Funny-looking rocket
October 28, 2009 4:28 PM   Subscribe

Anyone know why the Ares rocket is that shape?
posted by Idcoytco to Science & Nature (7 answers total)
 
Best answer: As in the way the diameter of the bottom is smaller than that of the top? The bottom is essentially a Space Shuttle solid rocket booster - its diameter is fixed but is longer to increase the thrust. The size of the upper stage is set by what the first stage can lift and the need to maximize mass to orbit. It ends up being about the same diameter as the spacecraft capsule on top. The diameter of THAT was set by the requirement to be able to fly six people.
posted by LastOfHisKind at 4:39 PM on October 28, 2009


LOHK is right. The rest of the shape is dictated by the need to be streamlined enough so that turbulence during launch doesn't tear the ship apart.
posted by Chocolate Pickle at 6:56 PM on October 28, 2009


But it looks like it'll tip over right? Gut tells you to have the wide bit at the bottom and the narrow bit at the top.

So the rocket bit is smaller 'cos it's not worth it/not needed to make it the same diameter as the payload bit ?
posted by Xhris at 7:33 PM on October 28, 2009


This is not unprecedented. The early Delta rockets did the same thing.
posted by Chocolate Pickle at 8:06 PM on October 28, 2009


Same as with the Standard Missile-2 and the SM-3 in its current 13.5" thruster configuration, the payload area is as wide as it needs to be to hold whatever you're trying to deliver, and then the booster is made only as wide as it needs to be for the acceleration required. For example, the SM-3 is being upgraded to a 21" thruster to give it enough acceleration for boost-phase ballistic missile interception.
posted by nicwolff at 8:21 PM on October 28, 2009


Best answer: Soyuz rockets also have cargo/crew capsules that are at least slightly larger than the secondary stage. But rockets come in all shapes and sizes. As long as they're long and cylindrical, anyway!

The basic Ares design comes out of 1980s-era Lego mix-and-match proposals called the Shuttle-Derived Vehicle program. At the time, Space Station Freedom was potentially going to be built using modules larger than the orbiter payload bay, and NASA wanted the program to have a variety of potential missions anyway. The SRB, notwithstanding the Challenger disaster, is considered one of the most reliable rockets ever built, and the SSME and tank are similarly reliable liquid-fueled engines. Both shuttle accidents were at least in part due to the ungainly side-by-side configuration. But Ares goes back to a simpler architecture that places the crew vehicle "safely" on top, where it can be nominally ejected with less risk of mishap to the occupants. Here are a variety of planning stage versions of the Ares I. So basically you have most of the original "parts" that made up the Shuttle, but you don't have to lift a winged re-entry vehicle (which was largely a military need, no longer married to the NASA program), so it's much easier to build the rocket the traditional way.

Keep in mind that it's only the first, oh, two minutes of flight that it's in any real atmosphere -- which would be one of two reasons to have a wider bottom, but isn't as critical as you might think. In fact a wider bottom generally means more rocket nozzles which means more things that have to work together precisely in order not to have what NASA jargon dubs a Bad Day. It's hard to comprehend the miracle that the Shuttle has never had an accident on launch due to all the things that must fire precisely when and how much in order not to tear the vehicle apart.

On the other hand with a tall stack you do have some vibration issues, but this flight will probably tell us a lot about how well they're solving those.
posted by dhartung at 8:47 PM on October 28, 2009 [2 favorites]




« Older What would happen to my lawn if I just didn't rake...   |   Women who runs with the Wolf Lecture Newer »
This thread is closed to new comments.