The second level trigger of the pamela space experiment

PAMELA is a satellite-borne experiment designed to study the charged component of the cosmic radiation of galactic, solar and trapped nature. The main scientific o bjective is the study of the antimatter component of cosmic rays over a wide range of energies. PAMELA is mounted on the Resurs DK1 satellite that was launched on June 15 th 2006 and is orbiting the Earth on a semipolar (70 ◦ ) elliptical (350 × 600 km 2 ) orbit. The experiment has a foreseen lifetime of at least 3 years. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoinci- dence shield. An electromagnetic calorimeter is used for particle identificatio n and energy measurements. If PAMELA data exceed the storage allowance on the satellite or the daily downlink quota (now�20 GB), a second level trigger may be activated by uplink from ground. Information from the anticoincidence sys- tem and from the calorimeter will be included in the second level trigger condition, providing a selective reduction of data. The data reduction and the systematic uncertainties in the p roton and electron spectra are evaluated with in-orbit data and compared to simulations.