O
ur universe emits radiation over an incredible
rangeofwavelengths,fromtheinfraredglow
of dust that shields the youngest stars to
gammaraysfromdistantsupernovae.Earth’s
atmosphereblocksallbutatinyfractionof
thesecolours,though,andthelightthatdoesmakeitto
Earth’ssurfaceblursasitpassesthroughtheair.
To compensate, astronomers build high-tech telescopes
on tall mountains. Yet even the highest astronomical
observatory in the world, the University of Tokyo Atacama
Observatory (5,640 metres), sits above only about half of
Earth’s atmosphere. An even better solution is to place
telescopes in space, but such projects are expensive: NASA’s
exoplanet-hunting Kepler mission cost US$600 million, and
that’sonthelowend.Thehighcostofspace-basedtelescopes
meansthatscientistscanconstructfewsuchsatellites.
A cheaper alternative is to attach a telescope to a helium
balloon and launch it into the stratosphere, typically for less
thanUS$1millionperflight.Agiantballooncancarrya
telescope weighing thousands of kilograms to altitudes more
than 30 kilometres above Earth’s surface — approximately
three times the cruising altitude of a commercial jet aircraft.
Such balloons are significantly closer to Earth than, say, the
Hubble Space Telescope, which orbits at 547 km. But because
atmospheric density drops nearly exponentially with altitude,
these balloons fly above 99% of Earth’s atmosphere.Because balloon telescopes can reach almost space-like
conditions for a small fraction of the cost of an equivalent
satellite, we can use them to test new technology and train
students, all the while obtaining cutting-edge scientific data.The birth of flight
The modern era of human flight began on November 21,
1783, when a hot-air balloon swept over Paris, carrying Jean-
François Pilâtre de Rozier and the Marquis d’Arlandes.
The balloon, a creation of Joseph and Étienne Montgolfier,
was made of linen paper and silk, then coated with the
compound alum to reduce the risk of fire. Outside, lavish
decorations included signs of the zodiac and illustrations of
King Louis XVI. But the scene inside was more adrenaline-
inducing than elegant: The first aeronauts frantically threw
wool and straw from a circular balcony onto a brazier as fast
as they could to keep their balloon from sinking. In just 25
minutes, they travelled 9 km.
This was a remarkably dangerous endeavour: In addition
to the potential for smashing into buildings, or the balloon
catching fire, no one was sure how high they would ascend
and whether humans could survive at such heights.
Less than two weeks later, the physicist Jacques Charles
made the first ascent in a hydrogen balloon, which launched
before a crowd of 400,000 people in Tuileries Gardens,
NASA’S GODDARD SPACE FLIGHT CENTER CONCEPTUAL IMAGE LAB Paris. This balloon was much easier to control than the
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