After their first full day in space, the shuttle Discovery and its six-member crew have settled in to their activities with a smoothness that stands in stark contrast to the delays the mission experienced to reach this point.
This mission marks Discovery's final trip to space as NASA prepares to retire its fleet of orbiters after 30 years of operation. Through a series of launch postponements, sparked by unexpected problems with the orbiter's external fuel tank, it seemed as though the craft was trying to avoid the inevitable.
But with a spectacular launch Thursday, the orbiter and crew – all veterans of previous spaceflights – are back in their element.
"Everything's going really well on board," Bryan Lunney, the mission's flight director, said late Friday afternoon of the crew's performance.
And the vehicle's systems are "in great shape" as controllers and crew look forward to a rendezvous with the International Space Station Saturday, he said.
But for all the kudos mission managers are giving Discovery's launch team for its successful efforts to track down the cause for the external-tank problems that delayed the mission, the managers are keeping an eye on data the shuttle crew relayed after spending about six hours Friday inspecting the orbiter's heat-shedding tiles.
During lift-off, video cameras on the external fuel tank recorded four instances where foam insulation from the tank broke free and traveled down the length of the orbiter.
All four events happened after the shuttle had reached an altitude where the atmosphere was too thin to impart a relative velocity to the debris that would have damaged the tiles, notes LeRoy Cain, who heads the mission-management team overseeing the 11-day flight.
A hunt for damaged tiles
Still, engineers will comb through images and laser-generated maps of the tile surfaces to hunt for damage.
Of particular interest is an event that occurred 3 minutes and 51 seconds after launch, Mr. Cain says. Debris from the tank appeared to strike the underside of the orbiter, ricochet off of a strut connecting the external tank to the orbiter, then strike the side of the fuselage before vanishing.
For now, managers are calling the second and third strikes "potential," because the camera only captures a two-dimensional view and the perspective could be deceiving. The first strike is the impact of interest because it hit the underside, which experiences the most heating during re-entry.
Photos the shuttle crew took of the tank just after the orbiter and tank separated show one telltale spot where foam broke free, although it's unclear if this is the spot that generated the foam projectile the team is most interested in.
The region of the tank "is an area of the tank we're very attuned to in terms of the potential for this kind of debris loss, so we don't have any concerns about this event," he says.
The likely cause, Cain explains: Air bubbles in the foam that expand as the orbiter burns off the frigid liquid hydrogen and liquid oxygen and the once frosty region warms, causing the air to expand and push off chunks of foam.
In addition to Friday's detailed inspection, the orbiter will perform a back flip well within camera range of the space station so station crew members can take high-resolution photos of the underside of the orbiter.
Mission managers say they anticipate that by Sunday, they'll have enough information to either give the thermal-protection system a clean bill of health, or know whether there is damage that warrants more detailed examination and, if possible, in-orbit repairs.
A space station first
A successful mating between shuttle and station Saturday will mark the first time in the station's history that each of the major partners will have a spacecraft docked to the station at the same time, NASA officials say.
Following lift-off, William Gerstenmaier, NASA's associate administrator for space operations, noted that after Kepler arrived, "I received a bunch of emails from my European partners telling me that we had a 'go' to launch Discovery today."
"That was kind of a strange occurrence for me," he added with a grin, noting that he usually doesn't need to get approval from them to launch.
Such is the delicate space-traffic-control dance the partners engage in as the shuttle program winds down and the unmanned craft become vital links in the station's resupply chain.