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NASA: 50 Years of Exploration

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The Human Factor

    By Roger D. Launius and Chuck Oldham

    Gemini twins - The Gemini VII spacecraft (astronauts Frank Borman and James Lovell) viewed from Gemini VI (carrying astronauts Wally Schirra and Thomas Stafford) during NASA’s first space rendezvous on Dec. 15, 1965. During their mission, Borman and Lovell lived in cramped quarters for 14 days.NASA's first launch of astronauts into space on May 5, 1961, was the beginning of a wondrous age of exploration. In nearly 150 separate missions spanning the Mercury, Gemini, Apollo, Skylab, Apollo-Soyuz Test Project and Space Shuttle programs, astronauts have engaged in sophisticated scientific experiments, complex engineering tasks, heroic voyages to the moon and no less significant cooperative programs with international partners. All of these activities have been critical in advancing America’s progress in what President John F. Kennedy called “the new ocean” of space.

    The first step was Project Mercury, conducted between 1961 and 1963. The Mercury Seven astronauts – Scott Carpenter, Gordon Cooper, John Glenn, Gus Grissom, Wally Schirra, Alan Shepard and Deke Slayton – became household names and heroes in the public’s eyes. Project Mercury, the astronauts, and the American space exploration program were destined to be something extraordinary in the nation’s history, and the astronauts reaped “perks” such as an exclusive and lucrative contract from Life magazine for their stories, and the Chevrolet Corvettes leased to them for $1 a year. Schirra preferred European sports cars and bought a Maserati instead.

    Band of brothers - Using parachutes for protective clothing, the original seven Mercury astronauts underwent survival training at Stead Air Force Base in Nevada. From left to right: Gordon Cooper, Scott Carpenter, John Glenn, Alan Shepard, Gus Grissom, Wally Schirra and Deke Slayton.Glenn, as befitted his image as the straight arrow of the Mercury Seven, preferred to keep the fuel-efficient little German-made NSU he had bought used.

    The first suborbital mission by Shepard was a shakedown cruise for the hardware and procedures necessary to fly in space. Gus Grissom’s repeat performance proved successful, but NASA lost the capsule in the Atlantic when it flooded with seawater. Years later the book and film The Right Stuff suggested that Grissom had blown the hatch of the capsule, whether deliberately or by mistake. But as Schirra proved later on his own Mercury flight, the recoil from the plunger activated to blow the hatch would badly bruise whatever body part was used to trigger it, and Grissom hadn’t a mark on him after his flight.

    On Feb. 20, 1962, Glenn became the first American to circle the Earth, making three orbits in his Friendship 7 Mercury spacecraft. The flight was not without problems. Glenn flew parts of the last two orbits manually because of an autopilot failure and left his normally jettisoned retrorocket pack attached to his capsule during re-entry because of concerns about a loose heat shield.

    Safely home - Gemini VIII astronauts Neil Armstrong and David Scott with Navy divers after their splashdown in the Pacific Ocean on March 17, 1966. Their mission was cut short after their Gemini spacecraft began rolling at an alarming rate.Glenn’s flight provided a healthy increase in national pride, making up for at least some of the earlier Soviet successes. The public, more than celebrating the technological success, embraced Glenn as a personification of heroism and dignity. A portrait of a smiling Glenn was featured on the cover of Time magazine with the headline, “The Space Race is GO.”

    Three more successful Mercury flights took place during 1962 and 1963. Scott Carpenter made three orbits on May 20, 1962, and, on Oct. 3, 1962, Schirra flew six orbits. The capstone of Project Mercury was the May 15-16, 1963, flight of Gordon Cooper, who circled Earth 22 times in 34 hours. The program had succeeded in accomplishing its purpose: to successfully orbit a human in space, explore aspects of tracking and control, and learn about microgravity and other biomedical issues associated with spaceflight.

    Welcome sight - With a half-Earth in the background, Apollo 11 command module pilot Michael Collins photographs the lunar module ascent stage shortly before his reunion with moonwalkers Neil Armstrong and Buzz Aldrin.Today, Project Gemini is not as well known as Mercury or Apollo, but without it, there would have been no Apollo moon landings. Gemini missions proved the concepts of rendezvous and docking in space, long-duration spaceflight, and extravehicular activity. Gemini’s astronauts flew side by side in two ejection seats beneath hatches that could be opened for spacewalks. The spacecraft’s orbital maneuvering rockets allowed it to truly be “flown” in orbit, a capability that was vital to completing their missions. Grissom had worked so closely with contractor McDonnell Aircraft in designing and building Gemini that the other astronauts called it the “Gusmobile.”

