The Space Shuttle Program

It will revolutionize transportation into near space, by routinizing it.

—President Richard M. Nixon, January 5, 1972

The U.S. space shuttle was supposed to make space travel a routine and frequent occurrence. Its conceivers envisioned shuttles regularly transporting humans and cargo back and forth between Earth and a fleet of orbiting space stations. The shuttle was expected to be much cheaper than previous spacecraft, because it would be reusable. This would mean low operational and maintenance costs and a quick turnaround time between flights. It was predicted to bring in lots of money by hauling satellites into space for paying customers. The shuttle was going to be part of a massive transportation system and open up space the way the railroad opened up the western frontier of the United States during the nineteenth century.

This vision never became a reality. Shuttle flights did not become routine, common, or frequent. In “Shuttle Missions” (February 23, 2008, http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/list_main.html), the National Aeronautics and Space Administration (NASA) indicates that between 1981 and 2007 space shuttles flew only 120 times, averaging less than 5 flights per year. Two shuttles exploded, killing fourteen crewmembers. Besides the human cost, the program experienced high operational and maintenance costs. Long turnaround times prevented the shuttle from flying frequently. However, the flights that took place did achieve many accomplishments. They put probes and observatories into space and were essential for building the International Space Station (ISS).

Nevertheless, many people believe that the United States has wasted too much time and money on a shuttle program that does not deliver what it promised. In January 2004 President George W. Bush (1946–) announced his own vision for the nation’s space program. It focuses on trips to the Moon and Mars and calls for ending the Space Shuttle Program (SSP) by 2010. Regardless, the dream of routine access to space remains an elusive one.

THE POST-APOLLO VISION

In the early 1960s NASA planners envisioned a space station program as the next step after Apollo. It was assumed that the United States would establish large space stations in orbit around Earth and possibly outposts on the Moon. In fact, NASA hoped to put at least one twelve-person space station in Earth orbit by 1975. This would require a new type of reusable space plane to carry cargo and personnel to and from the station.

However, these grand plans did not mesh with the political, cultural, and technological realities of the times. By the late 1960s the nation was heavily engaged in the Vietnam War (1954-1975). Domestic unrest and social issues dominated the political agenda into the early 1970s. Richard M. Nixon (1913-1994) was president of the United States from 1969 to 1974. According to historians, Nixon was not interested in pursuing any large and expensive vision for space exploration. T. A. Heppenheimer notes in The Space Shuttle Decision: NASA’s Search for a Reusable Space Vehicle (1999) that in a March 1970 statement on space policy, Nixon said, “We must build on the successes of the past, always reaching out for new achievements. But we must also recognize that many critical problems here on this planet make high priority demands on our attention and our resources.” NASA’s budget was severely cut, and plans for space stations were put on hold.

Regardless, NASA did not give up on the shuttle program. It began promoting the project as a transport business, rather than as an exploratory adventure. NASA officials argued that a shuttle could haul government and commercial satellites into space in a cost-effective manner because it would be reusable. Furthermore, the shuttle astronauts could service and repair these satellites as needed. The shuttle was touted as an investment because it would make money from commercial customers and save the government money on launching satellites for weather, science, and military purposes.

This argument was successful. In CAIB Report: Volume 1 (August 2003, http://caib.nasa.gov/news/report/pdf/voll/full/caib_report_volume1.pdf), the Columbia Accident Investigation Board explains that in 1971 NASA was given a $5 billion budget over a five-year-period for the development of a shuttle program. This was later increased to $5.5 billion. NASA assured the White House that each shuttle would be good for one hundred flights and that each flight would have an average cost of $7.7 million. The planners agreed that the shuttle program would have to operate about fifty missions a year to satisfy demand for satellite launches. It was expected that the shuttle program would be operational by the end of the decade.

Heppenheimer suggests that President Nixon had strong political motives to approve the shuttle program. A presidential election was coming up in 1972, and he wanted to gain favor in states such as Florida and Texas that would benefit from new NASA projects. Also, the Soviet Union had already put the space station Salyut 1 into orbit during 1971. The last Apollo mission was scheduled for 1972. On January 5, 1972, President Nixon announced to the nation that NASA would build a new Space Transportation System based on a new vehicle called a space shuttle.

SPACE SHUTTLE DESIGN AND DEVELOPMENT

Various space shuttle designs had been evolving since the 1950s. The U.S. Air Force had examined several options based on a reusable manned space plane that could be maneuvered in flight and glided to a landing. The best-known program was called Dyna-Soar (short for Dynamic Soaring). The Dyna-Soar concept included an expendable launch vehicle to carry a space plane out of Earth’s atmosphere.

