Having just missed the launch window in 2015 with the first flight of ValBal, the Stanford Space Initiative college group has returned in 2016 to win the 1st Place Best Design prize with a 1000km flight to Mexico with their Valve-Ballast latex balloon altitude stabilization system. Pretty sweet!
Link to report: here
From the team: "The Stanford Student Space Initiative, home of the GSBC, is in its fourth year of HABing, with over 40 recorded balloon launches featuring countless innovative technologies. The SSI HAB team has always had an emphasis on pushing the bounds of amateur ballooning by introducing solutions that advance payload capability and increase flight duration, as well as developing increasingly sophisticated avionics and control systems. After flights totaling over 5,000 miles of ground track and over 180 hours of flight time, the team was excited to launch the fifth iteration of it's ValBal (Valve-Ballast) latex balloon altitude stabilization system. ValBal, in development within SSI for over a year, was developed to increase the endurance of latex balloons, with the goal of traversing the continental United States. After a year of design iterations, ValBal Mk 5 was launched on May 8th from Laird Park, in Modesto CA and flew a over 1,000 km for a flight time of 16 hours. The team has nearly completed the next iteration, ValBal Mk 5.1, set to launch this summer."