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June 17, 2012

Irritating Science Fiction Technical Claims Investigated, No. 1 and 2: “Star Trek” and “Aliens”





A guest article by Joseph Friedlander for Brian Wang’s Next Big Future

A lot of geeky debate takes place on how plausible various science fiction weapon systems are. Some claims are so audacious or so repeated that they invite closer examination.

1) “Star Trek”: “Subject the entire planet to lethal neutron bombardment” (Actually this was misremembered, actual text below)

And 2)  “Aliens” "I say we take off and nuke the entire site from orbit. It's the only way to be sure.”




From the 1966 Old Series episode “Where No Man Has Gone Before” (written by Samuel Peeples)  http://en.wikipedia.org/wiki/Samuel_A._Peeples

An irritating technical claim is implied in the order tossed off by Captain Kirk (by no means causally because he is targeting a former friend but by no means with a sense of asking for the impossible from authorities who will never grant it--)

“Proceed at maximum warp to the nearest Earth base with my recommendation that this entire planet be subjected to a lethal concentration of neutron radiation”
courtesy of this wonderful site for science fiction transcripts.

Note that this is the 1960s equivalent of the captain of the battleship Iowa deciding to recommend (not actually casually order) use of a W-23 nuclear 16 inch battleship shell http://en.wikipedia.org/wiki/W19_(nuclear_artillery_shell) against an island that has an exceptionally dangerous mutineer on it. 

An irritating technical claim is implied in the 1986 Alien Franchise movie “Aliens”-- "I say we take off and nuke the entire site from orbit. It's the only way to be sure.”

This is a survivor assuming command and actually declaring readiness to order special weapon use.  But notice he is nuking only one site and not the entire planet. Still this means a field grade non-com (to whom command has defaulted) has the right to order nuclear use without higher authorization. Wow.

OK, shaky command and control structures never stopped science fiction for long, let’s see the weapon used.

Bishop: In nineteen minutes, this area's gonna be a cloud of vapor the size of Nebraska. 

They claim (or Bishop does rhetorically) that the reactor overload will produce a fireball the size of Nebraska.  Assume he means the fireball. That’s a big explosion. Elsewhere this is revealed to be an exaggeration: ”around 40 megatons.”

We prove from Wikipedia data that produce a fireball the size of Nebraska is impossible but the size of Ohama—maybe. One fifth bigger was the 50 megaton Tsar Bomba http://en.wikipedia.org/wiki/Tsar_Bomba whose fireball was estimated to be 4.5 miles (8 km) in diameter.

Broken windows might cover an area the size of Nebraska in that case--

 “One participant in the test saw a bright flash through dark goggles and felt the effects of a thermal pulse even at a distance of 270 kilometres (170 mi). The heat from the explosion could have caused third-degree burns 100 km (62 mi) away from ground zero. A shock wave was observed in the air at Dikson settlement 700 kilometres (430 mi) away; windowpanes were partially broken to distances of 900 kilometres (560 mi). Atmospheric focusing caused blast damage at even greater distances, breaking windows in Norway and Finland.”


So we have 40 megatons as the reactor sympathetic explosion yield.-- But that’s the reactor. What size warhead is needed to produce it?  (To “nuke the entire site from orbit”)

The script asserts http://www.imdb.com/title/tt0090605/quotes that: “10 millimeter explosive tip caseless standard light armor piercing round” will “rupture the cooling system” and “So you're talkin' about a thermonuclear explosion”

Wow again. Forget command and control procedures.  I was far too trusting…I want to talk to the reactor safety engineers. A few stray rounds… do they sell booze at the commissary?  Do they like to celebrate Fourth of July?  Any homesick, suicidal colonists have a few rounds handy?  Can you put those questions together?  Plainly any warhead you wish to use, including a W-54 set to 10 tons of TNT will produce the desired result. 

So the “Aliens” claim—while sounding audacious in memory, (I half remembered a fireball the size of Nebraska) is plausible—they could definitely nuke the site from orbit with a warhead not too different from a W-80 or a B-61.  An actual warhead for a fireball the size of Nebraska might be closer to the troop shuttle shown that dived from the mothership (and got the alien on board behind the pilot during the troop drop)

So that part of the “Aliens” claim was plausible.


