Discovery launch set for next Thursday, pending ISS issues
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 29, 2006
If all goes well, Discovery's countdown will begin at 11 p.m. EST Monday, setting the stage for a launch attempt at 9:35:45 p.m. EST Thursday. This will be NASA's first night launch since 2002.
But space station engineers are working two issues that must be resolved for Discovery to get off the ground next week:
Bill Gerstenmaier, NASA chief of space flight operations, said late today he's optimistic the Russians will resolve the reboost issue. Similar problems have developed in previous reboost maneuvers, he said, and the Russians managed to recover.
"There is pretty complex software and commanding that's associated with those Progress burns and typically we'll find something there that was out of configuration that cut that burn a little bit short," Gerstenmaier said.
But the timing in this case is critical and relatively quick action is needed. Because of the complexity of Discovery's mission, docking must occur on flight day three. The reboost maneuver is designed to ensure FD-3 docking opportunities through Dec. 17, the last day the shuttle can launch and complete its mission, with two contingency days, before the end of the year.
With today's premature engine shutdown on the station, the shuttle does not yet have a flight-day three docking opportunity for a Dec. 7 launch.
The actual close of the current launch window, based on thermal issues when the shuttle is docked to the station, is Dec. 26. Should Discovery be delayed significantly, flight controllers say a second reboost maneuver Dec. 14 would permit FD-3 dockings through the end of the window.
But any launch after Dec. 19 would require Discovery to be in orbit during the year-end rollover from Dec. 31 to Jan. 1.
Gerstenmaier said managers will revisit the issue if Discovery encounters any major delays. But as of today, Dec. 17 is the effective close of the launch window (additional launch window details are avaiable here).
The goal of Discovery's mission is to switch the space station's electrical system from from its current interim configuration, sufficient for the lab's initial assembly, to its permanent system, which is required before attachment of additional modules.
During two spacewalks, the astronauts and flight controllers will power down the station's two major circuits, one at a time, to make the switchover. Each time a channel is powered down, critical station systems will no longer have redundancy.
As part of the re-wiring work, the astronauts must retract one wing of a set of solar arrays that served the interim system to permit a new set of arrays, installed during a shuttle flight in September, to begin tracking the sun.
The arrays are designed to rotate like a giant paddle wheel using a solar alpha rotary joint, or SARJ mechanism. The SARJ also was installed in September and after troubleshooting a software problem, flight controllers successfully engaged the teeth of the main drive gear with the motors needed to turn the arrays.
To avoid similar problems in the future, controllers uplinked new software to detect SARJ gear tooth misalignments and make adjustments as required for smooth operation. During tests Tuesday, however, a circuit breaker known as a remote power controller, or RPC, tripped and engineers have been unable to reset it.
The RPC in question is one of two that route power to the SARJ motors. Both are needed to provide redundancy. In a worst-case scenario - the second RPC fails while one power channel is down for re-wiring - the solar arrays would stop tracking the sun and power output might drop below the threshold needed by critical systems on the one operational channel.
Gerstenmaier said complex testing is underway at the Johnson Space Center in Houston using the same software and electrical components that operate like the hardware in orbit. If the problem is software related, engineers should be able to devise a fix to put the breaker back in operation.
If the problem is hardware related, the issue will be harder to resolve. No spares are available on the space station and while parts could be taken from station components awaiting launch, it's not yet clear how that might affect Discovery's eventual launch date.
Hoping for the best, Discovery's crew - commander Mark Polansky, pilot William Oefelein, Nicholas Patrick, Robert Curbeam, European Space Agency astronaut Christer Fuglesang, Joan Higginbotham and Sunita Williams - plans to fly to the Kennedy Space Center Sunday to prepare for launch.
Here are countdown highlights (in EST). A detailed countdown timeline is available here.
