Thursday, October 11, 2012

21 December 2011 – H-bombs, Santa, and the Poop Spiral of Doom


The Yuletide season is upon us, and with comes the annual ritual of NORAD tracking the big guy in the red suit.  If you're so inclined, you can follow his progress here, on NORAD's on-line Santa Tracker:

As I write, we're currently 3 days and 17 hours (and some assorted minutes) away from launch.  As an Air Force brat, I've been familiar with NORAD's tracking efforts for most of my life, and I recall wondering whether Santa, like the Tu-4s that drop by from time to time, ever merited an escort.  You sort of had to be concerned about whether his IFF transponder was operating, and whether he had the right codes (which in turn makes me wonder whether Santa has to wait three years to get his security clearance updated like the rest of us so he can even be ISSUED the codes); because if he didn't, well, in an era of AIM-120s, a pilot might be cleared to engage from beyond visual range, and then it'd be Run, Run Rudolph! for real.

In today's world, however, an air-breathing intercept seems somewhat less likely.  After all, with the ground-based interceptors of the BMD system in place and operational, it might - given how fast Santa would have to be travelling in order to get through his assigned duties in the allotted time - be more realistic to forego the F-22s and simply send an exo-atmospheric kill vehicle his way.  It's worth working through the intercept from an air defence perspective, if only to get a better grasp of the nature of the problem.

Well, what are the capabilities of the system?  Assuming Santa's sleigh operates on a cold launch system (which is not necessarily true, but more about that later), his take-off probably wouldn't be detected by the Defense Support Program (DSP) satellites that watch missile fields for the thermal signature, or bloom, of an ICBM launch.  On a southbound trajectory from the North Pole, the first piece of equipment to pick up Dasher, Dancer and the rest would be the Ballistic Missile Early Warning System, from one of two stations: Clear, Alaska, or Thule, Greenland. 

Ballistic Missile Early Warning System Sites

Clear has a PAVE PAWS phased array radar system that operates in the UHF band, with two faces each giving 120 degree coverage, with elevation coverage from 3 to 85 degrees above horizontal.  At peak power (about 500 kW for the main beam) it can detect an object the size of a small car at a range of 5550 km (3000 NM).  Since that accords pretty much with a large sleigh, it's the figure we'll use.  Even if Santa has adopted stealth technology, we can assess 8 "tiny reindeer" as adding up to the radar cross-section of a small car - or 9, if it's a foggy Christmas Eve and Rudolph's on duty.

PAVE PAWS phased array radar system at Clear, Alaska

The problem, of course, is that Santa's flight profile doesn't come close to that of a ballistic missile launched from the Asian heartland, or of a SLBM launched from a sub lurking in the - let's face it - totally ice-covered Arctic Ocean.  There's never been any indication that the sleigh is pressurized, so unless he's wearing breathing apparatus, the old guy's going to have to keep it below 10,000 feet ASL.   That poses some horizon issues, but solving them is a relatively straightforward problem in geometry:

If the PAVE PAWS was capable of detection at the visual horizon, calculating its detection range D for a target at altitude X is simple.  Knowing that the polar radius of the Earth R is 6,356,752 m, and that R1 is therefore R+3077 or 6,359,829 m, then D would simply be the square root of R1 squared minus R squared, or 197,810 m - or about 197.8 km from the radar station.  However, the PAVE PAWS has a minimum detection altitude of 3 degrees above horizontal, so detection would be a little later, when the bogey was closer to the site.  I'd recalculate that for you but I don't feel that into trigonometry this morning.

With a detection range of only 200 km or so for a target at an altitude of 10,000', would there be enough time for the warning system to react?  Maybe; depends on how fast the sleigh is travelling.  From Santa's perspective, he could vastly improve his survivability by flying lower and faster.  That's the same conclusion that was reached by the designers of the B-1 Lancer bomber, the performance of which I've had occasion to witness.  It's true; the lower and faster you fly, the less time anyone watching has to find you, fix you, and intercept you.

