7

This answer which mentions blasting on the moon for excavation got me thinking. There may be many ways that blasting could potentially be useful on the Moon. Excavation for habitats or other structures, mining for things besides water, perhaps leveling for roads, or even for burying the occasional sub-surface 1:4:9 black monolith. There is more discussion of the use of explosives in the answers to the question Could explosives replace drilling for science and construction in space?

Would storage and use of explosives like TNT (or something more modern) and electronic detonators or detonator cord have any unique challenges, difficulties or safety issues on the Moon?

For background, here's the Periodic Table of Videos epsiode for Dynamite and TNT:

uhoh
  • 148,791
  • 53
  • 476
  • 1,473
  • 2
    Dynamite is made from liquid nitroglycerin and absorbents and stabilizers. I don't believe that dynamite would be vacuum compatible, the liquid would evaporate. – Uwe Oct 18 '17 at 12:10
  • @Uwe But would it require more of a casing than a plastic film wrap to contain the pressure of the outgassing? – LocalFluff Oct 18 '17 at 12:34
  • @Uwe et al. Related to evaporation: Why are some reaction wheels sealed with low pressure gas, others with vacuum?. – uhoh Oct 18 '17 at 12:40
  • 1
    Dynamite has no moving parts (in storage), so you could seal it up however you want and it would be fine. – Nick T Oct 18 '17 at 15:53
  • 2
    You do know how explosives are used in mining on Earth, don't you? You drill a hole, put the explosives in the hole, and back-fill with some kind of tamping. Otherwise you waste the vast majority of the energy. That is, you don't replace drilling with explosives you augment drilling with explosives. – dmckee --- ex-moderator kitten Oct 18 '17 at 22:27
  • @dmckee the only place that "drilling" appears in my question is in the title of a linked question and the only reason I've linked to it is to mention that there is "more discussion of the use of explosives (in space) in the answers" to that question. So your comment would be better placed there instead of here, or perhaps here. – uhoh Oct 19 '17 at 00:20
  • 1
    Pyrotechnics were used on the Moon long ago in each Lunar Modul of the Apollo mission, see https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090015395.pdf page 27 to 31. Careful designed initiators and and detonators were very reliable, not a single failure of more than a thousand devices used for the Apollo programm. – Uwe Oct 19 '17 at 10:21

3 Answers3

20

Besides problems of chemistry of explosives exposed to space (temperature/heating, electric charge due to ionizing radiation, evaporation/degradation) one major risk would be lack of air slowing down the debris.

An explosive blast ejects material at huge velocity. For most of that material, on Earth, air drag causes loss of that velocity within a very short distance - dust and small gravel falls within a hundred meters or so, of a typical quarry blast; only larger chunks fly farther, but they are relatively sparse and gravity brings them down to the surface, impacts removing their kinetic energy quickly - and due to the mass, initially they are usually slower than the smaller grains.

With lack of atmosphere and 1/6 Earth gravity, you have a lot of tiny shrapnel that can fly for many kilometers before impact, and hit whatever it hits at the same speed as when it was adjacent to the explosion. Particles thrown vertically upwards, will fall at the same speed they were ejected, possibly many minutes later. Pebbles bouncing off rock surfaces will lose some energy per bounce, but will continue to fly at speed from unexpected directions.

That means without massive shielding no blasting can occur near any infrastructure. Underground explosions like tunneling should be relatively doable, but all surface work, like leveling for roads would become very risky.

