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I was not entirely sure how to word the title question, so allow me to put my question into more detail here:

Suppose there was a planet with just the right conditions to allow humans to live there (atmosphere, close by, livable temperature, etc.), and there were valuable resources giving them reason to settle this planet. However, the problem is that the gravity on said planet is crushing (a random number for an idea of what I mean by crushing, 300 m/s squared). How might a society with advanced technology theoretically get around this problem. I see two possible solutions.

  1. Using some advanced technology, the society engineers a way for humans to live on the surface and retrieve these resources without being crushed.

or

  1. Using some advanced materials and engineering, the society uses robots/drones/some kind of automated system to get to the resources.

Assume that the value of the resources is greater than the cost of getting them. Either way, to be explicitly clear, I need some way for a technologically advanced society (we will say around 1500 years into the future for some reference) to retrieve valuable resources both on and beneath the surface (requiring both mining and harvesting) of a planet whose gravity is 100s of meters per second squared, and get them off planet, in the most practical and efficient manner possible without using handwavium antigravity. The precise method, materials, etc. used in solving this problem should be at least loosely based on science, however whatever works works.

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    $\begingroup$ I honestly don't think the resources you gather would ever be more valuable. People already have problems at 10G, so at 30G we would all pretty much die with the blood drained out of our pores. Your only option would be 2, and even then, the parts would all need to be designed to be thick and sturdy so that they can withstand the crushing weight. Maybe a giant space elevator would work? if the material is valuable enough and can be constructed by drones on the surface up, so you wont waste an astronomical amount of fuel trying to take off. $\endgroup$ – Shadowzee Apr 18 '18 at 3:45
  • $\begingroup$ That is close to the gravity on the surface of the Sun. No known planet has a gravity that come close to this. The gravity on Jupiter is only 2,5 times the gravity on Earth. So 25m/s is still a long shot to 100m/s. $\endgroup$ – Vincent Apr 18 '18 at 4:05
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    $\begingroup$ I don't see how with that gravity a breathable atmosphere can be kept at 1 atm pressure. $\endgroup$ – L.Dutch Apr 18 '18 at 5:03
  • $\begingroup$ @Vincent There are exoplanets with that kind of surface gravity as per my answer, although they are rare. $\endgroup$ – ohwilleke Apr 18 '18 at 5:59
  • $\begingroup$ Just do it. There is no way something of value is on such a planet. There is no way humanity advances that far without significantly changing how they work and adapt to each new situation on each new planet by advanced genetics and cybernetics and nobody knows what we would be like then. There is also no way you need actual humans on that surface to accomplish anything. Since your entire premise is unrealistic, why not say they have special suits or some genetic enhancement that just works? You glossed over everything else and said It's just the way things are. $\endgroup$ – Raditz_35 Apr 18 '18 at 7:37
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Short Answer

No.

There is nothing you can do consistent with real world science to mitigate extremely high gravity that would make the surface of such a planet habitable for humans, nor could an otherwise habitable environment exist at such a high gravity.

But, there are circumstances related to your scenario that could be workable that I explore.

Long Answer

What Kind Of Planet Could Fit This Description?

The specific gravity of the planet Earth is about 5.5. Lead is about 11; gold and depleted uranium are about 19; osmium, the most dense naturally occurring element is 22.6.

For an Earth radius planet to have 30Gs of gravity, it would have to have a specific density of 165.

This is much less than the specific density of a white dwarf star (about 200,000) or of a neutron star (about 200,000,000,000), but even the most dense planet ever discovered has a specific density of only about 23 g/cm^3 (incidentally and probably not coincidentally, it is a pulsar planet).

So, it is basically impossible to have a planet with a radius smaller than Earth that had gravity that strong. The most dense possible Earth radius planet would have a surface gravity of about 4G, and as it got smaller the gravity would decrease.

You can also increase gravity by making the planet much bigger in radius than Earth. Indeed, these are the only kinds of observed bodies with surface gravity on the order of 30Gs.