    Following two unoccupied orbital test flights, the first operational mission took place on March 23, 1965. Grissom commanded the mission, with John Young accompanying him. The next mission, flown in June 1965, stayed aloft for four days, and astronaut Ed White performed the first American extravehicular activity, or spacewalk. This was the world's second spacewalk after the Soviet Union’s Alexei Leonov. White left the depressurized Gemini through one of its two purpose-built hatches and returned to the spacecraft the same way, while, as the world learned many years later, Leonov had endured an extremely hazardous spacewalk through a jury-rigged inflatable spacelock grafted to the side of the Voskhod 2 spacecraft. Although the Soviet Union risked much to be first in such endeavors, NASA was purposefully perfecting the techniques and technology that would take Americans to the moon.

    Triumphant return - Apollo 11 astronauts Michael Collins, Buzz Aldrin and Neil Armstrong, showered with ticker-tape in New York City’s Canyon of Heroes (August 1969).Eight more Gemini missions followed through November 1966. In a triumphant demonstration of orbital rendezvous techniques on Dec. 15, 1965, the Gemini VI crew of Schirra and Thomas Stafford rendezvoused with the orbiting Gemini VII less than six hours after launch, and flew to within inches of the spacecraft housing Jim Lovell and Frank Borman.

    “There seems to be a lot of traffic up here,” Schirra radioed to mission control.

    “Call a policeman,” Borman replied.

    While the crews made it look easy, in fact, the orbital rendezvous was a difficult and exacting process that nevertheless proved the concept that would allow the Apollo program to make it to the moon and back. Gemini VI and VII were maneuvered, as Schirra later put it in his book Schirra’s Space, “window to window and nose to nose” close enough to wave to each other through the portholes and read Schirra’s “Beat Army” sign meant in jest for Borman, the sole West Point man among the three Navy pilots of the two spacecraft. Later, to note the flight’s proximity to the holiday season, Stafford reported “a satellite going from north to south, probably in a polar orbit. … Looks like he might be going to re-enter soon. Stand by one … You might just let me try to pick up that thing.” Then, the Gemini VII astronauts and mission control were treated by Schirra and Stafford to the strains of "Jingle Bells," performed on harmonica and sleigh bells, the first musical performance in space.

    Hubble servicing - Astronaut Story Musgrave on the space shuttle’s Remote Manipulator System and Jeffrey Hoffman, inside the shuttle’s payload bay, during their Hubble Space Telescope servicing mission in December 1993.Gemini VIII was an altogether different kind of mission, with only one of two primary tasks accomplished. However, a mission failure proved the importance of having humans aboard NASA spacecraft. Gemini VIII was to rendezvous and dock with an Agena target vehicle. Astronauts Neil Armstrong and David Scott performed a flawless rendezvous and docking with the Agena, marking the first time two spacecraft had docked in orbit. All seemed well but for a small yawing motion of the docked spacecraft. As soon as Armstrong corrected the movement, it began again. Both astronauts concluded that the Agena’s automatic control system thrusters were causing the problem, so Scott sent the Agena a command to shut them down. Instead of curing the problem, the yaw increased, and now, in addition to the yaw, the docked spacecraft began to roll together at an increasing rate. They used the Gemini’s thrusters to slow the rates enough to undock, Scott hitting the emergency release and Armstrong backing the Gemini away.

    Instead of easing, the movements grew more violent. The Agena, as it turned out, hadn’t been the problem. The problem was a stuck thruster aboard the Gemini capsule itself, and the roll rate was so rapid that loose items in the cockpit flew up and stuck to the bulkheads. Armstrong was worried that the spacecraft might come apart under the stress, and Scott thought that he might soon black out. Because the relay station in Zanzibar was shut down, it was 15 minutes until the astronauts could communicate with mission control again.

