Poster Presentation

Using a Servo Release Mechanism to Increase Peak Altitude and to Control Descent Profile on Dual-Weather-Balloon Flights

---

Abstract

    We have developed a robust, low-cost, low-mass servo release mechanismcalled “SMART” (Servo Motor Actuated Releasable Tether) for use to releaserigging lines during stratospheric balloon flights. The system consists of a6.2 gram micro servo, a plastic servo arm, a steel pin, and a body of laser-cutplywood parts. SMART is easy to install and can support and release a rigging lineeven when under 40 pounds of tension. This one-time servo release is actuatedvia a PWM signal from a microcontroller.

    Being able to release rigging lines, most notably main line(s), duringstratospheric weather balloon flights has a multitude of uses including flighttermination to decrease the total flight time and/or to avoid undesirabletrajectories or landing locations. Additionally, SMART units can be combined towith creative rigging techniques to achieve greater in-flight control ofballoon-lofted vehicles such as changing ascent/descent rates, opening doors,deploying panels, etc.

    As a sample application, we have used SMART mechanisms on ballooningmissions lifted by dual weather balloons to regularly reach peak altitudesabove 110,000 feet and also to provide either a “float” or a “slow-descent”phase, without requiring a venting mechanism. In these dual-balloon flights twoidentical weather balloons are symmetrically inflated to provide enough lift toachieve a reasonable ascent rate, but not inflated enough for either balloon tolift the payload stack by itself. When the main line to either balloon isreleased by a SMART mechanism at the desired altitude or time, the payload willeither enter a float mode or begin a slow descent (depending on the inflationplan). A second SMART unit is then used to terminate the flight later by severingthe main line to the second balloon, starting a standard (fast) parachutedescent.

    This dual-balloon-with-independent-release flight profile isparticularly useful for experiments that could benefit from additional time ataltitude or, in our particular case, for experiments that benefit from thesensing payload being the first thing to penetrate “undisturbed air” (ondescent), thereby avoiding potential “contamination” when collecting data from withinthe wake of the balloon/parachute (on ascent).

    Challenges with this particular dual-balloon technique, which we areworking to overcome, include keeping the balloons from tangling (and hence notdeparting cleanly when released) and/or having one or both balloons poppingearly (possibly due to interactions on ascent). If releases are to bealtitude-based, rather than timer-based, then having reliable gps-based (orpressure-based) altitude information is critical. Programming logic has beendeveloped to help payloads make appropriate decisions even if altitude data isnot 100% reliable and/or if the evolution of the flight does not go accordingto plan, such as if either balloon bursts before it was scheduled to bereleased. Implementation of a finite state machine based on altitude and timeallows the system to make autonomous in-flight decisions. The logic includeschecks for in-flight failures like premature popping of balloon(s),unexpectedly slow ascent or descent rates, inadvertently getting stuck ataltitude (i.e. going into an unplanned float phase), and more. Gps fences havealso been implemented to try to prevent stacks from landing in particularly wetor heavily forested locations.

Keywords: release, servo, float, slow, descent, stratospheric, ballooning

How to Cite:

Ally, A., Ailts, G., Stutler, J., Flaten, J., Jetzer, M., Peterson, S. & Nguyen, V., (2019) “Using a Servo Release Mechanism to Increase Peak Altitude and to Control Descent Profile on Dual-Weather-Balloon Flights”, Academic High Altitude Conference 2018(1). doi: https://doi.org/10.31274/ahac.242