SLS UPDATE: NASA to roll back its mega rocket after failing to complete countdown test.

NASA said that its contractors, as well as its agency’s, will use the next several weeks to address problems that cropped up during the fueling tests when the SLS rocket returns to the large Vehicle Assembly Building. For example, gaseous nitrogen system supplier Air Liquide will upgrade its capabilities. NASA will also replace a faulty check valve on the upper stage of the rocket, as well as fix a leak on the mobile launch tower’s “tail service mast umbilical,” a 10-meter-tall structure that provides propellant and electricity lines to the rocket on the pad.

The space agency announcement did not provide any information about schedule impacts. It seems probable that it will take a week or so to prepare and roll the SLS rocket back to the Vehicle Assembly Building. Work on the rocket at that location will probably take up most of the month of May, at least.

NASA will then have to make some difficult decisions. It could opt to roll the rocket and its mobile launch tower to the pad a second time and try again to complete the wet dress rehearsal test. Then, following its normal procedure, NASA would roll the rocket back to its assembly building to arm the “flight safety system,” before rolling for a third time to the launch pad for liftoff. It seems the absolute earliest the SLS rocket could launch in such a scenario would be August, but a fall liftoff may be more likely.

Scheduling a wet dress rehearsal usually indicates the rocket is basically ready to go but that doesn’t seem to be the case with SLS, after $23 billion and years of delays.

Also: “Agency officials are closely tracking the health of the fuel in the solid-rocket boosters, which were stacked about 16 months ago, among other issues.”