While the space shuttle may be grounded, the crew of the international space station is about to go on the move. Early Tuesday morning, the two astronauts will pack up their scientific results, load their Soyuz space vehicle, don their spacesuits, turn the space station to autopilot, dim the lights and leave the station.
And no, it's not an emergency.
Instead, the space station duo is taking advantage of the time they had otherwise scheduled to entertain Discovery's crew and moving up a maneuver originally planned for next month.
This road trip is a brief one, however. After undocking the Soyuz from the space station, pilot Sergey Krikalyov and flight engineer John Phillips will back it up, shift the spacecraft sideways about thirty feet and finally move back in to dock at another of the station's three ports.
The maneuver is routine (this is the sixth time it’s been done by station crewmembers), but Krikalyov and Phillips still must go through an extensive checklist to reconfigure the space station, in case a docking problem prevents them from getting back inside and they have to return to Earth. But experts consider the chance of any mechanical problem extremely remote. If there were difficulties at the new docking port — say, interference from a piece of stray insulation — the Soyuz could easily return to the docking port it had just left.
Prior to undocking at 6:35 a.m. ET, the two spacemen will don their ‘Sokol’ pressure suits, load the Soyuz with experimental results to be returned to Earth (so that they will have them if they have to suddenly return), and close all hatches securely. The flyaround is scheduled to occur while the station is crossing Russia, in contact with ground sites. They will be redocked within half an hour and then begin a day-long process of resetting the station's systems.
Safer port in a storm
There are three docking ports on the Russian segment of the space station, with two of them currently being used by Russian-made spacecraft. The robotic Progress supply ship occupies a docking port at the far end of the service module (the station's living quarters); the Soyuz is currently at the one at the end of a small side-mounted module launched in 2000. Called "Pirs" (Russian for "pier"), this port also serves as the main airlock for spacewalks using Russian spacesuits. The port the Soyuz will move to is on the FGB module that was the first section put into orbit in 1998.
“The re-docking will allow the crew to use the Pirs for a spacewalk in August,” explained NASA press officer Allard Beutel on Friday. "It has been decided to re-dock the spaceship and open the module for spacewalks,” Moscow Mission Control spokesman Valeriy Lyndin reiterated over the weekend.
However, this official reason is an oversimplification. Even with a Soyuz docked to the end of Pirs, the airlock can still be used for spacewalks — and it has been, in the past. It’s just that for safety reasons, the Russians don’t like the configuration.
That’s because in the event of a problem repressurizing the airlock at the end of a spacewalk, there would be no way for a third crewmember left inside the station to get to the Soyuz for an emergency return to Earth. Right now, that's not an issue: There are only two men on the station and during spacewalks both are outside the station, anyway. If an emergency occurred, they could let the air out of the Soyuz, enter it in their spacesuits, close the hatch and refill it. That in fact was the emergency plan for spacewalks last year that did occur from Pirs with a Soyuz docked at its end.
But the spacewalk planned for August was expected to occur after the arrival of a third station crewman, European astronaut Thomas Reiter, aboard the second shuttle mission. (Had Discovery launched in May, as first planned, Reiter would have flown to the station with the space shuttle Atlantis in July.) So for his safety, the Soyuz would have to be moved off the end of the Pirs module, and redocked at the FGB port. While the air was evacuated from the Pirs airlock during the spacewalk by Krikalyov and Phillips, Reiter would have had full access to the Soyuz on the neighboring docking port.
Nevertheless, doing the maneuver now makes good sense, space station operators say, because it allows the space station crew to use its time well while it waits for the shuttle. NASA flight controllers did review the effects of the station’s slight reconfiguration on plans for observing Discovery when it ultimately arrives, but found no problems.