Locklin on science

The most beautiful rocket

Posted in big machines by Scott Locklin on November 14, 2013

Rocketry is a field which peaked in the 1960s, probably never to improve appreciably. The space shuttle? A flying brick. The attempted replacement for the space shuttle, the Ares is a piece of junk. They originally tried to base it on shuttle technology “to save money” -a lovely demonstration of the sunk cost fallacy, but inexorably, fundamental systems (like the upper stage engines) were  replaced by 1960s era technology. The thing was such a piece of junk, it would have been more aerodynamically stable if it were flying backwards. Most flying machines are supposed to have more drag at the rear end then at the front end; otherwise they want to tumble. It looks wrong, because it is wrong. You could tell it was going to fail just by looking at the mock ups.

ares-i-rocket-667aac29c209b493

What a pogo stick looking piece of junk

Rockets are interesting in their simplicity. In liquid fueled form, they’re at their most complex, but they’re still pretty simple. There are some pumps to pump the liquid fuel and oxidizers into the combustion chamber. Inside the combustion chamber are some nozzles to squirt the stuff around and mix it together. There may or may not be a sparkplug to light it on fire. Once it is on fire, the gas gets very hot and squirts out a nozzle. The whole thing is essentially tank + pump + nozzle to burn it all in. There are gimbals and steering jets to keep the thing on its path, but the real business of the rocket is pretty simple. The rocket moves forward by flinging things out the back end of the rocket really fast. There is nothing complicated about rockets; they’re all nozzles and pumps and pipes and tanks. Really, they’re just a complicated spray can.

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Spray can

One of the amusing subtleties of rockets: ever wonder why the exhaust nozzles are there? Why not just have a big hole at the business end? You may think it is to prevent flames from licking up the rocket’s side or something like that, but the reality is more interesting. The angle of the nozzle is necessary to extract the maximum energy from the burning gasses. Part of the extracted energy comes from the gas expanding as it leaves the combustion chamber. This is captured by the nozzle. The expanding gas pushes on the nozzle, effectively. The shape of the nozzle is dictated by the heat capacity of the fuel used, and the pressure that the nozzle works at. So a nozzle designed to work at sea level looks quite different from one which is supposed to work in space, where there is no ambient pressure. The thermodynamics for this is quite cute; I had no idea until I read a book on rocket science (Rocket Propulsion Elements by Sutton; PDF link here). You can figure out optimal nozzle shapes using simple ideas like the ideal gas equation and some calculus.

Titan2_color_silo

My favorite rocket is the Titan II. The Titan II was the first military ICBM that was worth a tinkers damn. It carried a giant nuclear warhead, meant to wipe out large cities in one shot with a 9 megaton yield. It was the heaviest payload carried by an American ICBM, and as such, it was kept in service until 1987. As a NASA launch vehicle, it lasted over 40 years, and would still be used, but America is no longer an industrial power, so we no longer make the fuels for it in enough quantity to make it cost effective. Its fuel consists of a toxic brew of caustic, poisonous hydrazines and for an oxidizer, nitrogen tetroxide, which turns into nitric acid when exposed to water. Nasty stuff, but very practical nasty stuff compared to what most liquid fueled rockets use, since it is all liquid at room temperature. Cryogenics like liquid oxygen and liquid hydrogen (more common liquid rocket fuels) were more difficult to handle; and they take a long time to load into a rocket. For military applications this was important, as you want to be able to launch at a moments notice. These fuels were also hypergolic, meaning they light on fire when they touch each other: not having a spark plug means one less thing to fail. Astronauts loved these fuels also, as they meant for quick countdowns, rather than sitting on top of an explosive firecracker while fueling up with cryogenic fuels. I love these fuels because of their toxic insanity. The real chemistry of rockets is more insane than any science fiction.