Although a parting word on that “EZ Overload™” brand reactor—Star Trek also postulated a FUSION reactor overload (97.835 megatons yield in “The Doomsday Machine”) although it is not clear exactly how you get a FUSION critical mass.  Apparently the critical mass for fission stuck in the minds of the writers?  There is no critical mass for fusion. But suppose—suppose—if the alternative is going fusionless and running out of energy OR having a reactor that is hideously vulnerable to runaway overloads then I think you will be wanting to put them very far offshore and invest in long-distance power line networks.  But you are talking about hundreds of kilograms to low ton quantities of thermonuclear fuel in burning plasma being in close proximity and suddenly deciding to cut loose in no more than a microsecond rather than over a year.  Remember, ~7.5 megatons is a gigawatt year (thermal) How, exactly does this runaway reaction occur? What could conceivably be the mechanism?  The answer might give us the clue to a revolutionary new reactor design—which might be entirely safe as long as the reactor was never damaged.  I don’t see people moving within 50 miles of the things no matter how cheap the land prices, though.  And upwind. You definitely would want to be upwind.



But the “Star Trek” neutron bombardment claim-- that destroying all life on the surface of an entire planet is something within the powers of a ship captain (or perhaps at most a task force commander)—that seems considerably more audacious.

The claim once more:

KIRK: If you have not received a signal from me within twelve hours, you'll proceed at maximum warp to the nearest Earth base with my recommendation that this entire planet be subjected to a lethal concentration of neutron radiation.

The analysis:

We can imagine the sort of equipment needed to make this work, consistent with known physics and TOS (The Old Series) Star Trek Universe

1 gram of deuterium can give the equivalent in efficient D-D fusion of around 82.2 tons of TNT equivalent in output including fast (14.1MeV) neutrons
Fusion of pure deuterium: 82.2 kt/kg
About 10 percent of that would be enough to be lethal (conservatively) to say 150 meters radius in terms of neutron radiation (typically a great deal of the yield might be in neutron form.

Note that in a deuterium-tritium reaction (same as in the neutron bomb)  80% of the output is neutrons.  50% is cited in the below link (note that part of the neutron bomb reaction say ¼ is the fission trigger which brings the average down)

In a fission bomb, the radiation pulse energy is approximately 5% of the entire energy released
... A neutron bomb releases a much higher amount of neutrons than a fission bomb of the same explosive yield. Furthermore, these neutrons are of much higher energy (14 MeV) than those released during a fission reaction (1-2 MeV).


 Fusion of deuterium atoms (D + D) results in the formation of a He-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom (D + T) results in the formation of a He-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV.
http://en.wikipedia.org/wiki/Neutron_generator

The neutron fraction (80% with D-T)  is far less with D-D if that could be made into a pure neutron bomb (but still utterly lethal) IIRC around 30%-- ionizing radiation, mostly in the form of fast (14.1MeV) and slower  (2.5 MeV). neutrons.

 The reference below gives 25% plus neutron radiation output from D-D reactions, which is in that range.
Centauri Dreams blog says http://www.centauri-dreams.org/?p=7164

Unlike a DT micro-explosion where 80% of the energy goes into neutrons, unsuitable for propulsion, it is not much more than 25% for deuterium. A deuterium mini-detonation though requires at least 100 MJ for ignition, but this can be provided with a magnetically insulated Gigavolt capacitor, driving a 100 MJ proton beam for the ignition of a cylindrical deuterium target…
D-D uses hugely available materials (Deuterium today is around $500 a kilogram and if that price remains in the future two thousand tons of it would be a billion dollars) Of course the future may drop prices AND is richer, and even today the Captain of an aircraft carrier can basically spend a billion dollars in some extended military operations (including losses)

The disadvantage of D-D compared to D-T is that the energy confinement time (at a given pressure) must be 30 times longer and the power produced (at a given pressure and volume) would be 68 times less.
Caption from Wikipedia (Note green curve for D-D fusion)
The fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The deuterium-tritium fusion rate peaks at a lower temperature (about 70 keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy.