NASA engineers began designing a spacecraft much different from those used during the Apollo program. Apollo capsules and command modules were launched inside long cylindrical rockets. The thrust needed to get these vehicles off the ground was through the center of gravity of each rocket. The rockets were fueled by kerosene and liquid hydrogen-oxygen.

The shuttle design was completely different. At first, engineers hoped to develop a fully reusable vehicle. Budget constraints soon made it obvious that this was not going to be possible. Instead, NASA designed a three-part vehicle for the shuttle:

• A reusable space plane called an orbiter
• An expendable external liquid fuel tank for the orbiter’s three main engines
• A reusable pair of external rocket boosters containing a powdered fuel

Figure 4.1 shows the major components of the space shuttle design. The launch sequence called for the fuel tank and the rocket boosters to be jettisoned away from the orbiter during the ascent phase. The rocket boosters were designed to be recovered and refilled with fuel for the next launch. The external tank was to be jettisoned above Earth’s atmosphere and burn up during reentry.

The orbiter holds the crew compartment and payload bay. (For a typical orbiter layout, see Figure 4.2.) The payload bay measures sixty feet by fifteen feet. The shuttle was designed to transport the orbiter into space 115 to 690 miles above Earth’s surface. This is considered low Earth orbit (LEO).

The orbiter had to be capable of maneuvering while in space and during landing. The early designs were based on the air force’s X-series of high-performance aircraft. Unlike the Apollo capsules, the orbiter was intended to be reusable. It had to land on the ground, rather than splashdown in the ocean. At first, engineers included jet engines on the orbiter for use within Earth’s atmosphere. These proved to be too expensive and too heavy for the structure and were eliminated. Instead, the orbiter was designed to glide through the air to its landing site.

The orbiter was built to carry a crew of seven under normal circumstances, for a typical mission time of seven

days in space. The maximum mission time for this crew number is thirty days (assuming that adequate supplies have been packed). The orbiter was designed to hold up to ten people in an emergency.

One of the most difficult design problems for the orbiter was a thermal protection system that could be reused. Previous spacecraft had been well protected from the intense heat of reentry, but their thermal protection materials were rendered unusable after one reentry. At first, designers hoped to cloak the orbiter in metal plates that could withstand high temperatures. This proved to be too heavy. So the orbiter was built out of light-weight aluminum, and its underside was covered with high-tech thermal blankets and tiles. More than twenty-four thousand individual tiles had to be applied by hand. These light-weight tiles are made of sand silicate fibers mixed with a ceramic material.

The new spacecraft had to be light enough to get off the ground, but large enough to carry military payloads that weighed substantially more than what shuttle engineers had expected. The U.S. Department of Defense (DOD) also wanted the shuttle to be able to fly polar orbits (i.e., orbits crossing over the North and South Poles). This meant that a launching facility on the West Coast was required, so that the shuttle could launch in a southerly direction toward the South Pole. In April 1972

it was decided that the air force would build this facility at the Vandenberg Air Force Base (AFB) in California.

The primary launch facility was authorized at the Kennedy Space Center (KSC) in Florida. The KSC location allowed the shuttle to launch in an easterly direction over the Atlantic Ocean and assume an equatorial orbit (an orbit along lines of latitude near or at the equator).

Figure 4.3 shows the original launch azimuths (angles) planned for the Vandenberg AFB and the KSC. The azimuths were chosen so that launch trajectories did not cross over heavily populated areas or foreign soil. They also ensured that any parts jettisoned from the shuttle during ascent would fall harmlessly into the ocean. It was assumed that the shuttle would land at the Vandenberg AFB, the KSC, or the air force’s White Sands Testing Facility in New Mexico.

The DOD insisted that the shuttle be designed to return to the Vandenberg AFB after only one polar orbit. This was a technological challenge because it meant that the shuttle had to fly more than one thousand miles to the east during reentry. Engineers call this the “cross-range requirement.” To meet this requirement, the shuttle was given delta wings (symmetrical triangular wings designed

for subsonic and supersonic flight) and an enhanced thermal protection system.

NASA had to meet the design demands of the military to keep the project moving forward. However, this added substantially to the development costs for the spacecraft. Most of the design work took place during the mid-1970s, which was a time of high inflation for the U.S. economy. High inflation means that the purchasing power of the dollar goes down. NASA would be designated funds in one year, but by the time those funds were received in the next year, their practical value had decreased.

