June 2008 Edition

MEASUREMENT/INSPECTION

The Proof is in the Plastic

Three-dimensional printing technology translated scans of the space shuttle tiles for safety evaluation. The same technology allows proof of concept before metal is machined.

Just after lift-off, August 13, 2007, Space Shuttle Endeavour’s Thermal Protection System – TPS – suffered damage due to a strike by foam insulation falling from the shuttle’s external fuel tank. Sensors detected damage to the heat-resistant tiles lining the orbiter’s underbelly, posing a threat to the shuttle’s safe re-entry to Earth.

The TPS consists of thousands of heat-resistant silica-based tiles that keep the heat from atmospheric re-entry from being transferred to the shuttle’s aluminum structure. However, the tiles are relatively delicate and are easily damaged. Insulating foam shed from the external fuel tank due to aerodynamic forces can damage the tiles.

NASA called on Neptec Design Group, Ottawa, Ontario, Canada, one of its prime contractors since 1995, to collect three-dimensional information to evaluate the severity of the situation. Neptec provides machine vision systems for the space, defense, and quality assurance industries. Focused on providing 3D processing products, Neptec offers smart 3D sensors as well as intelligent, embedded image processing and analysis tools designed to increase the effectiveness of existing sensor platforms.

Neptec’s Laser Camera System – LCS – is designed to detect damage, if any, sustained by a shuttle during lift-off. The LCS is a mandatory system on every shuttle mission. The three-dimensional data it gathers is used to reproduce 3D models of the area of interest on the shuttle, providing NASA with the information needed to test damaged areas.

　

Scanning the Shuttle

LCS delivers 3D tracking capabilities with its flexible two-axis steering that provides standard raster scanning for imaging, and custom scan patterns for tracking targets and features. The LCS made its first appearance aboard the shuttle flight STS-105 in 2001. Since this initial mission, the LCS made improvements, including smaller and more efficient scan control electronics, improved acquisition speed, and optics optimized for detailed inspection.

LCS is now a permanent part of the shuttle’s 50' inspection boom, the Canadarm, which flies on every shuttle mission. Using the LCS, Neptec collected detailed 3D images of locations where sensors detected possible damage to Endeavour’s outer surface after lift-off.

Using a Dimension 3D printer, from Stratasys, Inc., Eden Prairie, MN, Neptec used the three-dimensional information from the LCS to print a 3D model of the damage aboard the Endeavour. The model provided visual representation of the tiles and was used to evaluate the damage to the shuttle’s Thermal Protection System.

Three-dimensional printing is a type of rapid prototyping. The Dimension printers build functional 3D models from the bottom up, one layer at a time from acrylnitrile butadiene styrene – ABS – plastic. Files are imported into the printer’s software which slices and orients the parts and creates any necessary support structures. The software plots a precise deposition path that the printer follows. ABS plastic – in filament form within auto-loading cartridges – is fed into an extrusion head, heated to a semi-liquid state and deposited in layers as fine as 0.010" thick. After completion of the build, support structures are removed.

Parts printed in ABS have been used for functional and field tests – from wind tunnel testing, to camera mounts on a M2 Bradley armored fighting vehicle, to a spray gun running at 60 psi.

"The LCS data gave NASA the information it needed to test the damaged tiles," Maureen Campbell, a Neptec manager, said. "This let NASA make an educated decision about bringing the shuttle home without filling the damaged area."

The Dimension 3D printer created a model of the damaged tiles so NASA mission managers could gain a heightened understanding of the harm the damage posed to the crew. Although the gouge was deep, mission managers believed it posed no risk to the space shuttle’s re-entry into Earth’s atmosphere.

Safe Return

On August 21, 2007, the Endeavour and its seven-astronaut crew returned safely to Earth. The shuttle’s landing completed a 5.3 million-mile, 13-day flight for the orbiter. On the mission, Endeavour’s astronaut crew performed four spacewalks and primed the station for the delivery of its fourth and final set of U.S. solar arrays on a future shuttle flight. NASA relaunched the Endeavour again on March 11, 2008 to install the first section of the Japan Aerospace Exploration Agency’s Kibo laboratory and the Canadian Space Agency’s two-armed robotic system.

This was not the first time Neptec used its Dimension 3D printer to assist NASA. On a previous space shuttle mission aboard the STS-118, a gouge was created after a piece of foam hit the shuttle 58 seconds after lift-off. Neptec’s LCS was used to scan the damaged area and 3D models were created for NASA’s engineering and mission management team to assess whether to repair the damage prior to letting Endeavour re-enter Earth’s atmosphere.

Located near the right main landing gear door, the gouge was 9cm long and penetrated all the way through the thermal shielding on the shuttle’s belly. Using data retrieved from the LCS, Neptec was able to make a 3D model of the damage to effectively address the situation in a time-sensitive environment and bring the STS-118 mission safely back to Earth.

"Due to the extreme nature of the environment, every space mission presents an elevated level of risk," Campbell said. "By providing accurate, three-dimensional information and clearly communicating the extent of the damage, NASA was able to make a better educated decision, which, in turn, brought the Endeavour crew home safely."

In addition to NASA, Neptec also uses its Dimension 3D printer to assist engineers in the design and development of its product lines.

"The 3D printer let us do a variety of testing issues, including a certain amount of fit and interference checking," Campbell said.

Time Saver

Using its Dimension 3D printer, Neptec saves up to 10 weeks of machine shop time per project. The 3D printer has also provided Neptec with detailed, life-like pieces – like a car door model and turbine vane – to demonstrate to its customers. The lightweight 3D models can be sent to customers or tradeshows for realistic demonstrations.

"Intelligent processing of 3D data has become central to Neptec’s technological advancements and beneficial to its business success," Campbell said. "Because we have a Dimension 3D printer, we can take our scans from the data we collect and turn them into actual physical models.

Dimension 3D printing lets companies and organizations quickly fine tune designs and cut weeks – even months – from development schedules. With the ability to evaluate more design iterations, 3D printers let users test form, fit, and function before metal is cut. Stratasys, Inc.

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