Space Transportation System

FIELDS OF STUDY: Aerospace Engineering; Spacecraft Propulsion; Space Technology

ABSTRACT: The Space Transportation System program focused on advancing space exploration through a piloted vehicle that would allow reliable, low-cost, and regular travel into space. This goal led to the development of the space shuttle, a partly reusable orbital spacecraft. Over the course of many decades, various space shuttles successfully performed numerous significant space missions. However, the overall success of the program has been debated.

A Brief History

In 1969, with Project Apollo in full swing, US president Richard Nixon set up the Space Task Group to study the United States’ future in space exploration. Sending a human to the moon was only the beginning. The group envisioned a space program that continued the exploration of space with piloted flights. This would benefit humankind through advances in communications, science, technology, navigation, and more. The team felt that by expanding humans’ understanding of the universe, the US space program had the potential to improve the quality of life on Earth.

Because of the success of Project Apollo, the Space Task Group found that the National Aeronautics and Space Administration (NASA) should accept a piloted mission to Mars as a key goal for the space program. They believed that NASA would be able to carry out such a program within fifteen years. Reliable, long-lived, yet low-cost and simpler operational space systems with flexible flight configurations would make this possible. The Space Task Group supported continuing any future robotic space exploration. However, the group proposed that these activities be carried out with the piloted Mars mission in mind for optimal benefit.

The Space Transportation System (STS) was the official name for NASA’s space shuttle program. The name was taken from the Space Task Group’s plan for a system of interrelated, reusable, multipurpose spacecraft. The objective of the STS was to offer NASA an efficient, reusable method of sending astronauts to a permanently piloted space station. Following the Apollo lunar landings, it was important to guarantee a permanent US presence in space. Space shuttles could also be used as satellite delivery vehicles. As a partly reusable, low-Earth orbital spacecraft system, the space shuttle was the only item in the plan that was eventually funded for development. Nixon announced the beginning of NASA’s development of the space shuttle system in January 1972.

Developing a Space Airplane

NASA’s space shuttle system differed from the rocket of the Apollo missions. More technologically advanced, the space shuttle combined attributes of the earlier, rocket-based spacecraft with the transportation qualities of a conventional airplane. The launch configuration and thrust mechanism of the shuttle were also different and more controlled. It was the first winged US spacecraft that could make a horizontal landing on a runway upon its return to Earth.

NASA had initially envisioned a reusable spacecraft that would be operated in two stages. Two piloted winged crafts would have been launched together. The smaller craft would have served as a booster to bring the second craft into orbit. The smaller craft would have then disconnected and landed back on Earth. Due to budget issues, however, NASA ultimately designed the three-part shuttle system used in the missions that would span several decades. Its main components were an orbiter, which held the crew; an external tank (ET), which contained fuel for the main engines; and two solid rocket boosters (SRBs), which gave the shuttle most of its thrust during the beginning of flight. With the exception of the ET, which was disposed of after the launch and burned up in Earth’s atmosphere, all of the components were reused.

The shuttle was the first operational orbital spacecraft that was designed to be reused. It carried payloads (cargo) into orbit, provided the International Space Station (ISS) with crew rotation and supplies, and performed service and repair on satellites. The space shuttle also recovered payloads such as satellites from orbit and carried them back to Earth.

Attributes of the Space Shuttle

The space shuttle was designed to transport cargo into a low orbit about 304 to 528 kilometers (190 to 330 miles) above Earth. The payload was held in a cargo bay measuring 4.6 meters (15 feet) wide and 18.3 meters (60 feet) long. The orbiter could carry a crew of eight people, with the capability of transporting a total of ten people under emergency conditions.

