NASA ground crews discovered a hole in the Space Shuttle Atlantis right-hand payload bay door radiator.

The hole, about a tenth of an inch in diameter, apparently resulted from something hitting Atlantis while it was on the mission to the International Space Station, well above Earth.

Some analysts speculate that the shuttle likely was hit by a micrometeorite.

The damage couldn’t possibly have been caused by foam insulation ripping loose from the external fuel tank and hitting the shuttle orbiter vehicle, a NASA spokeswoman said in response to a question. A chunk of foam insulation in 2003 hit the Space Shuttle Columbia orbiter vehicle, punching a hole in the leading edge of the wing.

Fiery hot gases during reentry poured into the wing and caused structural failure, causing loss of Columbia and its crew.

In subsequent launches of Discovery and Atlantis, video cameras have watched for foam hits on the orbiter during launch. Then, once in orbit, each shuttle was inspected minutely and repeatedly for any signs of damage.

However, those examinations have focused intensely on areas of the orbiter subject to extreme heating during reentry, such as heat tiles along the leading edges of the wings, and the nose cap. In contrast, the payload bay doors don’t experience blistering heat in reentry.

The hole in the payload bay door resembles a bb hole, or a miniature bullet hole.

For now, NASA can’t determine with any certainty just what hit Atlantis to create the hole.

“The impact occurred sometime during the STS-115 mission last month,” NASA reported in a statement. “The nature of the object that hit the shuttle radiator isn’t known.

“The hit, which left a hole about one-tenth of an inch in diameter, didn’t endanger the spacecraft or the crew, nor did it affect mission operations.”

During and immediately after the mission, NASA officials said Atlantis looked very clean, with no major damage visible. But they cautioned at the time that they wouldn’t be able to say no damage occurred until Atlantis underwent exhaustive examination on the ground.

Space junk and micrometeorites can pose a hazard to spacecraft, and to astronauts during spacewalks. But as commander Bill McArthur said in an interview, there always is some risk in space travel, a danger that astronauts knowingly and willingly accept. (Please see Space & Missile Defense Report, June 12, 2006, page 1.)