The original date for the first space shuttle launch was to be March 1978. This date was postponed several times due to budget and equipment problems. The shuttle’s main engines and thermal protection tiles proved to be particularly troublesome. In 1979 President Jimmy Carter (1924-) reassessed the need for the SSP and considered canceling it. According to the Columbia Accident Investigation Board, in CAIB Report: Volume 1, he decided to continue shuttle development because the United States wanted to launch intelligence satellites to monitor the Soviet Union’s nuclear missile program. As a result, the White House and Congress put their support behind the space shuttle. In early 1981 NASA declared that development was complete. The shuttle was “finished” and was only 15% over its original budget.

Table 4.1 lists the major design parameters of the shuttle and the orbiter. Figure 4.4 shows various views of the space shuttle orbiter.

SPACE SHUTTLE FLIGHT PROFILE

The ten panels of Figure 4.5 illustrate the major steps in a space shuttle flight from launch to landing.

Launch

The countdown to launch begins approximately four days before liftoff. During this time many systems checks are conducted on the spacecraft and its components. The flight crew is taken to the orbiter approximately two and a half hours before liftoff and strapped into their seats.

The shuttle is launched in a vertical position, with its nose pointing up. At 6.6 seconds before launch, the three main engines at the rear of the orbiter are ignited. These engines burn fuel contained in the external fuel tank. The external fuel tank includes two separate compartments. Liquid hydrogen is kept in one compartment, and liquid oxygen in the other.

When the countdown reaches zero, the solid rocket boosters (SRBs) are ignited. The SRBs are metal housings filled with solid fuel (aluminum powder and other dry chemicals). Ignition of the SRBs provides the powerful push needed to lift the spacecraft off the ground and overcome the effects of Earth’s gravity during ascent. The ride for the crew is very rough and bumpy while the SRBs are firing. However, the acceleration load on the humans is designed to stay below three Gs. In other words, the force of gravity “pushing” against the crew members as the shuttle accelerates is only three times the force of gravity on Earth.

Approximately two minutes after liftoff, the shuttle reaches a vertical distance of twenty-eight miles and travels at about three thousand miles per hour. At this point, the SRBs are jettisoned away from the vehicle because their fuel has been consumed. The SRBs are equipped with parachutes that open after the boosters have fallen a specified distance. The SRBs splash into the ocean and are retrieved for reuse.

The ride becomes smoother for the shuttle crew after the SRBs are jettisoned. The shuttle’s main engines continue to fire until they have used up all the fuel in the external tank. This occurs at 8.5 minutes after liftoff. At this point, the shuttle is above Earth’s atmosphere and traveling at a speed of five miles per second. The main engines are shut down and, seconds later, the external fuel tank is jettisoned away from the vehicle. The tank burns up during atmospheric reentry. Only the orbiter is left to continue the journey.

Orbit

The shuttle assumes an LEO, typically 150 to 250 miles above sea level, where it travels at about 17,600

miles per hour. It takes the craft approximately forty-five minutes after liftoff to reach its orbit.

The orbiter includes a series of small engines that allow the flight crew to maneuver while in space. These engines comprise the orbital maneuvering system (OMS) and the reaction control system (RCS).

The OMS engines are mounted on both sides of the upper aft fuselage. They provide the thrust needed to make major orbital maneuvers, for example, to move the shuttle into orbit, change orbits, and rendezvous with other spacecraft in orbit. Such instances are called orbit maneuver burns, because the engines are temporarily

ignited to achieve them. The RCS engines are located along either side of the orbiter’s tail and on its nose. They provide small amounts of thrust for delicate and exacting maneuvers.

During orbit the space shuttle crew performs a variety of tasks depending on the mission requirements. The shuttle was designed to carry payloads into space and to serve as a short-term laboratory for science experiments.

The shuttle can carry satellites or heavy equipment needed for space station construction in its large payload bay. Some satellites are intended for LEO, whereas others orbit at much higher distances. Shuttle crews can deploy, etrieve, and service LEO satellites from their spacecraft. Satellites that require higher orbits can also be deployed rom the shuttle. These satellites have built-in propulsion systems that boost them into their orbits once they are a safe distance away from the shuttle.

The payload bay is equipped with a fifty-foot-long robotic arm called the remote manipulator system (RMS). The RMS is also called the Canadarm, because it was developed by Canadian companies. A crewmember operates the RMS from the orbiter flight deck. The RMS is used to move things in and out of the cargo bay and on and off the ISS and to grab and position satellites. In 2005 a fifty-foot-long extension to the RMS was added to the shuttle. The orbiter boom sensor system (OBSS) is equipped with sensors and imaging systems and allows the crew to scan most of the outside of the orbiter for any damage.

