Well before the Columbia accident, researchers were working on better alternatives to the ceramic tiles that cover the surfaces of the space shuttle's air frame that are susceptible to damage from the intense heat that occurs during re-entry. At present, the only technology available to protect the vehicle and its crew is the small black tiles now in use.

The heat-resistant tiles that cover the belly of a shuttle are only part of the thermal protection system (TPS) that insulates each orbiter's ship and crew from temperatures as high as 3,000 degrees Fahrenheit as the orbiter returns to Earth at speeds in excess of 17,000 miles an hour.

"The bottom line is that these tiles work, they do the job that they're intended to," said Jeff Carr, communications director for United Space Alliance, which manufactures the shuttle tiles. "Their application is really unique to reusable launch vehicles like the shuttle."

But the effectiveness of the tiles comes at a cost. Inspections and preparations after every mission make for a slow shuttle turn-around time, averaging around 60 days or so, which have led some researchers to focus on larger metallic versions that need less attention.

"We would be looking for things that are much more robust," said Mark J. Shuart, director for structure and materials at NASA's Langley Research Center in Virginia, during an interview. "Tiles are very lightweight and efficient, but they take a lot of time after a flight for repairs and refurbishing."

Langley researchers are developing ARMOR, short for Adaptable, Robust, Metallic, Operable, Reusable TPS, as a potential system for future NASA spacecraft. The metallic tiles are roughly twice the size of the shuttle's 8-inch by 8-inch (20-cm by 20-cm) version, and composed of Inconel 617 and Inconel 718 metals, both nickel-based alloys. They are a bit heavier than the lightweight silica ceramic tiles NASA uses on the shuttle, which means they don't qualify as a potential replacement for the system just yet.

"A metallic TPS system drives a lot of the design philosophy behind a vehicle," said Garry Lyles, program manager for NASA's Next Generation Launch Technologies (NGLT). The technology group is part of the agency's Space Launch Initiative, which is working toward building an Orbital Space Plane as well as working on second - and third-generation reusable craft. "It is not an option you'd want to go with on the shuttle, you'd want to stay with ceramics," Lyles told SPACE.com.

Advanced ceramics, however, are not out of the picture. Scientists at NASA's Ames Research Center in California are developing ultra-high temperature ceramics that could replace the reinforced carbon-carbon composites used on the nose and wings of the shuttle in time.

The Ames center is home to the NASA's Thermal Protection Materials and Systems branch, but officials there said they could not comment on their TPS research until the conclusion of investigations into the loss of Space Shuttle Columbia. The exact cause of Columbia's Feb. 1 break-up, which claimed the lives of the seven astronauts aboard, has yet to be identified, though some speculate that heat tile damage could have allowed ultra-hot plasma to penetrate the craft's skin during reentry.

Designing a vehicle from scratch can give engineers more freedom when it comes to heat protection.

"Having to integrate a new TPS system into an existing airframe limits the amount of options available," said Lyles. "You would need to stay fairly close to the system already in use."

But all bets are off when designing something completely new. To date, NASA has spent about $25 million studying different thermal protection methods for second and third generation launch vehicles under the Space Launch Initiative.

In addition to new ceramics and metallic systems, the NGLT group is looking into improved thermal blankets and more durable low materials to protect the parts of a craft that are subjected to lower temperatures. New approaches to TPS support, such as a new spray-able waterproofing compound could reduce similar practices today from hours to minutes.

Most of these methods remain at the laboratory testing stage, including an effort to develop a "hot structure" TPS system that incorporates thermal protection directly into a craft's airframe. The approach would do away for external attachments - shuttle tiles and other TPS materials are affixed to the orbiter's aluminum shell - altogether. But some endeavors have made the leap out of the lab.

"We did design work for a metallic TPS for the airframe of the X-33, and were assembling a test vehicle when the program was cut," said Lyles, referring to a reusable launch vehicle scrapped by NASA in 2001. The program could see new light with NASA's rekindling of the X-37 spaceplane research last year, though that project is under the Space Launch Initiative's Orbital Space Plane program and will depend on how it might be accessible for research, he added.

Investigations into TPS systems with sharp leading edges, which would do away with the blunt body designs of the shuttle in favor of a more aerodynamic craft, have also found their way into experimental tests. In 2000, Ames researchers studied the reentry of aerodynamic nosecones during the Slender High-velocity Aerodynamic Research Probe (SHARP) program. The result could eventually lead to a reusable launch vehicle that flies more like a plane.

If Ames' research into ceramic leading edges was pushed and pushed hard, Lyles said, the material could be ready for review by vehicle designers in two years. When it might be deemed flight worthy, however, isn't easy to estimate, he added.

But aside from NASA's three space shuttles, and their possible successors, there's little market to spur advances in tile research. "There are always opportunities for improvement in the TPS system," Carr said. "The thing is, there's not a whole lot pushing the state of ceramic tiles other than reusable manned systems like NASA's."

The last heat tile advancement to be applied directly to the shuttle program occurred in 1996, when NASA engineers developed the Toughened Unipiece Fibrous Insulation (TUFI), he added. The new tile is stronger than its earlier counterparts but also conducts more heat so, which limits its use to the orbiter's upper body flap and main engine area.