Back in the 1970’s Convair engineers gave some thought to possible failure modes on the Atlas booster and concluded that one of the more scary possibilities was a simple hydraulic fluid leak. Excessive loss of hydraulic fluid could starve the vehicle of its flight control ability. The answer was pretty simple, as it turned out. A diaphragm was installed that enabled the booster’s RP-1 fuel to replace the lost fluid in the event of a leak. Someone even asked what would happen if the reverse happened and some hydraulic fluid leaked into the fuel. So Rocketdyne ended up running an engine with 100% hydraulic fluid as the fuel and found that it still worked pretty good (and if that sounds like going to an extreme for doing a test, you need to understand that such “extremes” represented lessons learned in their own right). The mod went into the new production Atlas Centaur vehicles. Then, 20 years later McDonnell Douglas built the Delta 3 booster, based on the Delta 2, but with larger solid strap-on motors. Those new motors required additional control authority and hydraulic systems were used to swivel the nozzles on the strap-on motors – but the Atlas fuel interface mod had never been incorporated on the Delta 3. On the Delta 3’s first flight the Delta 2-based guidance system had a little trouble handling the new vehicle and used up the solid motors’ hydraulic fluid before the solids burned out. The vehicle spread itself all over the sky. For the Falcon 1, SpaceX decided to dispense with separate hydraulic fluid entirely and use the vehicle’s fuel for the hydraulic system. No doubt the Delta 3 experience was fresh in their minds.
Posted on: Sat, 13 Jul 2013 18:57:50 +0000
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