A NASA team looking into design concepts for future space capsules has successfully demonstrated that an all-composite structure is a feasible alternative to traditional metal capsules for carrying astronauts into space and returning them safely to Earth.

The composite materials that make up the structure are basically the same as the tough, lightweight laminates used today for race cars, business jets and high-end sports equipment.

In combination with new space-age fabrication techniques, these advanced composite materials promise potential benefits over traditional metal structures. Among them is that they can easily be formed into complex shapes that may be more structurally efficient - a desirable trait for future generations of spacecraft.

A team led by the NASA Engineering and Safety Center (NESC) developed and tested the capsule - called a crew module - in a series of full scale structural tests at NASA's Langley Research Center, Hampton, Va., over a several month period.

The full-scale crew module was pressurized to design limits while critical interfaces - like the landing system main parachute fitting - were pulled to simulate the combined loads a future crew module might see during launch and return to Earth. No trouble spots were detected.

After passing those and other combined tests, follow-on tests checked for damage tolerance, a question of critical importance for composite structures.

The crew module was subjected to measured impacts in multiple locations to simulate the kind of damage that might take place in the life of the structure - specifically, the equivalent of tool drops and routine handling damage.

The module was then stressed to simulate the expected life cycle of a space-going composite structure. At points along the way, the damaged sites were inspected by non-destructive means, using both infrared thermography and ultrasonic techniques, to characterize subsurface damage and damage progression.

"Our tests showed that a composite module can 'achieve the mission' with damage that is likely to occur but could go undetected," said Mike Kirsch, manager of the Composite Crew Module (CCM) project. "The test article withstood twice the design internal pressures with known damage and then was subjected to cyclic testing to four times the design life with no detrimental damage growth," he added.

A follow-on round of impact assessments is planned to study the effects of higher impact energies.

"We are very pleased with the entire test series. Throughout testing, there were no anomalies and performance aligned amazingly well with analytical predictions," Kirsch said.

The composite crew module was designed, manufactured, inspected and tested in a collaborative partnership between NASA and industry.

Partners include subject matter experts from nine of ten NASA centers, the Air Force Research Laboratories, Alcore Corporation, Alliant Techsystems (ATK), Bally Ribbon Mills, Collier Corporation, Genesis Engineering, Janicki Industries, Lockheed Martin and Northrop Grumman.

The composite module was fabricated at ATK's Iuka, Miss., facility.

One of the many collaboration success stories was realized with the help of recently developed carbon fiber tooling provided by Janicki. The tooling technology produced large (approximate 12-foot diameter) precision cure tools that enabled joining of major subassemblies outside of an autoclave.

This feature would allow for large or cumbersome internal components to be installed and integrated at the subcomponent stage for easier access and for parallel work flow prior to assembly of the system. The technology also demonstrates possible approaches for assembling components too big for autoclaves, such as a heavy lift vehicle shroud.

Kirsch believes work on the CCM Project will enable more informed decisions about structural materials for future NASA spacecraft.

"One of the primary project objectives was to gain hands-on experience for NASA with our contract partners by designing, building and testing a full scale complex structure such as this, then communicate lessons learned to engineers working composites across the agency," said Kirsch.

"There have been many lessons learned, including the challenge of keeping weight down while meeting design requirements for a human-rated spacecraft," he said.

NESC sponsored the three-year CCM project as part of its mission to solve technical problems related to spaceflight and to make spaceflight safer. The CCM is an all-composite representation of the part-metal, part-composite flight crew module Orion, which is part of NASA's Constellation Program to return man to the moon and/or Mars.