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I've got a family using a jackhammer to excavate an asteroid habitat they intend to homestead in.

  • The jackhammer is large, and would normally need mounting on a column or tripod like this mining drill. In this case it's in microgravity so mobility is a non-issue. It hits with ~200 joules a strike at ~1,200 hits a minute with a cheap, very hard, and easily replaceable synthetic polycrystalline diamond-tipped chisel. To counteract its recoil, ducted electric fans are mounted on its sides and crampons mounted on its operator's boots. It is connected via Very Long Cord™ through a transformer and battery to an antique but reliable shipborne generation III microfission plant (~5 MWe) with adequate radiation shielding and radiative cooling capacity.
  • Superglued and zip-tied near the jackhammer's front is the nozzle of an ultra-sized shop vac's hose, which vacuums up floating tailings before the fans can ingest them and shunts them to an inflatable bubble puffing off the asteroid like a zit for volatile extraction and reuse as radiation shielding. Anything too large to fit in the nozzle won't fit through the fan grates. Any family members in good health not doing anything else useful at the time follow behind and clear more debris from the air with more shop vacs or by hand. Rubble removal will hardly slow the miner down.
  • Other excavation options such as autonomous robotic moles or laser bores are unaffordable while two surplus industrial jackhammers (one was cannibalized for spares) sourced directly from the factory outlet were not; the ship required to reach 241136 Sandstede was expensive. A larger jackhammer would've required larger ducted fans and been more difficult to maneuver.
  • The work area is pressurized (they're excavating their way like a borer beetle in from a ship clamped to the outer surface), well-ventilated, and kept at a temperature humans can safely work in. Heat and power are non-issues. Most parts of the jackhammer are shrink-wrapped to avoid dust entering its electronics. All family members in the mineshaft wear appropriate personal protective equipment and therefore will not need to pause due to (for instance) hearing loss or pneumoconiosis. The family will not accidentally mine their way into space as they know their location within the asteroid at all times thanks to a primitive sort of off-the-shelf-do-it-yourself GPS.
  • They are enough family members capable of safely operating the jackhammer that it can run 24/7 if they take shifts, and the faces being excavated are far enough from the family's living spaces that those 24/7 shifts won't drive them crazy via noise-induced insomnia.

Assuming the asteroid is uniformly made of a rock with all the properties of granite (I'm aware this approximation is inaccurate), how many cubic meters of it can the jackhammer excavate per day?

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    $\begingroup$ Suggest that you rearrange the dot points and add one word, so you lead with "The work area is pressurised, well-ventilated..." When I started reading it my automatic assumption was: asteroid excavation = working in vacuum, which led to a "What?!?" when I first saw the ducted fans mentioned. $\endgroup$ Dec 7, 2023 at 7:35
  • $\begingroup$ @KerrAvon2055 Finished. $\endgroup$
    – KEY_ABRADE
    Dec 7, 2023 at 7:43
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    $\begingroup$ Is there a reason they use a jackhammer instead of proper excavation equipment like caldwell drills or those horizontal rigs the opal miners use? They rip through rock and create rooms and corridors a lot more efficiently than a jackhammer ever would $\endgroup$
    – Kilisi
    Dec 7, 2023 at 9:56
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    $\begingroup$ How is the jackhammer anchored to the work surface? Normally you'd use the weight of the hammer itself, but that's obviously a non-starter in space. $\endgroup$
    – Cadence
    Dec 7, 2023 at 14:42
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    $\begingroup$ @DanielB It's not gravity itself that makes crampons work — it's downwards force. Gravity just provides that downwards force under most circumstances. In microgravity you can still use your feet to brace yourself off the sides of the shaft and the crampons help you dig in when you do that. $\endgroup$
    – KEY_ABRADE
    Dec 7, 2023 at 21:35

2 Answers 2

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This doesn't work well at all.

  • I've used jack hammers before. They depend on force, either the force of gravity when hammering something near your feet or the force of your body when using smaller hammers to hammer horizontally. I get the idea of using the tripod as you describe, but something must force the hammer forward. And unlike a drill, the hammer is constantly pounding on the mount. It'll eventually break.

