Implementation of Solar Tracking Onboard a High-Altitude Balloon Platform

The HELIOS program is a series of four solar tracking missions with the goal to demonstrate the feasibility of solar tracking on a high altitude balloon platform while maintaining a low mission cost. For this purpose, a tracking system was developed that could be accurate, simple, and cost efficient. This paper documents the tracking system utilized by HELIOS III and IV both physically and algorithmically, with a brief discussion of the performance of the HELIOS III tracking system during the most recent HASP flight. The marginal mission success experienced by HELIOS III and the early success of the refinements implemented by HELIOS IV strongly suggest that solar observation on a high altitude balloon is feasible. A successful HELIOS IV flight will confirm this and will open up options for high quality solar science to be performed with a low mission cost.