    “We have serious problems here,” Scott called when they were once more in contact. “We’re – we’re tumbling end over end up here. We’re disengaged from the Agena.” There was little mission control could do. Armstrong finally had to use Gemini VIII’s reaction control system thrusters to slow and finally stop the roll.

    Saving Skylab - Astronaut Joseph Kerwin during his June 7, 1973, spacewalk with Pete Conrad to repair Skylab.“Neither of us thought that Gemini might be the culprit,” Armstrong said years later in a NASA oral history interview, “because you could easily hear the Gemini thrusters whenever they fired. They were out right in the nose, in the back. Every time one fired, it was just like a popgun, ‘crack, crack, crack, crack.’ And we weren’t hearing anything, so we didn’t think it was our spacecraft.”

    Mission rules stated that use of the reaction control system mandated an immediate return to Earth. After 11 hours in space and the first successful docking in orbit, the two astronauts in Gemini VIII splashed down in the western Pacific, to be picked up three hours later. Without Armstrong and Scott’s expertise and experience, and the capability of actually maneuvering their spacecraft, they might have perished.

    Four more flights followed Gemini VIII. Despite problems great and small encountered on virtually all of the missions, the program achieved its goals. As a technological learning program, Gemini had been a success, with successful spacewalks, rendezvous and docking in orbit, and long duration missions its hallmark. The United States had chosen to go to the moon in 1961 as part of a Cold War endeavor to best the Soviet Union in space activities. The Apollo program succeeded spectacularly in the lunar landings because of effective leadership, creative engineering, heavy monetary investment and heroic efforts on the part of astronauts, engineers, scientists and many others. But the combination of a deadline to get men to the moon before the end of the decade and the practical problems of constructing the most complicated spacecraft yet meant there were many early problems. Grissom, for one, was so disgusted with Apollo’s engineering difficulties that he famously hung a lemon from the Apollo simulator at Cape Canaveral.

    Special delivery - The space shuttle Endeavour (STS-118, August 2007) delivering a third starboard truss segment, S5, supplies inside the SPACEHAB module (center of payload bay) and the external stowage platform 3 to the International Space Station.On Jan. 27, 1967, tragedy struck when fire broke out in the command module as the unfueled Saturn 1-B sat on Pad 34 during a routine test. Gus Grissom, Roger Chaffee and Ed White were killed, trapped as the fire roared through in the pure oxygen atmosphere of the capsule. The result was a thorough investigation that found deficiencies in the spacecraft and shortcuts in procedures that would have to be remedied if the program was to move forward. More than 1,000 individual wiring changes were made to the spacecraft, along with a revision of the hatch design, replacement of flammable materials and protection of plumbing and wiring. Apollo 7’s orbital shakedown confirmed that this most complex craft ever built was truly the state of the art and ready to go to the moon.

    While the Apollo 8 mission was planned to test the lunar module in orbit, the spindly-legged Grumman moon lander was not yet ready for flight. Borman, Lovell and William “Bill” Anders, the primary crew for the Apollo 8 mission, planned to fly in Earth orbit, but at the highest levels, the Apollo 8 mission was undergoing a metamorphosis. With fears that the Soviets would yet get a manned spacecraft to the moon before Apollo, NASA leadership had been discussing the possibility of sending the Apollo 8 crew around the moon.

    Although it would not achieve the goal of a moon landing, the mission would at least, in part, fulfill President Kennedy’s goal, and would certainly do so before the Russians. It was, for NASA, a considerable risk, but a calculated one, and the astronauts were game. No human had flown much more than 800 miles above Earth. Apollo 8 would travel 250,000 miles to the moon, the first time man had traveled beyond Earth’s gravity.

    9. (caption for three photos – 9a, 9b, 9c) Lost heroes Members of the three astronaut crews whose sacrifice will always be honored by the men and women of NASA. Top, left to right: Apollo 1 crew members; Edward White, Gus Grissom, and Roger Chaffee. Center, left to right: The STS-51L Challenger crew members; Ellison Onizuka, Mike Smith, Christa McAuliffe, Dick Scobee, Greg Jarvis, Ron McNair and Judy Resnik. Above, left to right: Space shuttle Columbia (STS-107) crew members; David Brown, Rick Husband, Laurel Salton Clark, Kalpana Chawla, Michael Anderson, Willie McCool and Ilan Ramon.The Apollo 8 astronauts became the first humans to see the far side of the moon, orbit in its gravity and see the entire Earth from space. After their third lunar orbit, as the astronauts emerged from behind the moon, they finally had time to look back at the half disc of Earth as it rose over the lunar horizon. Borman took a quick black and white photo of a sight no one had seen before, momentarily annoying Anders, as every shot had been programmed before the flight. He was worried about wasting film. But when he saw the blue half disc of Earth above the lifeless moon, he took two color shots himself. One remains among the most famous photographs ever taken, bringing home to those on Earth the incredible beauty and fragility of the planet as the astronauts saw it.