Planets with gravity that strong are rare, but they do exist. As of 5 August 2012:

[T]he exoplanet with the strongest surface gravity was Kepler-25 b. This planet has a radius of 0.23 Jupiter radii, a minimum mass estimate of about 12.7 Jupiter masses, and a calculated surface gravity of 633.7 times that of the Earth.

For example, the closest fitting known exoplanet to the planet in your question is KOI-423b has a mass about 5721 times Earth's mass and a radius of about 13 times Earth's radius, giving it a surface gravity about about 33 times that of Earth.

The radius of the Earth, in round numbers, is 4,000 miles. For exoplanet KOI-423b, you'd have a radius of about 64,000 miles (by comparison, the radius of Jupiter is 43,441 miles).

Surviving Near Such A Planet

There is no way to shield gravity. You can temporarily escape its pull on you by being in free fall, but that respite only lasts for a short duration and if you want to return to where you started, you need to accelerate away from the source of the gravity which temporarily makes the effective pull on you even worse.

The only sustainable way to escape its effects is to stay a long way from the source of the gravitational pull. Therefore, the only way for a human to survive in an environment like that would be to be at a substantial distance from the surface where it is 30G.

To get to 1G one would need to be about 4.5 times the radius of the planet from its surface. Of course, a human could survive with somewhat heavier gravity than 1G, but even 2G would be pretty intense. By the time someone is at 2.2 times the radius of the planet from its surface, gravity approaches 3G which is survivable in the short term but is close to the limit of what someone can survive on a prolonged basis.

Carrie Vaughn's 2017 stand alone novel, "Martians Abroad" explores a similar issue as third-generation Martians accustomed to life on Mars at about 1/3rd G are sent to college on Earth and suffer through the higher gravity to which they are unaccustomed. (On the whole it is a good account although it fails to recognize that a kilogram is a unit of mass rather than weight, which is annoying to someone whose had that distinction pounded into him many, many times.)

In the case of KOI-423b, the planet's gravity would have be Earth strength gravity at a distance 288,000 miles from the surface. At a distance 140,800 miles from the surface of KOI-423b, gravity would be 3G which is almost intolerable on a sustained basis for humans.

At 30G, a whole host of issues like breathable air pressure become pretty much untenable for any human. It takes a huge feat of bioengineering for giraffes to be able to keep blood flow going to their heads as they swing them from the ground to being fully erect without passing out or having a stroke. This situation would be unfathomably more difficult every second of the day.

Robots or remotely operated drones of some sort might be able to operate in those conditions with some extreme engineering ingenuity and extreme materials, but at 30G it starts to become very challenging to find materials and mechanisms that can do the job.

Extracting Material From The Surface

Perhaps just as importantly, getting materials that are being mined/harvested from the surface to a livable orbit would require immense amounts of energy because escape velocity would be so high.

The escape velocity formula is sqrt(GM/r).

For exoplanet KOI-423b, escape velocity is about 21 times that of Earth. Kinetic energy scales as the square of velocity, so it would take about 441 times as much energy to get a given mass of something off the surface of it as it would to get it off Earth.

To get something off Earth and into orbit, you need about 50MJ/kg in round numbers. To get something off exoplaent KOI-423b, you would need about 22,050 MJ/kg. So, you would need 500 kg of chemical fuel for each 1 kg of material you wanted to get off planet, and would need more if you couldn't convert all of the fuel into kinetic energy creating velocity instantly and with perfect efficiency.

Otherwise, the only way you could get enough energy to get materials off planet would be with a controlled nuclear reaction. Basically, you'd need to put the materials you want to retrieve on top of a small nuclear bomb.

Indeed, one ugly but potentially effective approach to mining something close to the surface of this planet would be to launch a missile deep into the surface so it penetrated below the material you are looking for, and then detonate a nuclear bomb it was carrying which would spew raw materials into low exoplanet orbit, where it could be gathered up for processing by less extremely engineered robots.

Conclusion

There is no way that humans could settle on this planet, or that this planet could have habitable conditions on its surface.

It might be possible to have a tolerable gravity and conditions on a small natural or man made moon orbiting a planet.

