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Vilkata
2013-Mar-10, 02:18 AM
In this book,

1.) It is claimed that "A traditional handgun would impart enough thrust to achieve escape velocity from [an asteroid 1/2 km in diameter]."

Call the "traditional handgun" a 9mm, firing 7.45 g (115 gr) FMJ at 390 m/s (1,300 ft/s) for an energy of 570 J (420 ft·lbf).

Call the asteroid of average density. Mr Spaceman is on the surface, gun pointed at the ground. Lets say he weighs 250lbs with a light sci-fi spacesuit, or 400lbs with a real world 250lb spacesuit.

Is the statement in the book accurate?

2.) In the book the asteroid/dwarf planet Ceres has been 'spun up' to provide a centrifugal gravity of .3g for the hollowed out cities.

In reality, Ceres only has an equatorial surface gravity of 0.028 g. Wouldn't Ceres simply disintegrate if it was 'spun up' enough to impart .3g centrifugal gravity? I'm reminded of that fast spinning KBO that's football shaped because it spins so fast.

3.) In describing a multiple nuclear detonation a distance away from a spacecraft: "They'd gotten lucky. Vacuum might protect them from an electromagnetic pulse, but the blast radiation could still have fried every sensor the ship had."

... What? Either I need to go back to school, or this statement is elemetary school level creative writing. Why would a vacuum protect against an EMP? But the "blast radiation" could still have "fried" every sensor? What am I missing here?

4.) Not really a question... In the book humanity hauls space icebergs from the rings of Saturn (Wikipedia says the ice chunks in the rings can get as big as 10 meters, which I suppose is "iceberg" sized) to Ceres to be processed into everything from fuel to water. (Nevermind the fridiculous waste of energy even with sci-fi voodoo engines this must entail...) It seems like the authors failed to even read up on Ceres, for we now know there's a possibility of Ceres having more fresh water locked in it than the Earth has. And yes the book is quite recent.

I'm only 70 pages into this book so far, and it seems like a sci-fi book written by someone with absolutely no interest in the history of sci-fi, or space, or astronomy. Or maybe it's just me, and all these statements and assumptions are factually correct.

Solfe
2013-Mar-10, 05:36 AM
For the first one, maybe mathematically, but from a physical standpoint it wouldn't work. If your feet were planted and you held a gun as you would on earth, I would expect you to rotate. I didn't do any math, but I have fired a gun. Floating and firing a gun wouldn't be great.

As I understand it, EMP's are a result of interactions between a nuke and the atmosphere. So I don't think it is fair to say a vacuum protects you from EMP's, it is sort of like saying a vacuum prevents wind burn.

Item four bothers me on an aesthetic level. Why wreck Saturn's rings???

Ara Pacis
2013-Mar-10, 07:17 AM
I think #1 has been debunked numerous times. The bullet might achieve escape velocity but the bullet is much smaller than a person. Theoretically, a small enough asteroid might have such a low escape velocity, but if so, save the bullet for the Reavers and just jump off of it, since a good kick may produce more impulse.

#2 might be plausible, depending on the material strength of Ceres, but I'd need to know the dimensions and locations of the hollowed out cities. Calculating rotational acceleraton for artificial-gravity is fairly straight-forward, but if the surface gravity is less than the rotational acceleration and the lithosphere is weak or a rubble pile then, I'd expect it to fly apart.

#3 True. An electromagnetic pulse is caused by the gamma rays emitted from the device interacting with the upper atmosphere and the magnetic field lines and creating 3 different surge components. Without an atmosphere and magnetic field lines, all you'd get is a lot of gamma rays, some x-rays, neutrons and some high speed plasma and dust from the vaporized bomb components. The effects on the spaceship would depend on its construction and the distance from the explosion.

I don't know if #4 is economically plausible or not. The delta-v required to get the ice out of Saturn's gravity well and on it's way to a processing station may not be that high, but stopping and starting the mass movements at different waystations may add up to make it expensive. But I'm not sure why it would be send to Ceres for processing. It might be more easily processed on site or en route and sent out on the interplanetary transport network (http://en.wikipedia.org/wiki/Interplanetary_transport_network). I wouldn't worry about depleting the rings as they seem to be regularly destroyed and recharged via moon interactions.

Vilkata
2013-Mar-10, 08:19 AM
Thank you for your replies. I had no idea EMP generation was so complicated! For some reason I had the idea that they were very straightforward.

May I assume that a "Explosively pumped flux compression generator" non-nuclear EMP device would also not work in space?

Daggerstab
2013-Mar-10, 10:35 AM
May I assume that a "Explosively pumped flux compression generator" non-nuclear EMP device would also not work in space?

