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  1. - Top - End - #91
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by factotum View Post
    Escape velocity on Mars isn't as low as you maybe think it is--it's about 5km/s (compared to 11km/s for Earth). You would need a lot of acceleration in your mass driver to achieve that speed, and a very robustly designed craft to survive going through even the thin Martian atmosphere so fast.
    We don't need to escape to be useful. Getting orbital allows the use of more efficient low thrust engines, meaning that the mass driver only needs to provide 3.8km/s. Lets call it 4 to give us a bit more time to circularise.
    The top of Olympus mons is at a pressure of 72pascal, which corresponds to an altitude on earth of more than 40km. The X43 was designed to fly at 3km/s for a sustained period* at more than 1000 pascals (30km). I could not find data on the temperature of the atmosphere of mars at that altitude, so not sure about the density, but it can't be below -100C as CO2 would snow out. The air at 30km is at -80C on earth, so together with CO2 being ~50% more dense, we still get that the X43 was designed for an order of magnitude more atmosphere. You would be rising pretty fast too, so the atmosphere is not much of an issue.

    One quirk to consider is that unlike earth the atmosphere does not contain oxygen or hydrogen. That means that carbon based heat shielding is considerably more robust than for earth. It will still react to give carbon monoxide, but this is not nearly so much of a problem.

    *It never did, but it was designed to.

    The size of Olympus Mons is... impressive. It is about as wide as France. You could build 150km of driver if you started right at the base. That corresponds to an acceleration of ~50G. Not exactly human capable, but not too far out there for bulk cargo when you consider what we can fire out of guns, and that we have built rockets that do 100G.

    If you were to build the driver for 1000km on the flat leading towards the mountain, and then just worried about the turn onto the 1~7 gradient up the side of the mountain, and allow ourselves 5G on the turn (11 seconds), we get that we would need about 44km horizontal distance, and only 3km vertical distance. If we pretend that Olympus mons is a perfect gradient with a flat plane beside it, the height above the base of the mountain would only be 750m.


    The 'easiest' way to get off mars involving infrastructure is probably an 'air' breathing engine up to 1.9km/s (surface), zoom climbing, and then catching a rope dangled from Phobos. Yes it looks like something out of a cartoon, and the challenges involved in catching the rope in those conditions are extreme, but the physics works just fine. Air breathing* could pretty easily get to 1km/s, so even with a rocket for the rest you only need 1km/s, which is pre-tyranny as far as the rocket equation goes. A rocket second stage would let you maneuver higher anyway, and could be used for propulsive landings and takeoffs (Wing landings on Mars are hard). With enough time we could raise the orbit of Phobos to bring the velocity down (though requiring a stronger rope), to bring the docking velocity down. We would probably need systems in place to do this anyway, as otherwise we would eventually crash Phobos into Mars (though bringing the docking velocity up beyond what is possible would stop us first).

    *Using the atmosphere as a mostly inert working fluid, while bringing both fuel and oxidiser. Some carbon would be oxidised by CO2 into CO, and you could build it with just fuel, but the technical challenges are extreme.

    Step 2 might be building a mass driver instead of the aircraft. Getting to the 2km/s required for a capture is considerably easier than getting to 4km/s. Still hard, and now we are tied to locations. I don't know how close to equatorial the orbit of Phobos is, but significant deviation would make tight management of Phobos' orbit required in order to keep the positions syncing up. Always catching in the same place could result in significant eccentricity too.

    Step 3 would be raising Phobos to Mars synchronous, and using a conventional elevator. Craft catching the rope in front of Phobos apply a slight prograde force, so if they then swung back (slowing them down) and let go again, they would raise the orbit slightly. This could be done with no loss terms except energy.

  2. - Top - End - #92
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    Default Re: How to make space exploration profitable.

    Pavonis, probably, not Olympus. Pavonis is exactly on the equator.
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  3. - Top - End - #93
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    Quote Originally Posted by Eldan View Post
    Pavonis, probably, not Olympus. Pavonis is exactly on the equator.
    I get that for the space elevator, closer to the equator is better than the height advantage of Olympus, but is it that crucial for a mass driver? That's 12 km of extra atmosphere you are piling on.

