The leading letter tells you which object catalog the object belongs to, as follows:
|A||auxcat (Auxiliary catalog)|
|C||csocat (Complementary catalog)|
|D||deepcat (Deep space catalog)|
|F||ftocat (Failed to orbit catalog)|
|L||lcat (low altitude catalog)|
|R||rcat (suborbital catalog)|
|S||stdcat (Standard catalog)|
|T||tmpcat (Temporary catalog)|
The second letter, possibly followed by digits, is the launch success fraction (see the definitions section ) Usually the launch success fraction code is S, F or U for Success, Fail or Unknown. Success implies propulsive success only, even if no data was returned from the payload. Also used is E, for pad explosion (no launch occurred, but included in the lists for completeness).
For orbital launches partial success/failure values are sometimes given, e.g. OS80 or OF40. The values between 00 and 99 indicate a percentage success to be used in statistical assessments of launch vehicle reliability as originally described in JSR 669 and here in the launch success fraction part of the definitions section.