Which brings me, in a roundabout way, to the topic of this week's message.  You think the B-1 is low, fast, and nasty?  Well, amigos, you ain't seen nothing yet.  A colleague who is also an aficionado of all things ancient and atomic brought to my attention the other day one of the historical gems from America's glorious nuclear past.  Back in the halcyon days of the late 1950s - the era that brought us the Pentomic Army and such weapons systems as Atomic Annie, the 280-mm nuclear howitzer, and the Davy Crockett, the A-bomb-firing recoilless rifle - there were no problems that couldn't be solved by judicious application of the Mighty Atom.

The Davy Crockett nuclear recoilless rifle; and the Atomic Annie 280-mm nuclear howitzer

Thing is, those weapons, crazy as they might have been (and the Davy Crockett was crazy enough that, under certain firing conditions and selected yields, its lethal radius exceeded its range), those weapons were actually deployed.  The ones that fascinate me are the ones that did make it off the drawing board, but only as far as proof-of-concept and test and evaluation stages.  The most infamous one is probably one that, although it was closely connected to military weapons research, wasn't really a Defense programme at all: Project Orion.

 Project Orion - MY kind of crazy

In a nutshell (ahem), Project Orion was a spaceship designed to be propelled by the explosion of nuclear bombs fired out of its base.  The force of the explosion against a pusher plate (equipped with, shall we say, "powerful" shock absorbing systems) would drive the ship forward.  Thousands of bombs would be needed to reach planets throughout our solar system, which required miniaturizing the weapons as much as possible.  The research aimed at miniaturizing nuclear weapons - remember, this was the late 1950s and early 1960s, when much research was put into making bombs as big and destructive as possible, leading to monstrosities like the boxcar-sized B-17 - eventually led to the nuclear artillery rounds small enough to be put into 155mm and 203mm projectiles - and to the enhanced radiation weapon or 'neutron bomb' that bedevilled the Carter Administration, and was responsible for so much Euro-angst in the late 1970s.

In between the Davy Crockett and the Orion spaceship, though, were a good many 'almost-rans.'  One of those was the Convair X-6.  Based on the Convair B-36 bomber, the X-6 was to have been propelled by nuclear reactor-driven engines.  The idea was that the plane would carry a 3 MW air-cooled nuclear reactor in the bomb bay - and a 12-tonne lead and rubber shield to protect the crew from the otherwise unshielded powerplant.  A testbed aircraft - the XB-36H - was built to trial the shielding requirements, and logged 215 hours of flight time, during 89 of which the on-board reactor was operated. 

Based on the results of the testing, the Convair X-6 project was scrapped in 1961.  Had the thing gone to trials, a number of problems would have had to have been overcome.  One was the weight.  The takeoff weight of the beast was expected to be 363,000 pounds - roughly the same as a 747, but decades before the 747 became a reality.  The testing facility was on the point of building a 15,000-foot runway when the programme was cancelled.  Also, there was the small matter that only the aircrew were protected against the radiation of the reactor; everything else, including the plane body and everyone around it on the tarmac, wasn't.  The nature of the problem might have been telegraphed just a little when the Air Force started advertising for pilots who were past child-bearing age.

The biggest problem with the plane, though, was the fact that the aircraft engines weren't...err...well, you couldn't really shut them off.  You see, in a real jet turbine, propulsive force is achieved by superheated exhaust expanding out the back end of the engine.  The heat is provided by burning fuel.  Turn off the fuel flow, the engines shut down.  In the X-6 concept, however, there was no fuel; the heat was supplied by the nuclear reactor.  Airflow over the reactor elements superheated the air, and the efflux from that drove the aircraft.  It also cooled the reactor, as there was no space in the plane for the hundreds of tonnes of water and other assorted cooling media associated with terrestrial or naval reactors.  The cooling provided by air rushing over the reactor elements at hundreds of miles per hour would still be needed even when the aircraft was on the ground and parked. 
Something of a poser, as they say.

