ORONO – Professor Vince Caccese and graduate student Chris Malm are baking, bending and breaking things for NASA.

The University of Maine researchers are testing the strength of joints between the exterior panels and the interior structural frame of the X-38, the prototype for a small spacecraft that will act as lifeboat and ambulance for the crew of the International Space Station. The station, which is being constructed by 16 countries at 220 miles average altitude in space, is due to be completed by 2007.

Caccese and his students are making things snap in their Orono lab so they don’t break up in space if the X-38 is returning to earth with an injured crew member or the entire crew of the space station after an emergency exit.

“We’re focusing on the joints between the outer shell panels and the vehicle’s metallic framework,” said Caccese, an associate professor of mechanical engineering who specializes in structural design. “Joints are typically an area of high stress. If something is going to go wrong it is usually at the connection.” The joints are where the panels and the framework are bolted together.

Ron Baccus, a NASA structural engineer and team leader of the X-38 composite-shell project at the Johnson Space Center in Houston, said in a telephone interview, “The joint is one part that we’re worried about.”

The shell panels are made of a fibrous carbon-graphite composite melded with a cyanate ester matrix material. It’s the first time it has been used in a space craft.

Composite materials are analogous to reinforced concrete, Caccese explained. In this case the matrix material acts like the concrete, while the carbon-graphite body is the steel reinforcing bars.

The material is not unlike that used in high-quality bike frames, he said.

Despite the fact that nine federal research facilities, the Army and Air Force, a raft of American corporations, the European and German Space Agencies, and 22 European companies are involved in the project, Caccese and his graduate students are the only ones testing the panels and joints, according to Baccus.

They came through at a crucial time for NASA. The space agency did not have the time or the lab space to test a new panel and joint design, Baccus said. NASA didn’t even have the thermal chamber, which is an oven, to do the testing.

The UMaine researchers “came through in a clutch situation for us. We needed it quick,” Baccus said.

Caccese’s graduate students built just what was needed in Crosby Laboratory. And it cost only $2,000 in materials plus student labor to design and to put together. They already had the control devices and measuring gauges on hand. A standard commercial oven would have cost $40,000.

In the test, a carbon fiber panel is bolted to aluminum plates to mimic the connection of the exterior shell to the vehicle skeleton.

The rig is then set in the oven where the temperature is brought up to 325 degrees Fahrenheit. At the same time two round steel bars press against the panel inside the oven. The panel is bent to see whether the joint holds under the load.

The panels only need to withstand temperatures of 325 degrees Fahrenheit for short periods. The X-38’s exterior tiles, like those on the nose and belly of the space shuttle, are what take the heat, at times facing temperatures of 2,900 degrees Fahrenheit during re-entry.

But even going from room temperature to 325 degrees, composite materials will experience some deformation or degradation, Baccus said.

Caccese’s most recent tests have been on panels with stiffening ribs to make sure the ribs don’t pop off under stress.

“We need to know the strength of the design,” Baccus said. “We had another design … but at our temperatures the sheets kept coming apart.”

The ribs are a piece of the composite material bent into the profile of a top hat with the brim bolted to the panel. Baccus said Caccese’s testing has shown that the design has the required strength.

Six to eight of the X-38’s 47 exterior panels will use this “hat-stiffened” designed. They will be on the vehicle’s flat belly, where the maximum aerodynamic pressure occurs, Baccus said.

Caccese and his mechanical engineering students are testing the panels and joints to the breaking point. So far, they’ve destroyed about 50.

“You need to know what the ultimate strength of something is,” Baccus said. “You design a little part of what you need and test it until it breaks. You break stuff at the small level so you don’t run into problems with the big vehicle.”

Caccese said, “The advantage of our testing is that we can break a panel. They can’t afford to break a prototype.”

NASA describes the X-38 as a space ambulance and a space lifeboat. It will be able to hold seven astronauts, the full complement of the International Space Station crew.

It will be able to depart from the station in just three minutes and to touch down on earth less than five hours later.

Instead of wings, the craft will rely on a parafoil to brake its descent as well as to steer it to a landing site.

Caccese said the desire is to develop a vehicle that is able to land at a steep angle of descent by using the parafoil, a steerable parachute. Parafoils are used by the skydiving teams that touch down at the start of major sporting events like the Superbowl.

The advantage of a parafoil is that it only needs a short landing area, thus increasing the number of available landing sites around the world.

The parafoil will enable the craft to touch down at a speed of just 30 mph and stop in only 150 feet. In contrast, the winged space shuttle lands at 200 mph and requires a landing strip 3 miles long.

The X-38 will scud into the atmosphere on its belly. Roughly 4.4 miles up, the parafoil will deploy. At 7,500 sq. ft., it is the world’s largest. It is one-and-a-half times broader than the wings on a 747 jumbo jet. The crew inside the vehicle will control it through winches, pulleys and lines.

Testing of the vehicle has been underway since 1995. The entire cost of the X-38 project is expected to be less than $1 billion, cheap by space standards considering the cost includes four operational spacecraft. An unmanned prototype is to be fully tested in 2002. It will be released from the space shuttle’s cargo bay.

Caccese first hooked up with NASA in 1996 when he went to the Johnson Space Center in Houston on a summer faculty fellowship, where he became involved in the structural design of the outer shell for the X-38.

In 1997, he went back to Houston with graduate student Ryan Gauthier of Manchester, N.H., who now works at Bath Iron Works.

Then last summer, Richard Mewer, a junior from Eliot, received a grant to begin designing and building the oven. Chris Malm, a graduate student from Caribou, completed the oven last fall.

Malm is at the Johnson Space Center for five weeks.

In a July interview, he said he enjoys the work for NASA because “we get to play around with electronics, wiring things up, and we get to see things break.”

But when the X-38 undergoes full-fledged unmanned testing the UM team hopes their work means that the outer skin holds fast.

Watching the test of the prototype, Caccese said, “will be riveting … no pun intended.”