 But this is Star Trek so I am not going to sweat it. Handwaving here--  and I am magically assuming the ability to efficiently fuse deuterium in tiny subgram packages a few hundred meters over any point on the planet (from orbit, at will)
Maybe they beam it down in tiny hohlraums  (radiation chamber capsules) http://en.wikipedia.org/wiki/Hohlraum the size of a pill at 150 meters local elevation


(Disclaimer: The National Ignition Facility did not design it's hohlraums for frying entire planets nor do they endorse such a policy. Illustrative only.)

and then teleport the expensive trigger mechanism in the nanoseconds before the fusion catches but after compression has taken place. After all, it’s Star Trek.  It takes say a gram of deuterium  a square kilometer—that much deuterium completely and efficiently fused will zap the planet’s surface with a lethal level of neutron bombardment.
Note that we are only concerned with deuterium consumption. Suppose you have a million hohlraums each holding a tenth of a gram of D and weighing a gram. So a ton of tiny capsules that get beamed down, fusion-initiated and are beamed back up and reconstituted from their own plasma.  If this works, then you have the capability to destroy say 100,000 square kilometers a second taking 10 hohlraums per square kilometer per second..  So about three hours (10,000 seconds) to neutron-fry a whole planet (note that one orbit of a planet the size of Earth takes 90 minutes so a couple orbits might do it. I assume you have to be line of sight and we are probably talking a high-inclination orbit for that reason)
We can calculate the needed thermonuclear fuel loadings--
So a gram of deuterium a square kilometer
A kilogram for 1000 square kilometers. Counting only Deuterium costs, $500 to kill 1000 square kilometers. Yow.
A million square kilometers zapped with a ton. $500,000 to kill an area the size of Bolivia or Egypt.literally in ten seconds. http://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_area 

And this ship would be able to neutron-fry the entire planet in about three hours. 

A billion square kilometers zapped with 1000 tons. (Earth’s entire surface is around 500 million square kilometers.) $500 million of Deuterium. I think we’re done. Not to mention the target planet. Well done. Even if it is a super-sized Earth with double the area.  And you get to reuse the beamed up and reformed - hohlraums on another planet. Does this happen often in the Star Trek universe? Because Kirk does not look particularly imaginative in that scene nor like he is asking for something that has never been done before. Sterilizing new colony worlds?  A dark side of the Federation never before seen? I’m shocked. Anyway--
If you want more over coverage (higher neutron yield for prompt fatalities) then double it or even go 10 times over. You are still talking the mass of a Liberty ship at most. A crew of 20. I can see it being a crew of 2 to 4. Destroying a planet is that easy given that transporter and ignition system we just postulated here.

How much water to generate 1000 tons of deuterium? Using calculations generated by M. King Hubbert 1 cubic meter of seawater contains about (~1.028—JF) 1.03 x 10e25 atoms of deuterium having a mass of 34.4 grams, and a potential fusion energy of 8.16 x 10e12 joules.
1 kWh represents 3600000 joules (3.600 x 10e6 J). So 2.26 gigawatt hours (at 857.2 tons TNT a gigawatt hour) 1937.272 tons TNT from 1 cubic METER of water.
The amount of water needed to refine enough deuterium?
Wikipedia says--
 1 in 6400 hydrogen atoms is deuterium, which is 1 part in 3200 by weight (hydrogen weight). http://en.wikipedia.org/wiki/Heavy_water

A billion tons of water would contain over 112 million tons of hydrogen but only only 34.4 thousands of tons of D. So you need to refine less than a hundred million tons of water to enable this miracle.  This is not a casual operation like cropdusting this is a major industrial operation, all on a Captain’s say so. But actually many major military operations are just exactly that. Quite an assumption but consistent with the Star Trek universe. On the other hand, this being Star Trek, maybe they just selectively beam up deuterium from a local sea cheaply  and use the same darn load of hohlraum capsules on victim world after victim world. With Star Trek technology vast technical barriers can vanish in a single episode. Just glad no Federation officer has ever emerged evil and grinning as an evil version of himself after a transporter accident--at least at the time of the above episode So I guess the Galaxy is safe-- oh, wait...

Conclusion:  So both irritating claims have been examined and found plausible. But I would not care to live near those reactors or those planets.  Too dangerous.  Can you say ‘disgruntled technician’ or ‘rogue neutron ship captain’? On the other hand, sure makes for an interesting story universe 
:->)




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