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  4. - Top - End - #94
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Grey_Wolf_c View Post
    I get that for the space elevator, closer to the equator is better than the height advantage of Olympus, but is it that crucial for a mass driver? That's 12 km of extra atmosphere you are piling on.

    Grey Wolf
    But it's also free extra launch speed from the rotation of the planet.
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  5. - Top - End - #95
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    Quote Originally Posted by Lvl 2 Expert View Post
    But it's also free extra launch speed from the rotation of the planet.
    Yes, I understand that, but does it really compensate? That is a lot more km of atmosphere to slog through for the sake of the extra v. I'm not saying its right or wrong, I'm just asking for the numbers. Yes, if launching at equator vs wherever Olympus is means you get an extra 1 m/s for free, and slogging though the 12 km of atmosphere only takes away .5 m/s, then it's worth it. But I don't know what the actual numbers are, thus my question.

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  6. - Top - End - #96
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    Default Re: How to make space exploration profitable.

    The main problem with not launching on the equator is that it makes it much harder to achieve an equatorial orbit. You can't just launch due east from some point far north or south of the equator and go into a nice equatorial orbit, because the orbit by definition has to be an ellipse around the centre of mass of the planet. This is especially a problem if you're launching via a ground-based mass driver, because any fuel you have to load onto your craft for manoeuvring subtracts from the payload capacity.

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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Grey_Wolf_c View Post
    Yes, I understand that, but does it really compensate? That is a lot more km of atmosphere to slog through for the sake of the extra v. I'm not saying its right or wrong, I'm just asking for the numbers. Yes, if launching at equator vs wherever Olympus is means you get an extra 1 m/s for free, and slogging though the 12 km of atmosphere only takes away .5 m/s, then it's worth it. But I don't know what the actual numbers are, thus my question.

    Grey Wolf
    Well, I mean, on Earth, launching eastwards at the equator gives you a boost of about 450 m/s.

    Quick back of the envelope calculation... radius of the circle... sin of 90° - the lattitude...

    Okay, at 18° lattitude, where Olympus mons is, you'd still get 95% of the boost.

    Probably irrelevant then.

    Edit: but as the previous poster says, your orbit would be super-wonky.
    Last edited by Eldan; 2019-02-19 at 11:11 AM.
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  8. - Top - End - #98
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    Quote Originally Posted by factotum View Post
    The main problem with not launching on the equator is that it makes it much harder to achieve an equatorial orbit. You can't just launch due east from some point far north or south of the equator and go into a nice equatorial orbit, because the orbit by definition has to be an ellipse around the centre of mass of the planet. This is especially a problem if you're launching via a ground-based mass driver, because any fuel you have to load onto your craft for manoeuvring subtracts from the payload capacity.
    Fair but - and I'm sorry I'm asking what must be basic questions at this point - what is the advantage of equatorial orbit? Is that where we'd expect to park inter-planetary ships? I'm guessing we couldn't just catapult the cargo directly into Hohmann transfer with a mass driver? Or is equatorial necessary for that as well? (Earth equatorial orbit isn't aligned with the planet plane, is it? So you still need to make corrections to go from Earth to Mars if you start from Earth's Equatorial orbit?)

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    But really, the important lesson here is this: Rather than making assumptions that don't fit with the text and then complaining about the text being wrong, why not just choose different assumptions that DO fit with the text?
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  9. - Top - End - #99
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Grey_Wolf_c View Post
    Fair but - and I'm sorry I'm asking what must be basic questions at this point - what is the advantage of equatorial orbit? Is that where we'd expect to park inter-planetary ships? I'm guessing we couldn't just catapult the cargo directly into Hohmann transfer with a mass driver? Or is equatorial necessary for that as well? (Earth equatorial orbit isn't aligned with the planet plane, is it? So you still need to make corrections to go from Earth to Mars if you start from Earth's Equatorial orbit?)