Well, put all of these problems and capabilities together, and what do you get?  Think about it: a plane powered by a nuclear reactor doesn't really need fuel, so it can fly pretty much forever, except that it produces so much radiation that nobody wants to get near it.  You can't shut it off, so it's pretty much a one-shot deal.  And it can go really fast.  REALLY fast, in fact, once you realize that the reactor can produce so much heat that the rate-limiting factor, really, is how fast you can get the air into the core to be superheated.  And once you realize THAT, you start thinking about something that the scientists had only just begun talking about after the X-15 programme was under way, which was...ramjets.  In a jet turbine engine, air is compressed to the necessary density by compressor blades (hence the name).  But if you get an air-breathing vehicle up to a high enough speed, you can do away with the compressor blades, and simply shape the intake to force the incoming air to the right density. 
Put all of these factors together, add a monocle and a white Persian cat, and what do you get?  That's right: a doomsday machine. 
Enter the Vought SLAM.

Imagine a cruise missile the size of a railway locomotive.  It's powered by a nuclear reactor similar to the one designed for the Convair X-6, but reconfigured a little.  It doesn't heat air for individual engines; it's the engine itself.  It has a big ramjet intake and is designed to heat compressed air so hot - 2330 degrees - that it needs no fuel at all.  It just blasts the superheated air out the tailpipe. 

Is this for real, you ask?  Well, for starters, they built the aerial reactor (amusingly nicknamed the 'Tory' Reactor), as part of Project Pluto, which eventually became the nickname for the whole project, including the airframe:

They also built (at the unbelievably appropriately-named Jackass Flats) the 25 miles of oil well pipe casing needed to contain enough compressed air to test the ramjet capacity of the engine...

...and they also built the Tory IIC engine, and tested it in 1964.

At full power, the Tory IIC engine produced 35,000 pounds of thrust and 513 MW of power.  For the sake of comparison, that's roughly the same as the reactor in a large nuclear generating station - except that the Tory IIC was only the size of a railcar.  Amazing what you can achieve when you do away with all of that pesky radiation shielding (although according to the test results, the engine produced less radiation than expected).  As an article about the SLAM project noted, the May 1964 test was observed by "dozens of admiring AEC officials and Air Force Generals"...all from "a safe distance".  Yeah, I'll bet. Like Tasmania.

Of course, to make the missile work you first have to get it up to ramjet speeds - well over Mach 3 - before the nuclear engine starts operating properly, so to do that you strap a few solid rocket boosters onto the thing.  Stick an inertial guidance system into it, like the one used by the infamous Snark cruise missile (and like the first-generation ALCMs would get about 10 years later) and you could program it to follow a preset course.  It can fly for so long (estimates put its range at an incredible 100,000 km, or two and a half times around the planet) that you could launch it and let it loiter, flying figure eights over an ocean for hours or even days before sending it a command to penetrate enemy territory.  It's virtually indestructible because compared to a manned bomber it has only a fraction of the moving parts; remember, it's really nothing more than an aerodynamic teakettle (the project manager dubbed it "the flying crowbar").  It'll fly so low that Soviet radars will never spot it; so fast that Soviet fighters (and SAMs) will never catch it (so fast, in fact, that the 150 DB of the shock wave was expected to smash windows and rupture eardrums all along its flight path); and it will never run out of fuel.  Awesome, eh? 
But wait...there's more! 

Now you turn it into a one-shot disposable aerial SSBN!

 File under "Seriously, who thought this was a good idea?"

You install a dozen vertical-deployment tubes, each carrying a one-megaton thermonuclear warhead equipped with an ejection mechanism and a parachute.  So now your low, fast, 100,000 km-range, unstoppable, nuclear-powered flying freight train can follow a pre-programmed course across the Soviet Union, 500 feet off the ground, at Mach 3, excreting H-bombs at predetermined deployment sites. 

Good freaking lord.

And did I mention that it would be spewing radiation all the way?

Yeah, no need for pilots means no need for shielding other than the minimum necessary to protect the electronics.  Given the amount of radiation the lightly-built, almost totally unshielded reactor would be producing, burst eardrums and broken windows would be the least of the problems afflicting anyone under the missile's flight path.  The intake would be sucking in dust, debris, water droplets and all manner of aerosolized contaminants, cooking them to a turn in a 600-MW reactor running at full power, and blasting them back out the tailpipe as, let's face it, fallout.  According to project reports, this was regarded as a bonus.  There were discussions during the project as to whether the missile, having discharged a dozen buckets of sunshine onto the heads of unsuspecting kulaks, should be programmed to then add insult to injury by flying back and forth over Soviet territory, sowing neutrons until it eventually melted down and crashed into Comrade Sergey's potato field.  Alternatively, it could be programmed to crash itself and its screaming hot reactor into a 13th target, sort of as an added treat.  An apocalyptic baker's dozen, if you will.

