In muddy fields, standing an arm's length apart, the searchers walk from dawn to dusk. With many of the big finds behind them, a 12-hour day may yield just a handful of tile pieces, airy and fragile as Styrofoam.
Five weeks after the space shuttle Columbia shattered over Texas, the hunt for debris has settled into a routine as teams of workers comb the brush and brambles, grid by methodical grid.
"If it's a little piece of material, we don't get disheartened," said Ron Romero, a firefighter from Umpqua National Forest in Oregon. "Seven people died in the shuttle. You never forget that. We're helping bring Columbia home. That's what keeps you going."
Romero is one of thousands of U.S. Forest Service firefighters from across the country who have helped search a 250-mile-long debris path across Texas. About 17% of the shuttle has been found. If each firefighter covers 4 acres a day, debris collection in Texas may stop by the end of April, said Dom Gorie, an astronaut who is leading the search effort.
For 20 firefighters from California's Los Padres National Forest, the day begins with a 6 a.m. meeting at a north Texas warehouse that serves as their base. Beware, they were told Friday: Although a rainstorm has passed, poisonous snakes, ticks, mosquitoes and fire ants may come out of hiding.
An added warning was issued after the group assembled in a cow pasture 60 miles south of Dallas: "Watch out for armadillo holes."
Standing in a line 20 across, the search team slowly walked across the field, all eyes trained on the mud and grass in the search for shuttle remnants.
During their two-week stint in Texas, these searchers waded through swamps; sloshed across fields ankle-deep with mud; cut through briars sharp enough to tear their clothes. But yesterday, with the sun rising against a violet-blue sky, the biggest hazard seemed to be prodigious piles of cow manure.
Suddenly, a shout went up: "Hold it!" Everyone stopped as three federal government officials hurried to inspect the find.
"Yup, it's a tile fragment," said NASA engineer John Connolly, peering at a small white piece no bigger than a pea resting in a clump of weeds. The fragment was put in a plastic bag and the location of the find plotted on a map.
So it went for two hours as the pasture was searched, section by section. For their trouble, the firefighters found three tiny pieces of tile before moving onto a neighboring field to start the process anew.
"You think it would be boring, but it's not," said firefighter Mike Salas, 36. "It's why we came out here. We don't know if that is the piece that could be the answer to what happened."
"The anticipation of finding stuff is what keeps you going," said firefighter Dave Sewell, 29. "We all asked to be here. We want to do this."
In Navarro County, the most significant find so far was a 30-inch by 24-inch piece of reinforced carbon that might have been on the leading edge of the left wing. "Most of the pieces in this area are from the tiles," Connolly said.
It's what you would expect, he added. Lighter pieces fell to Earth before the bigger, heavier pieces that were found east of here, he said.
Grid searches have not begun west of Texas because a clear debris field hasn't been defined, said Johnson Space Center spokesman Kelly Humphries. NASA is still studying photos and videos, trying to project where debris likely fell, he said.
"Finding something in an area that large is daunting, so you have to think it out before going there," he said.
The debris search in Louisiana is over, Humphries said. Navy divers are still searching the Toledo Bend Reservoir in East Texas, while 35 U.S. Forest Service helicopters have joined the air search in other parts of the state.
The tile fragments and mangled shards of metal that have been found lately may not look like much.
But Gorie said "every piece of debris is critical for getting the shuttle back flying into space. Every piece counts."