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The STS-1 mission relied on brand-new technologies that had never been used before. More advanced than any previous aircraft or spacecraft, this flight included a number of technological firsts that would be essential for more than 100 successful missions in orbit.
Space Shuttle Main Engine (SSME):
The Space Transportation System includes the orbiter, which is what people usually think of as the Space Shuttle, connected to a large external fuel tank and two solid rocket boosters. While the boosters contribute the main thrust to lift the shuttle off the pad to 150,000 feet, the fuel tank feeds the three main engines that burn for the entire ascent into space. Each engine produces about 400,000 pounds of thrust at liftoff, and is one of few rocket engines that can be reused for multiple flights1.
Using hydrogen fuel and oxidizer, Rocketdyne, the engine’s designer, achieved one of the highest thrust to weight ratios by increasing fuel pump pressure in the combustion chamber. This represented a new technology for a human-rated rocket engine, one of the most complicated ever built. The result was a system that would need to operate at greater temperature extremes than any mechanical system in common use: the liquid hydrogen fuel is -423 degrees Fahrenheit before ignition, and following ignition, the combustion chamber heats up to 6000 degrees Fahrenheit2. In addition to its technical complexity, the SSME could be reused on multiple flights unlike previous engine technologies.
This new technology paid off. Throughout its more than 20 years in use, the main engines have proved highly reliable, and have never resulted in a scrubbed Shuttle mission.
Avionics and flight controls:
Fly-by-wire and computer-aided flight controls may be common on today’s aircraft, but they were rare in the flying machines developed during the 1970s. The Shuttle was the most complex flying machine ever built and required sophisticated software to ensure a successful operation. Due to the unstable aerodynamic nature of the orbiter, constant computer aid would be needed to assist with rudimentary flight tasks and the safe operation of the Space Shuttle.
Digital fly-by-wire is a relatively simple technology that was extremely complex to develop. Conventional flight systems link the pilot’s controls directly to wing and tail surfaces through pulleys, cables, and other mechanical means. Fly-by-wire takes pilot inputs, turns them into electronic signals, and then sends them to flight controls. The benefit of this system is that computers can alter the electronic control signals to account for changing atmospheric conditions, high speeds, and other factors that would complicate a pilot’s job3.
Four IBM AP-101 B computers, including a fifth fail-safe, were tasked with providing assistance during critical moments in the flight by adding refinement to pilot inputs. The Space Shuttle Primary Avionics System Software (PASS) was developed with multiple redundancies to permit the routine safe operation of the Space Transportation System4. In addition, the Shuttle software required 30 times more coding than that of the Apollo Moon missions, and the instructions tested the memory limits of the orbiter’s computers5.
Nonetheless, IBM programmers were able to fit all the necessary software into the computer system with an accuracy rate of .11 errors per 1000 lines of code6. Though the Shuttle’s computer systems have since been updated, the original system paved the way for future electronic flight systems.
Thermal Protection System:
Without a doubt, a spacecraft’s reentry is one of the most dangerous parts of any space mission. During this time, the vehicle’s speed as it hits the Earth’s atmosphere causes intense friction that results in temperatures of nearly 3000 degrees Fahrenheit. While NASA had experience with reentry of spacecraft that were no larger than a tool shed, engineers faced new challenges when they had to ensure the safe return of a spacecraft the size of a commercial airliner.
Earlier space capsules used ablative heat shields that charred as they protected their crews from the intense heat of reentry. While this system worked well for one-time use spacecraft, the Space Shuttle required a method that would allow the vehicle to be reused. Originally, the Lockheed Missiles and Space Corporation developed a silica-based insulation that could be manufactured into heat resistant tiles in the 1960s. Tests of these tiny blocks showed that they could protect the aluminum skin of the Orbiter during the high heat of reentry.
Several hundred tiles of different shapes and sizes cover the surface of the Shuttle and protect it from the friction of reentry. Two main types of tiles are used: Low-temperature Reusable Surface Insulation (LRSI) and High-temperature Reusable Surface Insulation (HRSI). LRSI tiles protect the orbiter from temperatures of 700 and 1,200 degrees Fahrenheit, and are mostly situated on the top of the spacecraft. They are colored white to reflect solar radiation in space and keep temperatures down. HRSI tiles protect the bottom of the orbiter and a few other vulnerable spots from temperatures between 1,200 and 2,300 degrees Fahrenheit. They have a black ceramic coating that helps deflect the enormous heat caused by reentry7.