    Grey Wolf
    If you are only sending stuff up occasionally, very little. If you are aiming for more than one launch a day though, things start to get messy. Your 4 O'clock launch will end up in a different plane than your 5 O'clock launch, and meeting them up will not be easy. Simply having that much stuff orbiting in different planes is asking for trouble, and a mass driver doesn't make much sense for low launch numbers. A mass driver on the equator could have every launch go towards an equatorial mega-station with only minor orbital manoeuvres after circularisation. All satellites could be forced onto non intersecting orbits or resonant ones, minimising the risk of something colliding with such a structure.

    For transfer orbits, being stuck on the equator is actually a bad thing. The insight lander launched from Vandenberg partly because the initial launch window needed a highly inclined orbit anyway. The direction you leave a sphere of influence is restricted to the plane you are in unless you are prepared to spend a huge amount of delta V changing that plane somewhere. Off the equator you get a whole range of inclinations simply from varying the time of day. This has positives and negatives.

  10. - Top - End - #100
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Fat Rooster View Post
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    Thank you, I think I follow now.

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  11. - Top - End - #101
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    Default Re: How to make space exploration profitable.

    Yeah, what Fat Rooster said. It does depend what the ultimate destination of your payload is, but it seems to make sense to consolidate multiple launches in orbit before sending them on to their final destination.

  12. - Top - End - #102
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    OK, this is what I have understood. Please let me know if I'm still misunderstanding something.

    We'd want to put the mass driver on the equator because, even though the mountain there is significantly smaller, it allows us to inject the payloads directly into equatorial orbit rather than having to give them extra fuel for them to adjust orbits after the fact. Sure, it will probably take more energy for the mass driver to get them into orbit, but a) it's the orbit we want off the bat and b) who cares? the whole point of the mass driver is that we can plug it to a land-based nuclear power and thus our energy budget for each launch is no longer subject to the rocket equation, because the fuel doesn't need to be lifted with more fuel.

    Is that broadly correct?

    Thanks,

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  13. - Top - End - #103
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    One thing that I don't think has been mentioned is that Olympus Mons only works for something like a mass driver. If you are building a space elevator, you are stuck with the equator.

    I don't believe that launching from Vandenburg (and getting a high inclination) gave any direct advantage to the delta-v requirements for going to Mars, but probably did help a lot in allowing arbitrary launch windows (launching polar means every 24 hours you are lined up for a launch, low inclination could leave long months off the table).

    There's also the issue of your ultimate orbit. If you want a transfer to Earth (or anywhere else in the Solar System), it may well make more sense to launch a mass from Olympus Mons with nearly escape velocity and fix the inclination in the same burn that circularizes (or in this case merely raises periapsis outside of the Martian atmosphere. Note that you will need such a burn regardless (unless you are willing to have an orbit that dips down to your launch altitude each orbit), so combining the two shouldn't be that much of a cost.

    I suspect that it will be generations before anybody really cares about launching Mars-built satellites into "Low Martian Orbit".

  14. - Top - End - #104
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by wumpus View Post
    One thing that I don't think has been mentioned is that Olympus Mons only works for something like a mass driver. If you are building a space elevator, you are stuck with the equator.
    Eldan mentioned it and, as per Fat Rooster and factotum, no, Olympus would not work as well as Pavonis even for the mass driver.

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    Default Re: How to make space exploration profitable.

    I need more information about this can anyone suggest me with some ideas.
    Last edited by abhi pranesh; 2019-02-21 at 12:49 AM.

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    Quote Originally Posted by abhi pranesh View Post
    I need more information about this can anyone suggest me with some ideas.
    Bets that in 9 posts this account posts a helpful link about a natural medicinal product that will help your rocket launch as often as it did when you were a teen?

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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Xyril View Post
    Bets that in 9 posts this account posts a helpful link about a natural medicinal product that will help your rocket launch as often as it did when you were a teen?
    Just as a heads up: I've gotten an official warning for replying to a spambot before. Report them if you're feeling generous, or try to ignore them.
    Last edited by Lvl 2 Expert; 2019-02-21 at 09:34 AM.
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    Quote Originally Posted by Lvl 2 Expert View Post
    Just as a heads up: I've gotten an official warning for replying to a spambot before. Report them if you're feeling generous, or try to ignore them.
    Ah, thanks for the heads up.

