NASA - National Aeronautics and Space Administration

Frank Morring, Jr.
Aviation Week & Space Technology
02/05/2007, page 55

Engineers from across NASA are working on a design for an Orion crew exploration vehicle pressure shell made entirely of composite materials, but it will never get off the ground.

Instead, the effort led by the NASA Engineering and Safety Center (NESC) is aimed at gaining in-house composites experience for the agency to tap when it begins building other spacecraft needed for its lunar-and-beyond exploration effort, starting with an all-composite lunar lander and perhaps habitats for the Moon's surface.

The payoff could be huge for exploration engineers, who must count ounces and pennies as they design spacecraft to be hurled out of Earth's gravity well on a congressional budget. Weight savings of 25% or more over aluminum are possible, as are lower manufacturing costs.

But as always, the devil is in the details, and NASA's near-term objective is to make its engineers "smart buyers" when they consider composite materials for future exploration applications.

"NASA has not built a spacecraft where composites are the primary habitable structure, habitable meaning it can contain the pressure for the crew life support," says Mike Kirsch, NESC composites-project principal engineer. "The real objective is to gain the hands-on experience that comes with designing, building and testing that vehicle."

Kirsch's team gathered at Goddard Space Flight Center last week for a three-week stint at the concurrent engineering center there to wring out requirements and divvy up the work that will be necessary to build a composite pressure shell for Orion. The actual flight component will be built of aluminum lithium because NESC engineers didn't find a "significant discriminator" for composites over the lightweight aluminum alloy.

"When you're looking for differences of 10% to 15%, you really need to compare mature designs," Kirsch says. "The aluminum lithium design in the Orion project today is 1,200 or 1,400 lb., somewhere in there, plus or minus 20%, perhaps even 30%. If I have two designs that are two years away from being built, and I try and compare them, you've got Design A plus or minus 30% versus Design B plus or minus 30%, and you're looking for a difference of 10%. You just don't get to see it."

The NESC team examined three different composite approaches to the Orion problem--a stiffened honeycomb sandwich, a geometrically stiffened laminate and a monocoque design integrating the aeroshell and pressure vessel in one composite lay-up. Now, it will have 18 months to pick the best approach for Orion and design, build and test it.

Working with NESC will be Northrop Grumman, Janicki Industries and Collier Industries, chosen for their expertise in composite manufacturing and tooling and for their ability to spread the experience gained in the NASA effort into industry. Northrop Grumman was picked for the work because of its experience on an earlier NASA project that produced an all-composite liquid-hydrogen tank (AW&ST Apr. 12, 2004, p. 49).

"Several of the design features that we looked at on the tanks, we anticipate having similar issues with the composite crew module," says Tod Palm, Integrated Product Team lead for space structures at Northrop Grumman. "It's a pressure vessel. There's potential for a large assembly splice that would be similar to our belly-band joint that we had on the tank. They are concerned about containing ambient air and preventing leaks of that, rather than leaking the cryogenic hydrogen that we were concerned about on the tank. And there's a possibility of it being a sandwich stiffened shell."

The 5-meter-dia. Orion capsule will be larger than the cryotank Northrop Grumman built, which was about 6 ft. across. But aside from the need for a larger autoclave to cure the new structure, Palm doesn't expect technical difficulties. "The schedule is probably the most difficult part," he says. "They've been challenged with doing the whole design, analysis, a building-block type of test program and producing a full-scale shell for this within an 18-month window."

Kirsch's team has briefed Administrator Michael Griffin on the effort, which is aimed at lunar-lander and habitation applications rather than the Earth-to-orbit leg of the trip (AW&ST Jan. 22, p. 15). The design problem for the lunar hardware may actually be easier and produce more weight savings than Orion. Unlike a simple propellant tank, the capsule is a complex structure inside and must handle loads from the launch-abort system, parachutes and landing (or crashing) on Earth that a lunar lander wouldn't face.

Northrop Grumman tried hard to win the Orion prime contract, which ultimately went to Lockheed Martin. But its predecessor, Grumman Corp., built the Apollo-era Lunar Excursion Module. Northrop Grumman executives make no secret of their desire to use that heritage--and the composite heritage from aircraft like the B-2 bomber--to build the planned Lunar Surface Access Module envisioned to take a crew of four to the lunar surface by 2020.

The company has also teamed with the National Center for Advanced Manufacturing at the NASA-owned Michoud Assembly Facility near New Orleans to work on some composites-producibility issues using the state-of-the-art equipment there (AW&ST Jan. 22, p. 15). Bob Davis, business development director for the company's space exploration systems organization, says all the work aims to win a piece of the exploration pie.

"Jeff Hanley [head of the Constellation program, which is developing exploration vehicles at NASA] said ideally they would envision looking at a nearly all-composite lunar lander if it were the case that composites bear themselves out as meeting all of the specifications that would be imposed on them, and then having a cost payoff," Davis says.

The payoff would include lower life-cycle costs, less mass and perhaps radiation protection afforded by the composites against the sort of solar radiation astronauts can expect to encounter on the Moon.

"The secondary structure issues on the crew module itself are probably going to make it more difficult to realize the benefits if you are going to compare it to a launch-vehicle system or a cylindrical habitat that would be left on the surface of the Moon," Davis says. "We are certainly, as a company, interested in the use of composites. We are spending IR&D [independent research and development] to further our knowledge and our customer's knowledge of these exploration systems applications. We think there's a payoff there, or we wouldn't be wasting their time or our time."