“It’s not rocket science”

A not-law piece, about… rocket science.

That phrase, “It’s not rocket science” is one that people, including myself use all the time. I am broadly aware of the general principles of rocket science – you have a fuel, an ignition source and the fuel burns producing a downward thrust force, which drives the rocket forward.

What I didn’t know, until I happened across a marvellous book about the development of the fuel and ignition source, was just how much was involved in it, and how dangerous the whole history of rocket science really was.

This book is called “Ignition!” by  John D Clark, a bona fide rocket scientist, and a man who was involved in the process of identifying, inventing, and testing, chemicals to be used in rocket science, both in terms of missiles to be shot at people   (he didn’t deal with the payload stuff, just the ‘how to get the missile to fly about’ bit) and the space race rockets.

It is an incredible book, packed with not only hard science (if you want to know the ins and outs, you will find it there), but the human stories of how things came about, the competing interests of various groups, some idiotic bureaucracy, and lots and lots and lots of explosions.  And I just love the writers style, and as a science geek, I found it funny as hell.

This passage, for example

The old destroyer gun turret which housed our card-gap setup had become a bit frayed and tattered from the shrapnel it had contained (The plating on a destroyer is usually thick enough to keep out the water and the smaller fish ) So we had installed an inner layer of armor plate, standing off about an inch and a half from the original plating

 And, as the setup hadn’t been used for several months, a large colony of bats —yes, bats, little Dracula types —had moved into the gap to spend the winter

 And when the first shot went off, they all came boiling out with their sonar gear fouled up, shaking their heads and pounding their ears They chose one rocket mechanic —as it happens, a remarkably goosy character anyway—and decided that it was ail his fault. And if you, gentle reader, have never seen a nervous rocket mechanic, complete with monkey suit, being buzzed by nine thousand demented bats and trying to beat them off with a shovel, there is something missing from your experience.

The book is pretty expensive if you try to buy it  (I can see why, if I owned a copy, I would not part with it) . But it is available for free here (and as it is out of print, you aren’t depriving the author of any income)

http://library.sciencemadness.org/library/books/ignition.pdf

There were some major problems that they had to solve. They had to produce a fuel that would burn well, and efficiently (and that was easy to produce and cheap), and an oxidising agent that would make that fuel burn (again, that would do the job well and efficiently, and that was easy to produce and cheap)

They then needed also to have both of those chemicals be reasonably stable. If you are burning the hell out of tonnes of fuel to make a rocket go, you want that burning process to be safe and controlled and not to just blow up on the launchpad.

You also want the oxidising agent and the fuel to be safe – safe to store, safe to have sat in a rocket , safe to move about, safe to pour.

You also need the liquids not to boil too quickly and turn into gas. That would be bad. You also need them not to freeze too easily and turn into non-burning solids.

[This is a pretty big deal, both for space, and for firing rockets at the sort of places the Americans and British were thinking of firing rockets at during the forties and fifties, which were pretty cold places…]

And you want these chemicals not to react with the rocket itself, not to dissolve it, or undergo any sort of chemical reaction, or turn to tar or sludge or what have you.

A fundamental problem with all that being – in order to have a really efficient fuel and a really efficient oxidising agent  (because every pound of fuel has to be lifted, you want them to be doing a good job of producing thrust) tend to be lively, reactive and insanely dangerous chemicals in their own right, and what you are doing in rocket science is putting both in close proximity. So the stuff that works is dangerous, the stuff that is safe doesn’t work, and making the dangerous stuff still work but not kill everyone around it means inventing new stuff, so not cheap.

The book really recounts all of the work that went into solving these multiple problems; most of which were resolved by finding, or even inventing, the most dangerous sorts of chemicals you could imagine (generally putting as much nitrogen, hydrogen or fluorine as possible into them), making them blow up a lot and then trying to find something you could add to them that would make them safer without ruining their efficiency too much.

There really are LOTS of explosions.

If you remember any of your chemistry from school, the fact that the early rocket scientists hit upon nitric acid as their liquid oxidising agent might make you a bit nervous. The fact that the brands of choice of nitric acid were known as “Red Fuming Nitric Acid” and “White Fuming Nitric Acid” even more so.

“The only possible source of trouble connected with the acid is its corrosive nature, which can be overcome by the use of corrosion resistant materials.”