A pair of SRBs provided about 71.4 percent of the thrust the space shuttle needed to lift off the pad. The SRBs were the largest solid-propellant motors to ever be flown. Each booster measured 45.5 meters (149 feet) long and 3.7 meters (12 feet) in diameter. They were also the first solid-propellant motors designed for reuse. The propellant in the SRBs was a mixture of ammonium perchlorate (an oxidizer), aluminum (as fuel), iron oxide (a catalyst), and a polymer to bind the mixture together. This mixture provided a high thrust upon ignition, followed by a reduction in thrust after lift-off. This prevented excessive stress on the vehicle under dynamic pressure. The SRBs were ignited after the verification of the thrust level of the three main engines. The two SRBs also supported the weight of the ET and the orbiter. The boosters were spent in about two minutes and separated from the ET.

The ET contained liquid hydrogen fuel and liquid oxygen oxidizer. This pressurized propellant was supplied to the three main engines of the space shuttle inside the orbiter during lift-off and ascent. The SRBs were later recovered from predetermined points in the ocean so they could be reused on future space flights. Right before the spacecraft was inserted into orbit, the space shuttle’s main engines shut down and the ET was discarded into Earth’s atmosphere. It broke apart upon reentering Earth’s atmosphere and was not recovered. Once the orbiter was clear of the ET, the Orbital Maneuvering System (OMS) engines were initiated. The OMS provided the thrust needed to insert the orbiter into orbit, maneuver once in orbit, and reduce speed upon reentry.

Another unique feature of the space shuttle was a large cargo bay that had doors that opened at the top of the spacecraft. This cargo bay was used to carry the orbiter’s payload. The cargo door configuration allowed for the deployment of large satellites, including the Hubble Space Telescope. The cargo door also allowed for payloads to be captured and returned to Earth. The orbiter had an average payload capacity of 22,700 kilograms (50,045 pounds). This capacity could vary depending on the launch configuration.

Successes and Tragedies

After years of delays, the first orbital test mission began in 1981 with the historic launch of the shuttle Columbia on April 12 from Kennedy Space Center (KSC). It returned safely fifty-four hours later at Edwards Air Force Base. This successful mission proved that the shuttle could fly into orbit, remain in orbit while conducting operations, and return to Earth safely. In 1981 and 1982, this shuttle engaged in three more test flights. The final orbital test flight ended on July 4, 1982, with Columbia completing 95 percent of its objectives and the first scientific experiment of the shuttle program. US president Ronald Reagan declared that Columbia would be fully operational for its next flight. The space shuttle program’s first operational flight began at KSC on November 11, 1982.

From 1982 to 1985, additional space shuttles were added to the program’s fleet—Challenger, Atlantis, and Discovery. The shuttles ascended from the launch pad at KSC an average of four or five times annually. Most of the missions ended at Edwards Air Force Base. The program seemed to be a huge success.

On January 28, 1986, Challenger broke apart seventy-three seconds after launch. Americans watched in horror as the shuttle exploded. There were no survivors. The program was put on hold for more than two years while a commission formed by President Reagan investigated the accident. It was determined that the failure of an O ring in the joint between two segments of the SRBs had caused the disaster. The commission also found numerous management failures within NASA. Many managers were aware of the issue but did not take proper precautions. A review revealed that there was pressure to announce that the shuttle was operational and that this had led to system resources being stretched too far. The tragedy of the Challenger accident led to many tangible changes within NASA and the shuttle program.

On September 29, 1988, the program resumed flights with the launch of Discovery. For the next several years, the program was successful. Flights were more productive in terms of payload, while the number of missions increased to an average of six per year. On July 30, 1991, US president George H. W. Bush and Mikhail Gorbachev, leader of the former Soviet Union, agreed that their space agencies would work together. In February of 1994, a joint program commenced. The first Russian flew on a space shuttle that month, the first American went aboard the Russian Mir space station in 1995, and the space shuttle Atlantis docked at the station that same year. Millions of people around the world breathed a collective sigh of relief—the Cold War was officially over. Russia and the United States would go on to collaborate on other important projects that involved the space shuttles, including the International Space Station (ISS).

