In this case, size doesn't matter.
A diminutive hunk of space junk the size of a bullet sent three astronauts scrambling to their escape pod aboard the International Space Station just after noon on Thursday.
And no wonder.
That rogue token of some other orbital mission was traveling at more than 5 miles per second - a speed that would allow even something that small to rip a fatal hole in the space lab, orbiting 220 miles above Earth.
"We've cleared," commander Air Force Col. Mike Fincke told mission controllers in Houston as the 10-minute emergency stay in the Russian-made capsule ended.
"We're all happy. That's great news," they radioed back.
The trio of astronauts - Col. Fincke, NASA flight engineer Sandra Magnus and Russian cosmonaut Yury Lonchakov - had peered out the window, looking for the threatening debris.
"We didn't see anything, of course. We were wondering how close we were - we'd be interested in that," Col. Fincke said.
No one really knows how close the space junk came; its surprise appearance came too late for flight controllers to ease the space station out of the way - a "debris avoidance maneuver" that has been done eight times in the station's 10-year orbiting history.
This is only the second time astronauts have adjourned to an escape craft for safety's sake; in November, the remains of an old rocket came within 12 miles of the station. This time, the debris came within three miles.
"Crew members entered their Soyuz TMA-13 capsule and soft-locked the hatches, in case the debris affected the space station and they were required to undock," said a NASA report.
The exact origin of debris, which measured 9 millimeters long, was somewhat of a mystery.
NASA spokeswoman Laura Rochon theorized it was a motor part left over from a Delta rocket or from a passing space shuttle. Some analysts also thought it was a counterweight used in orbit stabilization - and could possibly be heading up a yard-long strand of other material.
Space junk has lingered above the planet since 1958, when the first defunct satellite began to orbit Earth on its own. The U.S. Space Surveillance Network now tracks 17,000 objects larger than 10 centimeters - from rocket parts to astronaut apparel and one lost tool bag.
The network also follows 200,000 smaller pieces - and "tens of millions" of the tiny types, under 1 centimeter.
During the past 40 years, an average of one cataloged piece of debris fell back to Earth each day according to NASA's Orbital Debris Program Office, which issued its first mitigation policy on the problem in 1995. The office is not alone.
Several international space agencies have formed the Inter-Agency Space Debris Coordination Committee to address the space junk problem. The United Nations Committee on the Peaceful Uses of Outer Space has also issued its own guidelines.