CAPE CANAVERAL, Fla. - NASA is poised to launch seven shuttle astronauts toward the International Space Station (ISS) Tuesday on what some have called the most ambitious orbital construction mission to date.
Commanded by veteran spaceflyer Pamela Melroy, the shuttle Discovery is slated to launch from Pad 39A here at NASA?s Kennedy Space Center (KSC) at 11:38 a.m. EDT (1538 GMT). Melroy and her crewmates plan to swap out one ISS crewmember, deliver an orbital hub to anchor future laboratories to the station and perform the complicated move of a 17.5-ton solar array segment to boost the outpost?s power grid.
?I think, by any measure, this will is one of the most challenging and audacious missions of the shuttle era,? said Discovery astronaut Scott Parazynski, lead spacewalker for the NASA?s STS-120 mission. ?We?re all very proud to serve and be a part of this flight.?
Set to launch spaceward with Melroy and Parazynski are Discovery pilot George Zamka and mission specialists Stephanie Wilson, Douglas Wheelock, Daniel Tani and European Space Agency astronaut Paolo Nespoli. Together, they will install the Italian-built Harmony node - the connecting point for European and Japanese laboratories waiting to fly.
During five planned spacewalks - the most-ever during a shuttle flight to the ISS - the STS-120 astronauts will also test new space shuttle heat shield repair methods, move the station?s $276 million Port 6 (P6) solar power truss segment from its mast-like perch to the station?s port-most edge, and then unfurl its expansive arrays. Parazynski compared the P6 relocation to moving an entire house from one neighborhood to another.
?We hit the jackpot, I won?t kid ya. I think this is every astronaut?s dream of a mission,? Melroy said before launch day. ?It?s going to be an enormous challenge.?
The flight will also be historic. Melroy, NASA?s second female shuttle commander, is set lead her crew into space to the ISS, where veteran U.S. astronaut Peggy Whitson is serving as the orbital laboratory?s first female commander. Whitson and her Expedition 16 crewmates took charge of the space station on Friday from its outgoing crew.
?The thing that is the best about this is that it happened totally by accident,? Melroy said. ?Nobody planned it.?
Tani will replace NASA astronaut Clayton Anderson, who is currently living aboard the ISS as an Expedition 16 flight engineer, during Discovery?s spaceflight. He and his crewmates hope to beat the weather for Tuesday?s planned launch. Current forecasts predict a 60 percent chance that rain showers and thick clouds could prevent the planned space shot.
Gateway to new labs, larger crews
Discovery?s STS-120 spaceflight will mark NASA?s 120th shuttle flight to date and the third mission this year to continue space station assembly.
But unlike this summer?s previous flights of the Atlantis and Endeavour orbiters - which delivered new truss segments, cargo, spare parts and solar arrays - Discovery is hauling up Harmony, which will increase the internal space of the ISS for the first time since Russia?s Pirs docking port arrived in 2001.
?Many people look at it as the gateway to the international partner piece of the space station,? Derek Hassmann, NASA?s lead ISS flight director during STS-120, told SPACE.com.
Harmony will serve as the anchor for the European Space Agency?s Columbus laboratory - slated to launch aboard Atlantis in December - and Japan?s three-segment Kibo laboratory. The new module will also hold quarters for ISS astronauts once the station?s crew complement doubled to six spaceflyers in 2009.
?It?s very exciting to think that the work we?re doing is going to enable this exciting new research and also enable a six-person crew capability in the future,? Parazynski said.
While Parazynski is making his fifth spaceflight with Discovery?s planned launch Tuesday, Zamka, Wheelock and Nespoli are making their first forays into orbit during the STS-120 mission.
?I can?t wait for the clock to count down to zero and the solid rocket boosters ignite,? said Zamka. ?Because that will be a nice reminder that the training is over.?
NASA will begin broadcasting Discovery?s STS-120 launch and mission operations live on NASA TV at 6:30 a.m. EDT (1030 GMT) on Tuesday. Click here for SPACE.com?s live launch coverage, mission updates and NASA TV feed.
- SPACE.com Video Interplayer: Delivering ?Harmony? with NASA's STS-120 Mission
- Test Your Smarts: Space Shuttle Countdown Quiz
- Complete Space Shuttle Mission Coverage