Engineers troubleshoot rocket engine issue Photo Credit/NASA TV
Shuttle Discovery’s final mission has been postponed until no earlier than Thursday to permit additional trouble shooting of a rocket engine computer that displayed some unexplained power readings during routine countdown testing on Tuesday.
A launching of Discovery from NASA’s Kennedy Space Center on an 11-day mission to the International Space Station would occur at 3:29 p.m., EDT.
However, Thursday’s weather outlook is poor. There was a 70 percent chance that a cool front could trigger scattered showers and low cloud ceilings, conditions outside NASA flight rules.
The launching had been set for Wednesday afternoon.
The difficulties with the backup controller on Discovery’s No. 3 main engine cropped up early Tuesday during routine engine checks. Initially the controller failed to activate, a difficulty that appeared to be associated with a circuit breaker, possibly contaminated with a bit or carbon, oil or dust, said Mike Moses, the chair of NASA’s pre-launch Mission Management Team.
It appeared the contamination was cleared with multiple re-settings of the circuit breaker. But then another small irregularity in the electrical current surfaced.
An overnight review of the system’s past performance was under way to establish an explanation, including the source and severity of the problem. Each of Discovery’s three main engines has a primary and back up controller to regulate performance and signal the shuttle’s flight control system of a serious problem.
“We don’t fly with unknown risk,” said Moses. “Right now, the risk is still a bit unknown to us. We are going to take the time to get to know it better and make this a risk we know and can quantify.”
However, if the difficulty cannot be placed squarely on the circuit breaker or another component, a longer delay is likely. The installation of another rocket engine or controller, for instance, could take a couple of weeks.
The Mission Management Team will reconvene on Wednesday to determine the next course of action.
Discovery’s launch period extends through Sunday, and the weather outlook is expected to improve to 70 percent favorable by Friday. Forecasters will be watching the winds through the weekend if Saturday or Sunday become launch day options.
The initial plan to begin Discovery’s 11-day mission on Monday was postponed by small leaks in the helium and nitrogen systems that pressurize one of the shuttle’s tail mounted orbital maneuvering engines. Both have been fixed.
Discovery’s astronauts have trained to deliver and equip the space station with a storage compartment called the Permanent Multipurpose Module and the Express Logistics Carrier, an external spare parts platform that holds a spare thermal control system radiator.
The mission also includes a pair of spacewalks for maintenance activities outside the space station.
Next Monday, could become a launch opportunity — if NASA’s Mission Management Team was willing to have Discovery’s six astronauts depart the space station a day early.
After Monday, however, the solar heating on the space station climbs to temperatures that are too hot for the shuttle.
The next launch period extends from Dec. 1 to 5. But a launching then would likely conflict with a previously scheduled Russian mission to the space station.
“This is part of the business. You fly when you are ready, and you don’t, when you are not,” said Mike Leinbach, NASA’s shuttle launch director.
The flight is to be Discovery’s 39th and final flight to space, after 26 years of service. All three of NASA’s shuttle orbiters are facing retirement next year.
“Discovery is not going out easy,” said Leinbach. “She’s giving us a little bit of trouble. That’s fine. She will fly perfectly when she goes.”