n INTEGRATED DEFENSE SYSTEMS Ready to go Boeing workers helped prepare shuttle for this month’s flight

By Ed Memi

oeing employees have played a ma- jor role in preparing for this month’s BSpace Shuttle flight, the final test flight before future International Space Station assembly missions can resume. The mission—STS-121, aboard Space Shuttle Discovery—will continue to test new equipment and procedures that in- crease the safety of shuttles while also de- livering critical cargo to the ISS. The biggest technical challenge has been to eliminate or reduce foam debris coming off the shuttle’s external fuel tank. During Discovery’s last flight in 2005, a 1-pound piece of foam insulation broke away from an air deflector called a protuberance air- load (PAL) ramp running outside of the tank. The PAL ramps smooth the flow of air across two externally mounted pressuriza- tion lines and an electrical cable tray. NASA decided last year to remove the At the Space Station Processing Facility at Kennedy Space Center, Fla., the Boeing ramps, based on computer modeling that in- Checkout, Assembly and Payload Processing Services team oversees the lowering of dicated the pressurization lines, cable tray the multipurpose logistics module Leonardo. The team is working to ensure a proper and attachment fittings would withstand fit of the module as it is placed inside the payload transportation canister—which will travel on Space Shuttle Discovery. predicted aerodynamic forces during ascent. NASA called removing the PAL ramp the NASA photo by K im S hiflett biggest change to the aerodynamic configu- ration of the shuttle in its 25-year history. ing and Integration. • Evaluating the effects of “tin whisker- Boeing engineers worked closely with Other Boeing accomplishments for the ing” in avionics boxes. Tin whiskering is a NASA, United Space Alliance and Lock- STS-121 flight include phenomenon where tin develops thread-like heed Martin to determine the changes in • Ensuring a replacement Trailing Umbili- growths from its surface. The concern is aero-heating, static and dynamic loads on cal System Reel Assembly (TUS-RA) can be these whiskers could break off and cause an the external fuel tank. The analysis, com- safely carried in the shuttle’s payload bay. On electrical short. Through analysis and test- bined with advanced wind-tunnel testing at the ISS, a mobile base station moves along ing, Boeing demonstrated there is sufficient NASA facilities, determined that the Space rails on the main solar-array truss to position redundancy in the orbiter design and the Shuttle is safe to fly. the lab’s robot arm for assembly work. The risks of an electrical short are very low. “When the ramps are removed, air can TUS-RA has power and data cables that un- • Assisting NASA and USA in developing travel underneath the cable tray and pres- reel or wind up in front of and behind the cart new installation procedures for gap fillers in- sure lines. The flow under and around as it moves. One of these two cables was cut stalled between tiles. During the STS-114 these components is what we assessed,” accidentally in 2005 when a safety device shuttle mission, two gap fillers were protrud- said Tom McGowen, Boeing project man- failed. Boeing station engineers helped trou- ing and had to be removed in space. n ager for Space Shuttle Systems Engineer- bleshoot the problem and devised a repair. [email protected]

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