Feb. 1 , 2003: Space Shuttle Columbia disintegrates during re-entry.

Aug. 26, 2003: The Columbia Accident Investigation Board (CAIB) issues its final report, concluding that a combination of politics, budgets, schedule pressure and managerial complacency were the underlying causes of the Columbia tragedy. The direct technical cause is identified as a hole in the leading edge of Columbia’s wing that was caused by a large piece of insulating foam from the orbiter’s external fuel tank that broke off during liftoff . In response to the CAIB report, NASA forms the Stafford Covey Task Group led by veteran astronauts Tom Stafford and Richard Covey. Its mission is to monitor NASA’s efforts to comply with the CAIB recommendations.

Aug. 27, 2003: NASA Administrator Sean O’Keefe vows to implement all of the CAIB recommendations report.

Sept. 8, 2003: NASA issues a Return-to-Flight implementation plan and targets March or April 2004 for the next shuttle launch.

Sept. 18, 2003: NASA managers acknowledge that a new safety rule requiring all future shuttle launches to occur only during daylight hours will likely lead to more and longer launch delays.

Sept. 23, 2003: Nine members of NASA’s Aerospace Safety Advisory Panel resign.

Sept. 25, 2003: Arthur Zygielbaum , one of the nine members who resigned from the Aerospace Safety Advisory Panel, tells Congress the international space station is vulnerable to a serious accident because of poor communication between Russian and American engineers on the program, and that the station’s safety flaws are being ignored the way NASA ignored the problem of foam falling off the shuttle’s external tank.

Oct. 21, 2003: A Russian Soyuz spacecraft, filling in for the grounded U.S. shuttle, delivers a new crew to the international space station for the second time since the Columbia accident.

Oct. 29, 2003: Retired U.S. Navy Adm. Harold Gehman, the CAIB chairman, tells Congress that NASA’s response to concerns about deteriorating conditions on the international space station is a step in the right direction, but that the U.S. space agency has a long way to go to reform the way it manages risky programs.

Oct. 31, 2003: O’Keefe says some NASA employees still have not accepted the idea that the agency has to change the way it does things.

Nov. 18, 2003: Jim Halse ll, an astronaut coordinating NASA’s return-to-flight effort, says the next shuttle flight will occur “when it happens” and that if NASA does not make the September 2004 target date, “that’s okay.”

Nov. 19, 2003: NASA reorganizes the Aerospace Safety Advisory Panel along lines the agency says more closely resemble the way it was when it was first formed in 1967.

Jan. 14, 2004: U.S. President George W. Bush unveils a new vision for NASA that calls for retiring the shuttle fleet in 2010 and preparing for a return to the Moon and eventual astronaut missions to Mars.

Jan. 20, 2004: The Stafford Covey Task Group issues an interim report that says NASA is a long way from returning the shuttle fleet to flight status, and has been less than forthcoming with detailed plans in response to the CAIB’s recommendations.

Feb. 12, 2004: O’Keefe says an autumn 2004 shuttle launch is unlikely.

Feb. 28, 2004: NASA releases an internal audit that concludes the agency is doing a poor job keeping track of breakdowns and other problems aboard the international space station and also failed to maintain a complete set of blueprints of space station equipment.

April 30, 2004: NASA issues its Implementation Plan for Space Shuttle Return to Flight and Beyond Revision 2, concluding that “considerable progress” has been made in the return-to-flight efforts. Wayne Hale, deputy manager of the shuttle program, says: “Right now, our launch date is based on fixing the tank and having some management reserve in that schedule for any surprises that we may encounter as we go down that fix path to make a launch in the spring” of 2005.

Aug. 4, 2004: NASA decides it will have rescue shuttles on standby, ready to launch for the first two post-Columbia shuttle flights in case the initial orbiter encounters serious problems.

Aug. 13, 2004: NASA announces there will be a camera on Space Shuttle Discovery’s external tank to record the launch and any foam that breaks away from the tank.

Sept. 8, 2004: O’Keefe tells Congress the agency will spend $2.2 billion on space shuttle safety improvements through 2008. The return-to-flight effort is estimated at $1.1 billion to $1.45 billion.

Oct. 2, 2004: NASA officials say a March or April 2005 shuttle launch is no longer feasible because of the damage caused by three separate hurricanes at Florida’s KSC.

