# What would the range of a laser weapon be in space?

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#### CarnivoreJoe

##### Guest
This is something that has been bugging me for quite a while, and I'd love to get a good answer to it. As a writer, I want to make sure that the technology and physics that I describe in my books and stories are realistic (or at least that I have an understanding of where the realism slips).

My question is best asked by first describing the following hypothetical situation (it's a bit sci-fi, but possibly not all that far off):

A spacecraft flying not far out of Earth's orbit has a large laser weapon installed for defense against attacking ships. A ship comes in to attack and our spacecraft fires her laser at it. The laser beam misses and heads off in the direction of Mars.

My question is: would the laser strike Mars, or could its power or potency diminish enough to be ineffectual by the time it reaches its destination. I would think that a sufficiently powerful laser (like one that would badly damage a large spaceship) would continue all the way to Mars. This, as I see it, would make laser's as ship's weapons not that realistic.

D

#### DrRocket

##### Guest
CarnivoreJoe":2ulqqnsb said:
This is something that has been bugging me for quite a while, and I'd love to get a good answer to it. As a writer, I want to make sure that the technology and physics that I describe in my books and stories are realistic (or at least that I have an understanding of where the realism slips).

My question is best asked by first describing the following hypothetical situation (it's a bit sci-fi, but possibly not all that far off):

A spacecraft flying not far out of Earth's orbit has a large laser weapon installed for defense against attacking ships. A ship comes in to attack and our spacecraft fires her laser at it. The laser beam misses and heads off in the direction of Mars.

My question is: would the laser strike Mars, or could its power or potency diminish enough to be ineffectual by the time it reaches its destination. I would think that a sufficiently powerful laser (like one that would badly damage a large spaceship) would continue all the way to Mars. This, as I see it, would make laser's as ship's weapons not that realistic.

The photons will maintain their individual energy, determined solely by the frequency, unless they interact with some form of matter or are affected by a gravitational field (the gravitational effect is very small unless the field is extremely strong). The delivered power of the beam, at a sufficient distance so that it can be considered to have emanated from a point source, will be determined by the power at the point of emission and by the angular dispersion of the beam. You have specified neither the laser power nor the angular dispersion. In addition to power, the damage done by the laser would be very dependent on the energy delivered, or power times time on target. If the target is moving or rotating about some axis the time on a vulnerable spot may be rather small.

A laser could be an effective weapon under the right circumstances. It is not a magic wand. At best all it would do is provide high local heating, depending on the absorptivity of the target at the laser frequency. The effect of that heating is extremely dependent on what it hits and the material of which it is composed. I do not see what the potential for a laser beam reaching Mars has to do with the potential use as weapon. The beam would certainly reach there, but probably would be rather diffuse, hence of relatively low power density -- but since your scenario implies sufficient technology to allow armed space vessels one might hypothesize very high laser power and very low dispersion.

Lasers at this time are practical as ship's weapons. We don't have any spaceships.

The U.S. has investigated the use of airborne lasers for anti-missile applications. I don't know the current status, but I am under the general impression that it has been something short of an unqualified success.

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#### EthanRiddle

##### Guest
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

O

#### origin

##### Guest
EthanRiddle":vlt8nttp said:
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

We already do. ICBM go into suborbital flight at about 150 - 400 KM above the earth, which is space. Not space based but definitely passing through space.

D

#### drwayne

##### Guest
origin":jh6n1lp1 said:
EthanRiddle":jh6n1lp1 said:
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

We already do. ICBM go into suborbital flight at about 150 - 400 KM above the earth, which is space. Not space based but definitely passing through space.

That being given, one can argue we have had weapons passing through space since the V2.

Wayne

V

#### vogon13

##### Guest
Keeping in mind the odds of accidentally hitting Mars (or any other astronomical object) are tiny.

Also, the relative motion of earth, Mars, and the laser device (if orbital), would result in the beam sweeping across the Martian surface at a likely speed of kilometers per second. Even at extremely high power levels, the dwell time on a specific target is going to be microseconds or (probably) much less.

You won't even notice it (if you're the target), even if the event is on the dark side.

