Consider a planet which is entirely Earth-like. Same mass, same rotation, etc. But in this world, resource-rich objects are suspended by some phenomenon at varying altitudes up to 200km above sea level (effectively from the surface, since the highest point, Mt Everest, is >9km above sea level). Clarification: some are at 200km, some are at 5km, 50km... They are fixed relative to the planet's rotation, thereby always being above the same point on the surface. The resource is valuable, and must be harvested by a machine such as a modern backhoe loader (e.g. the arm on the back of a JCB digger).

How might a society with approximately our level of technology exploit these resources?

Up to perhaps ~10km, specialized helicopters or airships could be flown.

Anything at or above the Kármán line would pose a problem: the orbital period is 1 day, but the altitude and hence orbital velocity is far lower. An asteroid in a Keplerian orbit would be straightforward, if not cheap to harvest: a spacecraft could match its orbit. But in this case, if a regular spacecraft or spaceplane attempted to orbit at the same altitude, it would fly past the target very quickly.

Between the limit of helium balloons and the edge of space, there may be other problems.

How could people harvest the resources of the higher objects?

  • $\begingroup$ @Abigail Let's suppose that the mechanism cannot be harnessed. $\endgroup$ Jan 12, 2019 at 11:01
  • $\begingroup$ How large are these objects, typically? $\endgroup$
    – notovny
    Jan 12, 2019 at 11:07
  • $\begingroup$ @notovny Linear dimensions of order 1 to 10m. $\endgroup$ Jan 12, 2019 at 11:12
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    $\begingroup$ Would shrapnel and debris chipped off of the objects fall to Earth, or would they continue in suspension? How does the magic determine what is to fall or hover? $\endgroup$
    – user44399
    Jan 12, 2019 at 18:59
  • $\begingroup$ Easy, you use vessels "suspended by some phenomenon". Until we understand that phenomenon, we don't go to space today. Y'all go ahead and build big dumb rockets; we're going to unlock the secrets of the cosmos. $\endgroup$
    – Mazura
    Jan 12, 2019 at 20:28

2 Answers 2


Ballistic Trajectories

This is actually easier than getting to space. Space is hard because you have to go really fast to be in an orbit.

Achieving orbital height is easy. Achieving orbital velocity is hard.

So you build a rocket right beneath your "geostationary" resource, and give it just enough fuel to reach the height you need. Your rocket releases a payload, which has exactly zero velocity when it reaches your resource. The payload grabs on to an outcropping, or uses a harpoon, or otherwise attaches itself to the valuable thing.

Now, either the magic that keeps the resource in the air keeps your payload in the air, and it starts harvesting, or the whole thing is now too heavy for the magic and it falls towards earth, in which case the payload controls the landing.

This is hard, but not as hard as actually harpooning an asteriod, which we have done.

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    $\begingroup$ Technically, would you not point the rocket slightly ahead of the object, since the object's ωr would be higher than the rocket's on the ground, so you need to increase your angular velocity a bit? $\endgroup$ Jan 12, 2019 at 14:06
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    $\begingroup$ Valentin - Yes, and you'd have to account for air resistance, cross winds, etc. The engineering implementation is non-trivial, but it's still easier than pretty much all other space operations. Your mass budget is much looser, because the speed is much lower. $\endgroup$
    – codeMonkey
    Jan 12, 2019 at 14:12
  • $\begingroup$ I would assume that you would need the active control systems of something like modern day's Falcon 9 to reach an object, probably use a small amount of thrust to loiter for some time, assess the situation etc and then have a controlled landing like F9's first stage. I think this would be trickier for Vostok 1 levels of technology, for instance. Of course, private companies would have a lot more incentive to innovate. $\endgroup$ Jan 12, 2019 at 14:27
  • $\begingroup$ Heck, up to 50 km or so you could use balloons. $\endgroup$
    – Joe Bloggs
    Jan 12, 2019 at 14:28
  • $\begingroup$ Valentin - probably not required but certainly very useful. I could see an alternate history space race where the US and USSR are struggling to mine this in the 70s and 80s. They would definitely develop Falcon like thruster systems eventually. $\endgroup$
    – codeMonkey
    Jan 12, 2019 at 14:34

Send impactors against them to reduce their momentum. They will lose altitude. After they descend some the increased atmospheric drag will cause them to deorbit and crash. You'll just need picks and shovels then.

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    $\begingroup$ What guarantee is there that impactors - even if they do manage to slow down the orbital velocity of one object - would reduce its altitude? Clearly, the objects are not purely "orbiting" the planet in a Keplerian sense. If our laws of physics hold, there must be an additional force opposing the gravitational attraction of the planet, to stop the objects deorbiting in the first place. $\endgroup$ Jan 12, 2019 at 13:56
  • $\begingroup$ Things are held in orbit by their velocity (perpendicular to the surface of the earth that they are directly over) as they move around earth. The higher their velocity, the further out from earth they can orbit without falling down due to gravity. Collisions with objects would cause a decrease in velocity, meaning they can't stay that high in orbit anymore. Then gravity takes over and does the hard work for you, dragging them down to earth from where you can collect them $\endgroup$
    – user43712
    Jan 12, 2019 at 14:11
  • $\begingroup$ @user43712 Yes, but clearly these objects must have an additional force keeping them in their orbits. Before firing an impactor, one could notice that the extra force is higher the lower the object's altitude (since, as noted in the question the objects have 1 day orbital period both at 5km and 200km). Gravity is always acting, it's just that there is an additional force (one that implicitly does not act on the "mined" resource alone). $\endgroup$ Jan 12, 2019 at 14:22
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    $\begingroup$ @ValentinAslanyan ahh yes that makes sense. In that case, what if the reason they float up there is simply density? They're so sparse that they are able to float on the edges of the atmosphere like clouds. The shuttles you send up could fly through the cloud, causing it to condense and have the valuable materials rain down as a liquid which can then be used/refined however its collectors decide $\endgroup$
    – user43712
    Jan 12, 2019 at 14:28
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    $\begingroup$ Hi, everybody. I'm from the Please Don't Drop Rocks On Us From Space society. If you could just sign here.... $\endgroup$
    – Mazura
    Jan 12, 2019 at 22:01

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