# Could explosives replace drilling for science and construction in space?

Drilling seems to require heavy equipment, preferably with humans on site for maintenance, much energy and might be even more problematic in low gravity and unknown geology. Deepest hole drilled in space was 292 cm by Apollo 17, manually operated on site.

Could a heavy drill be replaced by a rover dropping off a much lighter shaped charge, taking cover when it explodes, and returning to examine the debris from the deep which landed on the surface? Couldn't a modern shaped charge even cause a deep narrowish hole, rather than a flat crater, which could be inspected by "a ChemCam" and even by physically lowering down small instruments and tools? And then even by lowering down another explosive, much like construction and mining drilling on Earth often is done only in order to place explosives more favourably.

By blasting out a bay shaped cavity in a Martian or Lunar hill, radiation shielding and maybe thermal benefits might be provided for a habitat module later placed there. Explosives might make subsurface water ice much more available to a human space colony. With the advantage of using only a few tons of explosives which require almost no operational overhead, other than being placed by a rover. Even if a detonation gives an unwanted result, the investment lost was low compared to a heavy drilling station, and could be replaced by a new attempt on another site nearby.

What are the main problems which I optimistically leave out here?

Actual examples of explosives in space: Hayabusa2 will use a shaped explosive charge to create a crater from where it will land and take a sample (animation and an abstract of a paywalled article). That is more of a replacement for an impactor like Deep Impact, rather than for a drill. Except for explosive bolts, the only other use of (non-military) explosives in space I know of is Apollo 14, 16, 17 and that was for seismic purposes.

EDIT: Is there a way to roughly compare the launch mass and useful energy delivered of explosive devices compared to mining devices on the Moon, Mars, Asteroids given some performance criteria such as depth reachable or mass of rocks cleared? I imagine that explosives are pretty energy intensive payloads compared to solar powered machines.

• I believe you have the right idea burrowing in a lunar hill. But I believe Greg Baiden's robots are the way to accomplish this. See youtube.com/watch?v=FVmD3s1DODI – HopDavid Dec 27 '14 at 18:25
• @HopDavid Baiden talks there about such requirements as: delineation drill, development drill, some form of digging machine, explosives loading unit and a sintering machine. So quite a bit of heavy machinery and that's without the transport of excavated (dug, drilled or blasted) materials to the surface. He then goes on to describe machinery needed: digging machine, dump truck, spray-on machine, and a combined drilling and explosives unit. Am I missing something here? – TildalWave Dec 27 '14 at 18:39
• Baiden believes he can size the equipment to fit within launch mass constraints. But yes, it would be an ambitious undertaking. – HopDavid Dec 28 '14 at 14:31
• @HopDavid I personally don't think that would work very well. Mars, the Moon, asteroids et al. are rather cold places beneath the surface and there's only so much of miniaturization that can be done before brittleness of thin materials in extremely cold environments becomes an unworkable problem. It would also scale operations down along with it and with some things you can't construct in a modular fashion or ask whoever ordered the parts to also send smaller astronauts up there that will use smaller habitats because you can't build larger ones as the tools you built don't reach the ceiling :) – TildalWave Dec 30 '14 at 0:45

There's one quite peculiar application where explosives will not require much post-processing - using a nuclear charge to create a cavern under ground. While it may be considered illegal in terms of international treaties, it is a viable construction technique. Melt cavity radius would be roughly proportional to the cube root of the device's yield :

$r_{\textrm{(in meters)}} \approx 16.76 Y_{\textrm{(in kilotons)}}^{\frac{1}{3}}$ for some of Earth's rock types

However, a fully contained cavity at the current technology level requires drilling and concrete-filling as pre-processing steps. It might be possible to devise a ballistic/rocket-assisted penetrator contraption to dig into the ground from a hyperbolic orbit, but there's always the chance (4 per cent for the Earth, higher for less-studied planetary bodies) that the hole may be unsuitable, and another risk is penetration failure.

