Meteor Shower, Solid Rocket Risks Discussed

Space Shuttle Discovery is poised for liftoff from Kennedy Space Center Launch Pad 39B at about 9:35 p.m. ET Thursday, first-rank NASA officials told journalists. It will be the first night shuttle launch since the Space Shuttle Columbia disaster in 2003.

The launch countdown begins at 11 p.m. ET today.

Up until now, since foam insulation ripped loose from the external fuel tank on Columbia to damage the orbiter vehicle and cause loss of the ship and crew, the ensuing three shuttle launches have been conducted in daylight. NASA officials wanted sunlit launches so they could view via videocameras any foam that might hit those orbiters.

But no foam hits were seen, and what small pieces of foam broke loose were so late in each ascent that there was little atmosphere present to whip the foam to lethal speeds.

Now, NASA leaders are reasonably confident that fixes to the external fuel tanks such as reducing foam in certain areas has reduced risks of orbiter vehicle damage greatly, so that they can launch shuttles at night again.

During the two days of the pre-launch flight readiness review, “we talked about the night launch aspects” of the upcoming STS-116 Discovery mission, William H. Gerstenmaier, associate administrator for space operations.

In the end, there was no dissent among senior NASA officials from the decision to proceed with the night launch, Gerstenmaier said, adding that “we are ready to go fly this [external fuel] tank with these changes.”

In part, he said, that was because experts asked to judge the likelihood of another foam insulation catastrophe on the shuttle changed their earlier assessment of “probable catastrophic” down to “infrequent catastrophic,” he said. This is, he said, the right time to execute a night launch.

Further, he said, NASA leaders judged that there will be no unacceptable danger to the spacecraft from the Leonid meteoroid shower. Any objects in space, even relatively small items, may be able to punch through the outside of a spacecraft.

Chances of a micrometeorite doing so are about one in 300, according to Wayne Hale, space shuttle program manager. (For a picture of a hole found in Space Shuttle Atlantis after it landed, please see Space & Missile Defense Report, Monday, Oct. 9, 2006, page 6.)

The launch window for the STS-116 Discovery flight runs through Dec. 17, for the dozen-days mission that will feature three spacewalks. Even a launch at the end of the window could see Discovery return and touch down to end the mission before the end of the year, when the change to 2007 could create problems for computers.

“I’m looking forward to a spectacular launch a week from tomorrow,” Hale said of the Dec. 7 liftoff plan.

At the same time, he cautioned, because the risk from a type of foam insulation loss “dropped an order of magnitude,” to about one-tenth what it previously was estimated, there still is risk that insulation could damage the shuttle vehicle.

“The hazard is less than we thought last summer,” Hale said. “It is still a hazard.” Or, to put it another way, “we’re concerned, but we’re not nearly as frightened,” he explained. That’s because “we have a significantly better understanding of the hazard and the cause of the hazard,” that is, a comprehension of just why foam insulation breaks loose.

And that state of mind was found throughout senior NASA officials participating in the review, he said, a session he termed “collegial,” and ending with agreement that NASA is “ready to proceed” with sending Discovery and its crew aloft. In this flight review, there was “a significantly lower level of tension than the last couple” of reviews, Hale said. In one review, before Discovery launched July 4, foam loss concerns prompted two senior NASA officials to recommend no-go for the mission.

Aside from discussing foam insulation hazards and meteoroids – “We’ve tried to avoid the Leonid meteoroid showers” – there was ample discussion in the pre-launch review about the solid rocket boosters on the shuttle, Hale disclosed.

“We had quite a discussion about solid rocket boosters … today, by the way,” Hale said.

Two decades ago, shortly after liftoff and rotation, the Space Shuttle Challenger and its crew of seven were lost when an O-ring failed in the booster system. That problem, however, was solved long ago.

Heading aloft on Discovery will be a crew of seven: Commander Mark Polansky, Pilot Bill Oefelein, mission specialists Bob Curbeam, Joan Higginbotham, Nicholas Patrick, European Space Agency astronaut Christer Fuglesang and Sunita Williams. Williams will remain aboard the station for six months. ESA astronaut Thomas Reiter, who has lived on the station since July, will return to Earth on Discovery.

They will completely rewire and activate the station’s electrical and thermal control systems. The crew will deliver and install the P5 truss segment between the station’s existing P3/P4 and P6 truss segments during two of three planned spacewalks. Installation of the P5 truss will allow the solar arrays on the P3/P4 and P6 truss segments to operate and rotate without interfering with each other. The P5 truss will act as a conduit that will transmit power and data from the P6 segment to the other segments on the station.

Space Station Problems

When Space Shuttle Discovery lifts off on the STS-116 mission, it will head to the International Space Station (ISS).

Discovery will act as a delivery van, taking major components required to continue construction of the ISS, the artificial moon that is an international endeavor.

Astronauts will install a new segment of the ISS girder-like truss and activate the permanent, complex ISS power and cooling systems.

A tricky part here, however, is during the installation, they will have to shut down some portions of the ISS electrical system, so that the remaining portion must work well to avert any blackout on the space station.

And problems already have arisen, with a circuit breaker popping open, making it uncertain that a solar electrical generating array would have power to swivel and follow the sun. If the array doesn’t do that, it wouldn’t generate sufficient power for the ISS during the construction work. It’s unclear whether the circuit breaker came open on its own, or whether it was a commanded action, Gerstenmaier said. It’s also unclear whether there is a mechanical problem in this area, or a software problem,

Flight controllers analyzing the problem are focused on the giant ISS Solar Alpha Rotary Joint. The joint is used to rotate the new solar arrays, allowing them to track the sun. The new software is designed to realign the teeth of the joint’s gears automatically should they become misaligned, rather than requiring controllers to send commands for the realignment.

However, while running through a test of the software on Tuesday, a remote power controller, or station circuit breaker, opened. The circuit breaker was successfully reset on Thursday. Extensive analysis and troubleshooting appears to indicate there is no problem with any equipment aboard the station. Work continues, however, to refine the new software.

Yet another problem is that a rocket firing of a Russian Progress supply ship docked to the ISS was aborted far short of the burn time required to boost the ISS to a higher orbit. That higher position is needed for Discovery to be able to dock with the ISS and perform the construction job.

The Progress cargo craft’s thrusters fired for 3 minutes, 16 seconds before shutting off automatically. They were supposed to fire for 18 minutes, 22 seconds. Russian controllers plan to complete the reboost today with a 21-minute firing of the Progress thrusters and a software adjustment. The reboost, planned for around 4:35 p.m. ET, will optimize Discovery’s rendezvous with the station.