HS-81C55RH, HS-81C56RH March 1996 Radiation Harde.
HS9-81C55RH - Radiation Hardened 256 x 8 CMOS RAM
HS-81C55RH - Radiation Hardened 256 x 8 CMOS RAM
HS1-81C55RH - Radiation Hardened 256 x 8 CMOS RAM