Northrop Grumman are developing new large solid rocket motors for the SLS, because if they don't SLS could run out of the old shuttle parts they're using. This is part of a program called 'BOLE' Booster Obsolescence and Life Extension - rather than simply building new boosters they're removing all the bits that were needed for the Shuttle but no longer make sense for SLS. They're using a new casing, new fuel and new support systems.
But their first test did not go as planned.
NASASpaceFlight's Full Coverage
https://www.youtube.com/watch?v=EC9icOKGJ94
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