The shuttle is equipped with specialized laboratories in which crewmembers can conduct experiments related to astronomy, earth sciences, medicine, and other fields. Most of these experiments take place in pressurized modules specifically designed for shuttle flights. Similar containers called multipurpose logistics modules (MPLMs) are used as cargo vessels to transport equipment and supplies to and from the ISS. Figure 4.6 shows how payloads were configured in the payload bay for a shuttle flight in 2007.

A space shuttle crew normally consists of five members: a commander, a pilot, and three mission specialists. These are all NASA personnel. The commander has onboard responsibility for the mission, the crew, and the vehicle. The pilot assists the commander in operating and controlling the shuttle and may help deploy and retrieve satellites using the RMS. Mission specialists work with the commander and pilot and have specific responsibilities relating to shuttle systems, crew activities, consumables (food and water), scientific experiments, and/or payloads. Mission specialists are trained to perform extravehicular activities (EVAs; space walks) and to operate the RMS.

Besides the commander, pilot, and mission specialists, there may be one or two “guest” crewmembers called payload specialists. Payload specialists are not considered NASA astronauts. They perform specialized functions related to payloads and may be nominated by private companies, universities, foreign payload sponsors, or NASA. Payload specialists can also be foreign astronauts recommended by foreign space agencies.

The crew spends time in the crew module. This 2,325-cubic-foot module is pressurized and maintained at a comfortable temperature to provide what is called a “shirt-sleeve environment.” The crew module includes the flight deck, the mid-deck/equipment bay, and an air-lock. The airlock contains two spacesuits and space for two crewmembers to put on and take off these suits. Spacesuits are required during EVAs.

The flight deck is the top level of the crew module. (See Figure 4.7.) This is where the commander and pilot spend most of their time during a mission. During launch and reentry they sit in the two seats facing the front of the orbiter with the commander on the left and the pilot on the right. The orbiter can be piloted from either seat. Two other crewmembers sit behind these seats further back in the flight deck. Any other crew members sit in the mid-deck section during launch and reentry.

The mid-deck of the crew cabin includes stations for meals, personal hygiene, and sleeping. This area includes the waste management system, a table, and stowage space for gear. In an emergency three additional seats can be placed in the mid-deck crew cabin for reentry. This allows the shuttle to carry ten crewmembers back to Earth. Such a contingency might be needed to rescue astronauts from the ISS.

Reentry and Landing

To reenter Earth’s atmosphere, the shuttle has to decrease its speed by a substantial amount. This is performed via a deorbit burn in which the shuttle is turned upside down with its tail toward the direction it wants to go. The firing of the OMS engines slows the spacecraft down. It then flips over and reenters the atmosphere with the nose pointed up at an angle. (See Figure 4.5.) This ensures that the well-protected underside of the orbiter takes the brunt of reentry heat.

Reentry is a dangerous time for the shuttle. Any failure of the thermal protection system could allow super-hot gases to enter the orbiter. Reentry begins about seventy-six miles above Earth’s surface. Following reentry, the shuttle glides through the air to its landing site.

Emergency Flight Options

The SSP includes a variety of flight options in the event of an emergency. If there is a problem with the main engines up to four minutes after liftoff, the shuttle can undergo a procedure called Return to Launch Site (RTLS) abort. The SRBs and external tank are jettisoned and the orbiter is maneuvered into position to glide back to the launch site. If an RTLS abort is not possible, there is also the option to land the orbiter at an overseas location. This is called a Transatlantic Abort Landing (TAL). There are three TAL landing locations along the western coast of Europe and Africa: Moron, Spain; Ben Guerur, Morocco, and Dakar, Senegal.

If the orbiter launches successfully but cannot reach its intended orbit, then an Abort-to-Orbit procedure is followed. This means that the spacecraft assumes a lower orbit than planned. If the orbiter cannot maintain any orbit, it returns to Earth for reentry and landing. It may travel once around Earth before it does so. This option is called the Abort Once Around.

The final emergency flight option is called the contingency abort. This procedure is undertaken if the orbiter cannot land on a landing strip for some reason. It calls for the orbiter to be put into a glide and the crew to use the in-flight escape system. This includes a pole that is extended out the side hatch door. The crewmembers can then slide along the pole to the end and parachute to the ground.

