Crack found in third space shuttle

Shuttle engineers inspect Columbia's engines at Kennedy Space Center.

(CNN) -- NASA technicians detected a crack in the main propulsion system on the space shuttle Columbia this week, similar to those found on two of its sister ships.

The discovery of tiny fissures near the liquid hydrogen and oxygen lines on the shuttles Atlantis and Discovery prompted shuttle managers last week to ground the entire fleet indefinitely.

The decision put a damper on the space agency's ambitious shuttle launch plan.

Three shuttle flights were planned for the remainder of the year, including a 16-day science mission on Columbia, which was to begin in mid-July.

At NASA's Kennedy Space Center in Florida, shuttle workers removed Columbia's engine and will continue searching for additional cracks this week.

Whether the cracks pose a danger or lines need to be replaced remains to be determined, according to NASA, which earned praise from aerospace professionals for its quick decision to ground the fleet in the interest of safety.

"Several teams across the country continue to investigate all aspects of the flow liner issue," NASA said in a statement Tuesday. "No further results from those teams analyzing the issue are anticipated before next week at the earliest."

The space shuttle Columbia on the launch pad in Florida before an earlier mission

The metal flow liners are inside the fuel lines that transport super-chilled liquid hydrogen and oxygen for the shuttle's three main engines.

There is concern that a line break might interrupt the fuel flow or send a fragment into one of the engines. But whether such a scenario is even possible remains speculative.

If given the green light, Columbia could launch as early as mid-August, a NASA representative said.

The shuttle Endeavour will be examined for cracks in the near future, according to NASA. It was transported to Kennedy Space Center last week after completing a space mission and landing on a backup runway in California in late June.