    I opted not to report because it was literally the only post the guy made, and just from the phrasing I thought it was plausibly an incredibly awkward attempt to make conversation or to crowd source an idea for a startup.

    In retrospect, if it was the former, the new guy might not take gentle teasing particularly positively.

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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Grey_Wolf_c View Post
    Eldan mentioned it and, as per Fat Rooster and factotum, no, Olympus would not work as well as Pavonis even for the mass driver.

    Grey Wolf
    Don't forget you have to slog through closer to 40km of atmosphere (assuming a 12km rise: you'll need about 1.2km/s delta-v to get beyond the atmosphere and 3.6km horizontal velocity. This gives you about an 18 degree launch angle). Or you go for extreme results and launch horizontally (which might save a whole .2km/s plowing through a huge swath of atmosphere).
    -Note: I think I botched this and you need 3.8km/s launching horizontally (before air resistance). Expect to add another .2km/s to launch at 18 degrees (or adjust to balance air resistance vs. delta-v spent on launching less horizontally).

    Launching closer to escape values would likely make Olympus a better site. And for "wonky orbits", anything launched out of Kennedy has a considerably more wonky orbit: KSC is at 28 degree lattitude (Wallops is at 37, Baikonur launches to more than 50 degrees (ISS is 51.6), although some of that is to avoid launching over China. Vandenburg is irrelevant as it only launches polar orbits).

  20. - Top - End - #110
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    Quote Originally Posted by wumpus View Post
    And for "wonky orbits", anything launched out of Kennedy has a considerably more wonky orbit: KSC is at 28 degree lattitude (Wallops is at 37, Baikonur launches to more than 50 degrees (ISS is 51.6), although some of that is to avoid launching over China. Vandenburg is irrelevant as it only launches polar orbits).
    If I understood their point correctly, it is not that easy:

    KSC* launches things that carry their own fuel, and thus need to carry fuel to lift that fuel. And fuel to lift the fuel that lifts the fuel. Etc. But since they do carry all that fuel and have the engines, they can then do orbit correction.

    The idea for a mass driver is to minimize the need for all of that, though, so turning around and putting a whomping great engine so it can course correct seems unlikely to be as efficient as shooting the loads straight into the most useful orbit and send them up with just maneuvering fuel for tiny corrections. And in the spot where you'd put the fuel and engine, you can put more cargo. If it takes a bit more energy to get them through the extra 12 km of atmosphere, well, just throw another rod into the barbie of the planet-side nuclear power plant.

    Grey Wolf

    *I can't help but read this as "Kentucky Sfried Chicken". You Americans are way too good at branding.
    Last edited by Grey_Wolf_c; 2019-02-21 at 02:03 PM.
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  21. - Top - End - #111
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by Grey_Wolf_c View Post
    The idea for a mass driver is to minimize the need for all of that, though, so turning around and putting a whomping great engine so it can course correct seems unlikely to be as efficient as shooting the loads straight into the most useful orbit and send them up with just maneuvering fuel for tiny corrections. And in the spot where you'd put the fuel and engine, you can put more cargo. If it takes a bit more energy to get them through the extra 12 km of atmosphere, well, just throw another rod into the barbie of the planet-side nuclear power plant.
    The payload will still some sort of engine to circularise it's orbit, otherwise the best you can do is drop the payload back on the mass driver after one loop. Another option might be to have a tug in orbit to catch it, but then the tug will be using fuel to intercept then circularise the payload. Even if you're shooting for a transfer orbit to Earth, you'll need engines to stop when you get there. Unless you're shooting at Earth I guess.

    The mass driver can greatly reduce the fuel needed, bit it can't completely remove the need for engines.
    Last edited by Excession; 2019-02-21 at 04:28 PM.

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    Quote Originally Posted by Excession View Post
    The payload will still some sort of engine to circularise it's orbit, otherwise the best you can do is drop the payload back on the mass driver after one loop. Another option might be to have a tug in orbit to catch it, but then the tug will be using fuel to intercept then circularise the payload. Even if you're shooting for a transfer orbit to Earth, you'll need engines to stop when you get there. Unless you're shooting at Earth I guess.

