A Program That Defined A Generation
NASA’s space shuttle program began in 1972 when President Nixon approved the program that would ferry astronauts between Earth and the low Earth orbiting space station (though Reagan didn’t approve the space station part of the program). Formally, the shuttle project is called the Space Transportation System, which is how missions got their “STS” designation. From launch to re-entry, shuttle missions were incredibly complex and relied on some of the most sophisticated technology NASA developed.
Museum Exhibit: Multiplexers
The two Solid Rocket Boosters were responsible for getting the space shuttle into orbit. Each contained three rate gyro assemblies, and each of those in turn contained one pitch and one yaw gyro. These provided information about the boosters’ output proportional to angular rates of pitch and yaw compared to the shuttle orbiter’s guidance system. These control rates passed through devices called multiplexers and demultiplexers – the former is the unit shown here – to reach the orbiter’s general purpose computer. Without this unit to transfer data, the shuttle orbiter wouldn’t have a way of talking to the boosters.
Fun Fact 1: NASA's Workhorse
The orbiter Discovery is not only NASA’s most experienced shuttle, it’s NASA’s most flown spacecraft of any type. During the program’s 30 years, Discovery flew thirty nine missions between 1984 and 2011. This was also the orbiter that launched the Hubble Space Telescope and John Glenn on his second and last spaceflight.
Museum Exhibit: Heatshields
Returning from space puts a lot of pressure on a spacecraft mainly in the form of heat; as it falls through the atmosphere, friction with the atmosphere generates significant heat levels. To protect the shuttle orbiters during atmospheric re-entry, NASA coated the peak heating area with layers of insulating material. Part of the insulation material on the shuttle was the high temperature foil insulation displayed here. Reinforced Carbon-Carbon is a light gray, all-carbon composite that, along with inconel foil insulators and quartz blankets, protected the orbiter's nose, “chin,” and wing leading edges from the highest temperatures expected with atmospheric re-entry. There was even some insulating material like this inside the engine bells to protect them from the heat of firing the main engines. The other main part of the thermal protection system was the familiar black silica tiles. Designed to reflect about 90 percent of the heat of atmospheric re-entry and absorb the remaining 10 percent, these tiles kept the worst heat away from the orbiter’s body.
A Brief History of Re-Entry Methods
Not all spacecraft heat the same when they re-enter the Earth’s atmosphere. In the late 1950s and early 1960s, the Mercury, Dyna-Soar, and Apollo manned spaceflight programs faced very different re-entry concerns. The Mercury spacecraft was designed to land following a ballistic trajectory and protecting it during landing was a simple as rounding the bottom to create a cushion of air beneath the falling vehicle and adding an ablative heat shield to deal with the remainder. Dyna-Soar, a winged, one-man shuttle type of vehicle that never flew, used a lifting re-entry. It got less hot, but its re-entry was longer. Apollo, returning from the Moon with a semi-lifting trajectory, split the difference. It got a lot hotter during a re-entry that lasted longer than Mercury’s but was shorter than Dyna-Soar’s. This was the heritage of re-entry heating problems NASA could turn to when designing the shuttle.
The space shuttle was probably the most complex vehicle ever built, from the multi-stage launch system to the delicately laid out tiles to keep the orbiters safe during re-entry. But although it’s an iconic program for a generation, the shuttle failed to realize NASA’s ambitious program goals. It didn’t even come close. NASA hoped the shuttle would make spaceflight both routine and cost effective by launching up to 50 missions per year. That would be 1,500 over 30 years rather than the 135 we got. It seems the infrastructure couldn’t realize the full potential of the shuttle’s technology.
Fun Fact 2: Weight Loss in Space
The shuttle orbiters weighed a lot less when they returned from space than when they launched. That’s because the Solid Rocket Boosters and the main fuel tank didn’t return. On average, a shuttle weighed almost 4.5 million pounds at launch and just 151,000 pounds when it landed.