Spirit of Knoxville

Lore & Background

The project began in 2005, under the direction of students from the Amateur Radio Club at The University of Tennessee, with a series of technology demonstrator flights dubbed the 'Icarus' series. These flights tested small zero-pressure balloon designs, ballast dumping mechanisms and material, custom radio circuitry, the Distributed Tracking and Relay volunteer listening network, and command uplinking.

The first Spirit of Knoxville 'SNOX' designated flight was SNOX I, reaching a stable float altitude of approximately 11 kilometres (36,000 feet). Launched from Knoxville Downtown Island Airport in December 2007, the balloon travelled over 900 kilometers southeast to land just north of the Bahamas, fulfilling the objectives of the new balloon envelope. The flight ended due to the ballast system's inability to drop weight fast enough at nightfall after the loss of daytime solar heating. SNOX II launched in January 2008, but landed in minutes just a few kilometers away in an urban home backyard due to a rip in the top of the balloon from newly tested inflation procedures. SNOX III, launched in January 2008, was the first official attempt to cross the Atlantic Ocean; the onboard GPS failed shortly after launch, but crude radio direction finding indicated the balloon followed its predicted trajectory as far as the shore of the Atlantic Ocean in Virginia.

SNOX IV, launched on March 11, 2008, remained in the air for over 40 hours and 5,600 kilometers (3,500 mi), surpassing all flight duration and distance records for amateur balloons. The ballast system used all available weight on the first night, and the balloon system succumbed to the loss of solar heat on the second sunset, landing just a few hundred kilometers from Ireland. SNOX V, launched April 5, 2008, suffered a failure of the envelope itself, landing in southwestern Virginia approximately 8 hours after launch.

Reader's Guide

The Spirit of Knoxville project is significant as a notable amateur radio and high-altitude ballooning effort that pushed the boundaries of what volunteer scientists and students could achieve with limited resources. The project demonstrated the use of custom-built zero-pressure balloons, denatured alcohol ballast, and a distributed volunteer tracking network (Distributed Tracking and Relay) to attempt transatlantic crossings. As of November 2008, five flights had been made, with three intended to cross the Atlantic; the goal was later achieved in 2011 by the California Near Space Project. The project's legacy includes setting amateur balloon duration and distance records with SNOX IV, which flew over 40 hours and 5,600 kilometers. The flights also highlighted technical challenges such as ballast system response to solar heat loss, GPS failures, and envelope integrity. Amateur radio operators voluntarily assisted in tracking the balloons, underscoring the collaborative nature of the project. The need for continuous high-speed jet stream winds from Knoxville to Europe or Africa restricted the number of crossing attempts per year.

Did You Know?

• The project name was inspired by Charles Lindbergh's Spirit of St. Louis aircraft.
• SNOX IV set amateur balloon records for duration (over 40 hours) and distance (5,600 kilometers).
• The balloons used denatured alcohol as ballast to maintain altitude.