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 kilometers (68 mi) altitude and succeeded in re-entry, but sank in the Pacific after splashdown before it could be recovered.
[1][2] The experimental vehicle was covered in carbon–carbon, ceramic tiles, and flexible thermal insulation, which were materials that was to be used for HOPE.
[1] During its descent the craft glided in a right turn circling the island of Chichijima in the Ogasawara Archipelago.
HYFLEX had various sensors attached to each parts, and succeeded in gaining data on surface aerodynamic heating and pressure.