OTU Only: The Laser Beam That Misses

[Supplement Four]

We had a tragedy near my house New Year's Eve. This poor man, living a few streets over, went out to the sidewalk with his family to watch the (illegal) fireworks that people were popping off. Some idiot fired his handgun up into the sky, and has fate would have it, the bullet fell down on the man's head, killing him right in front of his family.

Not to belittle that very real story (I feel very sad for that family, although I did not know them), this made me wonder what happens to laser beams that miss in the Traveller universe....

Missiles, I assume explode at a certain point when they run out of fuel, if they don't hit their target. This would be a safety issue, I would assume. I can't imagine live missiles just floating out there, with no fuel, waiting to run into something. Too small to detect, especially cold with the propulsion long burned out.

What about laser beams.

In CT, the space combat round is over 16 minutes long. 1,000 seconds. One attack from a triple laser turret could represent hundreds or thousands of laser beams shot out across the void, hoping to hit the tiny speck that is the enemy vessel, tens or hundreds of thousands of kilometers away.

What happens to this destructive energy in space? Even with a successful hit, one can assume that hundreds or thousands of laser beams miss the target, with only a few hitting.

What happens to those beams?

A planet with any type of atmosphere would be safe. But, what about installations on atmosphere-less moons? What about other vessels?

 

[infojunky]

Er? Laser bursts? Basic inverse square situation there. Once you get past maximum effective (killing) range the beam still continues to spread i.e loses cohesiveness thus ability to damage anything.

 

[aramis]

We had a tragedy near my house New Year's Eve. This poor man, living a few streets over, went out to the sidewalk with his family to watch the (illegal) fireworks that people were popping off. Some idiot fired his handgun up into the sky, and has fate would have it, the bullet fell down on the man's head, killing him right in front of his family.

Not to belittle that very real story (I feel very sad for that family, although I did not know them), this made me wonder what happens to laser beams that miss in the Traveller universe....

Missiles, I assume explode at a certain point when they run out of fuel, if they don't hit their target. This would be a safety issue, I would assume. I can't imagine live missiles just floating out there, with no fuel, waiting to run into something. Too small to detect, especially cold with the propulsion long burned out.

What about laser beams.

In CT, the space combat round is over 16 minutes long. 1,000 seconds. One attack from a triple laser turret could represent hundreds or thousands of laser beams shot out across the void, hoping to hit the tiny speck that is the enemy vessel, tens or hundreds of thousands of kilometers away.

What happens to this destructive energy in space? Even with a successful hit, one can assume that hundreds or thousands of laser beams miss the target, with only a few hitting.

What happens to those beams?

A planet with any type of atmosphere would be safe. But, what about installations on atmosphere-less moons? What about other vessels?

Inverse square law renders them (eventually) harmless.If I have a 1m 250MW laser, that's 318MW/m² at source, and at 90000 km it's a 2m spot, , that's 79.5Mw/m². At 180,000km, it's a 4m spot, and 19.875MW/m². At 360,000km, it's an 8m spot, and 4.97 MW/m² - 49.7 J/cm² per second... a .22 LR is around 400j/cm²... so a 1 second beam is, at 1 LS, about the equivalent of a 22 lr per 10 cm²... TNE Pen = Nil at 1LS...

Eventually, it gets down to being a bright flashlight.

Mind you, the beam I just described is a TNE spinal laser for a small ship... it's much longer focal length than most Traveller lasers.

 

[Supplement Four]

Gotcha. Well, I guess that answers that. Thanks.

Not a science guy, if you can't tell. :coffeegulp:

 

[Lycanorukke]

DE weapons are not a problem as mentioned due to the inverse square law and meson guns don't even have to worry about that. Even N-PAW weapons would start to bloom after a while.

Missiles, I assume explode at a certain point when they run out of fuel, if they don't hit their target. This would be a safety issue, I would assume.

Missiles are bad (even if they auto destruct) - instead of a bit of solid metal you now have scatter shot shooting in every direction (a shotgun as opposed to a bullet). Mass drivers are even worse....

"Once you fire this husk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you're ruining someone's day, somewhere and sometime". Gunnery Chief - ME2

 

[BlackBat242]

"Once you fire this husk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you're ruining someone's day, somewhere and sometime". Gunnery Chief - ME2

I love this!

Misses by lasers and other projectile weapons in personal combat have never been a problem for me - coming from 1E AD&D the "check to see if the miss hits something else" is automatic - but I have to admit I never thought of extending that to ship combat!

Thanks for shaking things up a bit, S-4... this gives me ideas for "unexpected plot complications"!

 

[selunatic2397]

One of my players had a navigation skill of 5...there was a colony of nasty bads that pretty much pissed him off to no end...stole his main ship...shot his ship's cat... shot up his nobble ranch on Tarsus...ecetera...

He started with a minor asteroid that would hit the colonys capitol in 5 years...then he started long range plans...

The next asteroid would hit in 50 years...then 500...then 5000...and then give or take...50 thousand years.

He made all the rolls despite astronomical modifiers I imposed...

Somewhere out in space...several asteroids are cruising in the deep dark cold of pure vengeance...