SF.
  • 54,970
  • 12
  • 174
  • 343
  • Are radiation and evaporation in a space environment known problems for explosives, or are you just speculating? – uhoh Oct 18 '17 at 11:27
  • 5
    @uhoh: degradation of explosives in space is known; see Philae's harpoons. Mechanism of heating are generally known and there's no reason to exempt explosives from them. Coronal mass emissions tend to induce electricity, which might be a problem with electric ignitors (though that's my speculation). I'm not aware of actual problems UV or common cosmic radiation (CMB, standard solar wind) could cause, but I doubt they are entirely non-issue. – SF. Oct 18 '17 at 12:17
  • Good point! The surface of the moon is charged by UV photoionization - you may want to add charging and static discharge to your answer. Pretty low humidity up there :-) – uhoh Oct 18 '17 at 12:21
  • What about using blasting mats to prevent debris? They are reusable and might be possible to manufacture from mainly Lunar regolith. Even on Earth dynamite is wrapped in paper (so your fingers don't get sticky while handling it) so the radiation and vacuum problems seem to be very easily mitigated by already practiced standards. – LocalFluff Oct 18 '17 at 12:39
  • @LocalFluff: honestly, no clue. – SF. Oct 18 '17 at 13:07
  • @LocalFluff : wrapping dynamite into paper or cardboard would not be leakproof under vacuum. Sealing into plastic foil might work if it is done gastight. But the plastic foil needs protection against UV. – Uwe Oct 18 '17 at 19:24
  • 1
    Also, a high-speed bit of gravel is a minor annoyance on Earth. In a pressure suit, it can kill you. – Stig Hemmer Oct 19 '17 at 07:53
  • Detonation velocity of some explosives is much faster than the lunar escape velocity. If shrapnel is propelled at those velocities, it could even be a danger to spacecraft orbiting or approaching the moon. – Adwaenyth Oct 19 '17 at 13:51
  • @Adwaenyth Maybe this is going beyond the comments here, but meteoroids are now observed by amateur astronomers as they hit the Moon. Has that created a dangerous debris cloud in Lunar orbit? – LocalFluff Oct 19 '17 at 16:25
  • @LocalFluff unlikely. Otherwise we'd have likely found a dense debris cloud around the moon after billions of years of meteoroid bombardment. It's probable that most of it either falls back down to the moon's surface or is now far enough away to not pose a danger any more. – Adwaenyth Oct 20 '17 at 05:16
  • 1
    @LocalFluff: Orbital mechanics: the orbit must pass through the point of last maneuver (let's call 'explosive ejection' a maneuver). Therefore all that was ejected off the surface either escapes into Earth or Sun orbit, or returns to the Moon surface. No debris will remain in lunar orbit. – SF. Oct 20 '17 at 11:53
8

We have some data, in the form of high velocity debris from the Apollo LM descent engine:

... Dust particles accelerated by a rocket's exhaust could theoretically travel all the way around the Moon!

Metzger's team has analyzed how the impact craters formed on Surveyor 3 and finds that the particles must have been traveling at least 400 to 1,000 meters per second. "In fact, they may have been traveling as fast as the exhaust gases of the lunar lander - that is, at 1 or 2 kilometers per second."

Particles speeding horizontally at 1.7 kilometers per second will travel literally halfway around the Moon. Boost that speed to 2 kilometers per second, and the projectiles can completely circle the Moon. If no mountains got in the way, grit accelerated by a rocket landing could zip entirely around the Moon "and land back at the rocket's feet," says Metzger.

This isn't much of an issue if you're alone on the Moon, but when a serious colonisation effort is under way, you'll have to take precautions not to puncture every habitat in the entire hemisphere. The detonation velocity of modern explosives easily exceeds 2 km/s.

Some explosives are unsuitable for use on the Moon. Dynamite, for instance, sweats even on Earth (nitroglycerin migrates to the outside of the stick, and would evaporate in a vacuum).