 Ha! If they had known the trouble that nitric acid was to cause before it was finally domesticated, the authors would probably have stepped out of the lab and shot themselves.

This is Clark’s description of one early trial, WFNA is the White Fuming Nitric Acid I spoke of a second ago

Came the day of the first trial. The propellants were hydrazine and WFNA. We were all gathered around waiting for the balloon to go up, when Uncle Milty warned, “Hold it —the acid valve is leaking!”

 “Go ahead —fire anyway!” Paul ordered.

 I looked around and signaled to my own gang, and we started backing gently away, like so many cats with wet feet.

 Howard Streim opened his mouth to protest, but as he said later, “I saw that dogeating grin on Doc’s face and shut it again,” and somebody pushed the button.

 There was a little flicker of yellow flame, and then a brilliant blue-white flash and an ear-splitting crack. The lid to the chamber went through the ceiling (we found it in the attic some weeks later),the viewports vanished, and some forty pounds of high-grade optical glass was reduced to a fine powder before I could blink.

And Red Fuming Nitric Acid?

The RFNA of 1945 was hated by everybody who had anything to do with it, with a pure and abiding hatred. And with reason. In the first place, it was fantastically corrosive. If you kept it in an aluminum drum, apparently nothing in particular happened —as long as the weather was warm. But when it cooled down, a slimy, gelatinous, white precipitate would appear and settle slowly to the bottom of the drum.

 This sludge was just sticky enough to plug up the injector of the motor when you tried to fire it. People surmised that it was some sort of a solvated aluminum nitrate, but the aversion with which it was regarded was equaled only by the difficulty of analyzing it.

 If you tried to keep the acid in stainless steel (SS-347 stood up the best) the results were even worse. Corrosion was faster than with aluminum, and the acid turned a ghastly green color and its performance was seriously degraded. This became understandable when the magnitude of the change in composition was discovered. Near the end of 1947, JPL published the results of two acid analyses.

 One was of a sample of RFNA fresh from the manufacturer, which had scarcely started to chew on the drum in which it was shipped. The other was a sample of “old” acid, which had been standing for several months in a SS-347 drum. The results were eloquent And, if my own experience is any criterion, there was a bit of insoluble matter of cryptic composition on the bottom of the drum. Acid like that might have been useful in the manufacture of fertilizer, but as a propellant it was not.*

 So the acid couldn’t be kept indefinitely in a missile tank — or there wouldn’t be any tank left. It had to be loaded just before firing, which meant handling it in the field.

 This is emphatically not fun. RFNA attacks skin and flesh with the avidity of a school of piranhas. (One drop of it on my arm gave me a scar which I still bear more than fifteen years later.) And when it is poured, it gives off dense clouds of NO2, which is a remarkably toxic gas. A man gets a good breath of it, and coughs a few minutes, and then insists that he’s all right. And the next day, walking about, he’s just as likely as not to drop dead.

 So the propellant handlers had to wear protective suits (which are infernally hot and so awkward that they probably cause more accidents than they prevent) and face shields, and frequently gas masks or self-contained breathing apparatus

Things didn’t go much more smoothly when they tried using peroxide as the oxidising agent instead of nitric acid

But here an unexpected complication showed up. The peroxide was to be stored aboard airplane carriers in aluminum tanks. And then suddenly it was discovered that trace quantities of chlorides in peroxide made the latter peculiarly corrosive to aluminum. How to keep traces of chloride out of anything when you’re sitting on an ocean of salt water was a problem whose solution was not entirely obvious.

And there was always the problem of gross pollution. Say that somebody dropped (accidentally or otherwise) a greasy wrench into 10,000 gallons of 90 percent peroxide in the hold of the ship. What would happen —and would the ship survive? This question so worried people that one functionary in the Rocket Branch (safely in Washington) who had apparently been reading Captain Horatio Hornblower, wanted us at NARTS to build ourselves a 10,000-gallon tank, fill it up with 90 percent peroxide, and then drop into it —so help me God —one rat. (He didn’t specify the sex of the rat.) It was with considerable difficulty that our chief managed to get him to scale his order down to one test tube of peroxide and one quarter inch of rat tail

And chlorine trifluoride  (which even my 25 years ago recollection of chemistry just makes me go “NO! what are you thinking? Don’t open that bottle”  ) didn’t go a whole lot better     [hypergolic by the way, means spontaneously igniting – a very very good quality in rocket fuel, bad for people testing it who like to have a full complement of fingers]

Chlorine trifluoride, ClF3, or “CTF” as the engineers insist on calling it, is a colorless gas, a greenish liquid, or a white solid. It boils at 12° (so that a trivial pressure will keep it liquid at room temperature) and freezes at a convenient —76°. It also has a nice fat density, about 1.81 at room temperature.