Proof that in space things really do just keep on trucking.

[as for what brought on the nasty bads poor attitude? he shot off not one but a spread of nine missile that missed the target...but he rolled a 12 and joked "Well, that sure ruined someones day!" as a GM fiat I had it hit a minor planetary rulers yacht, and thats the rest of the story]

 

[Timerover51]

Missiles are bad (even if they auto destruct) - instead of a bit of solid metal you now have scatter shot shooting in every direction (a shotgun as opposed to a bullet). Mass drivers are even worse....

"Once you fire this husk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you're ruining someone's day, somewhere and sometime". Gunnery Chief - ME2

How what is left of a missile when it runs out of fuel depends on the warhead. If a nuclear one, then you basically do not have a problem it is detonates upon fuel exhaustion, as even a small warhead will effectively vaporize the missile body, leaving a steadily expanding oval of plasma that will cool and dissipate into the vacuum of space.

If you are dealing with a high explosive warhead, then the question will be is it a precision shaped-charged warhead to penetrate armor, a straightforward fragmentation warhead with limited armor penetration, or a penetrating warhead designed to penetrate a ship's hull and then explode. The last would imply a fairly thick casing for the warhead, with a smaller explosive charge. A blast warhead will not work in space.

What a warhead will be also depends on how you handle ship hull thicknesses in your Universe. See the following thread for a discussion on this topic.

http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=32898

The last determinant is the velocity vector of the firing ship. If fired directly ahead, the ship velocity, probably several miles to tens of miles per second, is added to the velocity of the missile, so that you have an expending cloud of fragments moving at a very high velocity in a straight line, with all fragments heading in the same direction. If fired at a tangent to the ship course, you have a velocity vector combining the forward speed of the ship and the tangent velocity of the missile. The fragment cloud will continue in the direction of the ship, but gradually diverging from the course. Lastly, if fired directly aft, the the velocity of the missile is subtracted from the velocity vector of the ship, but probably will not exceed the ship velocity. The result will still be an expending cloud of fragments moving in the direction of the ship, but at a lower velocity. Given the velocities that can be achieved by ship in-system in Traveller, most fragment clouds will eventually reach interstellar space, with their vectors possibly altered by near approaches to the gravity well of a planet or the system's star.

 

[Supplement Four]

How what is left of a missile when it runs out of fuel depends on the warhead.

The pure velocity of the missile is a factor, too. Remember, when a missile is fired, it begins at the same velocity as the ship. If a ship has a high velocity, then so does the missile.

If a ship is 3 hours into a 10 hour in-system journey, burning at a full 3Gs, then the vessel has built up quite a velocity--about 330 km per second. A missile fired will start, before acceleration burn, at that same velocity.

If the warhead is a dude, there's still a missile sized piece of metal out there traveling at 330 km per second.

 

[Lycanorukke]

If the warhead is a dude, there's still a missile sized piece of metal out there traveling at 330 km per second.

Assuming the missile is 50kg, then at that speed you are talking 2.2 Terajoules, or about 538 tons of explosive flying around waiting to hit something. Now add on the boost stage during combat if at long ranges and you could be talking a kiloton level boom if you miss the target.

In T5 you have the Kinetic kill missile which is described to be the size of a small car (say 1000kg). I dont think planetary authorities will take 'oops' as an excuse if the PC is having a bad day aiming.

 

[Jeff M. Hopper]

If the warhead is a dude....

Isn't using live male sophonts, or even dead ones, as kinetic energy kill weapons against the Imperial Rules of War? :CoW:

 

[Supplement Four]

Isn't using live male sophonts, or even dead ones, as kinetic energy kill weapons against the Imperial Rules of War? :CoW:

If the warhead is a dude...

Now, that's funny, too! :rofl:

 

[MCEvans]

One of my players had a navigation skill of 5...there was a colony of nasty bads that pretty much pissed him off to no end...stole his main ship...shot his ship's cat... shot up his nobble ranch on Tarsus...ecetera...

He started with a minor asteroid that would hit the colonys capitol in 5 years...then he started long range plans...

The next asteroid would hit in 50 years...then 500...then 5000...and then give or take...50 thousand years.

He made all the rolls despite astronomical modifiers I imposed...

Somewhere out in space...several asteroids are cruising in the deep dark cold of pure vengeance...

Proof that in space things really do just keep on trucking.

[as for what brought on the nasty bads poor attitude? he shot off not one but a spread of nine missile that missed the target...but he rolled a 12 and joked "Well, that sure ruined someones day!" as a GM fiat I had it hit a minor planetary rulers yacht, and thats the rest of the story]

that is just too funny :rofl::rofl::rofl:

 

[infojunky]

Ok, Pay attention to this quoted bit;

The last determinant is the velocity vector of the firing ship. If fired directly ahead, the ship velocity, probably several miles to tens of miles per second, is added to the velocity of the missile, so that you have an expending cloud of fragments moving at a very high velocity in a straight line, with all fragments heading in the same direction. If fired at a tangent to the ship course, you have a velocity vector combining the forward speed of the ship and the tangent velocity of the missile. The fragment cloud will continue in the direction of the ship, but gradually diverging from the course. Lastly, if fired directly aft, the the velocity of the missile is subtracted from the velocity vector of the ship, but probably will not exceed the ship velocity. The result will still be an expending cloud of fragments moving in the direction of the ship, but at a lower velocity. Given the velocities that can be achieved by ship in-system in Traveller, most fragment clouds will eventually reach interstellar space, with their vectors possibly altered by near approaches to the gravity well of a planet or the system's star.

