We plan to measure masses of very shortlived exotic nuclei far from β-stability by using the Experimental Storage Ring (ESR) of the GSI as an energy isochronous Time-of-Flight (TOF) mass-spectrometer which requires a special ion-optical setting of the quadrupoles in the ESR. Via projectile fragmentation a large variety of exotic nuclei can be produced, which can be separated in flight by the Fragment Separator (FRS) prior to being injected into the ESR. A special time-pick-off-detector has been developed, which uses secondary electron emission from a thin foil, which is penetrated by the ions under investigation. This detector has been designed for use in the ESR-vacuum of 10^-11mbar and has an intrinsic time-resolution of ≈ 85ps. Also a Time Recording System (TRS) with a time-jitter of only ≈ 50ps has been build. The TRS is capable of recording time-marks for a few ions over a large number (> 500) of turns.