NASA counts down to critical second test firing of huge SLS moon rocket

NASA and Boeing readied a gargantuan Space Launch System rocket for a second test firing in Mississippi Thursday to clear the way for a long-delayed maiden flight late this year or early next to kick off the space agency's Artemis moon program.

Two months after glitches cut short an initial attempt on January 16, the 21-story SLS core stage's four shuttle-heritage RS-25 main engines were expected to ignite one after the other, at 120 millisecond intervals, throttling up to a combined thrust of 1.6 million pounds. The two-hour test window opens at 3 p.m. EDT. Firmly locked down on a massive test stand at NASA's Stennis Space Center just east of New Orleans, the core stage's Aerojet Rocketdyne engines were expected to fire for up to eight minutes — the duration of an actual climb out of the atmosphere — consuming more than 700,000 gallons of liquid oxygen and hydrogen in the process.