    The mass driver can greatly reduce the fuel needed, bit it can't completely remove the need for engines.
    "Tug to catch it". Docking would require matching the exact [non] orbit of the launched device. Hitching a cable and pulling it in one direction might work, but I expect the length of cable to be extreme (and have to be some carbon fiber line). Hitching a fuel pipe and adding fuel would have even worse length issues, but might work if you can pump fast enough. The worst part is that the really high-efficiency bits that work out in space (ion thrusters) aren't likely enough to raise a mass driver shot to orbit. They might work fine for going from low Mars orbit to nearly escape orbit.

    I get the feeling that learning to use a "catch with a tug" orbital insertion will make SpaceX's "how to land a rocket" blooper reel seem dirt cheap. It might be a great technique, but it has a lot of challenges.

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    Quote Originally Posted by Grey_Wolf_c View Post
    *I can't help but read this as "Kentucky Sfried Chicken". You Americans are way too good at branding.
    I can't help but read it as a Kerbal Space Center. But this thread made me dig out Kerbal again, yesterday. I dicked around a bit and failed to get a mission back from the moon.
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    These are humans we are talking about. If we get a permanent presence in space, we will find a way to make it profitable.

    The most obvious thing, though, is the asteroids. They have metals, carbons, volatiles, water...everything needed to expand in space.

    Once you have ISRU working in the asteroids you have centuries of fuel, oxygen, construction material...whatever is needed.

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    Quote Originally Posted by halfeye View Post
    Following on from the life on the moon thread, if a little over one pound of e.g. toffee (because that's easy to make, something easier would be better, but I'm not a sweetmaker so I don't know what's easier than toffee) was made in space, and divided into pieces of approximately one half, one quarter, one eighth, one sixteenth down to perhap a one tenth of a gram size, then each piece auctioned off with a reserve price of three times the cost of production including the costs of taking the ingredients to orbit and bringing the product back down, I think that with a nice little certificate of authenticity those would sell.
    Gold. It is strongly suspected that the amount of gold that we actually have and the amount of gold that is "owned" though holding companies is not even close. Basically if a holding company can "sell" the same bit of gold to multiple folks . . ..

    When the apocalypse comes and gold, bullets, zombie ears, Twinkies, and cigarettes are the currency . . . that space gold will be worth its weight in gold.

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    Quote Originally Posted by darkrose50 View Post
    Gold. It is strongly suspected that the amount of gold that we actually have and the amount of gold that is "owned" though holding companies is not even close. Basically if a holding company can "sell" the same bit of gold to multiple folks . . ..

    When the apocalypse comes and gold, bullets, zombie ears, Twinkies, and cigarettes are the currency . . . that space gold will be worth its weight in gold.
    The problem is that the launch costs to orbit of any mass are greater than the value of that weight in gold. Getting stuff down from orbit in a collectable way (dropping it so it can be picked up by random people would lead to 70% going into the seas) is nearly as expensive, and you have to get whatevers going to do the mining up before you can even think about getting stuff down. Even diamonds and platinum aren't worth enough to make space mining profitable. There is also the problem that most value is based on rarity, and as the rarity drops, so does the price.
    Last edited by halfeye; 2019-04-05 at 01:38 PM.
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    Quote Originally Posted by halfeye View Post
    The problem is that the launch costs to orbit of any mass are greater than the value of that weight in gold. Getting stuff down from orbit in a collectable way (dropping it so it can be picked up by random people would lead to 70% going into the seas) is nearly as expensive, and you have to get whatevers going to do the mining up before you can even think about getting stuff down. Even diamonds and platinum aren't worth enough to make space mining profitable. There is also the problem that most value is based on rarity, and as the rarity drops, so does the price.
    As far as I know, all "space mining" proposals involve locating a valuable asteroid (preferably composed of something like platinum or iridium) and then bringing the metals back from the asteroid belt (probably smelted, but possibly just haul the whole asteroid).

