 NASA engineers plan to test a possibly broken liquid hydrogen valve assembly inside space shuttle Discovery after the shuttle's second launch attempt was scrubbed hours before the scheduled liftoff time when a fill-and-drain valve appeared to not have closed properly when commanded during fueling. The next launch attempt for the shuttle won't occur before Friday morning at the earliest, and possibly longer.
A Friday launch attempt depends on the problem being with an associated sensor that detects whether the valve is open or closed, and that the valve itself is operating normally.
FREE VIDEO: THE SECOND LAUNCH ATTEMPT IS SCRUBBED BECAUSE OF AN ERRONEOUS VALVE READING FREE VIDEO: POST-SCRUB PRESS CONFERENCE ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 150 KBS STREAM - PART 1 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 150 KBS STREAM - PART 2 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 150 KBS STREAM - PART 3 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 1.2 MBS STREAM - PART 1 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 1.2 MBS STREAM - PART 2 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 1.2 MBS STREAM - PART 3 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 1.2 MBS STREAM - PART 4 ALL-ACCESS SUBSCRIBERS: TANKING COMMENTARY, 1.2 MBS STREAM - PART 5 MORE COVERAGE OF DISCOVERY'S STS-128 MISSION If the problem lies in the sensor, it may be possible to resume the countdown Thursday for launch Friday morning at 12:22 a.m. EDT. However, if the valve, located inside Discovery's aft compartment, requires repair or replacement, launch would likely not be possible until October. Discovery's current launch window runs out August 30 in order to let a Russian vehicle and the first Japanese HTV cargo supply ship to dock with the space station. Additionally, the Air Force Eastern Range at Cape Canaveral is booked with other activity in September that will take priority over the shuttle. Based on data received in the Launch Control Center, engineers think the trouble lies with the sensor rather than the valve. "We have the pressure traces," said Mike Moses, Chairman of NASA's Mission Management Team. "We know it looks like the valve is going its full range of motion, but we have a much bigger database at ambient temperatures when we do valve checkouts on the ground prelaunch than we do here at cry conditions (when loaded with supercold propellant). So we want to get back to that prelaunch state where we know it's an inert system, go run some valve cycle tests, compare those two sets of data and show we really do have just a position indicator problem." It would be good news if testing points to the sensor as the cause since that would allow NASA managers to develop a flight rationale that would permit the shuttle to fly without that particular sensor data by getting information about whether the valve is open or closed via other means. That's the only scenario under consideration that would allow for a Friday launch. Repair work or replace would take too long to make the August window. "Right now, I'm pretty confident in the schedule of attack that says we'll be really good to go on Friday if we come out with a good technical story that says we can fly without instrumentation," Moses said. "So we both have to first prove it is instrumentation and then prove we're okay to fly without instrumentation." The valve problem cropped up near the completion of the external tank fueling operation at 5:52 p.m. EDT when the valve was commanded to partially close during the transition from liquid hydrogen fast-fill to topping. Specifically, the data was never received to indicate the inboard fill-and-drain valve closed when it was supposed to, although flow and pressure data in the propulsion system showed that it, in all likelihood, had closed. There are two 8-inch fill-and-drain valves in series. The outboard valve showed no signs of problems. Fueling was stopped immediately when it appeared the inboard valve hadn't closed and the launch attempt was scrubbed several minutes later. NASA's launch commit criteria require both valves to be operating properly before launch and also forbid cycling the valves open and closed to troubleshoot any problems during fueling. Cycling the valves repeatedly could introduce debris into the system that could cause the valve flappers to jam. "As we got into tanking, we ran across a failure signature today tha really was one of those that's in our LCC that doesn't give us a lot of options," Moses said, describing the launch commit criteria restrictions on the valves. "Basically, it was an LH2 inboard fill-and-drain valve. These are the big valves in the 8-inch lines that feed liquid hydrogen into the system." The valves are critical to the safe launch of the space shuttle. NASA documentation describes their operation: "Within the orbiter aft fuselage, liquid hydrogen and liquid oxygen pass through the manifolds, distribution lines and valves of the propellant management subsystem." "During prelaunch activities, this subsystem is used to control the loading of liquid oxygen and liquid hydrogen in the external tank. During SSME thrusting periods, propellants from the external tank flow into this subsystem and to the three SSMEs. The subsystem also provides a path that allows gases tapped from the three SSMEs to flow back to the external tank through two gas umbilicals to maintain pressure