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After five delays, the NASA space shuttle Discovery STS-119 has finally taken off toward the International Space Station in order to fit it with a final pair of power-generating solar wings.  With the recent delay involving leaking hydrogen gas which delayed last Wednesday's launch attempt, prior delays involved hydrogen gas valves inside the space shuttle's engine compartment. Forcing a tight docking schedule, with Russia needing to have a shuttle-port open by March 26 when they will send up a new space station crew, the U.S. NASA needed to have the U.S. Discovery up and out of the International Space Station before then. This will require the original 14-day mission to be cut short by one day while having a total of eight consecutive days at the ISS for the exhibition,  requiring a deadline of three spacewalks instead of the original four.

On-board are six astronauts (Lee Archambault, commander; Tony Antonelli, pilot; and mission specialists-Joseph Acaba, John Phillips, Steve Swanson, and Richard Arnold) along with a Japanese astronaut 7th crew member, Koichi Wakata, who will replace the US astronaut Sandra Magnus on the 75%-completed International Space Station, with the Discovery mission delivering the station's final 11-part external backbone. Once this is completed, the ISS would increase from three astronauts living on-board to supporting a total of six astronauts as of May.

"More crew means that we'll have to run more life support equipment, more crew support equipment – toilet facilities, water processing equipment and all of that stuff," said Kwatsi Alibaruho, the lead space station flight director for the mission. "We'll have to run more of all of that, so we need additional power."

With the space shuttle Discovery considered the oldest of the three orbiters in service, additionally the space shuttles Atlantis and Endeavour are currently the operational orbiters in the Space Shuttle fleet of NASA, soon retiring in 2010 with the Discovery the last space shuttle to fly on NASA's mission STS-134. Famous for launching the Hubble Space Telescope, along with the second and third service missions for it, the Discovery is also known for launching the Ulysses probe and three TDRS satellites.  Once it is retired, NASA has offered it to the Smithsonian Institution's National Air and Space Museum, part of the national collection for preservation and public display.

Not only is additional electricity needed for the extra crewmembers but also due to an expanded capacity for the ISS's science experiments. The new connecting node, Harmony, and its partner international laboratories, the European Columbus and the Japanese Kibo, had been added in the past year. Helping with double the man-power, the new solar arrays will provide a total of two solar array wings for a total wing span of 240 feet, generating 84 to 120 kilowatts of electricity. This amount of electricity will provide an equivalent of power available to over 40 average homes. It is estimated that the original arrays are already handling the ISS's life support needs and its day-to-day operations, so the newly added solar arrays will double the power available for scientific research.