MOFFETT FIELD, Oct. 15 -- NASA is testing the heat shields meant to bring astronauts home from the Moon and Mars by riding along on the space station's garbage.

When Northrop Grumman's Cygnus XL cargo ship left the International Space Station last week, astronauts had packed it with waste and activated a fleet of small capsules inside, designed by University of Kentucky students. As the ship breaks apart over Earth, NASA said, the capsules eject, measure what their experimental materials endure, and send the data by satellite as it happens.

The point is cheap flight data. "We're essentially hitching a ride on a vehicle that's already coming back to Earth," said Keith Peterson, a materials engineer at NASA's Ames Research Center. Each ca...