  • Jack hammers are useful when something can be cracked, such as a slab of concrete. They're terrible when trying to crush something, such as a large wall of granite. So unless you give the asteroid's geology seams to work with, this will be inefficient and difficult second only to using a sledge hammer.

  • A jack hammer tipped with a point can be used with some materials to punch a hole, not break apart significant chunks of anything (again, assuming a solid context and not a slab of something like a sidewalk).

Honestly, and I apologize for being blunt, but this solution is simply horrible. It would take forever and your family/miners will go through bit after bit after bit trying to mine out the asteroid like an old-fashioned chain gang slowly turning rocks to gravel. Only less efficient since those old timey rocks were more like slabs of concrete and less like mountains of granite (hard rock mining).

enter image description here

In this solution it would take years to mine out that asteroid. If we really are dealing with granite, then I'm having trouble believing a single cubic meter of mass per hammer per day.

There's a more believable solution...

I can believe you don't want to use explosives. Unless the asteroid were enormous, that would threaten the integrity of the asteroid. So...

First, use traditional mining drills to punch a half dozen holes in a circle with one more in the middle of the circle. Then, let's use an industrial grade hard-rock version of an exhaust pipe expander...

enter image description here

...that would slip into the center hole and, using ye olde traditional pneumatic or hydraulic wrench, would be expanded until the center of the circle shattered.

I once lived in a hard rock mining region. This is basically what they did only using explosives rather than the less violent and slower expander. However, doing this I can imagine moving up to 10 cubic meters of mass per drill operator per day.

All of which is assuming you have an adequate system in place to remove all the tailings. That's actually your bigger problem. If the drill operator is also removing the tailings then you can throw that 10 m3/day estimate out the window. Worse, it's not like you have an entire planet to dump the pile on and the act of throwing it off the asteroid into space could, believably, change the trajectory of the asteroid. The drilling process is conceptually nothing compared to the tailings removal process. Hope you don't need airlocks.

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  • $\begingroup$ Thanks for the different idea. The tailings are getting put in an expandable, atmosphere-filled bubble attached to the asteroid so that they're (a) out of the way, (b) still usable, and (c) not changing its orbit. $\endgroup$
    – KEY_ABRADE
    Dec 8, 2023 at 7:21
  • $\begingroup$ @KEY_ABRADE Cheers. Although as you think through your tailings removal process, think about the nature of chain shot, which was basically two canon balls held together with chain. They were used to mow down large groups of people because they naturally spin in the air. You'll have the same problem. Unless you have stabilizing thrusters of some type ("the ringworld is unstable!") that bag will sway around, changing the trajectory of the asteroid. And if the weight approaches, what, 30% of the total mass? It'll all start to spin. $\endgroup$
    – JBH
    Dec 8, 2023 at 7:35
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TL,DR: Probably not very fast, cheaply, safely or reliably.

Ducted fans don't typically provide a lot of thrust, unless they consume an awful lot of power. This ducted fan produces 20-25 kg of thrust, at the cost of the consumption of ~10-15 kW of power. Without sufficient thrust, in zero-g, the first strike will propel the tool away from the surface until it can be brought back into contact.

However, the production of fragments of stone in a low-g environment will result in foreign object damage to the fan blades, which will result in stoppages or clogging of any filter that may be applied to protect the thruster.

It would be far better to chemically bond anchors to the asteroid and stretch springs between the asteroid and the tool. When digging progress makes the springs too short, glue on new anchors, move the springs and repeat.

If the asteroid is so weak that glued-on anchors won't do the job, it's weak enough that you could mine it by hand.

As to rate of excavation, I would expect a rate similar to that of modern terrestrial jackhammer and shovel (or jackhammer and vacuum-cleaner) excavation, with allowances for breaks to reset the springs. Say, half to three-quarters of the expected rate on Earth.

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  • $\begingroup$ Agree that the ducted fans provide insufficient thrust, but the features mentioned (vacuum at front and protective grill on fan cowlings) are specifically designed to prevent FOD issues. $\endgroup$ Dec 8, 2023 at 5:41
  • $\begingroup$ @KerrAvon2055 The grill could still be clogged... but if these amateurs want to do it that way, the potential consequences are on them. $\endgroup$
    – Monty Wild
    Dec 8, 2023 at 5:45

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