What lights my jets about the Titan II; its symmetry. It doesn’t have a dozen engines at the business end: just two, and they look damn cool, like dual quads on a fast car. The ratio of diameter to over all length is 1:10, which is a ratio evocative of viking broadswords. Not squat and ugly like the Polaris or the early Soviet launchers. Nor does it have the ugly staggered cone shape of the Saturn-V. Nor did it lumber and loiter at the launchpad like so many launch vehicles; it shot into space with dispatch and purpose. Even the exhaust plume is more beautiful than other rockets; it’s orange, and the two engines make a dignified narrow column of fire as it hurtles up to space. It looks like a rocket should. It is a graceful design, and they didn’t ruin it by putting cowlings over the interesting looking combustion chambers and elegant exhaust nozzles. Even the second stage engines are partially exposed to the air, like the engine in a top fuel dragster. It looks like it means business. It looks like the type of thing which could flatten a city, or lob a Freemason or two into orbit. It sent men into space, and was a genocidal trump card in protecting the formerly Free World from communism. As a cold war aesthetic artifact it has few equals.


“The Titan took off quickly!”


“It also looked good in its roll over and second stage activation; like a real space ship; most rockets look ugly doing this”

“watch the whole thing from another angle”



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11 Responses

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  1. Brian said, on November 14, 2013 at 8:06 am

    You’re right, it’s pretty cool looking. On one of the youtube videos from space, not sure, but I think I saw Sarah Palin’s house.

  2. ian said, on November 14, 2013 at 6:44 pm

    You can see a Titan 2 up close in the KSC visitor’s center. The Titan was retired because it was very expensive compared to the Delta 4 and Atlas 5 that replaced it.

    • Michael Moser said, on November 23, 2013 at 5:43 pm

      Wikipedia says that they scrapped it because it was hard to handle.

      http://en.wikipedia.org/wiki/LGM-25C_Titan_II#Retirement

      “Because of the volatility of the liquid fuel and the problem with aging seals, the Titan II missiles had originally been scheduled to be retired beginning in 1971. After the two accidents in 1978 and 1980, respectively, deactivation of the Titan II ICBM system finally began in July 1982. … “

      • Scott Locklin said, on November 23, 2013 at 9:12 pm

        The Titan-2 was an ICBM, one that lasted far beyond its design lifecycle. Titan as a launch platform it indeed canceled because of expensive fuels (they were not expensive when Titan got started).
        “The high cost of using hydrazine and nitrogen tetroxide, along with the special care that was needed due to their toxicity, proved too much compared to the higher-performance liquid hydrogen or RP-1-fueled vehicles (kerosene), with a liquid oxygen oxidizer. Lockheed Martin decided to extend its Atlas family of rockets instead of its more expensive Titans”
        https://en.wikipedia.org/wiki/Titan_%28rocket_family%29#Rocket_fuel

  3. ian said, on November 14, 2013 at 6:47 pm

    The closest Soviet rocket was the R-36: another enormous ICBM. Check out the piston that flies away after liftoff.

    • Scott Locklin said, on November 14, 2013 at 7:58 pm

      I was going to mention the SS-18 Satan, but wanted to keep it focused. They still use it, the last time I checked. Quite a throw weight on that puppy. Our spooks were worried it had a 100MT warhead on the end when it first came out. There’s something on the CIA “Studies in Intelligence” page about it.

  4. Michael Moser said, on November 19, 2013 at 1:09 pm

    Today I learned that the Atlas V is powered by a Russian made RD-180 engine. Funny.

  5. phlyarologist said, on December 5, 2013 at 4:05 am

    If you visit the Kansas Cosmosphere museum in Hutchinson, Kansas, you can walk under a Titan they have mounted on a faux launchpad. Recommended.

  6. Andrew scarfacedeb said, on January 9, 2014 at 4:00 pm

    Did they stop using that kind of rocket fuel?

    • ian said, on February 19, 2014 at 6:06 am

      In the US yes, for lower stages. It is still used in satellites or some upper stages because it can stay stored nearly forever, whereas the current preferred oxidizer, liquid oxygen, boils off within minutes or hours. The Russian still use it in old ICBMs and the Proton satellite launcher.

  7. Stretch said, on April 2, 2014 at 10:51 pm

    Mercury/Redstone, Gemini/Titan, Apollo/Saturn … Ah, the duos of my youth.


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