Image: Endeavour
Stan Honda  /  AFP - Getty Images
The space shuttle Endeavour sits on Launch Pad 39A behind a blank countdown clock at Kennedy Space Center in Florida. NASA says Endeavour's final launch will take place no earlier than May 16.
By
updated 5/6/2011 2:16:16 PM ET 2011-05-06T18:16:16

The next-to-last space shuttle flight has been delayed again, this time to at least the middle of May for extra electrical tests.

Mission managers decided Friday that shuttle Endeavour would blast off no earlier than May 16.

The space station delivery mission, led by wounded Rep. Gabrielle Giffords' astronaut husband, has been on hold for a week. A heater malfunction halted the countdown April 29, and the trouble was traced to a switch box in Endeavour's engine compartment. The box was removed, and this week engineers discovered a blown circuit inside.

NASA spokeswoman Candrea Thomas said testing will be conducted throughout the weekend to find out if the circuitry problem was in the old box or somewhere in the external wiring that's still in the shuttle. A new unit was installed Wednesday.

Commander Mark Kelly will lead Endeavour's six-man crew to the International Space Station. They will deliver a $2 billion particle physics detector and a storage platform along with station spare parts.

Giffords, Kelly's wife, was shot in the head four months ago during a political event in Tucson, her hometown. She is recuperating at a hospital in Houston, Kelly's home base.

The congresswoman's staff said she will return to Cape Canaveral for another launch attempt. The April 29 launch attempt also drew President Barack Obama and his family.

A launch on May 16 would be at 8:56 a.m. ET.

On Thursday, space station astronaut Catherine Coleman told The Associated Press she's disappointed by Endeavour's delay. She also worries about the work that will have to be shared if she and two other astronauts are gone by the time the shuttle arrives.

Coleman, an Italian and a Russian are scheduled to depart for home May 23, via a Russian Soyuz capsule, leaving three residents behind. Their station replacements won't be on board until June 9.

"They'll come when everything is right," she said of the shuttle crewmen. "It's the way it goes for shuttle launches."

Only one other shuttle mission remains, by Atlantis this summer. That liftoff is targeted for June 28, but could be pushed back by Endeavour's repeated delays.

NASA is under presidential direction to end the 30-year shuttle program as soon as possible and to focus on interplanetary travel. Private companies, meanwhile, are competing for the opportunity to carry out cargo and crew haul to and from the space station.

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Photos: The life of space shuttle Endeavour

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  1. Special delivery

    Endeavour was the last space shuttle to join NASA's fleet: It was built to replace the shuttle Challenger, which was lost in an explosion shortly after launch in 1986. This view shows Endeavour perched atop a modified Boeing 747 on May 2, 1991, beginning the ferry flight from Palmdale, Calif. - where the shuttle was built - to Kennedy Space Center in Florida. (NASA) Back to slideshow navigation
  2. First liftoff

    Endeavour lifts off from Launch Pad 39B at NASA's Kennedy Space Center on May 7, 1992, beginning its first mission. The STS-49 mission's primary task was the repair of the Intelsat VI telecommunications satellite. Endeavour was the only shuttle to make its maiden flight from Pad 39B. (NASA) Back to slideshow navigation
  3. Grab that satellite!

    Endeavour astronauts Richard Hieb, Thomas Akers and Pierre Thuot hold onto the 4.5-ton Intelsat VI satellite after making a six-handed "capture" on May 13, 1992. The satellite failed to rise above low Earth orbit when it was launched in 1990. During Endeavour's maiden mission, astronauts retrieved the satellite, attached it to a new upper-stage booster and relaunched it to its intended geosynchronous orbit. This mission marked the first time that three people from the same spacecraft walked in space at the same time. (NASA) Back to slideshow navigation
  4. Science in space

    Endeavour astronauts Jan Davis, left, and Mae Jemison prepare to deploy the lower body negative pressure apparatus on Sept. 15, 1992. Scientific research was the main focus of this Spacelab-J mission, also known as STS-47. The mission's crew included the first African-American woman to fly in space (Mae Jemison) and the only husband-and-wife team to go into space together (Jan Davis and Mark Lee). (NASA) Back to slideshow navigation
  5. Fixing Hubble

