Sensors for Precision Airdrop Systems

Precision airdrop systems using GPS information to control the drop trajectory have the potential to transform military resupply operations by delivering payloads accurately from a safe height and offset distance. A number of guided parafoil systems have already been fielded, and further systems are currently being developed. While GPS-based control is sufficient for lateral guidance, the uncertainty of GPS height information results in high impact velocities and unacceptable overshoots and undershoots due to mistimed flaring maneuvers at landing. 

Creare developed a robust, reliable, and accurate Sodar Height Sensor (SHS) that allowed final deceleration maneuvers to be precisely timed. The SHS determines its height above ground by emitting acoustic pulses and analyzing the return signals.  It incorporates a speaker, microphone, barometer, and temperature sensor. Advanced estimation algorithms running on a digital signal processor produce continuous estimates of the sensor height above ground. The height sensor’s range is between 300 and 1000 feet depending on parachute noise and its accuracy approaches ± 2 feet as it nears the ground. The sensor can penetrate smoke, fog, dust, and rain and is not confused by ground vegetation or corrupted by electromagnetic interference. Creare’s initial sensor prototypes were successfully flown in over 50 airdrops from altitudes as high as 20,000 feet aboard systems ranging from 200 lbs to 30,000 pounds. 

With the success of these prototypes, Creare has teamed with Kaman Aerospace to deliver a production sensor system. Development of a production-representative prototype has been completed and first article units have performed successfully in airdrop tests. Creare has also successfully developed and delivered an airspeed sensor that deploys from the guidance unit during flight and retracts before impact. We are now working to demonstrate a Radar Height Sensor (RHS) that offers increased range and potentially lower cost for situations where vegetation penetration is not required.