Oct. 28, 2004: Dan Murphy, president of ATK, the company that makes the space shuttle’s solid rocket motors, tells Wall Street analysts he believes the shuttle will be flying until at least 2014 despite NASA’s official retirement date of 2010. Some NASA officials, meanwhile , are talking about retiring the shuttle before 2010.

Oct. 29, 2004: NASA officially retargets return to flight for between May 12 and June 3, 2005.

Dec. 12, 2004: O’Keefe acknowledges in an interview with the newspaper Florida Today that he may leave NASA to become chancellor of Louisiana State University. He resigns the following week.

Dec. 16, 2004: The Stafford Covey Task Group concludes that NASA has complied with eight of the 16 recommendations in the CAIB report.

Dec. 28, 2004: NASA officials say that after an 18-month investigation and redesign, the external fuel tank that will be used for the flight of the shuttle Discovery is ready to be shipped to Cape Canaveral, Fla.

Jan. 25, 2005: NASA outfits Discovery with a new inspection boom that is attached to the shuttle’s robot arm. The boom will be used to inspect the orbiter for damage, particularly any possible damage to the tiles on its underside.

Jan. 27, 2005: NASA employees pause to pay tribute to the 17 astronauts who died in the Apollo 1 fire (Jan. 27, 1967), the Challenger launch accident (Jan. 28, 1986) and Columbia’s re-entry.

Jan. 30, 2005: The Stafford Covey Task Group concludes there are no major hurdles to NASA’s return-to-flight effort, but expresses concern that astronauts still do not have the ability to make some repairs in orbit.

Feb. 11, 2005: The Center for Science and Technology Policy Research at the University of Colorado issues statistics that show the shuttle program has cost $145 billion over its lifetime, including $112 billion since the first flight. The average mission cost is $1.3 billion, a figure that had dropped to $750 million in the years immediately preceding the Columbia disaster. The estimated cost of post-Columbia missions is $1.3 billion, assuming 22 flights between 2005 and 2010.

Feb. 11, 2005: NASA selects three experiments for Discovery’s astronauts to practice methods for patching holes in orbit. Two repair kits will be on hand in case their ship is actually damaged by launch debris.

March 11, 2005: President Bush names Michael Griffin, head of the space department at Johns Hopkins University’s Applied Physics Laboratory and a former NASA exploration chief, to be the agency’s next administrator.

March 18, 2005: An effort to fix a problem with chafing that threatens to damage shuttle wiring delays the rollout of Discovery to the launch pad.

April 2, 2005: NASA is late delivering information to the Stafford Covey Task Group and agency officials acknowledge the delay could lead to postponement of the planned launch in May.

April 7, 2005: Discovery is rolled out to its launch pad even after NASA officials discover a three-centimeter-long hairline crack in the foam on the external tank on the opposite side of where the tank is attached to the orbiter. NASA officials decide there is no need to repair the crack because even if a piece of foam did break off from that location it would not strike the shuttle.

April 14, 2005: NASA announces plans to test Discovery’s redesigned external tank by filling it with super-cold fuel to see if any ice forms on the outside of the structure, a rare event in the history of the program and the first such test since 1998. The same day, the U.S. Senate confirms Griffin’s nomination.

April 18, 2005: Griffin says he will leave “absolutely no stone unturned” in deciding whether it is safe to launch Discovery.

April 20, 2005: NASA officials tell Congress they will accelerate development on a shuttle replacement vehicle. The agency delays Discovery’s launch until no earlier than May 22.

April 22, 2005: The New York Times reports that internal NASA documents obtained by the newspaper suggest the agency is downplaying the risk posed by debris from the shuttle’s external tank, and show at least three changes in the statistical method used to assess the risk of debris striking a shuttle during launch. NASA officials say in response that they have not relaxed their acceptable risk standards.

April 28, 2005: Griffin tells key members of Congress he has directed the agency to begin making plans for a shuttle mission to refurbish the Hubble Space Telescope, a mission that his predecessor had canceled. He also cautions that a Hubble mission will not be ordered until the agency is satisfied with the results of the first two post-Columbia flights.

April 29, 2005: NASA delays Discovery’s launch until July to address concerns that debris from the external tank could still cause catastrophic damage to the orbiter.

May 7, 2005: NASA officials announce the agency is replacing Discovery’s external fuel tank with one that had been slated for use on the second post-Columbia flight.

