Schiaparelli surface platform
This illustration shows the Schiaparelli surface platform, which includes the DREAMS package, UHF antenna, propellant and helium pressurant tanks, as well as the inertial measurement unit (IMU), and landing accelerometers. (Not visible in this image are the descent camera, DECA, and the Radar Doppler Altimeter.)
The IMU (indicated in this figure) contains three accelerometers and three gyroscopes, which are used to measure the flight motion during entry and descent. The IMU detects the initial deceleration upon reaching the atmosphere and determines the entry interface point, at an altitude of approximately 120 km. It measures continuously throughout entry and descent until landing.
The IMU, along with the Radar Doppler Altimeter (located beneath the surface platform and not visible in this image) and the Sun sensor (located on the back shell and not shown here) are part of the guidance, navigation and control loop for landing.
Upon landing, the three landing accelerometer units (indicated in this figure) measure the deceleration, on six axes. The accelerometers are separated by 120 degrees on the platform surface. This configuration allows engineers to reconstruct the motion of touchdown.