After more than a week of spaceflight, the crew of the space shuttle Discovery is taking a break from their orbital duties, while engineers on the ground study a couple of power unit glitches.
The shuttle’s crew, commanded by Steven Lindsey, awoke at 1:08 a.m. ET today to the theme song of the television show "Charlie’s Angels" with little else on their schedule aside from some rest and relaxation.
“Just taking the standard taking a break, looking out the window and enjoying the day on orbit,” NASA’s lead shuttle flight director Tony Ceccacci said about the astronaut’s day.
“Basically, the only thing we’ll do at the end of the day is starting the MPLM closeout activities.”
Discovery’s Leonardo MPLM, or Multi-Purpose Logistics Module, has been berthed at the international space station, where the shuttle too has been docked since July 6. All nine astronauts – six aboard Discovery and three aboard the space station – have been shifting thousands of pounds of cargo between the space station and Leonardo module.
At the same time, engineers are eyeing two glitches that have popped up with two of the three Auxiliary Power Units, or APUs, which supply power to Discovery’s hydraulics and other systems during landing.
In an update to the crew, flight controllers said that Discovery’s APU 1 is suffering from a higher than normal fuel pressure decay, suggesting a small leak in the unit’s hydrazine or nitrogen fuel tanks. APU pressure is expected to drop about 6 pounds per square inch over eight days, though APU 1’s tank pressure has dropped about 22 psi in the same time period.
“We hope to have more details on this subject tomorrow but as of today there is no change to any mission plans based on the data collected,” flight controllers reported today in the crew’s Flight Day 10 execute package, adding that APU 1 was not considered failed at this time.
Another unit, APU 3, has a heater hiccup that has caused a backup heater to fail. Engineers on Earth suspect that a new wrapping on the heater that may have come loose in flight or it may have become debonded, since both events would prompt the current glitch.
“APU 3 is not considered failed for entry at this time and there are no significant impacts to entry operations,” flight controllers said according to the execute package, adding that engineers continue to monitor this APU as well.
Of the three APUs aboard Discovery, only one is required to be fully operation for landing.
Lindsey and the six-astronaut crew are nearing the homestretch of their planned 13-day mission. The astronauts have completed most of their cargo transfer duties, three spacewalks and a series of heat shield repair demonstrations during their flight.
Discovery also ferried European Space Agency astronaut Thomas Reiter to the ISS, where he joined the then-two astronaut crew of Expedition 13 and returned the space station back to its three-person capacity for the first time since 2003.
Ceccacci said that Reiter and his Expedition 13 crewmates also have a light day today, to give the astronauts some rest and also prevent motivating the shuttle crew to pitch in.
“The station crew is very lightly loaded,” Ceccacci said. “If they were doing a lot of work, their shuttle buddies would want to come over and help and that’s what we’re trying to avoid.”
Instead, the STS-121 astronauts will spend today enjoying space and speaking with reporters on Earth and, more importantly, their families, Ceccacci said.
Discovery and its six astronaut crew are expected to land at NASA’s Kennedy Space Center on Monday at 9:07 a.m. ET.