 |
Feb. 14, 2003 — In early February, a Las Vegas Sun editorial cartoon depicted the Space Shuttle Columbia on the launch pad, about to begin its tragic final voyage on Jan. 16. One onlooker asks his companion: “The heat resistant pieces that cover the shuttle. … What are they called again?” The other replies: “The Achilles’ Heel.”
 |
Actually, it will be some time before NASA can conclusively say whether damage to the fragile insulating tiles that cover the underbelly of the space shuttle caused the Columbia to disintegrate in the skies over Texas in the early morning of Feb. 1. Investigators are still assembling a “fault tree,” which lists a number of possible causes for the disaster. They include defective wiring, corrosion and inadvertent triggering of an explosive device on board.
 |
The most likely scenario, however, is that something — a piece of foam insulation, space junk, a micrometeor — grazed the tiles, setting off a dreaded chain reaction known as the “zipper effect,” in which loss of one tile caused the tiles around it to peel off until a large area of the aluminum skin was exposed to temperatures exceeding 3,000 degrees Fahrenheit.
 |
What is known for certain is this: Columbia was destroyed by a “thermal event,” and the shuttle program uses thermal protection technology that is decades old. NASA would not talk to Small Times about the Columbia disaster or anything related to it, but several companies and universities say that NASA will increasingly look to small tech for ways to avert future tragedies.
Ryne Raffaelle, a physics professor and director of the NanoPower Research Laboratory at the Rochester Institute of Technology, is working on several nanotechnology projects at the NASA Glenn Research Center in Cleveland. He said that weight, power and volume are at a tremendous premium in space. The sort of diagnostic devices NASA currently use are much heavier than MEMS sensors. The current crop of diagnostic devices NASA uses are too heavy and require too much power, Raffaelle said.
“If we are ever going to get things moving in the interplanetary field, we’re going to have to develop MEMS diagnostic tools.”
Raffaelle said MEMS-based temperature sensors and strain gages both show promise in the quest to make space flight safer. These application-specific integrated microinstruments (ASIMs for short) could be mounted under the heat shielding tiles of orbital spacecraft and serve as a warning system the moment something goes wrong.
But before NASA can seriously consider MEMS as a way to improve reliability in manned spacecraft, MEMS themselves must become more reliable in order to stand up to the harsh conditions of atmospheric re-entry.
Hyper-Therm High Temperature Composites Inc. in Huntington Beach, Calif., received a Phase I grant along with additional NASA funding to develop MEMS sensors made from silicon carbide, which are more heat-resistant, stiffer and stronger than ordinary silicon MEMS. Robert Shinavski, Hyper-Therm’s materials research manager, said that in light of the Columbia disaster, NASA is likely to ramp up the research and development of high-temperature MEMS sensors.
At Luna Innovations in Blacksburg, Va., researchers have received a NASA grant to develop sensors that can record temperature gradients at multiple points along the length of a fiber probe. Bob Fielder, a materials engineer with Luna, said his company has had discussions with NASA about placing temperature probes under the tiles of the space vehicle. “It would basically give us a map” of temperature gradients on the surface of a spacecraft, he said.
Luna is also developing a prototype for a shear sensor measuring 2 millimeters in diameter (including the housing) that could be used to adjust the shape of a wing in response to forces acting on it. Working under a Phase II NASA grant, Luna plans to have a prototype built sometime in 2004.
Shear sensors, and the effectors that would actually change the shape of a wing in real time, could be of tremendous help in improving flight safety, said John Randall, chief technology officer for Zyvex Corp., a nanotechnology company in Richardson, Texas. More sensors equals more information, and “generally, the more information you’ve got, the better control you can have,” Randall said. Some experts have speculated that the damage to Columbia caused it to overcorrect its attitude, which made it tumble and break apart. If that’s the case, shear sensors mounted in strategic locations on the exterior surface could conceivably have saved the astronauts.
Nanocomposites will also play a role in making spaceflight more reliable. Zyvex has a grant from NASA to develop a structural epoxy composite using carbon nanotubes as the filler. Randall said his company has a processing technique for the epoxy composite that retains the remarkable properties of carbon nanotubes — namely, its high strength-to-weight ratio and durability. While such a material couldn’t be used as a heat-protecting spacecraft skin (carbon nanotubes are very poor insulators), if it were used as the structural elements of a spacecraft, the weight savings could allow engineers to use heavier, more effective, heat-shielding tiles and adhesives on the skin of the craft.
Most researchers interviewed for this article believe that the Columbia tragedy will spur interest in developing small tech for the space program.
“The shuttle fleet is quite a number of years old now,” Raffaelle said, “and although they keep replacing things and upgrading things as they go, it’s obviously not the technology that we’re going to be using for whatever ends up replacing the shuttle in the future. That development is going to utilize the best current technology, and with regard to the different sensors that we have, it’s highly likely that those would be MEMS devices.”