NASA shuttle managers decided Thursday not to test fuel the external tank that will feed the Discovery orbiter during a planned launch this July, space agency officials said.

Shuttle managers have debated the fuel-loading test since last month, when engineers opened up the aft end of Discovery's Lockheed Martin-built external tank to replace four engine cut-off sensors inside its liquid hydrogen compartment.

Known as a tanking test, the fuel-loading check operation involves pumping Discovery's 15-story fuel tank with the 526,000 gallons (about two million liters) of super-chilled liquid oxygen and liquid hydrogen into the orange vessel while it sits atop the launch pad. The test would verify the performance of the new ECO sensors and allow engineers a chance to see the changes made to ET-119's foam insulation covering - the most noticeable of which is the removal of a 38-foot (11-meter) ramp - under fully fueled conditions.

"There's a cost to it in a lot of places and that's what they were looking at, the pros and the cons," James Hartsfield, a NASA spokesperson with the agency's Johnson Space Center in Houston, told SPACE.com, adding that the test could reduce the contingency time at the pad for the planned space shot.

Discovery's launch will mark NASA's second shuttle mission - STS-121 commanded by veteran astronaut Steven Lindsey - since the 2003 Columbia accident. The spaceflight is currently slated to launch on July 1, but has a flight window that stretches through July 19.

NASA decided to swap out Discovery's fuel tank ECO sensors with new ones in March after identifying a wiring defect in similar units. The sensors are designed to shut down a shuttle's three main engines before its fuel tank runs dry. They can be checked during tanking tests or actual pre-launch fueling to verify that they are working properly.

Last week, shuttle managers also said that they would not make additional changes to Discovery's external tank aside from the already completed removal of a protuberance air-load (PAL) ramp that shielded a cable tray and pressure lines.

During Discovery's last launch - NASA's first return to flight mission STS-114 - a one-pound (0.4-kilogram) piece of foam popped free from the ramp during the orbiter's ascent. While the foam debris did not strike the orbiter, it was reminiscent the foam shedding problem that doomed the Columbia orbiter and its seven-astronaut crew in 2003.

NASA's space shuttle chief Wayne Hale said Friday that the PAL ramp removal marked "the largest aerodynamic change" to the shuttle launch system since its first flight 25 years ago.

At NASA's Kennedy Space Center (KSC) spaceport in Florida, preparations are underway to move Discovery from its hangar-like Orbiter Processing Facility to the 52-story Vehicle Assembly Building, where the shuttle's external tank has already been mated to the two solid rocket boosters that will launch the spacecraft into orbit, on May 12.

The complete launch stack is also on track to roll out to the launch pad on May 19, KSC spokesperson George Diller said.