What is "hyflex"

HYFLEX (Hypersonic Flight Experiment) was a NASDA reentry demonstrator prototype which was launched in 1996 on the only flight of the J-I launcher. It was a successor of OREX and was a precursor for the Japanese space Shuttle Hope.

HYFLEX tested the carbon-carbon heat shielding tiles that were intended to be used on HOPE, as well as having the same body shaping in order to gather data on hypersonic lifting. HYFLEX flew in space at 110 km altitude and succeeded in re-entry, but sank in the Pacific after splashdown before it could be recovered.