Researchers at NASA are using a novel thermal-imaging system on board a Navy aircraft to capture images of heat patterns that light up the surface of the space shuttle as it returns through the Earth's atmosphere. The researchers have thus far imaged three shuttle missions and are processing the data to create 3-D surface-temperature maps. The data will enable engineers to design systems to protect future spacecraft from the searing heat--up to 5,500 degrees Celsius--seen during reentry.

"We want to understand peak temperatures, when they happen and where, because that determines the type of material for, and size of, a protection system," says Thomas Horvath, principal investigator of the project, called Hypersonic Thermodynamic InfraRed Measurements (HYTHIRM), at Langley Research Center in Hampton, VA.

NASA has become more concerned with safety and developing tools for inspecting and protecting the shuttle since the 2003 space shuttle Columbia disaster, when damage to the shuttle's wing compromised its heat-resistant shield, causing it to lose structural integrity and break apart during reentry, killing all seven astronauts aboard. Horvath, also a support team member of the Columbia Accident Investigation Board (CAIB), says the HYTHIRM project was developed in response to the Columbia accident.

"I certainly think [the researchers] can learn something about what causes the heating," says Douglas Osheroff, a professor of physics and applied physics at Stanford University, and a member of the CAIB. He adds that the thermal images could also be used as a diagnostic tool to check the integrity of the shuttles tiles during reentry. Currently engineers must manually inspect the tiles upon the shuttle's return.

To image the shuttle, the researchers used a novel optical system called Cast Glance on board a Navy P-3 Orion aircraft. The system is used mostly by the Department of Defense for missile defense missions and so had to be slightly modified for the NASA project. The Navy researchers added a high-resolution, off-the-shelf video camera and adjusted it to filter infrared light. They then calibrated Cast Glance's optical sensors so that, by measuring the infrared radiation from the shuttle, they could calculate the surface temperatures.

The Navy aircraft flies to within 37 kilometers of the space shuttle when the latter is traveling at speeds of between two and three miles per second, acquiring eight uninterrupted minutes of data: approximately 10,000 to 15,000 images for each mission.

The researchers' focus was the underbelly of the shuttle, which is covered by about 10,000 thermal protective tiles. The highest heating areas, near the nose and along the leading edge of each wing, are made of a material called reinforced carbon-carbon (RCC). As the shuttle pushes air molecules out of the way, says Deborah Tomek, project manager of HYTHIRM, a boundary layer or protective region, similar to insulation, forms around the shuttle where temperatures are between 1,093 and 1,649 degrees Celsius. Just outside that boundary layer temperatures can rise to a sweltering 5,500 degrees.