Not mentioned in the article but touched in the conference is this is at least third time a 500N-class thruster failed on an ISAS probe. Last time it blew off on Akatsuki/PLANET-C Venus probe, before that was Nozomi/PLANET-B Mars probe, both cut apsis burn shorter than intended and later determined to be from salt buildups due to propellant leaks. Apparently apogee motors has been proving harder to do right than anticipated.
