Oak Ridge National Laboratory and Sierra Space Corporation have developed a new heat shield based on venerable 1980s Space Shuttle technology to protect the next generation of reusable spacecraft from the deadly heat of reentry.
The biggest barrier to getting spacecraft back to Earth safely is our own atmosphere. Just as the shell of air around our planet protects us from cosmic rays and the meteors that constantly rain down on us, it also burns up satellites whose orbits have decayed – provided they haven't been equipped with special protection.
The most common form of heat shield used today is made of phenol plastic. First developed in the 1950s, these protect returning spacecraft by what is called ablative shielding. This deals with the heat caused by a craft hitting the atmosphere at ultrasonic speed by vaporizing the plastic and carrying the heat away before it causes damage.
It works, but only by destroying the shield, so it can be used only once and with a very limited service life. An alternative to this was developed for NASA's Space Shuttle that began flying in the 1980s. The Shuttle fleet used a heat shield made of a vast array of ceramic silicon carbide tiles. These worked by absorbing the heat and very slowly releasing it. In fact, it released it so slowly that even when it was white hot you could pick up one of the tiles safely provided you did so by the sharp edges.
Unfortunately, these tiles had some major disadvantages. Over 24,000, six-by-six-inch (15-by-15-cm) silica-fiber tiles had to be applied to the under surface of the Shuttle. Each one of these had to be made by hand using molds and heating them to 2,350 °C (4,262 °F). In practice, these tiles had a nasty tendency to come loose and fall off. They were also very fragile.
The new tiles that are being installed on Sierra Space's Dream Chaser orbiter use a combination of silicon carbide and carbon fibers that provide protection, high strength and stable flight dynamics. In addition, new manufacturing techniques make these tiles much less labor intensive to produce. The result is a heat shield that moves on from the 1980s when NASA made five launches of the Shuttle a year to the next generation that could see five launches per day. It's set to be used on the Sierra Space Dream Chaser, the first-ever winged commercial spaceplane that is designed to transport crew and cargo to low-Earth orbit.
"The key to achieving a flight cadence that is driven by fast landing-to-launch turnaround times is reusability of the TPS," said ORNL principal investigator Greg Larsen. "The materials we are exploring will push the boundaries of reusability that translate directly to commercial viability for space-access providers."
Source: ORNL
