External tanks reach Final Four; last solid motor test fired

The 15-story external tank built to help launch Atlantis in May is expected to arrive at Kennedy Space Center early next week after shipping 900 miles across the Gulf of Mexico from Louisiana.

The solid rocket booster retrieval ship Liberty Star, with a United Space Alliance crew at the helm, is towing the booster in the enclosed barge Pegasus. The tank measures 154 feet long and 28 feet in diameter.

Only three more external tanks remain under production at NASA's Michoud Assembly Facility in New Orleans.

Two more tanks, for the final two shuttle missions, are scheduled for delivery to NASA on May 5 and June 29.

A tank for a rescue shuttle is set for delivery in late September, after the targeted landing of Discovery, if all goes well. The tank, dubbed ET-122, is being refurbished after sustaining damage during Hurricane Katrina.

"This will be it for us," said Harry Wadsworth, a spokesman for tank manufacturer Lockheed Martin Corp.

As delivery of the last tank nears, NASA today announced completion of the final test firing of a reusable solid rocket motor segment by ATK Launch Systems in Promontory, Utah.

You can read about the 123-second test here.

According to NASA's press release, the final test was conducted to ensure the safe flight of the four remaining space shuttle missions.

ATK boosters have successfully launched 129 space shuttle missions to date. There has been one notable failure, resulting in the 1986 Challenger accident.

IMAGE: Above, on Feb. 24, a New Orleans Saints fan directed ET-136 around a corner at NASA's Michoud Assembly Facility in New Orleans. Credit: Lockheed Martin Corp. Below, the final test firing of reusable solid rocket motor FSM-17 today in Promontory, Utah. Credit: NASA.