PFRX means Preflight Relmat
X-1,2,3...9 or A,B,C...Z in
NASA
Similar to PFRX
2IC - Second In Command
2M - Micro Miniature
2MASS - Two Micron All-Sky Survey
2STO - Two Stage To Orbit
3-DOF - Three Degree Of Freedom
3AAL - Three Axis Acoustic Levitator
6-DOF - Six Degree Of Freedom
View all in NASA