Preventing Another Space Shuttle Disaster
NASA engineers have developed a new 3-D wireless scanner to detect and measure damage to the space shuttle’s heat-insulation tiles–the type of damage that led to the 2003 Columbia disaster. Both before the shuttle’s launch and after its return, the handheld device can quickly scan the surface area of a tile, map it in 3-D, and if there is a crack or ding, calculate its dimensions. The data is wirelessly transmitted to an onsite laptop where engineers can assess the damage more accurately and efficiently than was previously possible and determine whether or not the affected tiles need to be replaced or repaired.
The scanner was used for the first time to inspect the space shuttle Endeavour preceding its launch on August 8, 2007, from NASA’s Kennedy Space Center. “The longest, biggest, and most tedious job engineers have is the inspection of the thermal protection system before, during, and after a mission,” says Joe Lavelle, a senior engineer at NASA Ames Research Center and the project manager. But for the safety of those on board, he says, it’s also one of the most important.
Currently, an engineer who finds a flaw on a tile, like a crack or ding, must measure it with a ruler in order to estimate the extent of the damage. For the foreseeable future, engineers will continue to perform visual checks–which remain faster than dragging the scanner across the entire surface of the shuttle–but the scanner will give them extremely precise measurements of any imperfections, so they can better decide whether a tile needs to be replaced or just repaired.
The scanner weighs approximately two and a half pounds and is about the size of a heavy-duty flashlight, making it small and light enough for an engineer to carry around during inspection. It is also wireless and thus has no encumbering cables. When an engineer notices a damaged tile, she places the scanner over it and with the press of a button produces a 3-D scan of a nine-inch-square area and also calculates the dimensions–length, width, area, and volume–of the defect.
The resulting 3-D surface map is wirelessly transmitted to an onsite laptop so engineers can immediately review the data. The speed of the scanner saves time, and its accuracy makes measurements more reliable, says Lavelle. “Replacing and repairing tiles is a vital function in the maintenance of a spaceship because you have to have a thermal protection system that has integrity. Otherwise, you are going to have major problems, like accidents that we have had,” he says.
The space shuttle’s thermal protection system is a combination of Reinforced Carbon-Carbon (RCC) on the wing leading edge, thermal blankets on the fuselage and thermal protective tiles covering the underside of the vehicle and nose cap. This system protects the spacecraft and its human occupants from the extreme heat of reentry into the Earth’s atmosphere. Without the RCC, blankets, and tiles covering the shuttle–the space shuttle Endeavour has more than 24,000 tiles–the structural integrity of the aluminum frame on the shuttle would be compromised. In 2003, the world witnessed a devastating disaster after the RCC on the port (left) wing of the space shuttle Columbia was damaged during launch. The damage went undetected and the shuttle, left with a compromised heat-resistant shield, lost structural integrity and broke apart during reentry.
NASA engineers used six 3-D scanners for their prelaunch inspections of Endeavour and plan to use them again when the shuttle returns. They will also use them for the ground maintenance of other spacecraft. The next step for the new scanner, says Lavelle, is to redesign it so that its components can withstand operations in space, and astronauts can use it to inspect the space shuttle during missions. Lavelle also says that there are many companies, which he declines to identify, interested in the 3-D scanner.
Aside from inspecting the space shuttle, the scanner is being used to evaluate thermal protection materials for a new crew exploration vehicle that NASA is developing. Engineers use the 3-D scanner to measure the materials both before and after they are tested in extreme environments; the difference between the two measurements indicates how well the material performed. Planetary rovers could also use the scanner to map the space around them in 3-D, helping them avoid collisions and better maneuver in unknown environments.
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