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I saw an awesome post by a user about 1g off-Earth habitats. Radiation protection is provided to humans when habitats have a lot of mass between habitation areas and sources of radiation. Long-term survival in our current evolutionary form absolutely requires gravity (or inertial equivalent) similar to terrestrial. It seems to me that habitats constructed inside circular tunnels are a solution achievable near-term.

Could the Boring Company Excavation Tool be used to create such tunnels in asteroids? (note that Elon Musk owns both The Boring Company and SpaceX)

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    $\begingroup$ Welcome to the Space Exploration Stack Exchange. The headline question is a reasonable one, but the explanatory text is a bit jumbled. Could you use the edit button and try and make it a bit clearer, maybe with a picture. It would also be very helpful to add some links to your sources and to details of the Excavation Tool. $\endgroup$ – Steve Linton Jun 28 '18 at 13:54
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    $\begingroup$ This isn't a bad idea in general. A habitat essentially built on a Hyperloop train cruising non-stop in a ring tunnel inside an asteroid. Boarding/disembarking would be tricky without stopping, though it could be done with a detachable car and a side track. Problem: find a good asteroid that isn't a bunch of loose gravel and moves on a friendly orbit. $\endgroup$ – SF. Jun 28 '18 at 15:49
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    $\begingroup$ @SF. find an asteroid that isn't gravel, in a friendly orbit, and not solid iron! $\endgroup$ – GdD Jun 28 '18 at 16:08
  • $\begingroup$ How large would your chamber be? I'm imagining you would want a chamber far wider than the tunnels that Boring is drilling. Is the BCET powered by a combustion engine? If so it would require an oxygen/air supply. It might not work too well in a vacuum! $\endgroup$ – joeytwiddle Jun 29 '18 at 3:35
  • $\begingroup$ I shortened the title down to better focus the question. If the parts about near-Earth are important to you, please expand upon that in the question body. Thanks $\endgroup$ – Machavity Jun 29 '18 at 12:33
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Definitely not in current shape, as it depends on tightly packed soil/rock to provide an opposing force to resistance of the ground/rock against the drill. Asteroids, with low gravity, will be far less stable and this sort of forces could easily break apart smaller ones.

Also, starting the tunnel would be a serious problem, as instead of 1g to keep the equipment stable on the ground, it would require active thrust or some sort of anchor system to initiate the tunnel - otherwise the drill will just send the whole machine flying away from the asteroid.

Then there's the whole slew of smaller problems - screw conveyors for loose material depend on gravity to keep it from spinning uselessly around instead of being moved. Cooling - only radiative; coolants like water are expensive and scarce. All bearings, joints, actuators, contact surfaces etc need to be passivated against cold welding. Common lubricants like grease need to be replaced with stuff that works in vacuum and temperatures of space. The tunnels on Earth are to be reinforced with concrete, not really a material you can manufacture in bulk in space; it won't bind in vacuum (where all the water will either freeze or boil off). With no air to slow down debris that get smashed by the machinery, they will keep flying like shrapnel until they bounce off different surfaces enough to come to a rest. There are countless other similar "small things" - none of them impossible to overcome alone, but the sheer number completely overwhelming.

The concept has some merit, but it's not 'pack a machine on a rocket and drill some tunnels' thing. Such a drill would need to be very thoroughly redesigned to be usable in space.

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    $\begingroup$ Minor point, but screw conveyors work just fine in microgravity. PDF link $\endgroup$ – Carl Kevinson Jun 28 '18 at 19:54
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    $\begingroup$ it's not 'pack a machine on a rocket and drill some tunnels' thing unless of course you bring Bruce Willis. $\endgroup$ – Ghanima Jun 28 '18 at 20:24
  • $\begingroup$ And its human crew is known to have difficulties operating in space $\endgroup$ – wedstrom Jun 28 '18 at 22:33
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    $\begingroup$ What ? Do you mean that Armageddon was not scientifically sound ? $\endgroup$ – Antzi Jun 29 '18 at 1:42
  • $\begingroup$ @CarlKevinson: That largely depends on the type of material and conveyor. Sure there are screw conveyors that e.g. are used to transport plastic at high pressure for mold injection. They don't care much about gravity - but you will destroy them if you put gravel instead of plastic. And your gravel conveyor won't be good for transporting nearly molten plastic as some will solidify into a plug and the rest will leak back along the sides. Torque, durability, screw pitch, wall texture, these things must be adapted to conditions and material. See the red paragraph in conclusion of the paper. $\endgroup$ – SF. Jun 29 '18 at 5:21
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SF. covered the problems with conventional boring on an asteroid. Then there's the problem of getting a conventional boring machine to the asteroid in the first place.

The Boring Company uses fairly conventional boring machines. They're increasing their tunneling speed mostly by making smaller tunnels, increasing power, adding supports while still tunneling, and automating the process. It's still a huge machine weighing in the order of 1000 tons.

Getting 1000 tons to even a near Earth asteroid is a problem. Just disassembling it into pieces which can fit inside a rocket fairing is a challenge. Getting it into LEO requires 10 km/s. From there to a near-Earth asteroid is, optimistically, about 4 km/s. This is roughly the same as getting to GEO. A Falcon Heavy can put about 25-30 tons to GEO, so you're looking at 30-40 Falcon Heavy launches just for the boring machine parts. At \$90 million per launch it's about \$3.1 billion in launch costs alone.

That's not totally absurd, the James Webb Space Telescope is at almost $10 billion, but that's just launch costs for just the boring machine. That doesn't include fuel and spare parts for the machine, personnel to assemble and run it, and food, water and shelter for them. Plus training, development, and operational costs of the mission. The actual cost would be much higher.

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    $\begingroup$ This group is so cool! I couldn’t figure out how to thank each individual for what they’ve done so far on this post. NASA had a mission that we scrapped where we were gonna drag an astroid to a La grange point with the earth. Over time we could drag a pretty big rock close to us. I think. I also had thoughts about spinning-up the astroid to a speed to allow for the 1-G. But it was very cool how another guy thought about putting in a train that was driving through the tunnel at speed. $\endgroup$ – Justice Foreall Jun 30 '18 at 12:39
  • $\begingroup$ @user32402 You'll probably be into Worldbuilding.SE. $\endgroup$ – Schwern Jun 30 '18 at 16:53
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No. A tunnel boring machine is an integrated system that not only cuts a cylindrical hole into rock, but also builds a tunnel (from concrete elements) behind the cutter. The cutter head moves forward by pushing against the completed tunnel segments. It is not designed to create large cavities. Those are made by blasting.

A TBM is also 100 m long (or more), which means you need a very large asteroid to maneuver in.

Using a TBM to hollow out an asteroid is very inefficient. If you want to remove 90% of the mass inside a 10-km asteroid you're removing 900,000,000,000 m3 of rock, significantly more than any construction project on Earth has ever done. It'd be much easier to mine the surface of the asteroid and use the rock you've broken off to construct a habitat that's hollow to begin with.

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