    On Christmas Eve, the astronauts made a live television broadcast from lunar orbit. The crew described the moon and even pointed the camera out the spacecraft windows for the benefit of the viewers at home. Borman had thought long and hard about what to say during that broadcast, and for the conclusion, the astronauts read from the Book of Genesis: “In the beginning God created the heavens and the Earth…,” Anders began. Lovell and Borman each read a passage, and just before Apollo 8 disappeared behind the moon, Borman signed off: “And from the crew of Apollo, we close with a good night, good luck, a Merry Christmas and God bless all of you – all of you on the good Earth.” More than a billion people watched the unforgettable broadcast. Flight Director Gene Kranz, off duty in mission control, was moved to tears.

    Apollo 9 thoroughly tested the lunar module, command module and service module in Earth orbit. Apollo 10 made the second trip to the moon, this time with the lunar module along for the ride. The lander, named Snoopy, was flown by Tom Stafford and Gene Cernan to within 8.6 miles of the lunar surface. These two missions confirmed the time had come for a lunar landing.

    It came during the flight of Apollo 11. The descent to the lunar surface was only the final step in accomplishing the task set out by President Kennedy, but in the approximately 12 minutes it took to cover that distance, billions around the world, and in mission control, watched with their hearts in their mouths. Apollo 11’s lunar module, named Eagle, overshot its landing site and experienced a number of computer alarms, and astronauts Armstrong and Aldrin had to manually fly the lander to a suitable area, using all but the last few seconds of fuel before they would have had to abort. Finally, at 4:18 p.m. Eastern time on July 20, 1969, Eagle’s landing pads touched the moon. “OK, engine stop,” Aldrin said, technically the first words spoken from the lunar surface. “Houston, Tranquility Base here,” Armstrong called. “The Eagle has landed.” Those were the words everyone remembered.

    After checkout, Armstrong set foot on the surface, telling millions who saw and heard him on Earth that it was “one small step for a man – one giant leap for mankind.” Aldrin soon followed him out, speaking of the moon’s “magnificent desolation.” The two plodded around the landing site in the one-sixth lunar gravity and planted an American flag, but omitted claiming the moon for the United States (as had been routinely done during European exploration of the Americas). They collected soil and rock samples and set up scientific experiments. The next day they launched back to the Apollo capsule orbiting overhead and began the return trip to Earth, splashing down in the Pacific on July 24.

    The flight surpassed the excitement felt in the early 1960s during the first Mercury flights and set the stage for later Apollo landings. An ecstatic reaction enveloped the globe. Ticker tape parades, speaking engagements, public relations events and a world tour by the astronauts created good will both in the United States and abroad. Five more lunar landing missions followed at approximately six-month intervals through December 1972, each of them increasing the time spent on the moon and the sophistication of the experiments undertaken, except, of course, for Apollo 13.

    So much has been written and said about Apollo 13 that its story has become a mixture of fact and myth. What is undeniable is that what was technically a mission failure was one of NASA’s finest hours, with the agency’s best and brightest finding a solution to bringing three astronauts and a crippled spacecraft home. Once again, people across the world were glued to television sets and radios, feeling an extraordinary connection to three lonely astronauts a long way from home. Unfortunately, that connection wasn’t sustained for the rest of the Apollo program, despite the fact more knowledge was being gained, with more benefit to humanity, than in the earlier missions. The last three Apollo missions used a lunar rover vehicle to travel in the vicinity of the landing site. That significantly increased the scientific return from humanity’s first ventures to the moon. By that time, however, the attentions of many Americans had turned away from the space program, and Apollo would never achieve the goal of 10 moon landings originally planned.

