Why fly a balloon before orbit
An orbital launch takes a year or more to arrange, and the satellite never comes back. A high-altitude balloon can fly every few months, reaches the stratosphere in a couple of hours, and lands where it can be recovered. Engineers get their hardware back, with its logs.
We flew our first, Stratos-1, to 42 km in May 2026.
Our Stratos missionsWhat the stratosphere simulates
Near-vacuum. At 40 km the air pressure is under 0.3% of its sea-level value. The air can no longer carry heat away, so electronics cool mostly by radiation and conduction, as they do in orbit. A thermal design that relied on convection shows it at once.
Cold. The coldest air is near the tropopause, where over the tropics it falls below −60 °C. Higher up, the stratosphere warms again, and sunlit surfaces heat fast. A payload sees a wide thermal swing in one flight.
A dark sky. Above almost all of the atmosphere, the sky is far darker than from the ground. That makes the stratosphere a good place to test star cameras and imaging chains against real skies and real ground scenes.
What a balloon cannot test
Radiation. The atmosphere above a balloon still shields it from most of the radiation a satellite meets. Single-event upsets and total dose need beam testing or orbit.
Orbital motion. A gondola swings and turns, but it does not move at 7 km/s or slew like a spacecraft. Interpret motion tests with care.
Launch loads and duration. Rocket vibration and shock need a shaker table, and a flight of a few hours says little about years in orbit.
A payload design checklist
Batteries. Lithium cells lose capacity in the cold and must not be charged below freezing. Insulate them, and budget power for the cold part of the ascent.
GPS. Many receivers stop reporting above 18 km because of export limits built into them. Use a receiver with a high-altitude mode, or tracking will stop when it matters most.
High voltage. At low pressure, gaps that are safe on the ground can arc. Check every high-voltage circuit against the pressures it will fly through.
Thermal. Model the payload without convection, test it in a thermal-vacuum chamber if you can, and log temperatures everywhere in flight.
Data. Log everything on board. The downlink will drop out, and the recovered storage is the flight record.
Recovery and permission. Plan the landing zone with a flight predictor, carry at least two trackers, and get clearance from the aviation authorities before launch.
How we use our flights
Every Stratos flight turns a figure we had simulated into one we measured. Stratos-1 flew our compute module and cameras to 42 km in May 2026. Stratos-2, in October 2026, validates the star camera, intelligent imaging and passive radiative cooling. We publish specifications only after they have flown.