EST...........EVENT Sun 12/03/06 04:15:00 PM...Crew arrives at KSC Mon 12/04/06 10:30:00 PM...Call to stations 11:00:00 PM...Countdown begins (T-minus 43 hours) Tue 12/05/06 03:00:00 PM...Begin 4-hour built-in hold 07:00:00 PM...Resume countdown (T-minus 27 hours) 08:30:00 PM...Fuel cell oxygen loading begins 11:00:00 PM...Fuel cell oxygen load complete 11:00:00 PM...Fuel cell hydrogen loading begins Wed 12/06/06 01:30:00 AM...Fuel cell hydrogen loading complete 02:30:00 AM...Pad open; ingress white room 03:00:00 AM...Begin 4-hour built-in hold 07:00:00 AM...Countdown resumes (T-minus 19 hours) 03:00:00 PM...Begin 13-hour 40-minute hold 07:00:00 PM...Communications system activation 07:30:00 PM...Crew module voice checks 08:50:00 PM...Flight crew equipment late stow Thu 12/07/06 12:27:00 AM...Rotating service structure moved to park position 03:40:00 AM...Countdown resumes (T-minus 11 hours) 09:40:00 AM...Begin 2-hour built-in hold (T-minus 6 hours) 10:30:00 AM...Mission management team tanking meeting 10:40:00 AM...External tank ready for fueling 11:40:00 AM...Resume countdown (T-minus 6 hours) 11:40:00 AM...Liquid oxygen/hydrogen transfer line chilldown 11:50:00 AM...Main propulsion system chill down 11:50:00 AM...LH2 slow fill 12:20:00 PM...LO2 slow fill 12:25:00 PM...Hydrogen ECO sensors go wet 12:30:00 PM...LO2 fast fill 12:40:00 PM...LH2 fast fill 02:40:00 PM...Begin 3-hour built-in hold (T-minus 3 hours) 02:40:00 PM...Closeout crew to white room 02:40:00 PM...External tank in stable replenish mode 03:30:00 PM...NASA TV coverage begins 03:56:00 PM...Astronaut photo opportunity (time approximate) 05:15:00 PM...Astronauts don pressure suits 05:40:00 PM...Resume countdown (T-minus 3 hours) 05:45:00 PM...Crew departs O&C building 06:15:00 PM...Crew ingress 07:05:00 PM...Astronaut comm checks 07:20:00 PM...Hatch closure 08:20:00 PM...Begin 10-minute built-in hold (T-minus 20m) 08:30:00 PM...Resume countdown (T-minus 20m) 08:41:00 PM...Begin final built-in hold (T-minus 9m) 08:51:44 PM...NTD launch status verification 09:26:44 PM...Resume countdown (T-minus 9m) 09:30:00 PM...Launch window opens (actual: 9:30:45 p.m.) 09:35:45 PM...Liftoff 09:40:45 PM...Launch window closes
Shuttle Program Manager Wayne Hale said senior managers today agreed to press ahead with a launch attempt even if one of four engine cutoff - ECO - sensors in the ship's external fuel tank fails during the final hours of the countdown.
The sensors are part of a backup system that ensures the shuttle's main engines don't run too long and pump the tank dry with potentially catastrophic results. In the past, all four sensors were required and launch of the shuttle Atlantis was delayed 24 hours in September when one of its ECO sensors at one point indicated it was submerged in supercold hydrogen rocket fuel when, in fact, it was dry.
Because of the logic built into the circuitry, one sensor can "fail wet" without compromising redundancy, engineers have concluded. If a single sensor fails wet during Discovery's countdown, NASA will proceed with launch. If multiple sensors fail, or if one "fails dry," the launch will be delayed.
Hale also said engineers have revised their estimate of the danger posed by so-called ice-frost ramps on the shuttle's external tank. The foam ramps are in place to prevent dangerous pre-launch ice buildups around external fittings that hold pressurization lines in place.
For the last two flights, the ramps were officially classified as "probable/catastrophic," meaning it was probable, over the 100-flight design life of a given shuttle, that foam debris could come off and cause catastrophic impact damage to the shuttle's heat shield. NASA Administrator Mike Griffin said he did not believe that classification was correct and approved flying anyway while a permanent fix was developed.
Hale said today the probability of a catastrophic failure due to the IFRs, once thought to be in the neighborhood of 1-in-100, had decreased by an "order of magnitude" based on the actual performance of the ramps over the past two flights. While he did not provide any numbers, he said the ramps are now classified as "infrequent/catastrophic."
"We now know that the hazard is less than we thought it was last summer," Hale said. "It's still a hazard, we're working on it, we are making improvements and doing real things to the tank to make ourselves safer, but it's not nearly as bad as we thought it was because we now know more. ... We're concerned, but we're not nearly as frightened as we were before."
NASA managers ultimately plan to replace the ice-frost ramps with titanium fittings that will virtually eliminate the threat of foam debris. They originally planned to implement an interim fix early next year, but Hale said the next flight, currently targeted for March, will fly with the same IFR design that is currently in place on Discovery's tank.
Engineers now are debating whether to call off the interim work and focus instead on implementing the permanent fix as soon as possible.