    Trailblazers - In space shuttle missions during the 1980s (clockwise from top left) Sally Ride, Guy Bluford, Ellison Onizuka and Franklin Chang-Diaz became the first woman, African-American, Asian-American and Hispanic-American astronauts to fly in space.Perhaps the one good thing to result was the Skylab program. Built within the third stage of one of the three leftover Saturn V boosters, Skylab was an orbiting laboratory with an interior volume equal to that of a small house. Astronauts could conduct experiments in life science, earth science and solar physics with Skylab’s Apollo telescope mount. Skylab roared aloft aboard a Saturn V on May 14, 1973, and reached the desired orbit at 270 miles above Earth. However, the station’s micrometeoroid shield had ripped off during the ride into orbit, taking one of the solar panels with it, and trapping the other against the side of the lab with debris. With little electrical power and temperatures climbing inside the lab to 130 degrees, Skylab was dying.

    Astronauts Pete Conrad, Joseph Kerwin and Paul Weitz were supposed to follow the lab into orbit on March 15, but now they stayed on the ground with NASA engineers, determining how to fix the problems. “The Skylab problem was the supreme test for the engineering team,” Kerwin said years later in a NASA oral history interview. “Both the contractors and the civil servants joined together as one, and they figured out what the problem was, and they developed three different solutions to the problem, in terms of what can we bring up that the crew can deploy over the warm side of Skylab to cool it down so that we can get on with the mission, A. And, B, how can we get that solar panel unstuck?”

    The answer to A was three different sunshields developed to be deployed in space, each using different systems to stretch a piece of Inconel (the gold foil-like material that coated the outside of the descent stage of the Apollo lunar module) over the lab compartment. The solution to B was “a pretty eclectic collection of aluminum poles that could be connected together, and a Southwestern Bell Telephone Co. tree-lopper with brown ropes to open and close the jaws,” Kerwin said. The backup crew had tried each of the solutions in the Neutral Bouyancy Simulator at Marshall Space Flight Center in Alabama and found them feasible. The mission launched on May 25, 1973, and during an initial fly-around, Weitz sent television images back to mission control to show the problem with the solar panel.

    After a soft docking with Skylab, the crew undocked, depressurized and opened the Apollo’s hatch to make the first attempt to free the solar panel. Weitz stood in the open hatch and hooked the debris with a “shepherds crook” while Kerwin held his ankles.

    “[Conrad would] fly it up within a couple of feet of the solar panel,” Kerwin recalled later, “and Paul would put his shepherd’s crook out there and get it hooked under the free edge. He’d pull back, and the two spacecraft would come together, and there would be jet firings everywhere. Conrad would say, ‘Oh my God.’ We never collided or anything, but it was fairly sporting.”

    Trying to cut the strap trapping the solar panel didn’t work either. There simply wasn’t enough leverage. After giving up on Plan A, their attempt to hard dock with Skylab failed. The crew had to depressurize the Apollo’s cabin and make repairs to the hatch before backing off and successfully docking. Deploying the solar shield was, by contrast, relatively simple. Housed in a case built to deploy a science experiment through a hatch on the lab, the Inconel solar shield worked almost perfectly, with only one of four stiffeners failing to completely deploy. Immediately, temperatures in the lab began to fall.

    The next few days were spent setting up equipment and getting the station up and running. On June 7, Kerwin and Conrad performed the spacewalk to release the solar panel, exiting the station with the tree lopper attached to the end of a 25-foot pole. After several abortive attempts to cut the aluminum strap pinning the solar panel shut while tethered to the station, they spotted an eyebolt closer to the panel. Kerwin tied himself in to the eyebolt and got enough leverage to cut the strap. Then, the two had to wriggle under a rope Conrad had rigged and stand up to break loose a frozen hinge. When it gave, the two were catapulted “ass over teakettle into outer space,” as Kerwin put it. Fortunately, both were still tethered to the station. The three astronauts had carried out the first inspection/repair mission in space, saving Skylab to make a host of contributions to human knowledge.

