Discovery to-do list: build COLBERT, lug huge coolant tank

For the space-shuttle program, Tuesday's early morning scheduled launch of Discovery and its seven-member crew to the International Space Station marks a final bend in the road toward retirement.

With one exception, the seven remaining missions focus on the detail work needed to ensure the space station's long-term operation once the shuttles are grounded.

Discovery astronaut Nichole Stott provides an indicator that for the shuttles, the end is near. Ms. Stott is bound for a nearly four-month stay aboard the station. She will be the last space-station crew member who will arrive and depart via the space shuttle.

Another indicator: With mostly interior work and some exterior maintenance remaining on the to-do list, this mission doesn't face the same intense pressure to do things in a specific order, as with past flights, notes Mike Moses, who chairs the mission management team.

But the mission "is challenging in its own regard," he adds.

Discovery's crew is hauling nearly seven tons of food and other crew supplies, hardware, and spare parts for the station itself, as well as large racks of lab equipment and experiments.

Among the hardware: a treadmill whose acronym spells out comedian Stephen Colbert's last name. The talk show host had asked viewers to participate in a NASA competition to name one last space station module. Instead of hewing to the NASA-approved suggestions – Serenity, Legacy, Earthrise, and Venture – they nominated "Colbert," which won the vote. NASA stepped in, choosing to name the node "Tranquility," but sportingly dubbed its new treadmill the Combined Operational Load Bearing External Resistance Treadmill (COLBERT).

The treadmill – some assembly required – will take about 30 or 40 hours to piece together, says Stott, who will remain on the space station when Discovery leaves. She drew the short straw on assembling the exercise machine, along with a second station crew member.

The machine is vital to ensure that the station has enough exercise equipment to meet the demands of a six-person crew. Exercising helps astronauts offset the physical effects of long-term weightlessness.

If all goes well, astronauts also will have a chance to set records for the most hefty piece of hardware ever manhandled by a space walker. During the second of three spacewalks at the station, astronauts Danny Olivas and Christer Fuglesang will swap a nearly empty ammonia-coolant tank with a new one they've brought up. The nearly empty tank has a mass of just over 1,800 pounds. Sweden's Mr. Fuglesang will in effect hand-carry it back to the shuttle's cargo bay while standing at the end of the shuttle's robotic arm.

Discovery's mission, scheduled for launch at 1:36 a.m. Eastern Daylight Time on Aug. 25, should be visible to residents along much of the US East Coast during the first eight minutes after launch, weather permitting.

The only additional mission with large-scale construction duties is scheduled for next February, when Endeavour will launch "Tranquility." The module will become the new treadmill's final home, and boasts a cupola giving astronauts remarkable views of Earth and space from orbit.

The last shuttle launch currently is scheduled for September 2010. But if unforeseen delays crop up, mission managers anticipate that the last launches could move into early 2011.