Tuesday, 28 July 2015

Random Numbers: How 'Powerful' is a 40 Watt phased plasma rifle?

Science Happens...

   For an Author writing SF can be challenging for many reasons.  Not least is the expectation that there must be some 'science' involved, especially for a 'hard SF' work.  Often this results in lengthy and boring expositions where the technology, setting, or related paraphernalia is explained in detail.  This isn't so bad; it is, after all, the reason many people read that particular kind of SF.  A bigger issue is when the author adds in a random number, not always necessary, in order to imbed more firmly in his reader/audience's mind that this is 'science' fiction.  But, often, the number is not as carefully selected as it should be.  Most SF fans will not care, but for some of us fanatics it is a major annoyance.

   The case in question is from Terminator, one of my favourite SF movies.  The terminator is buying guns and asks the shopkeeper if he has a 'phased plasma rifle in the forty watt range'.  So far so good. A single line that reinforces the fact that the terminator is a robotic killer from the future.

   But I got thinking, is 40W really a good number?  A big problem for hard SF authors wishing to include energy based weapons into their 'Verse is how much power to give them; making sidearms wight eh output of a thermonuclear warhead is an obvious no-no, for example.  So I made the following table, 'translating' the output of several modern kinetic weapons into a 'Power' rating.  It is not a perfect comparison, as directed energy weapons employ a different mechanism to do damage t the target than do KEW, but it provides a rough ballpark.

   It turns out that the terminator's preferred weapon is roughly equivalent to a .22 magnum rifle firing one round every fifteen seconds.  Not a very terrifying prospect.  If it had been forty kilowatts it would be another matter entirely.  While it is not an issue that detracts from the quality of a SF work overall getting details such as this correct is at the heart of hard SF, so hopefully this table will help with those details.  It also shows why multi-barrelled weapons are so deadly, even when they fire a relatively small projectile.  For anyone trying to do their own calculations, they are as follows;

Energy = (Mass * Velocity^2) / 2
mass in kg, velocity in m/s, energy in joules
Power = (Energy * RPM) / 60


EDIT
   It was pointed out in the comments that I had inadvertently used the wrong equation.  I've fixed that, and the table is updated as well.  If I've made any other errors feel free to point them out

17 comments:

  1. The 40 watts always bothered me...great post!

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  2. The 40 watts always bothered me...great post!

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    1. Bothered you no more! Because I've the answer for this 40Watt issue.

      Today in our world American count the energetic value of their food & beverage in calories.
      This unit, the calorie, is in fact an energy unit and been part of the metric system the American screw it up. When U see soda can labeled as 200 calories it really contains 200,000 calories of energy or 200 Kilo-calories (200Kcal). American of course won't write Kilo-calories, it sound too long/French so they emitting the Kilo and use '1 calorie of food' to indicate 1000 calories of energy.
      Similar thing could have been would happening (it’s a new tense, alternative continues past) in the Terminator timeline – few years before judgment day (1997) American soldiers/law-enforcers/citizens get their hands on plasma weaponry and the terminology have been would changing from caliber to power output.
      Those Americans emitted the Kilos from Kilowatts the same way they did to calories and from the same reason and kept the Watt unit to indicate weapon firepower.
      Those soldiers/law-enforcers/citizens how survived judgment day been the first resistance fighters against Skynet. To infiltrate to their strongholds, Skynet had to research the resistance fighter vocabulary and program its infiltration units with it.
      The T-101 sent back in time was a standard infiltration unit so that why it asked the gun shop owner for 'phased plasma rifle in the 40 watt range' – that what a citizen in alternative 1996 would have asked when wanting to buy a plasma rifle! Thanks the founding fathers for the 2th amendment!

      Yoel

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  3. Moran, Your first equation is wrong.
    Multiplying velocity with mass the result is momentum not energy. The kinetic energy of a bullet is E[joules] =0.5*{V [m/s] ^2}*M [Kilogram].

    There are a lot of fanatics in the world…

    Yoel

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    1. I cannot believe I did that! Thanks for catching it.

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  4. Moran, I love this blog!

    http://www.projectrho.com/public_html/rocket/sealofapproval.php#id--Information--SF_Worldbuilding

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    1. Atomic Rocket has been a source of inspiration to me, so thank you!

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  5. Moran, do you think plasma weapons are possible to create?

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    1. In the classic SF sense - a weapon that fires magnetically confined 'plasma bolts' - no. However, there are various ways to make a realistic plasma weapon, most of them more similar to a particle beam. The Casaba Howitzer nuclear shaped charges produced a relatively focused beam of plasma. So if you could make a atomic shaped charge small enough to detonate inside of a weapon, further collimating the beam with magnetic fields, that might be one option. But even then they would be likely to have, in relative terms, large size, mass, and power requirements compared to most other conceptual weapons systems. Although it must be said that a jet of 0.03c plasma is not something you'd want aimed at you!
      It is something that I'll have to address in a future post. Future War Stories has a pretty good post on the topic (http://futurewarstories.blogspot.com.au/2011/08/fws-armory-plasma-weaponry.html)

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    2. Yeah, That pretty good FWS post about plasma weapons is the beginning of my interest in plasma weapons ;) Small nuke is a problem because neutron radiation can kill the gun operator, but i'm not too sure, maybe it's possible to use small aneutronic fusion charge? This and compact torus technology can allow us to build cannons for spacecrafts and missile defence, ,,phased" plasma rifles, and more!

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    3. ICF technology is likely to be a necessity for these weapons, that or antimatter initiated microfission. Anti-missile defence is a likly role; the plasma gun is a closer to a nuclear shotgun than anything - due to the spread of the plasma - perfect for hitting small elusive targets. Also, the effects of the relativistic plasma could soft-kill the missiles electronics at ranges beyond hardball capacity. If possible, that also gives a solution for immobilising other spacecraft.

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  6. Have you heard about self containing plasma torus? This can be the key to higher range of the weapon, but not too much is known about it, sadly :(

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    1. I have heard about it, but my understanding is that it results from the interaction of the plasma toroid with the atmosphere - and it thus has a considerable drag force. This means that the power needed to give it good range is likely to be high enough that it would be better employed as the power supply for a laser. Of course, if you can get the plasma to undergo fusion that is another matter entirely... But as you say, little is known about it. Also, if I remember correctly, there was a group of researchers who claimed to have created ball lightning, so if true that might be another path to a plasma weapon.

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    2. http://m.phys.org/news/2013-04-plasma-device-revolutionize-energy-storage.html
      i found this on the web, they say that plasma creates its own magnetic field, and on video you can see that 28 inch ring of plasma :)

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    3. Edit: The vortex ring, where atmosphere contains the ring by some gasdynamics is something different i think, but i'm not sure

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  7. While lasers today are rated by power, I think a more useful rating for DEWs would be energy on target. If you have a 4 kj DEW, then you know it will do more damage per shot to a target than an AK-47 (3.6 kj). Still a ballpark figure since there probably is a difference between damage from a light source and a projectile, but close enough for government work.

    Ron

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