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Discovery set for fueling BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: March 15, 2009 Engineers at the Kennedy Space Center are gearing up to refuel the shuttle Discovery for launch this evening on a delayed space station assembly mission. Work to reconnect and test a gaseous hydrogen vent line is complete and NASA's Mission Management Team plans to meet around 9:45 a.m. to assess the weather and any open items before giving engineers a "go" to begin fueling. The vent line "is no longer an issue," said a NASA spokesman early today and forecasters are continuing to predict an 80 percent chance of acceptable weather for a launch attempt at 7:43:46 PM. Assuming the MMT gives formal permission to proceed, the three-hour fueling procedure will begin around 10:18 a.m. with transfer line chill down. A launch attempt Wednesday was scrubbed after sensors detected a significant gaseous hydrogen leak at a vent line umbilical fitting on the side of Discovery's external fuel tank. The leak only showed up when the tank was nearly full and excess hydrogen gas inside the tank was being vented overboard to maintain the proper internal pressure. The umbilical was disassembled, internal seals and fittings were replaced and the system was reconfigured for another launch attempt. But no "smoking gun" was found to explain the leak and engineers will not know whether the repair work succeeded until the external tank's hydrogen section is loaded with super-cold rocket fuel.
Liquid hydrogen "fast fill" begins around 11:18 a.m. and "topping" will start around 1:13 p.m. It was around the time of topping off Wednesday that the leak occurred, when the tank was 98 percent full. Here is the remainder of today's countdown, a timeline showing the crew's abort options and a flight plan for the first day in space (includes NASA TV sked (rev. A); best viewed with fixed-width font): EDT...........EVENT 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 11:18 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 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 steering test 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)
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VIDEO:
TIME-LAPSE OF SUNRISE AT LAUNCH PAD 39A 