"There are two primary propellant feed systems, a pressurized system and a turbo pump system," he said. The pressurized system uses tank pressure to deliver fuel. "These are fine as long as the system uses less than 300 psi pressure." The turbo pump system uses an exhaust gas generator to power the pump. " That works up to 3,000 psi and the higher pressure gives you higher performance." A third system known as sequential pumping lies between those two and may be best suited for long-distance travel. In that configuration, three fuel tanks are pressurized in sequential rotation from a main tank. As the first tank is about to be expended, valves switch from it to the second tank, and then subsequently to the third tank, then back to the first tank, and so on. Tanks not being used to fire the engine are being recharged in rotation from the main tank."This system gives you both high pressure and fail operational ability," Dr. Blackmon says. Rather than redundancy, where parts are duplicated so new ones can take over for failed ones, fail operational ability means that even if components in the system fail, the engine will continue to operate. "Rocket systems are typically designed so they can sustain one failure and be safe, but to have fail operational ability is great because you don't have to lose your mission" Dr. Blackmon said. "It is very cheap, very reliable and it gives you the same delivered payload as a turbo pump."The sequential system has a three to one advantage because of its lower weight, lower cost and greater reliability, but if there's one drawback to it, it's the valves. "Valves are often the source of trouble in spaceflight," Dr. Blackmon said. "You have these plunger valves slamming open or slamming closed, or ball valves clunking full open and clunking full closed."That's a lot of wear and tear over time, and here is where the new rotary valve excels. It uses a mechanism operated by one of two redundant motors to turn a shaft and slide a configured recess to a port, opening that port for either fuel delivery or recharge. One valve can control filling and emptying of all three rotational fuel tanks in the sequential system, and it can replace multiple older style valves with a device that is lower weight, lower cost and more reliable.