No. As AraPacis explained, the EMP effect of nuclear weapons is caused by the nuclear explosion interacting with the Earth's atmosphere and magnetic field. No atmosphere = no nuclear EMP, though I'm not sure what will be the effect of a nuclear explosion around planets with powerful magnetic/radiation belts (such as Jupiter, as far as I can remember). In contrast, EPFCG's generate a pulse directly, they don't need an atmosphere.

grapes
2013-Mar-10, 11:10 AM
The author may not have wanted to just kick/jump off though--maybe the escape velocity is an unintended consequence. If the gun were fired directly away from the shooter's center of gravity, say as held just above waist level, there would be no rotation. And escape velocity "works" even tangent to the surface.

ETA:

Call the "traditional handgun" a 9mm, firing 7.45 g (115 gr) FMJ at 390 m/s (1,300 ft/s) for an energy of 570 J (420 ft·lbf).
7.45 g times 390 m/s divided by 400 lbs mass (sheesh) is .016 m/s, or, to even further tempt the wrath of the gods of units, .06 km per hour. They should be able to send a message for help in time, even if by the US Postal Service.

EETA: I typed sqrt((Gravitational constant)*2*4/3*pi*2500kg/m^3)*250m into wolframalpha in an attempt to compute the escape velocity of a quarter-kilometer radius asteroid of density 2.5 times that of water. It seems to be .3 m/s, dunno why the discrepancy, I probably made a mistake.

Ara Pacis
2013-Mar-10, 08:05 PM
Thank you for your replies. I had no idea EMP generation was so complicated! For some reason I had the idea that they were very straightforward.The wikipedia article on nuclear EMP explains it well.

May I assume that a "Explosively pumped flux compression generator" non-nuclear EMP device would also not work in space?

If the hull of the ship is designed to act as a Faraday cage, then perhaps even a non-nuclear EMP device might not work.

slang
2013-Mar-10, 09:43 PM
Vilkata, would you like us to move this thread to Q&A, hoping for more answers there?

cjameshuff
2013-Mar-10, 10:23 PM
1.) It is claimed that "A traditional handgun would impart enough thrust to achieve escape velocity from [an asteroid 1/2 km in diameter]."

You're talking about an escape velocity of something probably less than 0.5 m/s, so...maybe. But you could probably reach escape velocity just by jumping or moving wrong.

2.) In the book the asteroid/dwarf planet Ceres has been 'spun up' to provide a centrifugal gravity of .3g for the hollowed out cities.

In reality, Ceres only has an equatorial surface gravity of 0.028 g. Wouldn't Ceres simply disintegrate if it was 'spun up' enough to impart .3g centrifugal gravity? I'm reminded of that fast spinning KBO that's football shaped because it spins so fast.

Almost certainly. It's largely water ice, which is not known for high tensile strength, and is known for deforming under external forces. Perhaps they were confused about how centrifugal gravity works...I've encountered a surprising number of people who thought the spin would increase apparent surface gravity.

3.) In describing a multiple nuclear detonation a distance away from a spacecraft: "They'd gotten lucky. Vacuum might protect them from an electromagnetic pulse, but the blast radiation could still have fried every sensor the ship had."

... What? Either I need to go back to school, or this statement is elemetary school level creative writing. Why would a vacuum protect against an EMP? But the "blast radiation" could still have "fried" every sensor? What am I missing here?

An EMP is produced by interactions between the portion of the upper atmosphere suddenly heated into a fireball by the gamma radiation from the detonation and the local magnetic field. Remove the atmosphere or magnetic field and you basically eliminate the EMP. You've still got a lot of ionizing radiation and just plain heat for sensors and unshielded equipment to absorb.

4.) Not really a question... In the book humanity hauls space icebergs from the rings of Saturn (Wikipedia says the ice chunks in the rings can get as big as 10 meters, which I suppose is "iceberg" sized) to Ceres to be processed into everything from fuel to water. (Nevermind the fridiculous waste of energy even with sci-fi voodoo engines this must entail...) It seems like the authors failed to even read up on Ceres, for we now know there's a possibility of Ceres having more fresh water locked in it than the Earth has. And yes the book is quite recent.

And Saturn is an extremely long way to go for water. Apart from asteroids, short period comets, and...well, Ceres, Jupiter's surrounded by iceballs, its irregular moons in high orbit probably have plenty of accessible ice. No matter how good your engines are, why go such a long distance for something right in front of you?

Vilkata
2013-Mar-10, 11:16 PM
Vilkata, would you like us to move this thread to Q&A, hoping for more answers there?

I believe I have the answers I came for :) . Thank you though.

And thank you all for your replies. I normally wouldn't care about the concepts in a sci-fi book, but this one has won some awards, and came out very recently, so I felt its concepts should be up to snuff.