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Another shuttle fueling test scheduled for Friday BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: May 19, 2005 NASA's launch team readied the shuttle Discovery today for a second fueling test Friday to help find the cause of two vexing problems that cropped up during a similar test in April. Other shuttle engineers, meanwhile, are assessing a clearance issue between the shuttle's main Ku-band TV antenna and a new on-orbit inspection boom that could delay the transmission of post-launch images of the ship's redesigned external tank. As part of NASA's post-Columbia safety upgrade program, a 50-foot-long boom equipped with a television camera and laser sensors was installed on the right, or starboard, side of Discovery's cargo bay. The boom, picked up by the shuttle's robot arm in orbit, will be used to inspect Discovery's wing leading edge panels and heat shield tiles for any signs of launch impact damage.
Just in front of the orbiter boom sensor system, or OBSS, on the starboard sill of the cargo bay is the shuttle's Ku-band dish antenna, which is used to send high-speed data and television signals from the orbiter to the ground via NASA communications satellites. Once in orbit, the antenna is deployed by swinging it out over the side of the cargo bay sill so it can lock onto and track the appropriate satellite. The antenna normally is deployed on the first day of a shuttle mission and in Discovery's case, flight controllers were counting on a flight day 1 deploy to downlink photographs of the external tank to look for signs of foam shedding. But an analysis of clearances between the antenna and the OBSS shows that as the dish swings out, it could come within six tenths of an inch of the forward end of the boom, sources said. And that doesn't include the boom's insulation blankets. That tiny margin could shrink to just three tenths of an inch in orbit due to thermal issues. The shuttle Atlantis has a similar problem. No one wants to risk damage to the Ku-band antenna, which is critical to the conduct of a mission, and NASA managers plan to meet next week to reassess the matter. But neither the boom nor the antenna can be easily repositioned. Barring a dramatic change, Discovery's crew could be forced to delay deployment of the Ku-band antenna until the second day of the mission, after the OBSS has been picked up by the robot arm. While downlink of external tank video and photographs would be delayed by one day, officials said the overall impact would be relatively minor. And it would not affect transmission of data from new wing leading edge sensors using the shuttle's S-band radio system on flight day 1. The clearance issue could have a more noticeable impact toward the end of the mission. Managers are debating two possible options: Stowing the antenna before Discovery undocks from the international space station or stowing the OBSS prior to undocking and then redeploying it the day before entry to re-stow the antenna. The first option would end normal television from the shuttle for the remainder of the flight while the second option would add complexity and additional failure scenarios. Agency officials do not yet know why the clearance issue took so long to come to light. A contractor analysis earlier this year concluded there was more than an inch of clearance and as such, no problem. But measurements carried out by the astronaut office showed the actual clearance was half the earlier estimate. The shuttle was designed so a robot arm could be installed on either side of the cargo bay. The OBSS was installed using those pre-existing mounting points. In that sense, the clearance problem has been there ever since the shuttle was built. But NASA never mounted anything on that side of the bay before the OBSS aboard Discovery. The clearance issue is just one of several nagging problems facing the shuttle launch team as it readies Discovery for takeoff on the first post-Columbia mission. Launch currently is targeted for July 13, the opening of a window that extends through July 31. Launch had been planned for May 22, but the flight slipped to the July window because of late-breaking concerns about ice formation on the external tank, and its potential for impact damage during ascent, and because of problems that were noticed during a tanking test April 14. During that exercise, two of four fuel depletion sensors, also known as engine cutoff sensors, in the liquid hydrogen tank failed to operate properly. In addition, a hydrogen pressure relief valve cycled more often than normal. The cutoff sensors are used to make sure the shuttle's three main engines do not run out of hydrogen while running, which would cause a potentially catastrophic oxygen-rich shut down. All four sensors are required to be operational for a countdown to proceed. As for the relief valve, it operated within specification but its behavior was clearly unusual and engineers want to understand why. One possible explanation involves the operation of a new post-Columbia heater installed at the base of the bipod struts that hold the nose of the shuttle to the tank. NASA managers earlier decided to move Discovery back to the Vehicle Assembly Building and attach it to a tank and booster set being prepared for the second post-Columbia flight. That tank will be equipped with a new heater to ease concerns about ice buildups on an oxygen feedline bellows assembly. Still unresolved is what to do about potential ice buildups on brackets near the top of the tank. Engineers have suggested using infrared spotlights to prevent or minimize ice formation, but additional tests are required to determine the plan's feasibility. In the meantime, NASA managers ordered a second tanking test Friday to collect additional data before Discovery is moved back to the Vehicle Assembly Building. The currently-installed bipod heaters will be on for part of the test and then turned off to find out whether the heaters influence the operation of the pressure relief valve. Here is a tanking test timeline (all times in EDT): May 19 08:00 p.m....Rotating service structure retraction 11:30 p.m....Final loading preps begin May 20 02:30 a.m....Pad cleared of personnel 04:00 a.m....Mission management team meets for go/no-go decision 04:30 a.m....Begin a 1-hour built-in hold 05:30 a.m....Resume countdown 05:30 a.m....Begin propellant line chilldown (fueling begins) 08:30 a.m....Fueling complete; stable replenish mode begins 08:30 a.m....Begin a 1-hour 45-minute built-in hold 10:15 a.m....Resume countdown with bipod heater on 01:35 p.m....Countdown is stopped at T-minus 31-second mark 01:35 p.m....Recycle countdown to T-minus 20-minute mark 01:45 p.m....Resume countdown with bipod heater off 02:45 p.m....Final cutoff at T-minus 31-second mark 02:45 p.m....Begin propellant drain back and boiloff May 21 03:00 p.m....Rotating service structure moved back around shuttle The launch team plans to test fire one of Discovery's three auxiliary power units, which generates the ship's hydraulic power, on May 23. The next day - May 24 - the orbiter will be moved back to the Vehicle Assembly Building for attachment to the new tank and boosters on June 7. Discovery's space station cargo is scheduled to be moved to launch pad 39B on June 9 with Discovery following suit on June 14. If all goes well, the shuttle will be ready for launch July 13 as currently planned. But engineers are still debating whether to stage a third tanking test to make sure the new tank operates normally when loaded with a half-million gallons of supercold propellants. If a separate, stand-alone test is required it likely would be staged around June 22, setting the stage for a launch attempt around July 19. But some engineers have suggested extending Discovery's countdown and inserting a tanking test a few days before the July 13 launch target. A decision on whether to stage a third tanking test is expected early next month.
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VIDEO:
TEST COUNTDOWN ENDS WITH SIMULATED ENGINE SHUTDOWN