Community
  • 1
Hobbes
  • 127,529
  • 4
  • 396
  • 565
  • That's in the ballpark of escape velocity - yikes! – uhoh Oct 18 '17 at 12:23
  • I think evaporation is a function of partial pressure, not total pressure. The evaporation rate of water depends on the partial pressure of water in the air (humidity): to first order it doesn't care about the pressure of N2 or O2. So I don't think evaporation in space-vacuum would be any different than evaporation in air. Temperature could certainly accelerate it though. – uhoh Oct 18 '17 at 12:30
  • related to evaporation: Why are some reaction wheels sealed with low pressure gas, others with vacuum?. – uhoh Oct 18 '17 at 12:40
  • Because of the lower gravity, I'd think that the surface material of the Moon (which is asteroidal and ejecta stuff tens of meters deep) requires less blasting power to perform the same excavation as on Earth. Would debris really fly much further on the Moon than on Earth when you dig the same sized crater? And of course, blasting mats are always used even on Earth. Maybe just a layer of mylar or something and putting regolith on top of it. – LocalFluff Oct 18 '17 at 12:47
  • 1
    The blast force to remove loose rubble from a hole will be less, but the force required to break up solid rock remains the same. – Hobbes Oct 18 '17 at 12:50
  • @LocalFluff let's assume there is equipment to move rubble - lunar bulldozers. The purpose of the explosive is to break solid rock into pieces, not to move it. – uhoh Oct 18 '17 at 12:51
  • And the speed of the ejecta seems to be a function of the shockwave speed, so a small explosion could sill generate high-speed debris. – Hobbes Oct 18 '17 at 12:52
  • The first use of explosives on the Moon or on mars would be as a replacement for drills, which are heavy and need complex operations. So, shaped charges to dig deep holes. The military seems to know something about that since quite some time. And it doesn't generate much debris. – LocalFluff Oct 18 '17 at 12:54
  • @uhoh Hmm, your partial pressure point is interesting and I don't really know the answer to that. But water does boil in vacuum in much lower temperatures, so I would expect it to also evaporate much faster (because boiling means a lot of water vapour is being generated). – jpa Oct 18 '17 at 17:54
  • @Hobbes Does the moon have enough of an atmosphere for such a thing as a 'shockwave' to meaningfully exist? – reirab Oct 18 '17 at 20:51
  • @jpa hmm... good point! I said "evaporation rate" and that does not now seem to be the correct. Total evaporation rate in a closed container will stop when the partial pressure reaches the vapor pressure, but until that point is reached it doesn't say anything about, the rate of evaporation. OK I will go off and get to the bottom of this. Given a choice between being productive and re-living my high-school science classes, I'll always go for the latter. :-) – uhoh Oct 19 '17 at 00:28
5

This is reviving some long dormant brain cells ...

Electric detonators can unexpectedly explode because of stray electrical currents. Also, they may even be sensitive to certain frequencies of radio waves. For this reason, electric detonators are transported in metal cases/boxes. Non electrical detonators are transported in wooden boxes.

The use of certain types of plastics, particularly conventional polyethylene, is prohibited with electrical detonators due to the potential for static electricity to develop and set off a detonator. Low static polyethylene can be used.

Because detonators, for what ever reason may explode, detonators and explosives are never transported in the same vehicles, nor in vehicles in close proximity to one another. Likewise, they are never stored in the same magazine, nor in magazines close to another, in case the explosives are initiated by the shock wave produced by the detonators.

You would not use dynamite, or any other nitroglycerine base explosives because they are shock sensitive. The sensitivity increases when the dynamite stick sweats - beads of nitroglycerine form on the outside of the stick. The sensitivity further increases if the beads of nitroglycerine crystallize.

Nitroglycerine based explosives are not used as much as they used to be for these reasons. They have been replaced by other types of explosives. Unfortunately, most people only know about dynamite and TNT because of movies and old cartoons. They're not aware of other types of explosives.

Because anyone handling explosives on the Moon would be wearing gloves, it would unlikely be an issue on the Moon, but handling nitroglycerine explosives and then wiping one's brow can cause nitroglycerine head aches, which are very unpleasant.

Blasting with electric detonators can be fiddly. The detonators have to be wired up correctly, have no earth (in this case Moon) leakages/short-circuits and the whole circuit of detonators need to be tested with a special tester, similar to a resistivity meter, for short-circuits, prior to initiation of the blast.

Fred
  • 13,060
  • 4
  • 41
  • 78
  • This doesn't sound like much fun at all! Hopefully there are, or will be more space-worthy materials than TNT. Thanks for the great answer! – uhoh Oct 18 '17 at 12:27
  • @uhoh Monopropellants are used in space, and explosive. – Cees Timmerman Oct 19 '17 at 11:06
  • There is a better explosive than TNT : "Hexanitrostilbene, a vacuum stable explosive used in the ALSEP" https://en.wikipedia.org/wiki/Apollo_Lunar_Surface_Experiments_Package Apollo Lunar Surface Experiments Package (ALSEP) https://en.wikipedia.org/wiki/Hexanitrostilbene . But Hexanitrostilbene is a derivative of TNT. – Uwe Oct 20 '17 at 20:42