D

#### DrRocket

##### Guest
EthanRiddle":1u0dc5gc said:
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

We already have weapons in space. The biggest weapon on the modern battlefield is information. Our troops know their position rather precisely from the GPS satellites, which also guide some weapons. Our troops have excellent electronic intelligence provided by some very sophisticated spy satellites. Other countries have their own intelligence sources.

If there were a major conflict with a real power, you can bet that satellites would be a major and early target. Armies fight wars for keeps. You would not expect them to ignore any potential advantage or threat. I certainly would not want our military to ignore such things.

The Navy recently shot down an errant satellite to control the re-entry and prevent it from landing in the wrong place. Don't you think that demonstration had a point other than just handling the immediate problem ?

Sure, I'd like to see there be no fighting in space. But on my list of priorities I rank not fighting a battle in Omaha a lot higher.

K

#### kg

##### Guest
I think a space battle could make for some really creepy fiction. Imagine traveling from mars back to earth and having rocket launched at you. You would have several weeks to ponder this thing traveling at you at thousands of miles an hour. It wouldn't even have to hit your spacecraft. It could kill you by forcing you to burn up enough rocket fuel trying to out manuver it and keep you from being able to correct your course back to earth!

D

#### DrRocket

##### Guest
kg":1iichjps said:
I think a space battle could make for some really creepy fiction. Imagine traveling from mars back to earth and having rocket launched at you. You would have several weeks to ponder this thing traveling at you at thousands of miles an hour. It wouldn't even have to hit your spacecraft. It could kill you by forcing you to burn up enough rocket fuel trying to out manuver it and keep you from being able to correct your course back to earth!

Not a problem.

1. It takes quite a bit of rather sophisticated engineering to hit a missile with a missile even when it is is in earth orbit or sub-orbital and you have lots of off-line radar data to tell you the basic trajectory of the target. Hitting an object traveling on an interplanetary trajectory from a planet would be terribly difficult. There is a lot of space out there and the target doesn't occupy much of it.

2. If you knew something was closing in on you from far off, then you would also know it is traveling rather rapidly with respect to you and countermeasures would be pretty simple. Just wait until it is quite close and closing and jettison some debris -- almost anything would do. You would have a dandy kinetic kill mechanism there. Since we are talking about a war situation, a machine gun would have tremendous range (and accuracy) in space (you don't need much) and would work quite well against an incoming warhead -- just like the 20mm Phalanx system that was once used on ships for just that purpose. And yes, a conventional gun would work just fine in the vacuum of space.

3. You would not take any evasive maneuvers until the incoming missile was pretty close. Saving the fuel for the end game is optimal.

4. Depending on the mechanism used by the missile to attack, there are contermeasures available. Infrared decoys, radar decoys, etc.

K

#### kg

##### Guest
With what NASA needs to do just to make a toilet work in space it figures that a machine gun would work just fine...
Are there times when a space craft is more vulnerable to attack? Say if you were traveling from the asteroid belt back to earth and you needed to make a flyby of mars to ajust your trajectory. Ok, you have a bunch of outstanding parking violations on mars and they decide that they need to rub you out. It seems that fly-bys are real nail biters because of the small margines for error even when there isn't any conflict envolved (I remember well the "fly Casini into the sun" folks)! Would it be difficult to destroy the incomming space craft or force it off course?
I would be far more interested in sci-fi that was more based in reality.

E

#### EthanRiddle

##### Guest
origin":9xk5mnyg said:
EthanRiddle":9xk5mnyg said:
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

We already do. ICBM go into suborbital flight at about 150 - 400 KM above the earth, which is space. Not space based but definitely passing through space.

You know what I meant.

E

#### EthanRiddle

##### Guest
I hope to god we don't bring weapons in to space. But you watch.. It will happen. It is, as they say, "in our nature".

We already have weapons in space. The biggest weapon on the modern battlefield is information. Our troops know their position rather precisely from the GPS satellites, which also guide some weapons. Our troops have excellent electronic intelligence provided by some very sophisticated spy satellites. Other countries have their own intelligence sources.

If there were a major conflict with a real power, you can bet that satellites would be a major and early target. Armies fight wars for keeps. You would not expect them to ignore any potential advantage or threat. I certainly would not want our military to ignore such things.