May 12, 2005: NASA sends Congress a revised spending plan that cuts funding for a space nuclear power and propulsion development program, some space science missions and a host of international space station experiments to pay for the space shuttle’s return to flight and preparations for a Hubble Space Telescope servicing mission. The same day Griffin acknowledges that the decision to retire the space shuttle in 2010 could affect the assembly and completion of the international space station.

May 20, 2005: NASA officials declare the refueling test of the new external tank a success.

May 23, 2005: Inspectors begin checking Discovery’s landing gear for fractures after cracks are found on the landing gear of the Space Shuttle Atlantis.

June 8, 2005: The Stafford Covey Task Group says NASA has met all but three of the CAIB report’s recommendations for return to flight.

June 24, 2005: NASA officials declare the risk that Discovery will suffer damage from debris during launch is minimal. “This is going to require constant vigilance, but as far as [STS] 114 is concerned, I believe our concerns are put to bed,” John Muratore, NASA’s manager for shuttle systems engineering and integration, said during a teleconference with reporters. “We’re ready to fly.”

June 26, 2005: NASA says it is abandoning development of state-of-the-art tools to inspect aging shuttle wiring, which is susceptible to electrical shorts that could trigger catastrophe. The agency’s inspector general says NASA is putting astronauts at risk and failing to comply with a CAIB recommendation.

June 30, 2005: Gehman says he is fine with NASA resuming shuttle launches in just two weeks, even though the agency still falls short of making three safety improvements he called for in 2003. Discovery’s launch is set for July 13.

July 12, 2005: Discovery is repaired after a window cover falls from the orbiter and damages heat-resistant tile on the left orbital maneuvering system pod at the rear of the vehicle.

July 13, 2005: NASA scrubs Discovery’s launch after one of four sensors in the external tank produces a different reading than the other three.

July 18, 2005: NASA announces Discovery will launch no earlier than July 26 while agency officials continue to search for the cause of the sensor glitch.

July 25, 2005: Sensor glitch does not recur when Discovery is refueled.

July 26, 2005: Discovery successfully launched.

July 27, 2005: Discovery’s crew begins using robot arm to examine wings and tiles for any potential damage. The same day NASA officials announce they will ground the shuttle fleet upon Discovery’s return to Earth because much-larger-than-expected pieces of foam insulation broke off of the external tank during launch. “Until we’ve fixed this, we’re not ready to fly,” Bill Parsons, NASA’s space shuttle program manager, said during a press briefing at Johnson Space Center. “You could say that we’re grounded.”

July 28, 2005: Discovery docks at the international space station.

July 29, 2005: Using the robot arm and a laser-tipped scanner, Discovery’s crew conducts a more up-close inspection of the orbiter’s heat shield. Griffin says he is confident NASA will be able to solve the foam debris problem.

July 30, 2005: Discovery’s crew tests heat shield repairs during first of three spacewalks. NASA extends the mission to give astronauts an extra day to move spare equipment and water into the international space station.

July 31, 2005: In a shuttle program first, NASA officials decide to send a spacewalking astronaut underneath Discovery to remove some loose material jutting out from the orbiter’s heat-resistant tiles.

Aug. 1, 2005: On the Discovery mission’s second spacewalk, astronauts replace a faulty gyroscope needed to keep the space station oriented properly.

Aug. 2, 2005: President Bush calls the Discovery and space station crews.

Aug. 3, 2005: On the mission’s third spacewalk, Discovery’s crew successfully removes the loose material sticking up between some of the orbiter’s heat-resistant tiles. Meanwhile, NASA conducts wind tunnel tests on the ground to determine if a fourth spacewalk is needed to repair a loose piece of insulation near the crew cabin window.

Aug. 4, 2005: NASA decides a fourth spacewalk will not be necessary and clears Discovery for return to Earth.

Aug. 5, 2005: Holding out hope that they can identify the cause of the foam shedding during Discovery’s launch, NASA officials say they will aim to launch Atlantis in the next launch window, but no earlier than Sept. 22.

Aug. 6, 2005: Discovery undocks from the space station.

Aug. 8, 2005: Discovery’s landing is delayed 24 hours because of low cloud cover over the Kennedy Space Center landing strip.

Aug. 9, 2005: Discovery lands at Edwards Air Force Base, Calif., after inclement weather prevents landing in Florida a second straight day.