Cleared Boeing engineers help resolve problem that stalled March for flight shuttle mission

By Ed Memi and industry team to determine what went wrong. “We learned the poppet broke due to high cycle stronauts who flew the Hubble Space fatigue, meaning a tremendous number of cycles are Telescope repair mission last month boarded incurred over a very short time. We suspected there Aa safer Space Shuttle Atlantis, thanks in part to might have been a hidden crack not caught by the some Boeing “detectives.” They helped NASA resolve inspection procedures in use at the time,” said control valve concerns that arose during the Space Mohammed Jebril, a Boeing space shuttle main Shuttle Endeavour’s STS-126 mission last November. propulsion system engineer. As engineers worked to resolve problems with the “To mitigate the issue, we now make sure—through gaseous hydrogen flow control valves that pressurize multiple inspection techniques—that we’re using the space shuttle’s hydrogen fuel tank, the subse- poppets that have no hidden cracks,” Jebril said. quent STS-119 mission was delayed several times. The analysis provided by Boeing was right on the The 5-inch valves, located in the aft of the space mark. When engineers looked at the three replacement shuttle orbiter, are part of its main propulsion system. flow control valves that flew on the subsequent There are three valves, each dedicated to one of the STS-119 mission in March, they saw no evidence of shuttle’s three main engines. The valves' function is cracking, resolving any lingering concerns about the to regulate the flow of gaseous hydrogen from the valves for the Hubble mission. main engines to the external fuel tank so the tank “It was challenging work to solve this complex can then deliver liquid hydrogen to the engines at issue,” Frazer said. “It was a great team effort across the correct pressure. NASA, United Space Alliance [the space shuttle During the November mission, gaseous hydrogen operations contractor and a joint venture between flowed from one of the shuttle’s engines at a Boeing and Lockheed Martin], Boeing and higher-than-normal rate. To compensate, the our suppliers. other two gaseous hydrogen flow control valves “There is still plenty of follow-on work to ensure automatically reduced the amount of their flow to we use only the best flow control valves and that prevent any problems during the ascent. problems are mitigated,” Frazer said. “But it’s a After the orbiter landed, Boeing engineers great feeling to deal with an issue this complex, one discovered the culprit. On the suspect line, a that we hadn’t previously faced, and come up with a poppet—similar to a pop-up on a sprinkler head solution that allows us to continue to fly safely.”n that regulates water flow—was cracked, and a small piece was missing. [email protected] “Our folks noticed there was a pressure differential on this flow control valve during the STS-126 launch,” said John Frazer, Boeing subsystem manager for the space shuttle main propulsion system. Engineers and shuttle managers were PHOTO: Boeing engineers played a leading role in concerned because the flow control valves serve a critical troubleshooting the failure of a gaseous hydrogen flow control function in pressurizing the fuel tank during ascent. Boeing valve on a recent space shuttle flight. The valve regulates the flow engineers in Houston, Kennedy Space Center, Fla., and of gaseous hydrogen from the main engines to the external fuel Huntington Beach, Calif., worked closely with a larger NASA tank so the tank can deliver liquid hydrogen to the engines at the correct pressure. Ryan Smith/Boeing

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