The shuttle program lost its second vehicle in February 2003. Sixteen minutes before its scheduled landing, Columbia disintegrated over Texas; all seven crew members died. In 2004, US president George W. Bush declared that all shuttles in NASA’s STS would be retired. Atlantis, Discovery, and Endeavor (the replacement for Challenger) flew regularly from 2006 to 2011, especially to finish putting the ISS together. Atlantis touched down for the final time at KSC on July 21, 2011, marking the end of the program. Discovery was installed at the Smithsonian National Air and Space Museum in 2012.

Significance

Piloted flights using the shuttle led to many advances in science and technology. Astronauts on Discovery placed the Hubble Space Telescope into orbit. Satellites placed into orbit by shuttles have enhanced national security. In addition, the shuttles were responsible for carrying remaining pieces and necessary equipment to the ISS. This station has fostered international cooperation and allowed humans to live and work in space for lengthy periods of time. With the entire program reportedly costing billions of dollars, however, some critics saw the shuttle program as an unnecessary loss of life and a disappointing, limiting distraction. They also argued that it was a poor use of resources based on a design that was unrealistic.

NASA has begun working to develop new technologies and modes of space travel for human exploration to Mars and beyond. Among these is the Space Launch System (SLS), which was in the testing phase as of 2022. NASA plans to use the SLS to power the Artemis mission, which is scheduled to return humans to the moon sometime in the mid-2020s. The SLS has an initial maximum thrust of about 8.8 million pounds, 15 percent more than the Saturn V rocket that took humans to the moon. The SLS is designed to allow improvements over time; more advanced stages are expected to achieve a maximum thrust about ten times that of the space shuttle's main engines.

Principal Terms

• external tank: a container that held fuel in the form of liquid hydrogen and an oxidizer in the form of liquid oxygen. The tank supplied the pressurized fuel and oxidizer to the three main engines of the space shuttle during lift-off and ascent.
• Orbital Maneuvering System: a system that provided the thrust needed for orbit insertion, transfer, and deorbit via two smaller engines.
• propellant: a chemical mixture contained in the space shuttle’s solid rocket boosters. When ignited, it helped thrust the shuttle into space.
• solid rocket boosters: two solid-propellant motors that provided the space shuttle with the main thrust needed to lift it off the launch pad and into space against the pull of Earth’s gravity.

Bibliography

Archaeological Consultants. NASA-Wide Survey and Evaluation of Historic Facilities in the Context of the US Space Shuttle Program: Roll-Up Report. Sarasota: Archaeological Consultants, 2008. PDF file.

Dowling, Stephen. "What Caused the Space Shuttle Columbia Disaster?" BBC Future. BBC, 30 Jan. 2015. Web. 1 July 2015.

Mosher, Dave. "Space Shuttle in Extreme Detail: Exclusive New Pictures." National Geographic. Natl. Geographic Soc., 16 Apr. 2012. Web. 1 July 2015.

"Overview." NASA. NASA, 7 Apr. 2002. Web. 29 May 2015.

"Report of the Space Task Group, 1969." NASA Headquarters. NASA, n.d. Web. 26 June 2015.

"Space Launch System." National Aeronautics and Space Administration, 9 Feb. 2022, www.nasa.gov/exploration/systems/sls/fs/sls.html. 16 June 2022.

"Space Shuttle Basics: Solid Rocket Boosters." Human Space Flight. NASA, 22 Oct. 2002. Web. 26 June 2015.

"Space Shuttle Basics: Space Shuttle History." Human Space Flight. NASA, 27 Feb. 2008. Web. 26 June 2015.

"Space Shuttle Program." National Geographic. Natl. Geographic Soc., 2015. Web. 26 June 2015.

"Space Shuttle Program Fast Facts." CNN. Cable News Network, 4 Aug. 2014. Web. 26 June 2015.

"What's Next for NASA?" NASA, 13 Dec. 2017, www.nasa.gov/about/whats‗next.html. Accessed 23 Apr. 2018.

Zeeberg, Amos. "How to Avoid Repeating the Debacle That Was the Space Shuttle." Discover. Kalmbach, 22 July 2011. Web. 26 June 2015.