the diamond market has and why DeBeers hordes them and doles them out sparingly.
Kniz is right about the unintentional effects of a large strike being to depress the market rather than enhance it.
Mining is actually a terrible occupation for an individual to go into. It’s oddly both heavily capital and labor intensive, in that you need enormous amounts of manpower to dig and process the enormous amounts of ore needed to get the fractional amounts of precious metal (or gems) that are at the core. Mining powers are huge firms, and usually oligopolies, so that they can control production and sales to keep the base price sufficiently high to keep all that machinery and labor in operation. And yet, when’s the last time you heard of a mining stock being touted for its fast growth potential?
A future society that has rickety old spaceships lying around also will have huge industrial interests that have already staked out all the really good potential asteroids. And buying the propellant is the least of the worries. How much does it cost to feed and confort a crew on a 10 month or two year voyage? What would it take to reduce an asteroid to 50 tons of pure metal? How pure could guys in a rickety old spaceship make it while in space? Who is the buyer for gold with lots of impurities anyhow?
Old-time prospectors got away with their lives mostly by starving. Their base costs were next to nil and they still found it hard to manage. Space prospecting base costs are in the tens or hundreds of millions. Mom and pop operations may still be possible in them, but the days of space galoots taking off from Mars City to mine a hull-load of goshwowium crystals so that they could party with the four-breasted hostesses at Madam Robotica’s Palace of Perversion went out with Overwhelming Tales of Stupor Science magazine.
In other words, you’re going to have to work out a plausible background to make the foreground possible. It’s one of the huge hurdles of hard science fiction.