Then add the fact the engagement envelope is spherical and the Inverse Square function is also working on all those fragments in the form of the density of the cloud of debris gets more disperse with every time increment. The chance of a detrimental encounter with any of said debris rapidly drops with time. The real risk is from the portions of the debris that gets trapped in a planetary bodies gravitational field, i.e. the bits floating around in commonly traveled bits of space, but even those will be limited to items that don't exceed the escape velocity for the Body in question.

So in the end, the risk of hitting a bit of debris from a previous battle quickly degrades to the background chance of hitting anything floating around in a system.

 

[Frankymole]

I hate to bring up Blakes 7 again but the debris from the battle (which presumably involves missile remnants since at least one of the capital ships carries them) manages to hole the prison transport and kick off the whole rebels-versus-Federation thing... so it can be a good plot driver - if you stray very close to the edges of a battle.

 

[Marchand]

I hate to bring up Blakes 7 again but the debris from the battle (which presumably involves missile remnants since at least one of the capital ships carries them) manages to hole the prison transport and kick off the whole rebels-versus-Federation thing... so it can be a good plot driver - if you stray very close to the edges of a battle.

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...)

 

[wbyrd]

Fortunately for spacers everywhere there is a whole ot of space out there. Tghe odds of a stray round from an energy weapon, missile or mass driver hitting anything at random are really slim...

well unless your target just happens to be setting in front of a station or planet when you miss.

A rail gun round itself could spend a million years in deep space cruising along at it's launch velocity, slowed down only by the occasional impact with a dust particle. 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.

I used the idea of a "ghost round" in a game recently,( well I substituted it for a Hostile vessel encounter) my players took a hit from a stray round and spent the next hour trying to figure out how a ship had gotten into range, hit them with a rail gun, and then slipped away before they could detect it.....of course they finally gave up, and made a bee line right out of the system before the cloaked raider fired on them again.

They are still pretty steamed that they had to pay for a new set of sensors without getting a chance to fire back on the ship that attacked them though..and they are still determined to go back and find the "cloaked Raider"

 

[salochin999]

Inverse square law renders them (eventually) harmless.If I have a 1m 250MW laser, that's 318MW/m² at source, and at 90000 km it's a 2m spot, , that's 79.5Mw/m². At 180,000km, it's a 4m spot, and 19.875MW/m². At 360,000km, it's an 8m spot, and 4.97 MW/m² - 49.7 J/cm² per second... a .22 LR is around 400j/cm²... so a 1 second beam is, at 1 LS, about the equivalent of a 22 lr per 10 cm²... TNE Pen = Nil at 1LS...

Eventually, it gets down to being a bright flashlight.

Mind you, the beam I just described is a TNE spinal laser for a small ship... it's much longer focal length than most Traveller lasers.

So lasers should really have a penetration / range?

edit:
This made me wonder - something I expect others figured out decades ago - if a ship is accelerating at 3G or whatever then isn't there a risk they can fly into their own ammunition - maybe not lasers but projectile weapons or missiles?

Also back to lasers it seems you could create quite a complex space combat system just around lasers taking into account
size of laser
power supply
dissipation with range
so for example a ship with ten lasers might have the power to fire all ten at short range but only one at long range or four at medium range

and basing the combat around heat dissipation both on the firing ship and target so both firing and getting hit increase "damage"

 

[Ulsyus]

Just thinking abut s4's original question but located on the ground. I imagined something like the images we see on TV of those places east of Cypress and south of Turkey. However instead of bullet pockmarks and broken windows everywhere, what we'd see is burn marks on buildings and windows partly slagged or melted around holes in them.

Those beam shots would end up somewhere. Who ever thinks about the collatoral damage their PC's cause when they get into a nasty dustup?

 

[aramis]

Just thinking abut s4's original question but located on the ground. I imagined something like the images we see on TV of those places east of Cypress and south of Turkey. However instead of bullet pockmarks and broken windows everywhere, what we'd see is burn marks on buildings and windows partly slagged or melted around holes in them.

Those beam shots would end up somewhere. Who ever thinks about the collatoral damage their PC's cause when they get into a nasty dustup?

The beam focal lengths for ground action are much shorter, and the spot diameter grows at a similar proportion, and drops its penetration similarly.

If a beam has about a 100m penetration of about 1cm of steel, then it's 200m penetration is about 1mm, and at 300, it's about 0.7mm, at 400m, it's about 0.5mm... but at that point, dust, vapor, smoke, pollen, etc, are also causing great issues. So an air-to-air is not going to do a lot, and in open fields, either it's burning individual plants, making a direct line back to the shooter, or it's fading out into the pollen, dust, etc.