    NASA entered a new era in human spaceflight in 1981 when the first space shuttle reached orbit. With much public excitement, Columbia, the first orbiter that could be flown in space, lifted off from Kennedy Space Center, Fla., on April 12, 1981. The flight took place six years after the last American astronaut had returned to orbit following the cooperative U.S./U.S.S.R. Apollo-Soyuz Test Project in 1975. After 36 orbits during two days in space, Columbia landed like an aircraft at Edwards Air Force Base in California, successfully accomplishing the first such landing of an orbital vehicle in history.

    The shuttle greatly expanded the opportunity for human spaceflight. After a crew of three for Apollo missions, the shuttle routinely flew seven, and NASA inaugurated a program to fly individuals associated with specific payloads and experiments. NASA was able to expand the astronaut complement to non-pilots and to women and minorities during the shuttle era, and by February 2008, the number of Americans flown stood at 259 men and 39 women. In June 1983, Sally Ride became the first American woman to fly in space, aboard STS-7, and in August 1983, Guion Bluford became the first African-American astronaut to fly in space during STS-8. Also, Ellison Onizuka became the first Asian-American to fly in space on the STS-51-C mission in January 1985, and Franklin Chang-Diaz became the first Hispanic-American in space on the STS-61-C mission in January 1986. In addition, astronauts from several other nations flew aboard the shuttle.

    The shuttle undertook a range of new and different activities, launching its first two commercial communication satellites on the STS-5 mission in November 1982, and deployed 24 additional communication satellites through 1985. At the time of the loss of the space shuttle Challenger, NASA had a backlog of 44 orders for commercial launches. But those missions did not always go as planned. On STS-41B in 1984, the boost engines of both satellites failed to fire correctly, leaving the Palapa-B2 and Westar-6 communications satellites in useless low Earth orbits. Fortunately, the shuttle offered another unique capability – one that could not be matched by an expendable vehicle – for retrieving those satellites. In November 1984, under contract to insurance companies, the space shuttle Discovery retrieved Palapa-B2 and Westar-6 and returned them to Earth. The insurance companies already had paid for the loss of the satellites, so both were refurbished and resold to new customers. This capability, as well as others such as in-orbit repair and redeployment, changed the nature of spaceflight.

    All in a day's work - Astronaut Scott Parazynski during his daring 7-hour, 19-minute spacewalk to repair the solar array on the International Space Station during the STS-120 mission on Nov. 3, 2007.The tragic loss of Challenger during its launch on Jan. 28, 1986, when a leak in one of the two solid rocket boosters detonated the main liquid fuel tank, changed everything. Seven crew members – Francis Scobee, Michael Smith, Judith Resnik, Ronald McNair, Ellison Onizuka, Gregory Jarvis and Christa McAuliffe – died in this accident.

    The shuttle program went into a 30-month hiatus while NASA redesigned the hardware and the shuttle’s management structure. When the space shuttle returned to flight with the launch of Discovery on Sept. 29, 1988, it was a safer program than before. Despite the removal of commercial and Department of Defense payloads, the shuttle had a surprisingly busy launch schedule afterward.

    Numerous increasingly sophisticated missions followed throughout the 1990s. For example, the four Hubble Space Telescope servicing missions proved exceptionally difficult but were impressively executed. After Hubble was launched in 1990, many believed that a spherical aberration in the mirror of the telescope would cripple it. Because of the difficulties, in December 1993, NASA launched shuttle Endeavour on a dramatic repair mission to insert new components to correct for the aberration and service its other instruments.

    During a weeklong mission, Endeavour’s astronauts conducted five spacewalks and successfully completed all programmed repairs to the spacecraft. The first reports from the Hubble spacecraft afterward showed the images were more than an order of magnitude crisper than those obtained before. For this outstanding effort, NASA’s Hubble Space Telescope Recovery Team received the Robert J. Collier Trophy for “outstanding leadership, intrepidity and the renewal of public faith in America’s space program by the successful orbital recovery and repair of the Hubble Space Telescope.” Three additional servicing missions extended the capabilities of the telescope beyond the first decade of the 21st century, and another mission in 2008 was scheduled to extend the life of the telescope yet another decade.

    Bridge to the future - The Orion crew exploration vehicle will begin sending crews to the International Space Station by the middle of the next decade. Photo Credit: Lockheed MartinAs of February 2008, there have been 121 space shuttle missions, and the extent of activities on each has been impressive. They have included International Space Station construction and logistics missions, pure science missions, national security missions, collaborative flights with Russian cosmonauts and satellite deployments, retrievals and repairs.

