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Arrow Launch System - A few words on propulsion

Posted 02-06-2012 at 06:10 PM by Hurricane

Okay, I'll keep this one short, but I really had to address this problem.
So, a short calculation revealed that the RS-68, that produces about 3,370,000 Newtons of thrust, gives me about 350,000 kgf of thrust.
That's way too much, considering that I have 2 of these engines on the Arrowhead and it weighs about 42,500 at gross takeoff weight (by gross takeoff weight I mean fully loaded, no fuel.).
Now I saw that the J-2X gives me about 1,310,000 Newtons, about 131,000 kilograms force of thrust. 2 of these engines means that I have about 262,000 kgf total, which is enough for my purpose I suppose.
Now here's the logic behind the transfer to the J-2X:
1. It has a higher Isp.
2. A single RS-68 at its lowest thrust setting can shoot an empty Arrowhead straight up at an acceleration of 5 g. That's a lot, and I plan on using two: for redundancy's sake. 2 J-2Xs have about 3/4 of the RS-68's full thrust, and so at full power can only take the Arrowhead at an acceleration of about 7.4 g straight up, and anyway it's going to be full of fuel for most of the flight, making it about 3-5 g and they are also throttleable, making it possible to accelerate slower.

That's about it, I just thought I'd give you this heads-up so you'll see that I'm serious about it, and I work about it, and I want it to be totally realistic.

~Take care, Oz.
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  1. Old Comment
    Kaito's Avatar
    OR, you can just stick with the RS-68 and up the payload ability...
    Posted 02-07-2012 at 06:33 AM by Kaito Kaito is offline
  2. Old Comment
    Originally Posted by Kaito View Comment
    OR, you can just stick with the RS-68 and up the payload ability...

    I already thought about that. It's impossible since:
    A) There's no room inside the payload bay.
    B) It would require me to use more fuel, which, again, there's no free room for that. Every bit of free volume I now have will be taken by APU's, Helium tanks, RCS fuel tanks, perhaps solar panels, and much more. So there's no room at all.

    ~Take care, Oz.
    Posted 02-07-2012 at 12:03 PM by Hurricane Hurricane is offline

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