SSP ORGANIZATION

The SSP is administered and operated by NASA, with the help of thousands of contract employees. Figure 4.8 shows the locations of key NASA and contractor facilities involved in the SSP. Strategic management of the program is handled at NASA’s headquarters in Washington, D.C. This is where major decisions are made about future missions.

The Johnson Space Center (JSC) in Houston, Texas, is home to the operational offices of the program. This office administers the Space Flight Operations Contract, a contract originally signed in 1996 between NASA and the United Space Alliance (a joint venture between the Boeing and Lockheed Martin corporations). The United Space Alliance (2008, http://www.unitedspacealliance.com/) performs the day-to-day operations of the SSP. The original contract included two two-year extension options, both of which were exercised by NASA. The contract expired at the end of September 2006; however, a new contract (Space Programs Operations Contract) was signed and is good through 2010—the expected end date of the SSP. As of 2008 the United Space Alliance employed more than ten thousand people. Most of these people work at the JSC, the KSC, and the Marshall Space Flight Center (MSFC) in Huntsville, Alabama.

The JSC also hosts the mission control center, astronaut training, and shuttle simulation facilities. The KSC supplies the shuttle launch and landing facilities; maintains and overhauls the orbiters; packages components for the orbiter laboratories; and assembles, tests, and refurbishes motors for the SRBs.

The manufacturing contracts for the SSP are overseen by NASA at the MSFC. Major contractors include Boeing, the United Technologies Corporation’s Pratt & Whitney Rocketdyne, Lockheed Martin, and ATK Thiokol Propulsion. These companies manufacture the space shuttle main engines and turbopumps, the external tank, the solid rocket motors, and the reinforced carbon-carbon panels for the thermal protection system. The MSFC is also involved in the research and development of pay-loads that fly on the shuttles.

The shuttles’ main engines and external tanks are tested at NASA’s Stennis Space Center in Bay St. Louis, Mississippi. The Dryden Flight Research Center is located at the Edwards AFB in California. This is the backup landing site for the shuttle.

Other NASA centers assist the SSP by developing or testing shuttle components or fuels at their facilities. The shuttle thermal protection system is developed at the Ames Research Center in Moffett Field, California. The highly toxic fuels called hypergols that are used to run the orbiter’s OMS and RCS engines are tested at the White Sands Test Facility in New Mexico. The orbiter structure is tested in wind tunnels at the Langley Research Center in Hampton, Virginia.

SPACE SHUTTLE MISSIONS

On April 12, 1981, Columbia became the first shuttle to fly into space. The flight’s purpose was to test the shuttle’s systems, and the mission lasted only two days. It was considered a huge success. Three more test flights were conducted during 1981 and 1982, all with the orbiter Columbia. On July 4, 1982, President Ronald Reagan (1911-2004) announced that shuttle testing was completed. The next flight of the shuttle was to begin its operational phase.

Space shuttle flights including the orbiters Columbia, Challenger, Discovery, and Atlantis carried out twenty-four missions before disaster struck.

On January 28, 1986, Challenger broke apart only seventy-three seconds after liftoff. The seven crewmembers who were killed in the accident were Francis R. Scobee (1939-1986), Michael J. Smith (1945-1986), Judith A. Resnik (1949-1986), Ron McNair (1950-1986), Ellison S. Onizuka (1946-1986), Gregory B. Jarvis (1944-1986), and Christa McAuliffe (1948-1986). McAuliffe was a teacher who had been selected for the mission by NASA to capture the imagination of U.S. schoolchildren.

An investigation of the accident revealed that a faulty joint and seal in a solid rocket booster allowed hot gases to escape from the booster and ignite the hydrogen fuel. The resulting explosion tore the shuttle apart. The tragedy brought intense scrutiny and criticism of the SSP from government investigators.

President Reagan appointed a panel called the Rogers Commission to investigate the accident. The commission issued its findings in Report of the Presidential Commission on the Space Shuttle Challenger Accident (February 3, 1986, http://science.ksc.nasa.gov/shuttle/missions/51-1/docs/rogers-commission/table-of-contents.html). The commission complained that the decision to launch Challenger was flawed because of poor communication. The managers making the launch decision did not have access to all the information. For example, they were not aware that some contractor engineers were concerned about the cold weather forecast for the morning of the launch. They feared that cold temperatures might compromise the integrity of the SRB seals. These fears were downplayed by NASA officials and not passed on to those making the launch decision.

