Missile Casing Weight Question


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21 April 2009
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I was reading an article about the Reuseable Solid Rocket Motor ("RSRM") and it had details of propellant and rocket casing weight. Due to the fact that the RSRM is built robustly in order for it to be reused the casing weight has to be a higher ratio of total weight of the system than an ICBM for example. I could not find comparable information for SLBMs or ICBMs. Can someone provide me with a link or a rough estimate of how much lighter a one time use carbon fibre casing would be.

The information I have on the RSRM is; Total weight 1,300,000 lbs made up of propellant - 1,100,000 and casing, 200,000 lbs for a casing to system weight ratio of 15.38%
RSRM has a propellant mass fraction of about 85.15% (propellant mass is in fact 1.107Mlb). Compare to non-reusable steel-wall solid boosters of similar age; Titan III's SRM has a propellant mass fraction of 85.26%, and Titan IV's 86.2%. Castor VIA (Delta) has a propellant mass fraction of around 86% (depending on whether or not it is ground lit).

By far the dominant loading is due to chamber pressure, which is independent of reuse. Aside from parachutes and such (which are, compared to the steel case, of negligible weight), I'm not sure why one would assume a reusable booster would weigh a great deal more than a throwaway, assuming the same materials. Indeed, experience seems to bear this out. Certainly I expect the weight cost of designing a man-rated system would be as bad or worse.

Filament-would cases (ie composite) can hit substantially higher mass fractions, as you'd expect; GEM-40 is around 90.5%, as is Titan-IV SRMU. Shuttle's ASRM/FWC would probably have had a similar mass fraction.
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