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Subject: 
Re: A dark blue starfighter
Newsgroups: 
lugnet.off-topic.geek
Date: 
Thu, 20 Oct 2005 17:50:52 GMT
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3008 times
  
In lugnet.space, Ryan Wood wrote:
   In lugnet.space, Tony Hafner wrote:
   Nits only, but: Logically, the engine exhausts seem small and are so far below the center of mass that this would never work in space... but they look so durn good!

I don’t understand the science of real spaceflight, but I thought the engines worked pretty well where they are!

Don’t get me wrong- they look great. And a lot of popular sci-fi (especially Anime) does the same thing. This is Lego, where for the most part style trumps reality.

I’m assuming Newtonian (reactionary) physics. In other words, you’re pushing something out behind you to propel yourself forward, as opposed to hyperspace, warp bubbles, gravitic or magnetic propulsion, etc. Rocket engines and fusion thrusters would typically be Newtonian reaction thrusters.

The basic principle is that the center of thrust needs to push through the center of mass. Picture a line running up the tailpipe- the ship needs to balance along that line. If you have multiple engines, you sort of average their centerlines. If the ship isn’t balanced on that line, it will tumble.

In atmosphere, you would still want to be mostly balanced on the centerline, but you can use aerodynamics to make up for some degree of offset. In space it’s way more critical. You can use directional thrusters to prevent tumbling, but unless you’re willing to spend a ton of fuel on it, that only works for small corrections.

I found an article on the web on lunar module stability. It covers this subject in very readable terms.



   Tony Hafner
www.hafhead.com



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