Collision Hazards

The largest ocean going ships are about half a million tons. I would expect that any interstellar ships we or others might build would have to be at least that size in order to survive a journey lasting decades or centuries. Let's estimate a million tonnes - 10^9 kg - roughly twice the mass of the supertanker the Seawise Giant.

I remember the first time I saw a piece of armor plate that had been struck by a hypervelocity projectile. Even though the projectile was only a bit larger than a beebee, it had drilled a hole right through two inches of armor plate. Lower velocity projectiles spread their energy over larger areas. The operative factor is the speed of sound. If the projectile is moving significantly faster than the speed of sound in the target material, there isn't enough time for the forces to be transmitted laterally, and the projectile just keeps boring a hole until it has piled up enough mass in front of it to slow the whole procession, including the shock wave at the front, below the speed of sound.

It's a bit more complicated than that of course.

Suppose you had a large interstellar space craft moving a something like half the speed of light. The kinetic energy would be pretty large:

m*c^2(gamma - 1), where gamma = 1/sqrt(1-v^2/c^2) = 1/sqrt(3/4) = 1.1555, so that available kinetic energy is 1.4 * 10^16 J/kg, or 1.4 * 10^25 J for a million tonne behemoth like that described in the first paragraph. That amounts to the equivalent of 3 billion megatons of TNT - not enough to blow a planet to bits, death star style, but possibly enough to blast a hole right through it. So you might not want to aim your interstellar ship directly at a habitable planet, just in case you had trouble slowing down.

Comments

Post a Comment

Popular posts from this blog

Anti-Libertarian: re-post

The most pointed critique of social security and liberalism in general is the libertarian critique. The problem with libertarians, for a liberal, is that we have too much in common. We both believe in individual rights, tolerance of individual differences, and dislike government prescription of religion. The basic difference, it seems to me, is the different answers we give to Cain's (with thanks to the Captain - my original version had the corpse asking the question!) famous question: "Am I my brother's keeper?" That's not really my basic bitch against the libertarians though. My real complaint is the same as my complaint against most religion - its premise is a fraud. For those who can't stand to wait for the punchline, I believe that trying to implement libertarian principles leads to tyranny or social disintegration. Demonstrating that takes some historical (and pre-historical) context. For all but the last 15,000 or so of the 100,000 years the human spec...
Read more

Uneasy Lies The Head

Uneasy lies the head that wears a crown ........... Shakespeare Henry IV, Part II. So it is with us and our slightly distant primate cousins , so it seems. A 9-year study of wild baboons in Kenya by Princeton University and the Institute of Primate Research may turn conventional assumptions of alphas males upside down. The study found that alpha males have high testosterone levels, which allows them to dominate other baboons, get access to more food, and attract better mates. This is expected. Surprisingly, though, the alpha males also have high levels of stress hormone glucocorticoid, which scientists measured from their feces samples. In fact, the stress of alpha baboons was on par with low-ranking baboons. The convention wisdom is that access to food and females provides life security and thus less stress for dominant males. Conversely, weak males who are constantly threatened by starvation and physical violence from stronger males are thought to be more stressed. The st...
Read more

We Call it Soccer

The US played its best, and maybe only good game of World Cup, but lost thanks to brilliant goalkeeping by the Swedish keeper and the bizarre method soccer uses to settle ties when three US stars could not put the ball on frame from the 12 yard spot.  At the end it came down to a blocked shot that spun in by maybe a couple of centimeters. Well, that's football - too much like life.   Which brings me to a modest proposal.  Replace the thirty minute overtimes with as many 7-player 15 minute periods as needed to settle it.  Scoring should be much easier with fewer players.
Read more