4 ms·

The quoted top speed for micrometeorites has to be wrong. Perhaps missing a 0? 45 mph is silly low, there's no way Martian atmospheric drag could slow them that

The quoted top speed for micrometeorites has to be wrong. Perhaps missing a 0? 45 mph is silly low, there's no way Martian atmospheric drag could slow them that much, let alone the case of the moon.

CapitalistCartr 9y ago
Probably should be meters per second.
valuearb 9y ago
Yea, in space it's 10 km/sec. My guess is that it's still many m/sec by mars surface.
VLM 9y ago
I found the exact source of the falsehood, its from a stackexchange discussion about theoretical sci fi aspects of lunar sports injuries and if you jumped down a vertical lunar mineshaft pressurized to 1 atm the lower gravity means terminal velocity would be reached in about 1 km of falling (handwavy) at roughly 45 MPH (actually 49 m/s). https://space.stackexchange.com/questions/4678/how-far-can-you-fall-on-the-moon-without-injury https://space.stackexchange.com/questions/4678/how-far-can-y... a 100+ MPH impact on earth would require a survival capsule too tough for normal purposes so we use parachutes. However a 45 MPH impact is unsurvivable if naked but a car like structure for an elevator means you could likely walk away from a mining accident where your elevator falls down a mineshaft on the moon. Its likely lunar mineshaft elevators will require little more than extensive crumple zones in the floor, unlike on earth. Also on the earth stuntmen require weird inflated balloons to break their fall but on the moon a terminal velocity of only 45 MPH means something like a ball pit or a relatively shallow (compared to earth...) water pool would make falls survivable. I'm too lazy to run the math to figure out the maximum gravity where a human could fall from a very far height and hit the ground at less than a survivable 10 MPH or whatever is defined as survivable. https://space.stackexchange.com/questions/4678/how-far-can-you-fall-on-the-moon-without-injury https://space.stackexchange.com/questions/4678/how-far-can-y... The big mistake of course is the lunar atmosphere is, as an engineering approximation, 1e-15 atm not 1.00 atm. In practice its interesting to think about a micrometeor strike hitting a large structure, given the very low mass and low structural stability of a random rock chunk vs aerodynamic forces, it would blast clean thru the ceiling, then shatter and lose velocity very quickly down to sonic range or perhaps far below. Something like a giant balloon stretched over a tall crater would be reasonably survivable when hit by a meteor. Decades ago how to repair the tiny slow leak would be a major puzzle, today its just a boring job for an autonomous drone. Possibly the assumption in the article is if the roof is thousands of meters overhead and a meteor breaches the roof, it'll hit a human in the head at 45 MPH, which is quite survivable if the colonists wear construction hard hats but not so good out in the open. Sleep with a roof over your head, even rather minimal, and you probably won't wake up dead, if the balloon ceiling is far enough overhead.
ridgeguy 9y ago
From a 1969 paper titled" The Meteorite Flux at the Surface of Mars". [1] The abstract says that Martian meteorites having a mass greater than 1 metric ton hit the surface with essentially their space velocity, undecelerated. Those with mass less than 10 grams hit at terminal velocity, whatever that is for Mars. In between, I suppose there's a continuum of impact velocities depending on the mass. [1] http://adsabs.harvard.edu/full/1969PASP...81..399D http://adsabs.harvard.edu/full/1969PASP...81..399D (paywalled, but they show you the first page with the abstract, which tells the tale)

The quoted top speed for micrometeorites has to be wrong. Perhaps missing a 0? 45 mph is silly low, there's no way Martian atmospheric drag could slow them that much, let alone the case of the moon.

CapitalistCartr 9y ago

Probably should be meters per second.

valuearb 9y ago

Yea, in space it's 10 km/sec. My guess is that it's still many m/sec by mars surface.

VLM 9y ago

I found the exact source of the falsehood, its from a stackexchange discussion about theoretical sci fi aspects of lunar sports injuries and if you jumped down a vertical lunar mineshaft pressurized to 1 atm the lower gravity means terminal velocity would be reached in about 1 km of falling (handwavy) at roughly 45 MPH (actually 49 m/s). https://space.stackexchange.com/questions/4678/how-far-can-you-fall-on-the-moon-without-injury https://space.stackexchange.com/questions/4678/how-far-can-y... a 100+ MPH impact on earth would require a survival capsule too tough for normal purposes so we use parachutes. However a 45 MPH impact is unsurvivable if naked but a car like structure for an elevator means you could likely walk away from a mining accident where your elevator falls down a mineshaft on the moon. Its likely lunar mineshaft elevators will require little more than extensive crumple zones in the floor, unlike on earth. Also on the earth stuntmen require weird inflated balloons to break their fall but on the moon a terminal velocity of only 45 MPH means something like a ball pit or a relatively shallow (compared to earth...) water pool would make falls survivable. I'm too lazy to run the math to figure out the maximum gravity where a human could fall from a very far height and hit the ground at less than a survivable 10 MPH or whatever is defined as survivable. https://space.stackexchange.com/questions/4678/how-far-can-you-fall-on-the-moon-without-injury https://space.stackexchange.com/questions/4678/how-far-can-y... The big mistake of course is the lunar atmosphere is, as an engineering approximation, 1e-15 atm not 1.00 atm. In practice its interesting to think about a micrometeor strike hitting a large structure, given the very low mass and low structural stability of a random rock chunk vs aerodynamic forces, it would blast clean thru the ceiling, then shatter and lose velocity very quickly down to sonic range or perhaps far below. Something like a giant balloon stretched over a tall crater would be reasonably survivable when hit by a meteor. Decades ago how to repair the tiny slow leak would be a major puzzle, today its just a boring job for an autonomous drone. Possibly the assumption in the article is if the roof is thousands of meters overhead and a meteor breaches the roof, it'll hit a human in the head at 45 MPH, which is quite survivable if the colonists wear construction hard hats but not so good out in the open. Sleep with a roof over your head, even rather minimal, and you probably won't wake up dead, if the balloon ceiling is far enough overhead.

ridgeguy 9y ago

From a 1969 paper titled" The Meteorite Flux at the Surface of Mars". [1] The abstract says that Martian meteorites having a mass greater than 1 metric ton hit the surface with essentially their space velocity, undecelerated. Those with mass less than 10 grams hit at terminal velocity, whatever that is for Mars. In between, I suppose there's a continuum of impact velocities depending on the mass. [1] http://adsabs.harvard.edu/full/1969PASP...81..399D http://adsabs.harvard.edu/full/1969PASP...81..399D (paywalled, but they show you the first page with the abstract, which tells the tale)