The Navy recently shot down an errant satellite to control the re-entry and prevent it from landing in the wrong place. Don't you think that demonstration had a point other than just handling the immediate problem ?

Sure, I'd like to see there be no fighting in space. But on my list of priorities I rank not fighting a battle in Omaha a lot higher.

If there was "a major conflict with a real power", satellites won't be much use any more with all the radiation plumes circulating in to the stratosphere. But I do agree that spy satellites have prevented arms races and nuclear arms races. Hence we can see our so called "enemies" actions. As far as satellite information being a "weapon", ya I guess. Could be considered a "part" of a weapon. Could be considered a weapon by itself. Depends what you use it as. Depends on what your definition of a weapon really is. etc..

E

#### EthanRiddle

##### Guest
I don't know if the lazer in your scenario would reach Mars. I hope one of these "scientists" will try to answer your question soon. This post has been up for a few days now. Good luck with your book.

E

#### EthanRiddle

##### Guest
CarnivoreJoe":qoa71yyx said:
This is something that has been bugging me for quite a while, and I'd love to get a good answer to it. As a writer, I want to make sure that the technology and physics that I describe in my books and stories are realistic (or at least that I have an understanding of where the realism slips).

My question is best asked by first describing the following hypothetical situation (it's a bit sci-fi, but possibly not all that far off):

A spacecraft flying not far out of Earth's orbit has a large laser weapon installed for defense against attacking ships. A ship comes in to attack and our spacecraft fires her laser at it. The laser beam misses and heads off in the direction of Mars.

My question is: would the laser strike Mars, or could its power or potency diminish enough to be ineffectual by the time it reaches its destination. I would think that a sufficiently powerful laser (like one that would badly damage a large spaceship) would continue all the way to Mars. This, as I see it, would make laser's as ship's weapons not that realistic.

How close are you to your book being published? I would like to check it out. Sounds really cool. Go ahead and make the lazer reach Mars! :lol: That would rock, and make a good point too.

M

#### MeteorWayne

##### Guest
Yes, but of course if it caused any damge on Mars, it would then be PURE ScyFy, with no basis at all in physics...

T

#### Testing

##### Guest
DrRocket":21faiozl said:
CarnivoreJoe":21faiozl said:
This is something that has been bugging me for quite a while, and I'd love to get a good answer to it. As a writer, I want to make sure that the technology and physics that I describe in my books and stories are realistic (or at least that I have an understanding of where the realism slips).

My question is best asked by first describing the following hypothetical situation (it's a bit sci-fi, but possibly not all that far off):

A spacecraft flying not far out of Earth's orbit has a large laser weapon installed for defense against attacking ships. A ship comes in to attack and our spacecraft fires her laser at it. The laser beam misses and heads off in the direction of Mars.

My question is: would the laser strike Mars, or could its power or potency diminish enough to be ineffectual by the time it reaches its destination. I would think that a sufficiently powerful laser (like one that would badly damage a large spaceship) would continue all the way to Mars. This, as I see it, would make laser's as ship's weapons not that realistic.

The photons will maintain their individual energy, determined solely by the frequency, unless they interact with some form of matter or are affected by a gravitational field (the gravitational effect is very small unless the field is extremely strong). The delivered power of the beam, at a sufficient distance so that it can be considered to have emanated from a point source, will be determined by the power at the point of emission and by the angular dispersion of the beam. You have specified neither the laser power nor the angular dispersion. In addition to power, the damage done by the laser would be very dependent on the energy delivered, or power times time on target. If the target is moving or rotating about some axis the time on a vulnerable spot may be rather small.

A laser could be an effective weapon under the right circumstances. It is not a magic wand. At best all it would do is provide high local heating, depending on the absorptivity of the target at the laser frequency. The effect of that heating is extremely dependent on what it hits and the material of which it is composed. I do not see what the potential for a laser beam reaching Mars has to do with the potential use as weapon. The beam would certainly reach there, but probably would be rather diffuse, hence of relatively low power density -- but since your scenario implies sufficient technology to allow armed space vessels one might hypothesize very high laser power and very low dispersion.

Lasers at this time are practical as ship's weapons. We don't have any spaceships.