Besides problems specific to the Challenger accident, the commission blamed NASA for fostering an overall culture that put schedule ahead of safety concerns. To reduce the scheduling pressure, it was decided that the shuttle would cease carrying commercial satellites and phase out military missions as soon as possible. The air force had hoped to stage the first shuttle launch ever from the Vandenberg AFB in 1986. The Challenger accident and the resulting decision to cease carrying military payloads put an end to these plans. The launch facilities at Vandenberg were dismantled and abandoned, and most of the equipment was transferred to NASA facilities.

NASA explains in Shuttle Triumphs and Tragedies (October 25, 2006, http://aerospacescholars.jsc.nasa.gov/HAS/cirr/ss/2/6.cfm) that a number of organizational changes were made within NASA in response to the Challenger accident. Shuttle management was moved from the JSC to NASA headquarters in Washington, D.C. In addition, NASA created a new office in charge of safety, reliability, and quality assurance. The entire orbiter fleet was grounded and upgraded with new equipment and systems. A new orbiter named Endeavour was built to replace Challenger. A White House committee later estimated that the shuttle disaster cost the nation approximately $12 billion. This included the cost of building a new orbiter.

Table 4.2 provides general information about each orbiter in the shuttle fleet.

The shuttle flew again on September 29, 1988, with the successful launch of Discovery thirty-two months after the Challenger accident. Space shuttles flew eighty-seven successful missions between 1988 and 2002. Then, tragedy struck again. On February 1, 2003, Columbia broke apart during reentry over the western United States. Seven crewmembers were killed: Rick D. Husband (1957-2003), William C. McCool (1961-2003), David M. Brown (1956-2003), Kalpana Chawla (1962-2003), Michael P. Anderson (1959-2003), Laurel B. Clark (1961-2003), and Ilan Ramon (1954-2003). Ramon was a colonel from the Israeli air force who traveled on the shuttle as a guest payload specialist. Following the accident, the shuttle fleet was grounded for more than two years.

THE COLUMBIA ACCIDENT

Immediately after the Columbia disaster, President Bush appointed a panel to investigate what happened. The panel was called the Columbia Accident Investigation Board (CAIB). In August 2003 the CAIB released its report, CAIB Report: Volume 1, which concluded that the most likely cause of the accident was a damaged thermal protection tile on the orbiter’s left wing. Video clips of the launch showed a large piece of foam falling off the external tank and striking the left wing eighty-two seconds after liftoff. This piece of foam fell a distance of only fifty-eight feet. However, the space shuttle was traveling very fast when this occurred, so the foam struck with extreme force.

NASA engineers knew about the foam strike, but were unsure whether it had caused any damage. Even though Columbia was in orbit, some engineers suggested that high-resolution photographs be taken of the orbiter using DOD satellites or NASA’s ground-based telescopes. This suggestion was overruled by NASA officials, who believed that the foam strike did not endanger mission safety.

During reentry to Earth’s atmosphere, one or more damaged thermal tiles along the left wing likely allowed hot gases to breach the shuttle structure. Aerodynamic stresses then tore it apart. Debris from the shuttle was found spread along a corridor across southeastern Texas and into Louisiana.

The CAIB was extremely critical of the entire SSP and complained that NASA shuttle managers had once again become preoccupied with schedule, rather than safety. Beginning in 1998 the SSP was under tremendous pressure to meet construction deadlines for the ISS. Nearly every shuttle flight undertaken between 1999 and 2003 was in support of the ISS.

The CAIB recommended a number of major changes within the SSP and within NASA management. One of the recommendations was that NASA develop a means for the shuttle crew to inspect the orbiter while docked at the ISS and repair any damage discovered. Such a procedure might have saved the Columbia crew. Implementation of the so-called Safe Haven program was recommended before any future shuttle flight.

THE RETURN TO FLIGHT

Soon after publication of the CAIB report, the NASA administration appointed a Return to Flight (RTF) Task Group to assess the agency’s progress of implementing CAIB recommendations before shuttle flights were resumed. The task group was an independent advisory group consisting of more than two dozen non-NASA employees with expertise in engineering, science, planning, budget, safety, and risk management. Its members were granted access to NASA facilities and meetings as the agency regrouped and developed new safety strategies.

The most critical technical issue was debris shedding from the external tank during ascent and subsequent damage to the orbiter’s thermal protection system. The primary focus was on eliminating external tank debris and using devices to detect debris impacts. The procedures were changed for applying foam insulation to the external tank, and quality control and inspection programs were expanded. Equipment changes were implemented to provide a smoother surface for foam application and to impede ice formation.