 It is also quite probably the most vigorous fluorinating agent in existence— much more vigorous than fluorine itself. Gaseous fluorine, of course, is much more dilute than the liquid ClF3, and liquid fluorine is so cold that its activity is very much reduced.

 All this sounds fairly academic and innocuous, but when it is translated into the problem of handling the stuff, the results are horrendous. It is, of course, extremely toxic, but that’s the least of the problem.

It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water —with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminum, etc. —because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere.

If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

And even if you don’t have a fire, the results can be devastating enough when chlorine trifluoride gets loose, as the General Chemical Co. discovered when they had a big spill. Their salesmen were awfully coy about discussing the matter, and it wasn’t until I threatened to buy my RFNA from Du Pont that one of them would come across with the details.

It happened at their Shreveport, Louisiana, installation, while they were preparing to ship out, for the first time, a one-ton steel cylinder of CTF. The cylinder had been cooled with dry ice to make it easier to load the material into it, and the cold had apparently embrittled the steel. For as they were maneuvering the cylinder onto a dolly,

it split and dumped one ton of chlorine trifluoride onto the floor. It chewed its way through twelve inches of concrete and dug a threefoot hole in the gravel underneath, filled the place with fumes which corroded everything in sight, and, in general, made one hell of a mess.

If you want to know more about chlorine trifluoride, I can recommend the wonderful In the Pipeline blog, where Derek Lowe talks about it in his wonderful column “Things I won’t work with”

http://pipeline.corante.com/archives/2008/02/26/sand_wont_save_you_this_time.php

Let’s put it this way [Derek says]: during World War II, the Germans were very interested in using it in self-igniting flamethrowers, but found it too nasty to work with.

And points out that it is so reactive, it cheerfully sets fire to wet sand. To wet sand. The stuff that you keep in labs to throw on chemicals that are reacting too violently, to get the reaction to stop. Not much sets wet sand on fire.

If you are even more curious, you can see some footage of some insanely brave French scientists testing out how reactive chlorine trifluoride is here

http://pipeline.corante.com/archives/2013/04/05/chlorine_trifluoride_some_empirical_findings.php

A seriously seriously scary chemical.

And back in the Fifties, the author of Ignition was not only using that chemical, but working out how it could be mixed with liquid hydrogen and how quickly it would burn…

There’s a lovely passage where he is advising a fellow scientist not to go near a chemical called Ethyl Perchlorate   (frankly, if Clark of all people is telling you that a chemical is too dangerous to use, you really really really should listen to him, but they didn’t)

I read in a Wyandotte report that they intended to do this, and phoned Bill to read to him what Sidgwick, in “Chemical Elements and their Compounds,” had to say on the subject of the ethyl compound.

“Hare and Boyle (1841) say [Sidgwick wrote] that it is incomparably more explosive than any other known substance, which still seems to be very nearly true. . . . Meyer and Spormann (1936) say that the explosions of the perchlorate esters are louder and more destructive than those of any other substance; it was necessary to work with minimum quantities under the protection of thick gloves, iron masks [Ha, there, M. Dumas!], and thick glasses, and to handle the vessels with long holders.”

But Cuddy (presumably investing in leather gloves and an iron mask first) went ahead anyway. He told me later that the esters were easy enough to synthesize, but that he and his crew had never been able to fire them in a motor, since they invariably detonated before they could be poured into the propellant tank. It is perhaps unnecessary to add that this line of investigation was not further extended.

The chemicals would detonate during the act of POURING it into the fuel tank. That is some lively stuff.

Anyway, “Ignition!” is a great book (and if any book earned the right to have an exclamation mark at the end of its title, it is this one) whether you are a hard scientist or you just like reading about really brave men making things blow up in dazzlingly different ways.

It has given me a new found respect for rocket science, as well. I had thought it was largely maths and engineering, but it was clearly proper lunacy going on too. Perhaps our job isn’t as tough as we imagine.