The attempt by NASA to conduct a full countdown dress rehearsal of the SLS core stage, including loading its tanks, was scrubbed early in the countdown yesterday when engineers encountered problems loading oxygen into the rocket’s tanks.

An issue with the LOX chilldown process run on Monday meant that the LOX propellant tank couldn’t be filled, which meant that the full WDR test wasn’t possible.

NASA’s post-scrub statement indicated the vehicle systems performed well and that the Core Stage engineering community and the test team at Stennis were working on fixes and determining when the tanking and countdown demonstration parts of the WDR test can be retried.

This dress rehearsal is intended to preparatory to what NASA dubs the Green Run test static fire of the core stage, set to last for the full 500 seconds the core stage would fire during an actual launch. Whether this scrub will prevent that Green Run test from occurring before the end of the year remains unclear. Either way it must happen soon if NASA is to maintain its schedule for the long frequently delayed launch of SLS, now scheduled for November ’21.