Japanese space experiment proves another SF film trope wrong ...
#1
Japanese scientists fired a cannonball into an asteroid last year, according to this CNN article. What they learned is that the 3000-foot-wide asteroid's gravity was enough to keep the debris from the impact from floating off into space.

So when you see big, huge honking spaceships falling apart in space battles on TV and in the movies - they're wrong. They should have enough mass for the debris to collapse back onto their surfaces.

Allowing for variations between hypothetical spaceship design and asteroids, as well as the energy of the impact events, one can argue that spaceships might still fly apart if critical reactors explode. But in most cases you see stuff fly out into space just because it's been blasted off the surface of a ship. That appears to be incorrect.

If a space battle results in a rupture, such that the ship's atmosphere vents into space, that should create enough pressure to send stuff flying away from the ship. But if a blast just knocks and antenna off (or even shatters it) the debris should still remain close to, if not fall onto, the giant ship.
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#2
I think the "energy of the impact events" is one of the keys to this question. You describe the Hayabusa2 spacecraft as firing a cannonball into Ryugu. I saw many sources saying it was a little larger than a tennis ball. What kind of velocities will debris have if the impact is not the size of a tennis ball but say a fighter spacecraft crashing into it? I would think the velocities would be much higher with a fighter impact than a tennis ball.

What size, and mass, spaceship are you talking about? For the Death Star you might be right. I looked at the estimated mass of a Star Destroyer, "Given a calculated volume of about 54,000,000m³ for Star Destroyers at 1600m length, and a density range of 500-1000kg/m³, the mass of a Star Destroyer should fall somewhere between 27,000,000,000 and 54,000,000,000 kilograms. That's 27 to 54 million metric tonnes." http://weblog.st-v-sw.net/2010/01/star-d...nsity.html. The Enterprise-D is at 4,960,000 metric tons-wikipedia. The StarDestroyer is an order of magnitude less massive, and the Enterprise-D is two orders of magnitude less massive than Ryugu, (4.50±0.06)×10^11 kg. I highly doubt the Enterprise-D would have enough mass to prevent debris from escaping.

I'm also wondering if the size of the Hill Sphere of the spaceship is relevant to this question. The Space Shuttle's Hill Sphere is 120 cm in radius, much smaller than the shuttle itself.
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#3
I think the important number is the escape velocity. Anything traveling faster than the escape velocity gets out of the gravitational pull of the attracting object. The escape velocity is given by v = sqrt(2*G*M/r), where G = 6.67x10^-11, M is the mass of the attracting object in kilograms, and r is the distance from the attracting object in meters. If we take something the size of the Bismarck (about 40,000 tons), at a distance of 10 meters from its center of gravity, the escape velocity is about 0.023 meters/second (about one inch per second). That's a pretty small number (walking speed is about 1.4 meters per second). Chances are anything that gets blown off a rocket ship that size will escape into space.

If the Enterprise-D is really 100 times heavier than the Bismarck, then the escape velocity at 10m would be 10 times higher (about 9 inches per second, or just under one kilometer per hour). That's still pretty low compared to the speeds you see pieces fly off blasted ships in the movies. So I think a lot of the stuff blasted off ships would never come back.
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#4
Well, we also have to allow for relative velocities. One movie that took that into consideration was the 1998 Lost In Space, where Don West (Matt LeBlanc) uses his spacecraft to gently nudge the vehicle of Jeb Walker (Lennie James) in the middle of a space battle.

So if the object (regardless of size) is traveling in a similar direction and speed with the ship, the impact energy will be less than if the object is traveling counter to or perpendicular to the velocity of the ship being targeted.

I don't know what velocities were involved with the Japanese experiment. I should have thought about that.
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#5
I haven't looked at the papers on the Japanese experiment, but I would guess that they are looking into the effect of impacts from small objects in the asteroid belt. The larger asteroids are probably agglomerations of pieces of ice and rock and dust, and may not be very tightly packed. It's possible that a fast-moving rock would just penetrate into the asteroid and most of its energy would be expended under the surface, without much material coming off. The experiment sounds like it didn't see much material leave the asteroid when they shot a cannonball into it. Rocket ships are constructed quite differently from such asteroids, so it's likely that the results from the Hayabusa2 experiment may not directly apply to space battles.
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#6
I am just glad nobody got hurt.
Don't insult the precious, my precious!:book:
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#7
You know, badlands, Chaos Theory says the jury is still out on whether firing a cannonball into an asteroid will have some bizarre effect on anyone here on Earth.
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