When the space shuttle Discovery begins its fiery, hypersonic re-entry for landing at Cape Canaveral March 28, NASA engineers will be keeping a close eye on a deliberately flawed thermal tile. Tucked under Discovery's left wing, the single tile's design will increase the temperature of the 3-inch tiles around it as a test for future spacecraft designs that anticipate significantly more re-entry heat.
Called a "bump," the test tile will interrupt the normally smooth air flow around the existing tiles. The quarter-inch molded bump in the tile will be exposed to almost 3,000 degrees Fahrenheit during re-entry. NASA will send a Navy airplane to fly below Discovery with an infrared camera to monitor the heating as the shuttle heads over the Gulf of Mexico for a landing in Florida.
With the current shuttle fleet scheduled for retirement by the end of 2010, NASA is considering the tile for the next generation of spacecraft designed to make trips not only to the ISS (International Space Station) but even further to the moon and Mars.
"We have returned to using the space shuttle as a research vehicle," NASA Shuttle Program Manager John Shannon told the BBC. "We're trying to learn more and more about space flight and hypersonic re-entry."
The design of shuttle heat shields is a particularly sensitive issue at NASA. The space shuttle Columbia spun out of control and broke apart on Feb. 1, 2003, after a hole in its heat-resistant tiles allowed superheated air into the wing and precipitated the space disaster leading to the deaths of all crew members.
The Discovery crew spent March 27 preparing for re-entry, including a complete check of the craft's flight control surfaces that will guide Discovery's unpowered flight through the atmosphere to a landing. NASA is calling for a 1:39 p.m. EDT landing at the Kennedy Space Center. A second landing opportunity comes one orbit later at 3:14 p.m.
After several delays, Discovery launched March 13 for the trip to the ISS and docked with the space station March 17, its seven-person crew delivering a fourth set of solar array wings and a replacement part for the ISS' urine recycling system that converts urine to potable water. Over the course of three space walks, astronauts installed the solar array, which increases the space station's power by 25 percent. The increased power and operating urine recycling system are necessary to support plans to double the size of the ISS crew from its current three members to six.