The U.S. has investigated the use of airborne lasers for anti-missile applications. I don't know the current status, but I am under the general impression that it has been something short of an unqualified success.

Aerospace Corp. has a pretty good synopsis. And Crosslink is an excellent read.
I pushed the button on a ground demonstation near 20 years ago. It will work fine.

http://www.aero.org/publications/crossl ... 08/08.html

D

#### dryson

##### Guest
I think that the lasers would begin to diminish once they left the focal point of their release from the ship. This would be the poin at which the most energy is released and able to be maintained. Once the laser crosses the distance of space it would have diminished. I dont think it would even reach Mars. I think you are think of the laser as being like a release of energy from the sun, although along the same concept, the laser energy is man made and thus less energetic then the sun.

O

#### origin

##### Guest
dryson":2kugmns9 said:
Once the laser crosses the distance of space it would have diminished. I dont think it would even reach Mars. I think you are think of the laser as being like a release of energy from the sun, although along the same concept, the laser energy is man made and thus less energetic then the sun.

It does not matter what the origin of the photon is, whether the sun or a flashlight, the only thing that matters is the energy of the photon. In other words a photon that has a wavelength of red light say about 650 nm would travel without losing any energy to pluto whether it came from the sun or your red flashlight. That is assuming that it did not 'run into' anything. A laser that was perfectly collimated would travel to mars with no problem. The trouble is there is no such thing as perfect collimation. Collimation can be thought of as how much a beam 'spreads out'. Those little pointer lasers have a beam of about a diameter of few millimeters at 100 cm but spread out to about a diameter of 1 meter or more over the distance of 100 meters. I don't remember my optics all that well, so I do not recall if the photons in a laser beam interact with each other and cause the beam to spread out (I don't think they do).

L

#### lensman01

##### Guest
origin":150kwj8z said:
dryson":150kwj8z said:
Once the laser crosses the distance of space it would have diminished. I dont think it would even reach Mars. I think you are think of the laser as being like a release of energy from the sun, although along the same concept, the laser energy is man made and thus less energetic then the sun.

It does not matter what the origin of the photon is, whether the sun or a flashlight, the only thing that matters is the energy of the photon. In other words a photon that has a wavelength of red light say about 650 nm would travel without losing any energy to pluto whether it came from the sun or your red flashlight. That is assuming that it did not 'run into' anything. A laser that was perfectly collimated would travel to mars with no problem. The trouble is there is no such thing as perfect collimation. Collimation can be thought of as how much a beam 'spreads out'. Those little pointer lasers have a beam of about a diameter of few millimeters at 100 cm but spread out to about a diameter of 1 meter or more over the distance of 100 meters. I don't remember my optics all that well, so I do not recall if the photons in a laser beam interact with each other and cause the beam to spread out (I don't think they do).

Quite right collimation is the big sticking point here.
If I remember precisely collimation is dependant on the quality of the optics rather than an inherent effect of photon interaction.

O

#### origin

##### Guest
lensman01":cnxiwhj1 said:
Quite right collimation is the big sticking point here.
If I remember precisely collimation is dependant on the quality of the optics rather than an inherent effect of photon interaction.

Tha's what I thought, and with a name like 'lensman01' I would go with your take.

S

#### sentrynox

##### Guest
Depending on the technology behind the laser it could cross our whole solar system...
Neutral lasers could do just that and even reach other solar systems, but we are still far off that potential and years away from experimenting a workable neutral laser.
But theorically plasma lasers could use our sun to create an even bigger laser... Luckily we are still a long way from being capable of doing this.

M

#### MeteorWayne

##### Guest
What's a neutral laser?

What's a plasma laser?

K

#### kg

##### Guest
sentrynox":1td3rg1g said:
Depending on the technology behind the laser it could cross our whole solar system...
Neutral lasers could do just that and even reach other solar systems, but we are still far off that potential and years away from experimenting a workable neutral laser.
But theorically plasma lasers could use our sun to create an even bigger laser... Luckily we are still a long way from being capable of doing this.

Maybe this person is thinking of some kind of astrophysical maser?

http://en.wikipedia.org/wiki/Astrophysical_maser

M

#### MeteorWayne

##### Guest
Unlikely, since they like lasers are just EMF.

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