The Gusteau Balloon Telescope, the largest cosmic Christmas ball, is almost ready for its space flight

It's less crazy than it sounds: launching a telescope with a balloon. After all, launching a balloon is cheaper and faster than launching a telescope into space using a rocket. Moreover, the chance of catastrophic failure is reduced. If something goes wrong with the rocket launch, you will lose billions of euros and countless years of development time. If something goes wrong with the balloon, the telescope can safely return to Earth, hanging from the parachute.

NASA's Gusto hot air balloon telescope will soon float 30 to 40 kilometers above the Earth's surface after launch. It's not yet close to the “border” with space, but it's high enough to be less affected by water vapor in the atmosphere, which emits radiation at exactly the frequencies Gusteau wants to measure.

When you think of a telescope suspended under a balloon, don't think of the wobbly strings you can see under toy balloons. It is relatively calm at high altitudes and the balloon also moves with the air currents.

The void between the stars

Once it reaches its target altitude, Gusteau will peer deep into our galaxy, the Milky Way, for at least the duration of its 55-day mission. In addition, you will see our neighboring galaxy, the Large Magellanic Cloud. In both systems, the focus is on the so-called interstellar medium, which is the matter that circulates in the large spaces between stars, and the radiation that permeates such regions. In this way, astronomers hope to learn more about how stars form and how galaxies evolve.

Although GUSTO is a NASA mission, Dutch scientists and engineers are closely involved in both the construction and scientific analysis of the measurement data. “I've been mainly busy checking everything lately — detectors, electronics, that kind of stuff,” Jose Silva of the Dutch space research institute Sron says by phone from Antarctica, where Gusto won't arrive until Christmas Day. . As soon as they will be released. “It's actually a bit like tuning a car.”

There are several reasons why Gusto was launched from Antarctica. For example, there is less water vapor over the continent than elsewhere, summer in Antarctica is good for power supplies – Gusto is equipped with solar panels – and airflow from the polar vortex ensures that the telescope stays over the continent. For a longer period. Additionally: Gusto does not cross any politically sensitive national borders, and in the event of an emergency landing, the telescope does not accidentally end up in someone's home.

However, despite all these advantages, the harsh environment also poses many practical challenges. “For example, the balloon facility is located 15 kilometers from the camp here,” he says. “By the way, this building is 15 meters high. Did you know that makes it the tallest building in the whole of Antarctica?’” he says with a laugh. “That’s a fact I always like to share with people.”

Heavy snow storm

The flight to this modest, record-height structure from its home in Antarctica takes about 45 minutes – an extraordinary flight time for ordinary passengers. “Just: There's really nothing else out there.” When I had just arrived in Antarctica, I had to return to our accommodation after half an hour because a heavy snow storm was about to pass and it would not be safe in the balloon facility. In the end it turned out to be a false alarm, but something like that would cost you half a day.

Silva has been working on Gusteau detectors for a few years, and they are “the heart of this telescope,” as he describes them. “That's why most of the attention is paid to it.” Are all pixels working? Are they sensitive enough? This is my biggest fear.”

Because although launching a balloon is relatively cheap, it is still not possible to simply lower the telescope for repair, or fly an engineer to an altitude of 40 kilometers to solve an on-site problem.

The extenuating circumstance is that the telescope will soon be “on” when it takes off. This is often impossible in the interior of the rocket, so there is tension after launch to ensure all the hardware is working properly. The tension here is already over.

269 ​​degrees below zero

However, the launch itself is not entirely without technical challenges, Silva says. “For example, our detector must be cooled to minus 269 degrees Celsius,” he says. This detector uses superconductivity, which only occurs at very low temperatures. “Even 250 degrees below zero would be very hot.”

At the time of launch, all this technology has already been extensively tested. “We first run a test to see if everything is working, by checking every part of the device.” Silva and his colleagues hung the telescope on a crane and turned it on. “This test was actually the most exciting moment – ​​more exciting than the balloon launch itself.”