NASA decided that the first two shuttle flights after the Columbia disaster would be “test” flights to assess the effectiveness of new safety changes. Discovery was selected for the first RTF mission. More than one hundred cameras were installed on exterior spacecraft surfaces and at ground locations to provide an array of observation angles during ascent. The fifty-foot-long OBSS was installed on the end of the shuttle remote manipulator system to allow visual inspection of the wing tips and most of the orbiter underbelly while in flight. (See Figure 4.9.)

A team of image analysts was assembled at the JSC to inspect the images for any signs of damage. Dozens of sensors were installed on the wing edges of Discovery to take temperature readings and record the time and location of any debris impacts.

On July 26, 2005, Discovery launched from the KSC for a fourteen-day mission. The orbiter, with a seven-member crew onboard, docked with the ISS and unloaded equipment there. Three space walks were conducted including one in which astronauts tested new repair techniques for the thermal protection system. The shuttle landed safely at the Edwards AFB on August 9, 2005. NASA proclaimed the first RTF a success. However, camera footage showed that foam debris had shed from the external tank during shuttle ascent. Luckily, the debris did not hit the orbiter. NASA and the public realized that the hazard that had doomed Columbia had not been eliminated, but merely avoided by chance this time.

The Final Report of the Return to Flight Task Group (July 2005, http://www.nasa.gov/pdf/125343main_RTFTF_final_081705.pdf) was released to the public after the landing of Discovery. However, the task force’s findings were communicated to NASA directors before launch. The task force reported that NASA had “met the intent” of twelve of the fifteen most critical recommendations made by the CAIB. (See Table 4.3.) The other three recommendations were considered “so challenging” that NASA was unable to comply with them before the RTF. The three problem areas were:

• External tank debris shedding
• Orbiter hardening
• Thermal protection system inspection and repair

The task force noted that “it has proven impossible to completely eliminate debris shedding from the External Tank. The hard fact of the matter is that the External Tank will always shed debris, perhaps even pieces large enough to do critical damage to the Orbiter.” Technical and time limitations also prevented NASA from successfully hardening orbiter surfaces to prevent damage from debris impacts and from proving that a damaged thermal protection system could be repaired while a shuttle was in orbit.

On July 4, 2006, the second RTF mission began with the launch of Discovery on a thirteen-day mission. Discovery carried the Leonardo MPLM to the space station. The mission also involved crucial tests of the orbiter’s thermal protection system and testing of techniques for inspecting and protecting the system. Over one hundred high-definition cameras recorded the launch and ascent phases so the images could be scoured for signs of damage to the orbiter. In addition, the shuttle crew used the OBSS to carefully inspect the craft while it was docked at the ISS. Fortunately, no significant damage was detected. Discovery landed safely on July 17, 2006.

MISSIONS SINCE THE RETURN TO FLIGHT

As of December 2007, the space shuttle had undertaken five successful missions since the second RTF flight. All the missions were dedicated to ISS assembly. Extensive imaging and visual inspections were conducted during each shuttle flight to identify any damage to the thermal protection system due to foam debris impacts during launch. In all cases the orbiters were deemed structurally sound for reentry. A freak hail storm in February 2007 damaged Atlantis as it sat on the launch pad for an expected launch of STS-117 in March 2007. That mission had to be delayed for nearly three months, seriously affecting the shuttle’s future launch schedule. Prelaunch sensor problems postponed the scheduled launch of Discovery in December 2007. That mission was not expected to take place until February 2008, at the earliest.

ACCOMPLISHMENTS OF THE SSP

A historical summary of all the space shuttle missions conducted as of December 2007 is presented in Table 4.4.

NASA refers to each shuttle flight using a Space Transportation System (STS) number. Thus, STS-1 was the first shuttle flight into space. NASA assigns numbers to space shuttle flights in the order in which they are planned (or manifested). There is typically a period of several years between the time a mission is planned and the time of its scheduled launch. During this period

priorities can change, and missions are often reshuffled or canceled. This explains why the STS numbers in Table 4.4 do not always match the flight order number. For example, Columbia’s flight in 2003 was called STS-107, yet it was actually the 113th flight of a space shuttle. The missions numbered STS-108 through STS-113 wound up launching before STS-107 because they moved up in priority as launch time approached.

