The Balloon
A solar-powered hot-air balloon that reaches the stratosphere. No helium. No rocket science. Just plastic, tape, and sunlight.
Stratospheric Science, Democratized
What once required expensive equipment and specialized expertise is now achievable with hardware store materials.
Radically Affordable
At ~$30 for materials, you can build a balloon that does what professional equipment costing thousands cannot easily do: sustained stratospheric flight.
Zero Helium
With helium prices rising 10% annually, the heliotrope uses only ambient air heated by the sun. It's sustainable and infinitely renewable.
Edge of Space
Float altitudes exceed 24 km (79,000 ft) - well into the stratosphere where the sky turns black and you can see Earth's curvature.
All-Day Flights
Unlike weather balloons that burst after minutes, heliotropes float for 10-16 hours, landing gently at sunset. In Arctic summer, flights lasted 72+ hours.
Payload Capable
Carry hundreds of grams to several kilograms of sensors, cameras, or experiments. The 6m balloon lifts 700g to 23 km altitude.
Truly DIY
Two people can build one in 3.5 hours using painter's plastic and packing tape. No welding, no specialized tools, no expertise needed.
Inflation, liftoff, and ascent of a solar balloon in the desert
How High Does It Go?
How to Build Your Own
From hardware store to stratosphere. Choose your view below.
Two Ways to Learn
Quick overview for the curious, or detailed steps for the builder.
Cut the Plastic
Cut five 30ft strips from painter's plastic roll, unfold to 30x12ft rectangles
Stack & Fold
Fold each rectangle twice, stack all five sheets aligned perfectly
Draw the Gore
Draw quarter-sine curve on top sheet using the gore formula
Cut All Layers
Cut through all layers at once - you now have 5 balloon gores
Tape Together
Join gores with overlapping clear tape from pole to pole
Create Vent Hole
Cut ~1m opening at bottom, reinforce with paracord loop
Darken Interior
Add charcoal powder inside to absorb sunlight
Attach Payload
Tie rigging lines across vent hole at gore seams
Performance Specifications
Based on 26 flights conducted by the research team over 4 years.
Standard 6m Balloon
- Diameter~5.8 m (19 ft)
- Circumference60 ft (18.3 m)
- Number of Gores5
- Envelope Mass1.2-1.3 kg
- Vent Hole Diameter~1 m
Flight Performance
- Max Float Altitude24+ km (79,000 ft)
- Typical Float19-23 km
- Ascent Rate1.8-2.4 m/s
- Flight Duration10-16 hours
- Landing Speed<10 m/s
Payload Capacity
- 6m to 23 km700 g
- 6m to 19 km1.7-1.9 kg
- 9m to 20 km2.4 kg
- 9m to 24 km2.3 kg
Build Specs
- Material Cost~$30
- Build Time (2 people)3.5 hours
- Plastic Thickness0.31 mil (7.87 μm)
- Plastic TypeHDPE (painter's)
Independent Fan Project
This website is not affiliated with Sandia National Laboratories, NASA JPL, or the research authors. It's an independent tribute to their remarkable open-science work.
All technical information is derived from their peer-reviewed paper. For the official source, original figures, and complete scientific details:
Read the Original PaperBowman et al. (2020). "Multihour Stratospheric Flights with the Heliotrope Solar Hot-Air Balloon"
Journal of Atmospheric and Oceanic Technology, Volume 37, pp. 1051-1066