Just how serious was the SLAM project?  Well, as noted above, serious enough that they built the engine, tested it, and were working on a Mach 4+ version when the plug was pulled on 1 July 1964.  A number of factors contributed to the decision to kill the project.  One was the cost; each missile was expected to run about $50 million, an exorbitant figure at the time.  The Navy was preparing to deploy the Polaris SLBM, and the Air Force had ICBMs, both of which were totally invulnerable to the SAMs of the time, and both of which arrived at their targets much faster than the SLAM (which one critic redubbed 'Slow, Low And Messy').  There were other problems, too.  Which ally would be crazy enough to allow a SLAM to overfly their territory en route the USSR?  And for that matter, how could you test the thing?  One proposal was to have it fly lazy figure-eights near Wake Island in the Pacific - and, once the test was complete, to ditch the missile, with its red-hot reactor, into the ocean.  Another (hilarious) proposal was to test it in Nevada using a long tether.  One project expert remarked rather drily, "That would have been some tether."  And what if one got away, either during testing, or in some sort of operational scenario?  After all, a SM-62 Snark cruise missile test-fired in 1956 using a similar inertial navigation system had been aimed at Puerto Rico, and was last seen on radar heading into the Amazon.(Note A)  What if that Snark had been carrying 12 thermonuclear warheads and a blazing hot, neutron-spewing reactor?

Worse, what if it didn't crash?  Remember, it didn't need fuel, and didn't have a whole lot of moving parts.  How long could such a thing stay up?  How would you bring it down?  For that matter, where would you bring it down?

Good lord, why hasn't somebody made a movie about this thing?  Oh, wait, they did:

Except that the SLAM moved a thousand times faster than any Terminator.  Plus it flew, spewed radioactivity, and was stuffed full of H-bombs.

Bottom line, beyond the sheer horrifying craziness of the concept, the SLAM was inferior to ballistic missiles in every conceivable way, and so it ended up on the chopping block.  The USN and USAF went on to deploy thousands of SLBMs and ICBMs which, for all their faults, were at least cheaper and faster; and while SSBNs were driven by nuclear reactors, none of the missiles were themselves nuclear-propelled.  When cruise missiles eventually were deployed a decade or so later, they were much smaller, carried only one warhead, and required fuel to fly.  Quite a different concept from the invulnerable, unstoppable "flying Chernobyl" dreamed up by the USAF, AEC, and the frighteningly innovative wrench-benders at Vought.

For those of you interested in reading more about the SLAM, you can find fascinating articles at the following websites:

A final thought about the discussion that sparked this whole line of investigation in the first place.  If you're Santa, then you're looking for something that can travel very low, very fast, for very long distances without refuelling, and that is capable of delivering packages at predetermined sites. If Santa were looking to upgrade the old sleigh to something a lot more capable, the SLAM would be a fantastic choice.  The hazard to the big guy himself shouldn't be too much of a worry, because let's face it, he's a long way past child-bearing age.  Like the Project Pluto folks, the radiation should be considered a bonus.  There'd be no need to drag Rudolph along to provide additional illumination: 
"Mommy, why is Rudolph's nose blue?" 
"Actually, sweetums, that's called the Cherenkov effect..."

And on that happy note, dear colleagues, Merry Christmas to all - and to all, a good night!  See you next year.

P.S. As a contemporary note, nearly a year later, here's an example of why I think creating a nuclear-propelled autonomous flying H-bomb delivery truck might be a bad idea:

(Source: Failbook)

You see, I don't think the robot apocalypse is going to be the result of our preprogrammed servants freaking out or conspiring to destroy us all in some sort of Skynet Götterdämmerung.  I think we're in much more potential danger from a combination of our own laziness and our chronic lack of imagination about the potential consequences of robots doing exactly what we built them to do. 

"Judgement Day" is a whole lot cooler and much less embarassing as an explanation for the demise of humanity than "The Poop Spiral of Doom".