Design of a Payload Recovery Device in case of accidental breakage of tether of an aerostat

摘要

An Aerostat is an aerodynamically shaped envelope filled with a Lighter-Than-Air (LTA) gas and tethered to the ground. It can be used as an aerial platform to carry payloads for several applications such as surveillance and photography. One of the main operational problems faced by an aerostat when deployed at a site is accidental breakage of tether, which results in drifting of its payload. This paper describes a Payload Recovery Device (PRD) that gets activated if tether of an aerostat breaks. The recovery of payload is accomplished in three stages, viz., tether breakage detection, signal transmission and device activation. The envelope of aerostat is deflated by deploying a mechanism that results in a small circular hole on its top. As the LTA gas in the envelope escapes, the buoyancy of the aerostat decreases and it gradually descends. The size of the hole controls the gas leak rate and hence the velocity of descent. A prototype of this device was fabricated and tested successfully on a small indoor aerostat. Results of simulation of the trajectory and velocity of descent of the payload after tether breakage are presented for single chamber as well as double chamber aerostat envelopes.