I would imagine one that always had the same side facing the planet, because at the right distance from the planet, so that the planet could provide the right gravity and could pin an atmosphere and water that the moon otherwise couldn't hold to itself in place, ideally within a steep crater facing away from the planet that would prevent the atmosphere or water from leaking over the edge and falling back down to the planet.

(I'm analyzing this scenario more carefully in light of a comment to confirm that this might be possible. But, certainly some moon or asteroid or space station in the vicinity of the planet, in some configuration, could be habitable.)

Exploiting resources on the surface of the planet, which would be uninhabitable, might be possible with robots or drones, although it would be at the limited of extreme engineering to manage one that could handle those conditions, and would be extremely costly to remove from the planet in terms of energy requirements to get the materials to orbit. So, this would only be worthwhile for something that was very hard to find elsewhere and was otherwise extremely expensive and difficult to synthesize (e.g. crown jewel sized diamonds).

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  • $\begingroup$ On a space station in orbit you would experience no gravity because of the continue free fall. $\endgroup$ – L.Dutch Apr 18 '18 at 5:59
  • $\begingroup$ @L.Dutch I'll have to think that analysis through. But, its midnight where I live, so I'll have to think about it later. I'm not sure if "orbit" is a poor choice of words for the scenario I'm contemplating, or if that scenario simply isn't possible. The logic of gravitationally caused tides make we think that it is the former, but I don't have the bandwidth to properly think it through. $\endgroup$ – ohwilleke Apr 18 '18 at 6:03
  • $\begingroup$ Food for your brain before you sleep: the ISS is few hundreds km above earth surface, so not really at 0 g, yet astronauts there "float" with no weight. Same they do on the vomit comet, just less than 10 km above surface. $\endgroup$ – L.Dutch Apr 18 '18 at 6:24
  • $\begingroup$ @L.Dutch The ISS situation is on point. The vomit comet is actively alternating between rushing towards the ground and rushing up, so it isn't really a relevant reference point. $\endgroup$ – ohwilleke Apr 18 '18 at 6:27
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Either way, to be explicitly clear, I need some way for a technologically advanced society (we will say around 1500 years into the future for some reference) to retrieve valuable resources both on and beneath the surface (requiring both mining and harvesting) of a planet whose gravity is 100s of meters per second squared, and get them off planet, in the most practical and efficient manner possible without using handwavium antigravity

The simpler way would be using "telepresence rigs" - semi-humanoid robots, probably turtle centaurs for stability (30 G means you need reflexes way faster than a human's), controlled by stations in orbit, and therefore in free fall, or by a mixture of downloaded personality/gestalt integration (this could supply several interesting plot points - telecontrollers getting PSTD, and bots and controllers "drifting" too far for their minds to reintegrate optimally...).

To get the resources off-planet, you need a lot of energy.

Given the thickness of the atmosphere you'll have to do this in stages:

  • the resource vessel is hooked to the Atmospheric Elevator, a 500 km untapered cable of diamond nanotube fibers going from the surface to Atlantis Station, which floats over the dense atmosphere made possible by a 30 G gravity field.
  • once past the thick of the atmosphere, the vessel is mounted on the "solid light" rig. This is a laser so powerful that the backscatter alone makes an area 250 km in radius effectively a no-fly zone at each takeoff. The ship is mounted on an ablative/reflective disk made of a special alloy which can be kept electromagnetically stable even in its molten state, acting as a mirror with 99.999% efficiency (the remaining 0.001% is where the ablative part kicks in: the ship leaves behind a trail of scattered metal ions).
  • the ship is propelled far enough to arrive within grappling range of the Skyhook, a tapered diamond fullerene cable rig extending the rest of the way to stationary orbit. The cable cannot extend further downwards because the gravity field makes it impossible to lift its own weight with reasonable tapering factors. The cables are electrified and act as a non-contact linear motor, supplying the traction necessary for the the ship to finally reach orbit.

The cost per pound of such a lift, even if the ship is essentially unpowered (it only contains the stabilizing/cooling system for the liquid alloy mirror) will still be staggering. Whatever that stuff is, it had better be worth a lot.

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