Shuttle Discovery returns to launch pad after tank repairs

 With repairs to its external tank complete, engineers began hauling the shuttle Discovery back to launch pad 39A Monday evening for work to ready the ship for blastoff Feb. 24 on a flight to deliver critical spare parts, supplies and a final U.S. module to the International Space Station.

Carried by a powerful crawler-transporter, Discovery and its mobile launch platform began slowly rolling out of NASA's Vehicle Assembly Building at 7:58 p.m. EST, witnessed by scores of Kennedy Space Center workers who gathered nearby to watch what is expected to be Discovery's final trip to the pad. The shuttle reached the launch complex and was secured at 2:53 a.m. Tuesday.

"I have full confidence we've done everything we need to do on that tank," Stephanie Stilson, the engineer in charge of Discovery's ground processing, told CBS News. "Seeing those guys work and knowing how hard they worked to do the modifications, I have confidence in the way the shuttle program works and the fact that they're always investigating and asking more questions, more so than I've ever heard in the past."

Shuttle program managers plan to conduct a flight readiness review Feb. 10, followed by an executive-level review by senior NASA managers Feb. 18. Assuming no additional problems develop, the agency hopes to restart Discovery's countdown at 3 p.m. Feb. 21, setting the stage for launch Feb. 24 at 4:50:19 p.m.

NASA originally hoped to launch Discovery on its 39th and final flight Nov. 1, but the mission was repeatedly delayed, first by relatively minor technical problems that pushed launch to Nov. 5 and then by a gaseous hydrogen leak in a vent arm attached to the external tank.

The hydrogen leak was quickly resolved, but engineers also discovered cracks in structural rib-like "stringers" in the shuttle's external tank that triggered what turned into a nearly four-month delay.

The stringers are used in the ribbed "intertank" compartment of the external tank that separates the liquid oxygen and hydrogen sections. Engineers initially found four stress-relief fractures in two adjacent stringers on the side of the tank facing the shuttle that apparently were the result of exposure to the extreme low temperature -- minus 423 degrees Fahrenheit -- of liquid oxygen.

Engineers repaired those cracks at the pad by splicing in pristine stringer segments and attaching "doublers" to provide additional strength.

After an instrumented fueling test Dec. 18, Discovery was hauled back to the Vehicle Assembly Building for X-ray inspections of the backside of the tank, which engineers could not carry out at the pad. Additional cracks were found in three stringers, prompting NASA managers to order installation of "radius-block" doublers on most of the remaining intertank stringers.

A detailed analysis of the cracks found to that point indicated manufacturing tolerance issues and problems with a specific batch of aluminum-lithium alloy used in most of the 108 intertank stringers that left them more brittle than usual and more susceptible to stress-relief fractures.

Testing showed the radius-block modifications would provide the required margin of safety, easing concerns about the tank's structural integrity and the possible loss of foam insulation during the climb out of the dense lower atmosphere that could pose a threat to the shuttle's fragile heat shield.

When all was said and done, the five cracked stringers were repaired using a combination of doublers and radius blocks and 94 were modified with radius blocks alone. Nine stringers were not modified, one because of access issues and eight others because they were made from a different lot of aluminum-lithium alloy.

As if the crack problem wasn't enough of a headache for NASA, one of Discovery's crew members -- flight engineer Timothy Kopra -- was injured in a bicycle mishap in Houston Jan. 15. He was replaced by veteran astronaut Stephen Bowen, who will take Kopra's place in two planned space walks.

Bowen and his crewmates -- commander Steven Lindsey, pilot Eric Boe, Nicole Stott, Michael Barratt and spacewalker Alvin Drew -- plan to fly to the Kennedy Space Center on Feb. 20 for the start of their countdown to launch.

NASA Ends 30 Years of Shuttle Flights

 The Space Shuttle Discovery is scheduled to launch from Cape Kennedy in February to begin its final journey into space. The mission, the 133rd of the Shuttle fleet, is one of only three remaining flights in a program that has spanned three decades and sent over 300 humans into space. Since 1981, five Space Shuttle Orbiters have carried communications, defense and scientific satellites into space, acted as orbiting laboratories for scientific, medical and technological research and have been posts for observing Earth weather patterns as well as climate and ecological changes. Space shuttles have brought the Hubble telescope to orbit, built the International Space Station (ISS) and helped humans learn to live and work in the harshest and most unforgiving environment they have ever faced.

A presidential mandate in 2004, following the disintegration of Columbia, instructed NASA to retire the Shuttle by 2010 and begin work on a program to send humans back to the moon. NASA developed Project Constellation and successfully test-launched the new Ares rocket in October 2009. Unfortunately, President George W. Bush failed to provide the funding needed to reach the goals he had set. When President Obama and the Augustine Commission reviewed the Bush plans, they considered them unfeasible under the current NASA budget. Rather than providing the funding necessary, however, Obama canceled Constellation and sent NASA in a "New Direction" wherein private companies would begin developing the next generation earth-orbit launch vehicle, allowing NASA to focus on designing more advanced spacecraft to reach deep space.

The Obama plan faced much criticism because of its vague and distant goals and reliance on foreign nations to send humans to the ISS. Many NASA employees, past and present, expressed concerns that the private sector is not advanced enough to conduct spaceflight operations yet. Some astronauts who have come out in support of the plan — most notably Buzz Aldrin, who, along with Neil Armstrong, became one of the first men to land on the moon in 1969 — have emphasized its importance to the private sector as a driving force for American business and ingenuity.

Recent attempts in Congress to alter the "New Direction" plan, combined with the results of the 2010-midterm elections, leave the future of American spaceflight very much in question. Recent successes in the private spaceflight sector show some hope for this plan, but without any specific goals and far too much reliance on a new industry, NASA is on thin ice. For the first time in American history, we will be ending a manned space program without having one to take its place. At this crucial turning point, it is important to look back at the Shuttle and the programs before it, to honor their contributions to this nation and the world and to emphasize the importance of scientific discovery, research and exploration to humanity. All this is best expressed through the words of the select few who have traveled beyond our planet.