Discussing future and (im)possible carrier technology

Geographer

Geographer

Junior Member
Lasers exert no pressure on objects, how would they knock a missile off course? By blinding the seeker? Most anti-ship missiles are radar guided, not optically guided.
 
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NikeX

Banned Idiot
Light by its very nature exerts pressure. See below: What is being said is that research is underway looking at ways to nudge attacking missiles off of their courses

Light exerts physical pressure on objects in its path, a phenomenon which can be deduced by Maxwell's equations, but can be more easily explained by the particle nature of light: photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by c, the speed of light. Due to the magnitude of c, the effect of light pressure is negligible for everyday objects. For example, a one-milliwatt laser pointer exerts a force of about 3.3 piconewtons on the object being illuminated; thus, one could lift a U. S. penny with laser pointers, but doing so would require about 30 billion 1-mW laser pointers.[7] However, in nanometer-scale applications such as NEMS, the effect of light pressure is more pronounced, and exploiting light pressure to drive NEMS mechanisms and to flip nanometer-scale physical switches in integrated circuits is an active area of research.[8]

At larger scales, light pressure can cause asteroids to spin faster,[9] acting on their irregular shapes as on the vanes of a windmill. The possibility to make solar sails that would accelerate spaceships in space is also under investigation.[10][11]

Although the motion of the Crookes radiometer was originally attributed to light pressure, this interpretation is incorrect; the characteristic Crookes rotation is the result of a partial vacuum.[12] This should not be confused with the Nichols radiometer, in which the motion is directly caused by light pressure.[13]
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NikeX

Banned Idiot
If this research is successful incoming supersonic anti-ship missiles can be nudged to miss by pulses of laser light impinging on their bodies. When a missile is in terminal homing mode it is very sensitive to disruption of its flight path. Point defense lasers could provide that disruption.

And if you look at the quote below you will see that missiles using reflective surfaces on their bodies are especially vulnerable to radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light. If the radiation is totally reflected, the radiation pressure is doubled. For example, the radiation of the Sun at the Earth has a power flux density of 1,370 W/m2, so the radiation pressure is 4.6 µPa (absorbed).
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NikeX

Banned Idiot
The novelty item, a Crookes radiometer, demonstrates the principle of radiation pressure. Follow this link to see what I am talking about. Everyone has played with one at one time or another

"Crookes radiometer - Wikipedia, the free encyclopedia
The radiometer is made from a glass bulb from which much of the air has been removed to form a partial vacuum. Inside the bulb, on a low friction spindle, is a rotor with several (usually four) vertical lightweight metal vanes spaced equally around the axis. The vanes are polished or white on one side, black on the other. When exposed to sunlight, artificial light, or infrared radiation (even the heat of a hand nearby can be enough), the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing. Cooling the radiometer causes rotation in the opposite direction."
 
siegecrossbow

siegecrossbow

General
Staff member
Super Moderator
^^ Nikex, I think most of us here understand that light exerts a pressure. The real question is whether the light exerted by a laser beam will have a significant effect altering the trajectory of a missile.
 
D

delft

Brigadier
NikeX said:
What does a bacterium have to do with things? Besides the use of a laser knocking something off course is still being researched. It is too early to rule anything out.
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It comes from the citation in your post #45.
 
D

delft

Brigadier
Indeed asteroids are influenced by light pressure, but that can only be measured after millions of years. With more than 30 million seconds in a year that's a time 13 orders of magnitude larger than that available to your defensive laser. The missile is much smaller but the time to influence the missile by light pressure is still too small. Heating by the laser will be more important.
 
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NikeX

Banned Idiot
My answer is that the research these labs are conducting shows promise in using the pressure of light by a laser. I will say that again: The pulse of a powerful laser is what is showing promise. That said all we can do is wait and see if this line of research is successful. I think we all agree that it is possible due to the physics of light. The particle nature of light can influence the path of an object. That has been demonstrated as fact. Can the energy of the pulse or series of pulses be made strong enough to alter the path of an oncoming missile remains to be seen

Anyway you look at it, it is an exciting concept for point defense of a ship. Comments welcome.
 
N

NikeX

Banned Idiot
siegecrossbow said:
^^ Nikex, I think most of us here understand that light exerts a pressure. The real question is whether the light exerted by a laser beam will have a significant effect altering the trajectory of a missile.
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It seems that a ground based low power laser(5 kw) can alter the trajectory of orbital space junk or at least NASA thinks so. In the point defense role it may have something to do with multiple lasers combining their output to do the job of altering an incoming weapon's course.


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Engineer

Engineer

Major
You have hours to days to alter the course of a piece of space junk, assuming it works. On the other hand, you only a minute at best when it comes to a missile. These are not even close enough for comparison.

Even if we were to assume light pressure is non-negligible, it is still extremely weak compared to aerodynamics disturbances and any deviation to the missile's course will get corrected by the on-board flight control system.

It is much easier to heat the missile up and cause structure failure.
 
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