OTU Only: The Laser Beam That Misses

[Frankymole]

I bow to no-one in my love of B7, but as others have argued, the odds against hitting random debris from a battle are literally astronomical. (The characterisation was a lot stronger than the physics I think...)

It depends how close the damaged ship was to the recipient of the debris, though... the Liberator was on top of the London when the sensors came back online, maybe it was terribly close already when the fragments were blown off it - perhaps even about to attempt a boarding action? Might have been the crew's first attempt to escape - take over a relatively undamaged ship that still had motive power to escape - before resorting to the escape pods.

 

[Murphy]

Fortunately for spacers everywhere there is a whole ot of space out there.
...
However, If Murphy is in a really bad mood that round could sail right into a traffic lane after a million years and knock a big hole in someones shiny new far trader.

It's when I'm in a good mood that you wanna watch out

I used to think interstellar dust slows it down. But let's do some math.

I assume the bullet would halve its speed once it hit an amount of dust particles equal to its mass. This means the smaller the round, the better it will be slowed down (because of larger cross section relative to mass). So let's take a railgun bullet (or missile fragment) 1 cm^2 in cross section and see how long a way does it need to hit 10 grams of interstellar matter.

The dust density in the local interstellar medium of the Local Bubble is approximately 10^−6 × dust grain/m3 with each grain having a mass of approximately 10^−17 kg.

Further,

By mass, 99% of the ISM is gas in any form, and 1% is dust.

This means the dust has density of 10^−23 kg/m3, and the interstellar medium as a whole is 100 times denser, with 10^−21 kg/m3.

Now, at that density you need 10^19 cubic meters of volume to amass 10 grams of matter. A cross section of 1 square centimeter would cross that much volume over a length of 10^23 meters. That is... um, 3 megaparsecs.

Of course, star systems are very small targets. The parsec unit is named after the fact!

 

[wbyrd]

Remind me never to run into Murphy when he's happy

Id say 3 Megaparsecs is a long enough flight to ensure that most stray rounds end up in interstellar void....

I'd imagine the odds of encountering a naturally occurring rock of the same mass are far greater than the odds of getting hit by something manufactured even if it ended up in an orbit in the same system it was fired in.

 

[WistfulD]

It's when I'm in a good mood that you wanna watch out

I used to think interstellar dust slows it down. But let's do some math.

I assume the bullet would halve its speed once it hit an amount of dust particles equal to its mass. This means the smaller the round, the better it will be slowed down (because of larger cross section relative to mass). So let's take a railgun bullet (or missile fragment) 1 cm^2 in cross section and see how long a way does it need to hit 10 grams of interstellar matter.


Further,

This means the dust has density of 10^−23 kg/m3, and the interstellar medium as a whole is 100 times denser, with 10^−21 kg/m3.

Now, at that density you need 10^19 cubic meters of volume to amass 10 grams of matter. A cross section of 1 square centimeter would cross that much volume over a length of 10^23 meters. That is... um, 3 megaparsecs.

Of course, star systems are very small targets. The parsec unit is named after the fact!

First of all, you should be flogged for that joke.

More importantly, the interstellar medium is only relevant if the battle takes place in interstellar space. Since most battles take place near something worth fighting over, they tend to occur in solar systems. There, not only is the stellar medium quite a bit thicker, but the fragment risks getting caught in an orbit around the star instead of simply drifting on until dust collisions turn its speed into a random walk.

As for missiles, is there any indication that they explode if they don't hit anything? For all we know, maybe if after six hours they simply set themselves to disarm, and maybe even turn on a low-power beacon for SDS ships to come clean them up (using robots of course, no one is going to trust a PC's assurance that something is "disarmed":smirk.