Durham astronomers team with NASA to launch telescope tethered to giant balloon

By Cameron McAllister

Is it a bird? Is it a plane? No, it’s a telescope suspended from a football stadium sized balloon developed by an international team including astronomers from Durham University. The collaboration, which also includes NASA, the Canadian Space Agency and Toronto and Princeton universities, is an ingenious solution to the problems faced by ground-based and space telescopes.

The giant helium balloon will suspend the telescope, known as SuperBIT (the Superpressure balloon-borne imaging telescope), to a height of 40 kilometres, above 99.5 percent of the atmosphere. This is vital as atmospheric fluctuations are the bane of astronomers on Earth; they distort the light that passes through the atmosphere making high-resolution imaging of space from the ground extremely difficult.

Space telescopes, on the other hand, are expensive and troublesome to repair. The Hubble Space Telescope – which SuperBIT will be able to match in image quality – cost £3.5 billion at its launch in 1990 and required servicing by astronauts travelling via the now-defunct space shuttle. In contrast, SuperBIT has had a budget of only £3.5 million, meaning it has cost almost one thousand times less than an equivalent satellite.

The telescope has incredible pointing stability, equivalent to being able to accurately thread a needle from one kilometre away

SuperBIT relies on superpressure balloon technology recently developed by NASA. As the balloon rises, the helium inside expands due to the drop in the surrounding atmospheric pressure, but unlike in other balloons, the extra helium is not vented off.

Instead, the expansion of the gas is used to pressurise the balloon. The differential pressure (the difference between the pressure in the balloon and the pressure of the surrounding atmosphere) increases during the day as the sun heats the helium and decreases during the night. Though as no helium is lost from the balloon, it is able to stay afloat for months at a time with very little vertical movement, perfect for astronomy.

The final test flight in 2019 showed incredible pointing stability, equivalent to being able to accurately thread a needle from one kilometre away and to hold that direction exactly for an hour.

The fact that the balloon will eventually land is also something of a bonus, as it will provide a perfect opportunity for repairs to be carried out and new parts to be fitted. This means that while space telescopes can be stuck with decades old equipment, SuperBIT can be continually upgraded to make use of the latest digital camera technology.

There’s also lots of room for improvement in the mirror of the telescope, with larger mirrors being able to image at higher resolution. SuperBIT currently has a 0.5 metre diameter primary mirror, and the team already has funding to upgrade to a 1.5 metres telescope. The maximum carrying capacity of the balloon is even larger at two metres, so further upgrades will be possible.

Prof. Richard Massey, of Durham University’s Department of Physics, with SuperBIT prior to its final test flight in 2019. Photo: Richard Massey (Durham University)

When the telescope untethers from Wanaka, New Zealand, in April 2022 for its months-long voyage, it will be aiming to measure the properties of dark matter by watching collisions between clusters of galaxies. Dark matter is predicted to make up most of the universe’s mass but can only be perceived by its gravitational effects on ‘normal’ matter. No particle colliders on Earth can accelerate dark matter.

“Cavemen could smash rocks together, to see what they’re made of,” explained Prof. Richard Massey, of Durham University’s Department of Physics. “We’re going to use SuperBIT to look for the crunch of dark matter. It’s the same experiment, you just need a space telescope to see it.”

Telescopes like SuperBIT could be the future of astronomy. The low cost combined with regular opportunities for repairs means it would be possible to have a fleet of many similar telescopes floating high in the atmosphere in the coming years, allowing more astronomers to see the universe with such extreme clarity.

Photo: Richard Massey (Durham University)

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