    Each of the shuttle’s flights has undertaken some scientific experiments, including the deployment of important space probes to other planets, periodic flights of the European-built “Spacelab” science module, and a dramatic set of Earth observations for more than 25 years. One stunning science experiment occurred with the flight of the Shuttle Radar Topography Mission in 2000. This aboard Endeavour obtained elevation data on a near-global scale to generate the most complete high-resolution digital topographic data ever created. Virtually the entire land surface between plus or minus 60 degrees latitude was mapped. It has been an enormously significant data set for scientists.

    The shuttle also delivered satellites for Earth observation and beyond. Since the Challenger accident in 1986 there have been seven major scientific payloads that required the unique capabilities of the shuttle. It launched the Magellan spacecraft to Venus, the Galileo spacecraft to Jupiter and the Ulysses spacecraft to study the sun. The shuttle also deployed the Compton Gamma Ray Observatory, the Hubble Space Telescope, the Upper Atmosphere Research Satellite and the Chandra X-ray Telescope.

    In addition, 16 Spacelab and SPACEHAB missions could not have been conducted by any other spacecraft. These shuttle flights allowed significant scientific work to be accomplished, and shuttle advocates often cite these activities as important contributions that justified the cost of the program. Spacelab, a sophisticated laboratory built by the European Space Agency, fit into the shuttle’s cargo bay and enabled a complex array of scientific experiments to be completed. Others note that more than 2,000 life sciences experiments have flown aboard the shuttle, as well as numerous other science activities in orbit.

    Without question, from the first flight to the present, the shuttle has been an important component of NASA’s human spaceflight effort, and recognized as such by the American people and the larger international community. Its final set of missions has involved the construction of the International Space Station and its periodic resupply. The first two space station components, the Zarya and Unity modules, were launched and joined together in orbit in late 1998 during the STS-88 mission. Through February 2008, 24 shuttle missions have flown to the station.

    On Oct. 31, 2000, the first crew to occupy the International Space Station inaugurated a new era in space history. When American astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev lifted off in a Russian Soyuz spacecraft from the Baikonur Cosmodrome in Kazakhstan, it represented the last day in which there were no humans in space. Shepherd was commander of the three-person Expedition One crew, the first of several crews to live aboard the space station for periods of about four months.

    On Feb. 1, 2003, tragedy struck again, as shuttle Columbia and its crew Rick Husband, Willie McCool, David Brown, Laurel Clark, Michael Anderson, Kalpana Chawla and Ilan Ramon, were lost in a re-entry accident minutes from touchdown. NASA grounded the shuttle fleet after the accident, but wanted to return to flight as soon as possible, and did so in July 2005. As 2005 ended, most concerns over the future of the shuttle seemed settled.

    Since Columbia, the shuttle program has flown six missions, four of which continued construction of the space station. One of the most important in demonstrating NASA’s “human factor” was the STS-120 mission. After one of the International Space Station’s solar arrays was damaged while being relocated from the top of the station to the far port end of the main truss, repairs had to be made to the torn solar panels. Astronaut Scott Parazynski, perched precariously at the very end of the swaying orbiter boom had to cut away the array guidewire and install five 5-foot “cufflinks” across the tears in the solar array.

    Parazynski’s spacewalk took place farther from the station than any previous spacewalk ever attempted. His tools and metal joints in his spacesuit were wrapped in insulating tape, and fellow astronauts Pamela Melroy and Doug Wheelock watched his clearances from the live electrical circuits. After a 7-hour, 19-minute spacewalk, the array was redeployed successfully, the only casualty being a pair of needle-nose pliers lost in Earth orbit. An Aviation Week and Space Technology article placed the achievement on a par with the Apollo 13 and Skylab repair missions.

    Today, NASA is planning for the retirement of the space shuttle after 25 years of orbital missions, and building the Orion crew exploration vehicle, which will be powered by the Ares I launcher.

    NASA’s human spaceflight effort is fast coming to a crossroads as it transitions from the space shuttle to Orion. After 50 years of stunning success, much has been accomplished, and much remains to be done. The next 50 years will be just as exciting as what has gone before.