After each flight, the orbiter’s surface is carefully inspected and all damaged or missing tiles are repaired or replaced. The insulation that fills the gaps between the tiles is also replaced as necessary. Following the flight of STS-1, the heat-resistant tiles were replaced and the Shuttle became the first space vehicle to be reused. Since then, the Shuttle thermal protection system has flown more than a hundred astronaut crews safely.
Throughout the Space Shuttle’s career, there have been problems with the heat shield tiles. On STS-1, astronauts John Young and Robert Crippen noticed that several tiles had fallen off the orbiter’s skin sometime after liftoff. Though STS-1, and countless other shuttle missions returned safely to Earth, heat shield tile loss was a constant occurrence. Heat shield tiles were also often easily knocked off by foam falling from the external tank during liftoff. This issue proved disasterous for the crew of STS-107. During re-entry on February 1, 2003, tiles on the leading edge of Shuttle’s left wing that were damaged at the beginning of the mission allowed hot gases to enter the spacecraft’s structure and break it apart. All seven crewmembers perished aboard the Shuttle that carried Crippen and Young into space two decades earlier. The Columbia Accident Investigation Board determined that foam falling off the Space Shuttle’s external tank resulted in the tile damage. While another crew would return to space safely aboard the Shuttle two years later, NASA engineers continue to search for a reliable method to protect the Thermal Protection System from damage.
Payload Bay and Remote Manipulator System:
One of the hallmarks of the Space Shuttle is its cargo lift capability. In addition to being able to up to eight people, with a regular crew of seven, the orbiter has a 60- by 15- foot payload bay that can accommodate anything from satellites to experiment bays to a crewed laboratory, such as SPACELAB. The payload bay is shielded by two large doors that are opened in orbit and closed before reentry.
While STS-1 successfully tested the operation of the Payload Bay doors, another important cargo support component of the Shuttle would not be tested until the next flight. The Remote Manipulator System, which flew on STS-2, is a 50 foot long jointed boom that is operated by astronauts within the crew compartment. The “Canadarm,” so nicknamed after its country of production, has helped deploy numerous satellites, captured the Hubble Space Telescope for repairs, and aided in the construction of the International Space Station.
Aerodynamic Design:
In addition to functioning as a spacecraft, the Space Shuttle Orbiter is also a glider that can be safely and accurately piloted to a runway landing after a mission. Previous capsules provided little accuracy following reentry, but the Shuttle was designed to be safely returned to the Kennedy Space Center for processing or to a separate site for easy transportation to the Florida Spaceport.
The Shuttle grew out of research into lifting body designs in the 1960s, designs that included wedge-shaped aircraft such as the Martin Marietta X-24A that use their entire structure to generate lift8. The Orbiter is essentially a lifting body with wings attached to provide the extra lift that would give the Shuttle the gliding ability to land at runways far away from its reentry path. This cross-range capability was required by the Department of Defense to facilitate landings at remote Air Force bases. A vertical stabilizer, or tail, was also added for extra stability.
The vehicle’s wings support elevons – combined elevators and ailerons that permit control over pitch (vertical orientation of the Shuttle) and roll (side-to-side tilting motion). The Shuttle’s tail has a rudder that controls yaw (horizontal orientation of the craft) and also can split apart to act as a speed brake. Despite these control surfaces, the Shuttle is a highly unstable and complex vehicle that is difficult to fly. Nonetheless, STS-1 Commander John Young brought Columbia to a textbook landing, and no other orbiter has ever lost control due to aerodynamic instability.
- Lewis, Richard S. The Voyages of Columbia: The First True Spaceship. New York: Columbia University Press, 1984. p 63.
- “SSME Incredible Facts.” The Boeing Company. http://www.boeing.com/defense-space/space/propul/SSMEamaz.html, accessed 3/7/06.
- Tomayko, James E. Computers Take Flight: A History of NASA’s Pioneering Digital Fly-By-Wire Project. Washington, DC: NASA History Division, 2000. pp 10-12.
- Jenkins, Dennis R. Space Shuttle: The History of Developing the National Space Transportation System. Marceline: Walsworth Publishing Company, 1993. pp159-160.
- Ibid, p 160
- Ibid, p 161
- Day, Dwayne A. “Shuttle Thermal Protection System (TPS).” U.S. Centennial of Flight Commission. http://www.centennialofflight.gov/essay/Evolution_of_Technology/TPS/Tech41.htm, accessed 3/7/06.
- Reed, R. Dale. Wingless Flight: The Lifting Body Story. Washington, DC: NASA History Division, 1997. p 9.
By Gabriel Okolski
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