    Astronauts flew on Endeavour to take on the first Hubble servicing mission in December 1993. In this picture, spacewalkers Story Musgrave and Jeffrey Hoffman perform an orbital ballet. The coastline of western Australia is visible below. The complex and highly successful repair mission allowed Hubble, which was launched with a defective mirror, to see into the universe with unprecedented clarity. (NASA) Back to slideshow navigation
  6. Building the station

    Endeavour spacewalker Jim Newman holds onto the International Space Station's Unity connecting module as he removes covers and works on connecting cables on Dec. 7, 1998. The STS-88 flight marked the shuttle fleet's first space station assembly mission. (AFP/Getty Images) Back to slideshow navigation
  7. Erroneous endeavor

    The shuttle Endeavour sits on its launch pad at Kennedy Space Center in Florida on July 11, 2007. "Endeavor" is spelled incorrectly on the banner. The shuttle was named after the HMS Endeavour, the British sailing ship that carried Captain James Cook on his first voyage of discovery from 1768 to 1771. That's why Endeavour reflects the British spelling of the word. (Eliot J. Schechter / Getty Images) Back to slideshow navigation
  8. Spacewalkers at work

    During the first spacewalk of the STS-118 mission, on Aug. 11, 2007, astronaut Rick Mastracchio and Canada's Dave Williams (out of frame) attach a new segment of the International Space Station's truss and retract a collapsible radiator. (NASA) Back to slideshow navigation
  9. Class portrait

    The crew members of Endeavour's STS-118 crew pose for their official portrait on Aug. 8, 2007. From left are Rick Mastracchio, Barbara Morgan, pilot Charles Hobaugh, mission commander Scott Kelly, Tracy Caldwell, Canadian astronaut Dave Williams and Alvin Drew. During this flight, Morgan became the first educator astronaut to go into orbit. In 1986, she was the backup for Christa McAuliffe, the New Hampshire teacher who died in the Challenger explosion. (NASA) Back to slideshow navigation
  10. Great view

    Endeavour spacewalker Rick Mastracchio relocates communications equipment on the International Space Station during an outing on Aug. 15, 2007. (NASA) Back to slideshow navigation
  11. A gouge in the tiles

    Tiles on the underside of the space shuttle Endeavour show evidence of damage in a photo taken on Aug. 12, 2007, using the shuttle's robotic arm and a camera-tipped extension boom. The close-up imagery helped mission managers determine that the gouge would pose no threat during Endeavour's atmospheric re-entry. (NASA via AP) Back to slideshow navigation
  12. Eye of the hurricane

    Crew members aboard the shuttle Endeavour captured this picture of Hurricane Dean's eye in the Caribbean on Aug. 18, 2007. The STS-118 mission ended on Aug. 21, one day earlier than planned, to avoid potential complications due to the storm. Forecasters worried that Hurricane Dean could have swept over Houston around the time of landing - but in the end, the storm took a different course. (NASA) Back to slideshow navigation
  13. In control

    NASA Administrator Michael Griffin watches the liftoff of the space shuttle Endeavour from the Launch Control Center at NASA's Kennedy Space Center on Nov. 14, 2008. The STS-126 mission delivered two spare bedrooms as well as a second kitchen and bathroom to the International Space Station. (Bill Ingalls / NASA) Back to slideshow navigation
  14. Repairs at the pad

    Workers perform repairs on the shuttle Endeavour's external fuel tank at the Kennedy Space Center launch pad on June 14, 2009. The launch team detected a leak of hydrogen fuel from the tank, forcing a delay in Endeavour's STS-127 launch. The mission's main task was the delivery of the final segment of Japan's Kibo laboratory to the International Space Station. (Tim Jacobs / NASA) Back to slideshow navigation
  15. Lightning strikes

    A giant bolt of lightning hits Endeavour's Florida launch pad on July 10, 2009. Technical problems and severe weather forced five delays in Endeavour's STS-127 launch. (Gene Blevins / Zuma Press) Back to slideshow navigation
  16. Liftoff at last!

