The History of Shuttle Launch Delays
Minutes before launch its fourth launch scrub, the space shuttle Endeavour waits for liftoff on Launch Pad 39A on July 12, 2009.
Credit: NASA/Scott Andrews.

This story was updated at 10:00 p.m. EDT.

CAPE CANAVERAL, Fla. - NASA?s latest launch delay for the space shuttle Endeavour on Monday marked the fifth failed attempt to get the beleaguered mission off the ground. The tally may seem high, but it is not the record for the most vexed shuttle flight.

That title belongs to two NASA missions, the STS-73 flight in 1995 and the STS-61C in 1986, both aboard the shuttle Columbia. Those missions each endured six scrubbed launch attempts and lifted off on the seventh try, according to space history and artifacts expert Robert Pearlman, who founded the Web site collectSPACE.com and is a SPACE.com partner.

If NASA can successfully blast off Endeavour on Wednesday evening, its sixth time will be a charm. The shuttle would have to miss two more launch attempts and lift off on the eighth try to take the title for most scrubbed mission. Endeavour?s new launch time is late Wednesday at 6:03 p.m. EDT (2203 GMT).

Launch scrub lowdown

Endeavour was originally scheduled to launch June 13, and is now running just over a month late. That delay pales in comparison to earlier missions, some of which were held back for years after the Challenger and Columbia disasters, according to NASA. The agency officially marks launch scrubs by how many times a shuttle is fueled, not the number of launch date changes, a NASA spokesperson said.

A 2007 analysis of shuttle launch delays by the Associated Press found that the NASA spacecraft launched about 40 percent of the time. The AP analysis found that of the 118 shuttle flights that had flown at the time, 47 lifted off on time. More than half of the delays were caused by technical malfunctions, while foul weather made up about a third of the delays, the Associated Press reported then.

NASA has launched 126 shuttle missions, including eight flights which have lifted off since the 2007 AP analysis. The space agency currently plans to launch eight more flights by September 2010 to complete construction on the International Space Station.

Endeavour?s STS-127 mission is NASA?s third shuttle flight of 2009. The shuttle Atlantis launched toward the Hubble Space Telescope on May 11 on the first actual try, but the mission had been delayed since Fall 2008 due to a non-shuttle failure on the telescope. The shuttle Discovery lifted off on March 15 after a four-day delay due to a hydrogen gas leak similar to Endeavour?s.

The price of launch delay

Repeated stalls aren't just frustrating, but expensive.

For every one-day scrub when a shuttle mission is called off after its external tank has been loaded with fuel, NASA spends about $1.3 million, said NASA spokeswoman Candrea Thomas. Paying for the wasted liquid hydrogen and liquid oxygen propellants costs about $500,000, and $700,000 goes toward paying personnel, she said.

Over time, repeated delays can have a ripple effect across NASA?s later shuttle missions, since the launch schedule must sometimes shift to accommodate a difficult flight.

Endeavour?s launch delays have already prompted NASA to delay the following shuttle flight, STS-128 aboard Discovery, by a few weeks. But overall, it should not affect the agency?s plan to finish space station construction and retire its three-orbiter fleet next year, mission managers have said.

Endeavour's flight plans were foiled twice in June by a gaseous hydrogen leak, which has since been repaired, and three times by weather. Plans to launch on Saturday were abandoned to allow more time for ground crews to investigate possible lightning damage from strikes that occurred the afternoon before. Sunday and Monday's liftoff attempts were both cancelled because of thunderstorms that approached Kennedy Space Center here, threatening both Launch Pad 39A where Endeavour stands, and the Shuttle Landing Facility which must remain clear for an emergency landing if needed.

NASA hopes Endeavour can launch Tuesday, but must replace a disconnected thruster cover on the shuttle's nose in time. If that is not possible, NASA may aim for Wednesday, if the Russian Federal Space Agency agrees to postpone a planned launch of an unmanned cargo ship. The STS-127 mission is a space station construction trip to deliver spare parts and the last segment of the Japanese Kibo lab.

SPACE.com is providing continuous coverage of STS-127 with reporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed. Live launch coverage will begin at 1:30 p.m. EDT (1730 GMT).