Complex sentence: The durability of the capsule was tested for temperature, pressure and acceleration/deceleration using three unique testing installations: temperature durability was checked in a high-temperature vacuum system emulating the upper layers of the atmosphere.
Split into simpler sentences: The durability of the capsule was checked by exposing it to high temperatures, pressures and accelerations using three unique testing installations. The heat resistance was checked in a high-temperature vacuum system emulating the upper layers of the atmosphere.