    This almost certainly involves ion propulsion and a lot of time (possibly using gravity tricks, which greatly limits your choice of asteroids). The time between launching the miner and returning with [each] asteroid is probably what makes the whole process uneconomical: the "interest counter" starts when you begin construction of miner and pay launch costs, while the payback doesn't happen until after you collect the asteroid dropped back onto the Earth (presumably involving wildly fun politics to find somewhere that will allow things returned from orbit *and* have sufficient rule of law to allow the miners to claim their property without too much competition from bandits).

    It probably isn't that hard to price out a mission where the raw value of returned ore is more valuable than the raw value needed to obtain it. The 10 year delay (or more) that accounting demands interest be added to the cost is something else. Maybe, just maybe you could cover the costs on the third trip to the asteroid belt (ion propulsion is great at that type of thing), but that means you are just barely breaking even. The whole point is that economic space mining can't look anything like a NASA return sample mission (or even picking up large diamond isn't profitable): it has to move things like asteroids that aren't locked at the bottom of a gravity field (even if you need plenty of delta-v to send them to Earth).

  28. - Top - End - #118
    Ettin in the Playground
     
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by wumpus View Post
    As far as I know, all "space mining" proposals involve locating a valuable asteroid (preferably composed of something like platinum or iridium) and then bringing the metals back from the asteroid belt (probably smelted, but possibly just haul the whole asteroid).

    This almost certainly involves ion propulsion and a lot of time (possibly using gravity tricks, which greatly limits your choice of asteroids). The time between launching the miner and returning with [each] asteroid is probably what makes the whole process uneconomical: the "interest counter" starts when you begin construction of miner and pay launch costs, while the payback doesn't happen until after you collect the asteroid dropped back onto the Earth (presumably involving wildly fun politics to find somewhere that will allow things returned from orbit *and* have sufficient rule of law to allow the miners to claim their property without too much competition from bandits).

    It probably isn't that hard to price out a mission where the raw value of returned ore is more valuable than the raw value needed to obtain it. The 10 year delay (or more) that accounting demands interest be added to the cost is something else. Maybe, just maybe you could cover the costs on the third trip to the asteroid belt (ion propulsion is great at that type of thing), but that means you are just barely breaking even. The whole point is that economic space mining can't look anything like a NASA return sample mission (or even picking up large diamond isn't profitable): it has to move things like asteroids that aren't locked at the bottom of a gravity field (even if you need plenty of delta-v to send them to Earth).
    People keep saying it's difficult to move asteroids to Earth. It's not trivial, but it's a lot easier than people seem to think, the Earth is in the plane of the Ecliptic, and so, approximately, are the asteriods. The asteroids are in higher orbits, so you need to slow them down a bit, but then if you get it right, they will just drop down towards Earth's orbit, and if you hold them in a slightly higher orbit until the Earth comes by, then you can drop them into an orbit near Earth, and then catching them is a matter of getting the approach right. I think we really ought to avoid anything Chicxulub big while we're practicing.

    For propulsion I favour solar sails myself, They're as near to a free lunch as we're going to get.
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  29. - Top - End - #119
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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by halfeye View Post
    For propulsion I favour solar sails myself, They're as near to a free lunch as we're going to get.
    But they need to be positively huge to have an impact on anything happen, and they get the most traction moving away from the sun. I guess you could drag one behind an asteroid like a drag parachute, tipping it slightly towards the sun, pulling outwards to slow down, but it's going to take a while. Fuel cost for that stage is minimal, I'm just unsure of all other costs.
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  30. - Top - End - #120
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    BlackDragon

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    Default Re: How to make space exploration profitable.

    Quote Originally Posted by halfeye View Post
    The asteroids are in higher orbits, so you need to slow them down a bit
    You need to slow them down a *lot*. To get from Mars orbit down to Earth orbit requires about 2.9km/s delta-V, and that just gets the asteroid to Earth--you need to do another manoeuvre once it gets there in order to capture it, else it'll just swing right back out to Mars again. Anything beyond Mars orbit (e.g. most asteroids) will take more delta-V than that.

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