Mechanisms for Lowering Tethered Payloads: Lessons Learned from the Mars Exploration Program

Compact, lightweight, highly reliable lowering devices capable of paying out tether to lower a payload some number of meters with exacting performance, from a balloon or a parachute or part of a spacecraft, typically appear in systems so unique that there is little historical precedent to build upon when preparing designs. However the NASA Mars Exploration Program has in recent years sent three such lowering devices to the red planet, producing an abundance of lessons learned and three satisfactory - though not flawless - landings. Anomalous drag behavior on the first MER lander, results from tests seeking to find the cause of change in brake drag, basic equations for centrifugal brakes and tapered spool descent mechanisms, tether design, and a lowering device designed for an upcoming Mars landing will be discussed.