    The space shuttle Endeavour rises from Kennedy Space Center's Launch Pad 39A on July 15, 2009, on the STS-127 mission's sixth launch attempt. (NASA) Back to slideshow navigation
  17. Parting glance

    The space shuttle Endeavour is photographed from the International Space Station soon after its departure on July 28, 2009. A Soyuz spacecraft docked at the station is visible in the foreground. (NASA) Back to slideshow navigation
  18. Twilight of the shuttle

    The shuttle Endeavour is silhouetted against different layers of the sunlit atmosphere during its approach to the International Space Station on Feb. 9, 2010. The primary payloads for Endeavour's STS-130 mission were the Tranquility module and the Cupola observation deck and control station. (NASA) Back to slideshow navigation
  19. Check out this view!

    Astronaut George Zamka, Endeavour's commander for the STS-130 mission, peeks out a window of the International Space Station's newly installed Cupola observation deck on Feb. 19, 2010. The Cupola provides an unparalleled view of Earth below. (NASA) Back to slideshow navigation
  20. Tanks for the memories

    The external fuel tank for Endeavour's final mission, STS-134, is transported to the Vehicle Assembly Building at the Kennedy Space Center in Florida on July 14, 2010. STS-134's main payload is the $2 billion Alpha Magnetic Spectrometer, an international physics experiment. (John Raoux / AP) Back to slideshow navigation
  21. The view from above

    The space shuttle Endeavour is lowered into place for attachment to its external fuel tank and solid rocket boosters in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida on March 1, 2011. (NASA via Getty Images) Back to slideshow navigation
  22. Greeting the day

    The sun rises as photographers gather on a hill to take pictures shortly after the shuttle Endeavour's arrival at Kennedy Space Center's Launch Pad 39A on March 11, 2011. (Roberto Gonzalez / Getty Images) Back to slideshow navigation
  23. Into the clouds

    Photographers track the space shuttle Endeavour's ascent as it pierces the clouds and disappears after launch from NASA's Kennedy Space Center in Florida on May 16. (Craig Rubadoux / Daytona Beach News-Journal via AP) Back to slideshow navigation
  24. Godspeed, Endeavour!

    Spectators react as the space shuttle Endeavour lifts off from NASA's Kennedy Space Center in Florida on May 16. Hundreds of thousands of people watched the start of the next-to-last space shuttle flight. (Scott Audette / Reuters) Back to slideshow navigation
  25. Above the clouds

    Stefanie Gordon captured this remarkable picture of the space shuttle Endeavour rising above Florida's cloud cover on May 16 while she was on a commercial flight from New York to Palm Beach, Fla. (Stefanie Gordon / for msnbc.com) Back to slideshow navigation
  26. The last spacewalk

    NASA astronaut Greg Chamitoff holds a handrail during the fourth and last spacewalk conducted by the shuttle Endeavour's crew at the International Space Station on May 27. Chamitoff and astronaut Michael Fincke (visible in the reflections from Chamitoff's helmet visor) transferred an inspection boom system, completing U.S. assembly of the station. The May 27 outing marked the last scheduled spacewalk to be conducted by a space shuttle crew. (Nasa T.V. via EPA) Back to slideshow navigation
  27. Night passage

    Backdropped by a nighttime view of Earth and the starry sky, the space shuttle Endeavour is seen docked to the International Space Station on May 28. (NASA via Reuters) Back to slideshow navigation
  28. Landing in the dark

    The space shuttle Endeavour lands for the last time at NASA's Kennedy Space Center in Florida on June 1, 2011. The touchdown capped Endeavour's 16-day mission to deliver a $2 billion science experiment to the International Space Station on NASA's next-to-last shuttle flight. (Joe Skipper / Reuters) Back to slideshow navigation
  29. Blastoff into history

    A NASA poster pays tribute to Endeavour and its space missions over the past two decades. The shuttle is shown rising to orbit, with patches for each of its missions laid out in a spiral. The HMS Endeavour, which inspired the spaceship's name, is shown at lower right. At upper left, pictures of Endeavour are framed in the windows of the Cupola. The background image depicts the nebula NGC 602 as seen by the Hubble Space Telescope, which was first serviced by Endeavour in 1993. (NASA) Back to slideshow navigation
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    Above: Slideshow (29) Shuttle Endeavour, this is your life
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    Slideshow (12) Month in Space: January 2014

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