Still no 'smoking gun' found for hydrogen vent line leak
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 14, 2009;
Updated after news conference
Engineers fell several hours behind schedule today fixing an alignment issue and re-connecting a gaseous hydrogen vent line to the shuttle Discovery's external tank, but NASA managers say they should be able to make up the lost time and stay on track for a launch attempt Sunday at 7:43:46 p.m. While no "smoking gun" was found to explain a vent line leak that grounded Discovery Wednesday, Launch Director Mike Leinbach said he was hopeful the repair work resolved the problem.
"We're going to put this back together and go tank and if it doesn't leak we're going to be perfectly safe to go fly," he said. "While we like to have a smoking gun, good root cause, right now we don't have that."
If all goes well, Discovery's countdown will resume at the T-minus 11-hour mark at 3:18 a.m. Sunday. Fueling will begin around 10:18 a.m. and the crew will strap in for launch just before 4:30 p.m.
Shuttle forecasters are predicting an 80 percent chance of good weather Sunday, with just a slight chance of low clouds that could cause problems. The outlook drops to 70 percent "go" on Monday and just 40 percent go Tuesday, the last day this month Discovery can take off. If the shuttle isn't off the ground by then, the flight will slip to around April 7, after a Russian mission to rotate space station crew members.
The primary goals of Discovery's mission are to attach a fourth and final set of solar arrays to the space station; to replace outgoing flight engineer Sandra Magnus with Japanese astronaut Koichi Wakata; to deliver a replacement urine processor sub-assembly needed by the station's water recycling system; and to bring water samples down to assess the purity of the processed water.
NASA originally hoped to launch Discovery Feb. 12, but the flight has been repeatedly delayed, first by problems with suspect hydrogen flow control valves used to pressurize the external tank during ascent and again last Wednesday, by a leak in a gaseous hydrogen vent line.
The 7-inch vent line hooks up to the external tank with a quick-disconnect fitting that is part of a ground umbilical carrier plate. During fueling, pressure in the tank is maintained by venting gaseous hydrogen overboard through the vent line. At launch, the vent line disconnects and drops away from the tank.
During fueling Wednesday, sensors detected a significant gaseous hydrogen leak in or near the umbilical plate. Fueling was halted, launch was scrubbed and the tank was drained.
Engineers have now disassembled the umbilical plate, replaced the quick-disconnect fitting and the seal on the tank side. While that seal was found to have "rolled" edges, Leinbach described it as more a case of use than anything wrong. Engineers also noted discoloration on an internal surface that apparently indicates the general area of the leak.
But the hardware showed no obvious defects that might explain the leak.
"Smoking gun? No," Leinbach said. "There was some evidence of the flight seal on the external tank side of the disconnect with a slight roll to it. I'm not sure that was the cause. There was a little bit of discoloration on one of the surfaces inside the quick disconnect. I'm not sure that is particularly related. It's probably the result of hydrogen leaking through that area. So no obvious smoking gun."
While he said he was "a little surprised that we didn't find something more obvious, because it was a healthy leak." But he said he was comfortable proceeding with another launch attempt Sunday because the trouble involves a ground system and poses no threat to the crew and because replacing all the hardware likely eliminated whatever was causing the problem.
The only trouble today occurred when engineers ran into "a little bit of an alignment issue with that connection," Leinbach said. "We've performed a standard routine where we installed some guide pins to verify the external part of the QD and the internal part on the external tank itself are exactly aligned. Those pins went in perfectly fine, so we know we have a good connection there. So technically, we're in great shape. To do that little bit of extra work costs us probably three or four hours. So we're three or four hours down on the timeline, but we think we can make that up tonight and support the launch tomorrow.
"We'll finish all the closeouts and get into that leak check tonight," Leinbach said. "That final re-torque that was an issue for us, that'll come up at about 6 o'clock tonight. The testing we did on the bench with that new technique for re-torquing actually proved out better than we had anticipated. So I feel real good about positive results.
"We'll get into the ordnance reconnect right after midnight and pick up the count at T-minus 11 hours at 3:18 tomorrow morning," Leinbach said. "Again, we're a little bit down on our timelines, but technically we're exactly where we want to be. So we feel really good and really, really outstanding for a launch attempt tomorrow."
Here is a revised countdown for Sunday's launch attempt (best viewed with fixed-width font):
EDT...........EVENT 03:18 AM......ASP cockpit config 03:38 AM......Pad clear of non-essential personnel 03:38 AM......APU bite test 04:28 AM......Fuel cell activation 05:18 AM......Booster joint heater activation 05:48 AM......MEC pre-flight bite test 06:03 AM......Tanking weather update 06:48 AM......Final fueling preps; launch area clear 07:18 AM......Red crew assembled 08:03 AM......Fuel cell integrity checks complete 08:28 AM......Safe-and-arm PIC test 09:18 AM......External tank ready for loading 09:41 AM......Mission management team tanking meeting 10:18 AM......Resume countdown (T-minus 6 hours) 10:18 AM......LO2, LH2 transfer line chilldown 10:28 AM......Main propulsion system chill down 10:28 AM......LH2 slow fill 10:58 AM......LO2 slow fill 11:03 AM......Hydrogen ECO sensors go wet 11:08 AM......LO2 fast fill 11:11 AM......Crew medical checks 11:18 AM......LH2 fast fill 01:13 PM......LH2 topping 01:18 PM......LH2 replenish 01:18 PM......LO2 replenish 01:18 PM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours) 01:18 PM......Closeout crew to white room 01:18 PM......External tank in stable replenish mode 01:33 PM......Astronaut support personnel comm checks 02:03 PM......Pre-ingress switch reconfig 02:30 PM......NASA TV coverage begins 03:18 PM......Final crew weather briefing 03:23 PM......Crew suit up begins 03:48 PM......Resume countdown (T-minus 3 hours) 03:53 PM......Crew departs O&C building 04:23 PM......Crew ingress 05:13 PM......Astronaut comm checks 05:38 PM......Hatch closure 06:08 PM......White room closeout 06:28 PM......Begin 10-minute built-in hold (T-minus 20m) 06:38 PM......NASA test director countdown briefing 06:38 PM......Resume countdown (T-minus 20m) 06:39 PM......Backup flight computer to OPS 1 06:43 PM......KSC area clear to launch 06:49 PM......Begin final built-in hold (T-minus 9m) 07:19 PM......NTD launch status verification 07:34:46 PM...Resume countdown (T-minus 9m) 07:36:16 PM...Orbiter access arm retraction 07:38:46 PM...Launch window opens 07:38:46 PM...Hydraulic power system (APU) start 07:38:51 PM...Terminate LO2 replenish 07:39:46 PM...Purge sequence 4 hydraulic test 07:39:46 PM...IMUs to inertial 07:39:51 PM...Aerosurface profile 07:40:16 PM...Main engine steering test 07:40:51 PM...LO2 tank pressurization 07:41:11 PM...Fuel cells to internal reactants 07:41:16 PM...Clear caution-and-warning memory 07:41:46 PM...Crew closes visors 07:41:49 PM...LH2 tank pressurization 07:42:56 PM...SRB joint heater deactivation 07:43:15 PM...Shuttle GPCs take control of countdown 07:43:25 PM...SRB steering test 07:43:39 PM...Main engine start (T-6.6 seconds) 07:43:46 PM...SRB ignition (LAUNCH)