in the external tank's liquid oxygen and liquid hydrogen tanks. After MECO, this subsystem controls MPS dumps, vacuum inerting and MPS repressurization for entry." "All the valves in the MPS are either electrically or pneumatically operated. Pneumatic valves are used where large loads are encountered, such as in the control of liquid propellant flows. Electrical valves are used for lighter loads, such as in the control of gaseous propellant flows." "During prelaunch, liquid hydrogen supplied through the GSE liquid hydrogen T-0 umbilical passes through the liquid hydrogen outboard fill and drain valve, the liquid hydrogen inboard fill and drain valve and the liquid hydrogen feed line manifold. The liquid hydrogen then exits the orbiter at the liquid hydrogen feed line umbilical disconnect and enters the liquid hydrogen tank in the external tank. During loading, the liquid hydrogen tank's vent valve is left open to prevent pressure buildup in the tank due to boiloff. The main propulsion system propellant fill/drain LH 2 inbd and outbd switches on panel R4 are in the gnd position, which allows the LPS to control the position of these valves as required." "After external tank separation, approximately 1,700 pounds of propellant is still trapped in the SSMEs and an additional 3,700 pounds of propellant remains trapped in the orbiter's MPS feed lines." "Approximately 18 seconds after MECO occurs, the external tank separates from the orbiter. The GPCs automatically initiate the liquid oxygen dump provided the MPS prplt dump sequence LO2 switch on panel R2 is in the GPC position. The liquid oxygen trapped in the feed line manifolds is expelled under pressure from the helium subsystem through the nozzles of the SSMEs. If the main propulsion system manf press LO2 switch on panel R4 is left in the GPC position, the pressurized liquid oxygen dump continues for 90 seconds. At the end of this period, the GPCs automatically terminate the dump by closing the two liquid oxygen manifold repressurization valves, wait 30 seconds and then command the engine controllers to close their SSME main oxidizer valve." "Simultaneously with the liquid oxygen dump, the GPCs automatically initiate the MPS liquid hydrogen dump provided the MPS prplt dump sequence LH2 switch on panel R2 is in the GPC position. The GPCs command each engine controller to command a 10-second helium purge of its SSME's fuel lines downstream of the main engine fuel valves, command the liquid hydrogen manifold repressurization valve to open provided the main propulsion system manf press LH 2 switch on panel R4 is in the GPC position, and command the two liquid hydrogen fill and drain valves (inboard and outboard) to open." "The liquid hydrogen trapped in the orbiter feed line manifold is expelled overboard under pressure from the helium subsystem through the liquid hydrogen fill and drain valves for six seconds. Then the inboard fill and drain valve is closed; the three liquid hydrogen prevalves are opened; and liquid hydrogen flows through the engine bleed valves into the orbiter MPS, through the topping valve, between the inboard and outboard fill and drain valves, and overboard through the outboard fill and drain valve for approximately 88 seconds. The GPCs automatically terminate the dump by closing the two liquid hydrogen manifold repressurization valves and 30 seconds later closing the liquid hydrogen topping and outboard fill and drain valves." "If necessary, the flight crew can perform the liquid hydrogen dump manually utilizing the start and stop positions of the MPS prplt dump sequence LH 2 switch on panel R2. When the liquid hydrogen dump is initiated manually, all valve opening and closing sequences are still automatic. Placing the MPS prplt dump sequence switch in the start position causes the GPCs immediately to begin commanding all the required valves to open automatically and in the proper sequence. The liquid hydrogen dump continues as long as the switch is in the start position, but the pressurized portion of the dump with the two liquid hydrogen manifold repressurization valves open is still limited to 88 seconds. Placing the switch in the stop position causes the GPCs to begin commanding all of the required valves to close automatically and in the proper sequence." "Approximately 19 minutes into the mission and after the MPS liquid oxygen and liquid hydrogen dumps, the flight crew initiates the procedure for vacuum inerting the orbiter's liquid oxygen and liquid hydrogen lines. Vacuum inerting allows any traces of liquid oxygen or liquid hydrogen remaining after the propellant dumps to be vented into space." "The liquid oxygen vacuum inerting is accomplished by opening the liquid oxygen inboard and the outboard fill and drain valves. They are opened by placing the main propulsion system propellant fill/drain LO 2 outbd, inbd switch on panel R4 to the open position." "For liquid hydrogen vacuum inerting, the liquid hydrogen inboard and outboard fill and drain valves are opened by placing the main propulsion system propellant fill/drain LH 2 outbd, inbd switch on panel R4 to open. The external tank gaseous hydrogen pressurization manifold also is vacuum inerted by opening the hydrogen pressurization line vent valve by placing the main propulsion system H 2 line vent switch on panel R4 to open." (The Spacearium / Space Media Corporation)
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