This story was updated at 11:12 a.m. EST.
NASA has delayed the last launch of the shuttle Endeavour toward the International Space Station by at least 10 days, to April 29, in order to avoid a space traffic jam with an unmanned Russian cargo ship, also headed for the orbiting laboratory later this month.
Endeavour is now targeted to blast off on its STS-134 flight on Friday, April 29 at 3:47 p.m. EDT (1947 GMT), NASA officials said. The decision to postpone the launch removes a scheduling conflict with a Russian Progress cargo ship, which is currently scheduled to launch April 27. The robotic Progress vehicle will arrive at the station on April 29.
"Looking at the International Space Station, it was the best thing to do to have Endeavour stand down for a week and a half, and launch once the Progress is already docked to the space station," NASA spokesman Allard Beutel told SPACE.com today (April 4).
Discussions between NASA and its international partners have been ongoing for weeks, Beutel said, and the decision to delay Endeavour's flight was made after several other options, including moving the Progress' launch date, were deemed impractical.
"Apparently there is a biological experiment onboard the Progress that has a very short shelf life onboard that spacecraft," Beutel said. "We even looked at the possibility of putting that experiment on Endeavour, but logistically that didn't work out as well."
Balancing traffic at the space station and on the ground has proved challenging for the various space station partners, but is especially crucial for NASA, in order to capitalize on the unrivaled cargo-carrying capabilities of the space shuttles. The main objective of the remaining shuttle flights is to ferry supplies to the station so that the orbiting laboratory is in a good position for the years ahead, following the retirement of the agency's shuttle fleet later this year.
NASA managers will hold a Flight Readiness Review meeting on April 19 to assess the space shuttle's readiness to launch. An official launch date will be selected at the conclusion of the meeting, NASA officials said.
Endeavour was initially slated to blast off on April 19, carrying commander Mark Kelly, pilot Gregory H. Johnson, and mission specialists Michael Fincke, Greg Chamitoff, Andrew Feustel and Italian astronaut Roberto Vittori to the International Space Station. The shuttle will deliver supplies and a $2 billion science experiment, called the Alpha Magnetic Spectrometer, during the 14-day spaceflight. Four spacewalks are planned for the mission.
Over the weekend, engineers at NASA's Kennedy Space Center in Cape Canaveral, Fla., also assessed minor damage to the foam of Endeavour's external fuel tank sustained during severe storms in the area last week.
Evaluations indicated that there was no significant damage to the spacecraft, NASA officials said.
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