Shuttle flights have deployed more than fifty satellites for military, governmental, and commercial clients. In addition, three interplanetary craft were launched from shuttles: the Magellan spacecraft that traveled to Venus, the Galileo spacecraft that traveled to Jupiter, and the Ulysses spacecraft that traveled to the Sun. Shuttles have also deployed important observatories into space, including the Hubble Space Telescope (HST), the Compton Gamma Ray Observatory, the Diffuse X-Ray Spectrometer, and the Chandra X-Ray Observatory.

The shuttle has carried more than three million pounds of cargo and over six hundred crewmembers into space. Hundreds of scientific experiments have been conducted in orbit. Shuttle crews have also serviced and repaired satellites as needed, particularly the HST. Between 1995 and 1998 shuttles docked nine times with the Russian space station Mir. Flights to construct the ISS began in 1998. Shuttles carried major pieces of the ISS into space and traveled to the station twenty-three times through the end of 2007.

Despite these accomplishments, the shuttle has not met many of the original goals that NASA set for the program. NASA planners had promised that the shuttle would fly dozens of times per year. As shown in Figure 4.10, the most shuttle flights ever accomplished in one year was nine flights in 1985. For the twenty-seven-year period from 1981 through 2007, the shuttle averaged fewer than five flights per year.

NASA also promised that each shuttle orbiter would be good for one hundred flights. Figure 4.11 shows the number of flights achieved by each orbiter in the shuttle fleet as of December 2007. Discovery has made thirty-four flights, the most of any orbiter. Challenger made only ten flights before it was lost. Columbia made twenty-eight flights during its lifetime.

There are only three orbiters left in the fleet: Discovery, Atlantis, and Endeavour. As of 2008 Discovery was seventeen years old, and the other two were not much younger. Most of the original facilities and infrastructure built on the ground for the SSP are more than three decades old. To make matters worse, Hurricane Katrina inflicted severe damage to two crucial SSP facilities during the summer of 2005: the Michoud Assembly Facility in New Orleans, Louisiana, and the Stennis Space Center in Bay St. Louis, Mississippi.

The CAIB report was extremely critical of the SSP overall. Even though the panel acknowledged the shuttle as an “engineering marvel”with a wide range of abilities in Earth orbit, it nevertheless concluded that “the Shuttle has few of the mission capabilities that NASA originally promised. It cannot be launched on demand, does not recoup its costs, no longer carries national security payloads, and is not cost-effective enough, nor allowed by law, to carry commercial satellites. Despite efforts to improve its safety, the Shuttle remains a complex and risky system.”

THE FUTURE OF THE SSP

In January 2004 President Bush announced a new vision for the future of the U.S. space program. It calls or NASA to send astronauts to the Moon by 2020 and to Mars after that. This would require a completely new spacecraft because the space shuttle was not designed to fly farther than a few hundred miles from Earth. The SSP would be ended by 2010, assuming that existing U.S. commitments to build the ISS are completed by then. The billions of dollars spent each year on the SSP and the ISS would be transferred to the new projects, which would also be allocated new funds.

During the grounding of the space shuttle fleet, American ISS crewmembers were transported aboard Soyuz rockets by the Russian Federal Space Agency (Roscosmos). NASA was unable to pay for this service because of the Iran Nonproliferation Act of 2000, which forbids payment of “extraordinary” amounts of money from the United States to Russia until it is proven that Russia is not sharing with Iran any technology related to missiles or weapons of mass destruction. To raise badly needed funds, Roscosmos charged “space tourists” millions of dollars to fly to the ISS. In November 2005 the U.S. Senate approved amendments to the Iran Nonproliferation Act allowing NASA to pay Roscosmos until 2012 for launches supporting the ISS.

Space shuttle difficulties affect other ongoing missions. For example, NASA originally planned to send shuttle astronauts to service the HST in 2006. However, in January 2004 the NASA administrator Sean O’Keefe (1956-) announced that the 2006 HST servicing mission had been canceled due to safety concerns. The HST orbits far from the ISS, and NASA feared that a shuttle sent to service the HST would not be able to make it to the ISS in case an emergency developed.

Cancellation of the shuttle servicing mission virtually ensured that the HST would malfunction to the point of

being unusable. Then it will lose its orbit and fall to Earth sometime between 2011 and 2014. This caused an uproar in the scientific community and resulted in intense lobbying to NASA to reinstate the mission. In October 2006 Michael D. Griffin (1949–), the new NASA administrator, announced that the agency was reinstating the HST servicing mission. As of January 2008, this mission had not taken place, but it was listed on the proposed shuttle flight manifest. (See Table 4.5.) NASA plans to accomplish thirteen shuttle flights before the program ends in 2010.