To sum it up: at the current level of technology nuclear explosions will likely require drilling. Future advances may replace drilling with ballistic penetrators.

For the record, I am not insensitive to the environmental and biological risks posed by nuclear explosions. An unsuccessful launch abort may set up the stage for another Broken Arrow. The explosion may poison aquifers (if they exist) or vent contaminants into the atmosphere, or kill local life. The real reason I added this answer is we have to always keep in mind the whole gamut of techniques the humanity possesses. Nukes pack enormously large energy in low volume and mass.

For scientific purposes, like exposing near-surface materials, probing with seismic explosives, or prospecting for pockets or veins of subsurface materials, I guess it could work, and you already give a few good examples in your question. But for industrial purposes, on its own and without rolling in heavy machinery once you, say, reduce some heavy boulder into rubble, not very likely. Precision required is too great and there's too many uncertainties involved, some, you'd only make worse with the use of explosives;

Explosives are otherwise used all the time in both subsurface and surface blast-mining on Earth. Quarries would also be one such example. But laying and precise detonating charges in sequence so they also clear the resulting craters off ruble would be incredibly difficult and it wouldn't result in perfectly clear tunnels to roll into them some form of autonomous or remotely operated vehicle to place new charges either. No rock is exactly homogenous and fault-free, and with each explosion you're deepening these cracks that can give-in at any time. So you'd be laying support structures (roofing and walls support) that requires heavy machinery, after you managed to clear the path for them, usually using smaller, but still heavy loaders and trucks or carts (which would also require rails, again, laid by heavy machinery). The deeper you go, the tougher this gets and you're constantly laying your charges along its way, increasing stress with each detonation. But, I guess, you could start like this, then roll in heavy machinery as you need to deepen the hole.

So, in a nutshell, not really. At least not for construction work or heavy mining operations. But you could manage to crack open tougher regolith to expose subsurface pockets of water ice, use smaller amounts of it as seismology charges, explosive bolts, and so on.

• Even "taking a bite" out of, as opposed to caving into, a hillside leaving no roof and with slanting sides, even that would protect against most of the cosmic radiation and solar heating from three sides. Maybe the rubble left could be largely cleared by a new set of explosives applied to blast it out in the open? – LocalFluff Dec 27 '14 at 19:32
• @LocalFluff Yes, that would probably work, especially in smaller gravity environment and on frozen ground. Or the rubble could be compressed and flattened to provide a more sturdy surface to build on. But the cliffs would still have to be secured somehow to prevent later avalanche of debris falling on top of you. Note that here lower average surface temperatures work against you and the rock is more brittle due to it. And the large temperature difference between the parts exposed to the Sun and the ones in shadow could further destabilize it due to thermal expansion. – TildalWave Dec 27 '14 at 19:39
• BTW, re your edit, it would probably be easier making explosives in-situ than transporting them between celestials (maybe a good topic for a new question?). And re blasting an alcove, to prevent as much of sherd as possible I'd suggest blasting through already existing fault-lines of suitable geometry. On Mars, that might mean simply removing excess aeolian sedimentation (read: compacted sand) on the sides of steep slopes or cliffs. – TildalWave Dec 27 '14 at 20:05

It depends on what you are trying to achieve.

Depending on the condition of what is being drilled, drilling a hole will produce a neat hole of uniform diameter. Explosives however, always produce a significant zone of fractured material around where the explosive was detonated.

If you want to take a sample of anything, drilling is the best option.

If you want to produce holes for foundations for stilts, drilling is still the best option.

If you want to maximize a crater it is still better to drill a hole, or holes, to the required depth, fill the holes with explosives, as required and then blast.

By burying an explosive in a drilled hole all the energy of the blast is direct to fracturing the rock and moving the rock. By detonating an explosive on the surface a significant portion of the energy of the explosive will be lost, even in a vacuum, which is inefficient.

On Earth we tend to be wasteful because it is easy to obtain resources. In Space however, resources are scarce and their efficiency needs to be maximized.