When you think of innovative new space launch concepts, you likely think of rockets like SpaceX’s Starship or NASA’s Space Launch System carrying telescopes or robotic explorers out into orbit and beyond. And certainly, rockets are here to stay, remaining the principal way of carrying things beyond Earth’s gravity. However, an alternative and cheaper option might come from a much older form of technology: Balloons.

Balloons filled with hot air or gas have been lofted up into the skies for centuries, with records of the ancient Chinese military using balloons for signaling as far back as the 3rd century AD, and crewed balloon flight beginning in Europe in the 1780s. And they have been used in astronomy research as well, like the U.S.’s Project Stargazer of the 1960s which sent two men and a telescope 82,000 feet (25 kilometers) into the air in a high-altitude balloon to observe the stars.

Now, recent developments in balloon technology from NASA mean balloons may once again prove their worth for cutting-edge astronomy projects, carrying high-tech telescopes up into the atmosphere from where they can observe the cosmos. We spoke to one of the researchers working on a new generation of balloon-based telescopes, Mohamed Shaaban of the University of Toronto, to learn how this old technology is being put to brand new use.

Up, up, and away

To understand why balloons have such great potential for use in telescope missions, you need to understand why we send telescopes into orbit to begin with. While there are plenty of telescopes located on the ground doing sterling work, if you want to look at really distant objects then you need to account for the problems caused by Earth’s atmosphere.

The big issue is the water vapor in the atmosphere, which blurs images taken by ground-based telescopes. That’s why telescopes are often placed in locations that are very dry and at very high altitudes, like Mauna Kea in Hawai’i or the Atacama desert in Chile. But the best solution is to look at distant objects from above the atmosphere, hence why telescopes like Hubble are put into orbit.

The SuperBIT balloon in flight.
The SuperBIT balloon in flight, above NASA’s Columbia Scientific Balloon Facility, Texas, in June 2016 Richard Massey / Durham University

Traditionally, if you want to put a telescope above the atmosphere, then you send it into orbit on a rocket. That’s expensive and not easy to do — and it’s hugely expensive to fix any problems which occur and require hardware replacement — but it’s a highly reliable method for avoiding Earth’s atmosphere.

Balloons, on the other hand, have been used in scientific research for decades, typically over Antarctica. The problem with using balloons for telescopes before now has been a matter of light. Most scientific balloons are launched in Antarctica because the research hardware is generally powered by solar panels, which can only operate during daylight hours, and Antarctica has 24-hour daylight during its summer. But that means you’re limited to the kind of research that can be done during the day, which isn’t great for telescopes.

But the newly developed balloons from NASA, called super-pressure balloons, can operate in Earth’s mid-latitude region and work during both day and night cycles. “For the first time we’ll be able to do night-time science [with balloons],” says Shaaban, which opens the door to enabling a whole range of astronomy projects.

A new kind of balloon

There are big advantages to balloons as a method to carry telescopes. Firstly, launching a balloon is tremendously cheaper than launching a rocket. Also, you can very easily bring a telescope back to Earth and then relaunch it, so if you have to perform any maintenance then it’s relatively easy. That’s a big deal when you consider how difficult and complex it was to perform maintenance on the Hubble telescope when it experienced hardware problems shortly after its launch in 1990.

“With ballooning, the beauty of it is that you have recoverable launches,” Shabaan said. “So you launch the system multiple times. So you put something together, and it doesn’t have to work the first time – because you’re going to launch it for a single night to test it, then bring it down and reiterate. So you don’t need the very aggressive testing structure that you need for orbital [missions].”

It’s this complex testing that drives up the price of orbital missions. Making sure every piece of hardware works right out of the gate, that everything has multiple redundancies, and all these redundancies work with each other too — this is what can send the budgets for space projects soaring.

With ballooning, it’s easier to iterate and adjust hardware design as you go along. And if you send a balloon high enough into the edges of the atmosphere, you get almost all the water vapor-reduction advantages of being in orbit.

Traditional balloons, called zero-pressure balloons, work by venting gas when the sun comes up and makes the gas expand. When the sun goes down, the gas contracts and the balloon goes down as well. The new super-pressure balloons work by keeping the gas contained, even when it expands. Because it isn’t vented, the balloon can stay aloft when the sun goes down, allowing it to continue working at night for months. NASA’s super-pressure balloon is expected to last between 30 and 100 nights of operation, compared to the few days that were possible previously.

A telescope lofted by a balloon

It’s this new class of NASA balloon that Shabaan and his colleagues are making use of in their telescope project. They have a project called SuperBIT which will keep a telescope in the air and pointing in the right direction using sophisticated autonomous software. By sensing the minute movements of the balloon and automatically compensating for them, their telescope can look out to the stars with an unprecedented level of detail for a balloon-based mission.

The issue of keeping the telescope pointed in one direction is crucial for accurate observations, and it’s something that SuperBIT has a unique approach to. The telescope sits in an outer frame, a middle frame, and an inner frame, each of which moves on a different axis: Yaw, pitch, and roll. In combination, these allow the telescope to point anywhere in the sky.  “That means that if I experience some movement I can undo it by moving in any of those three directions,” Shaaban explained.

“It’s hard to steer exactly, but it’s relatively easy to kind of steer.”

This provides a basic level of stability, but for really accurate readings it needs to be even more stable. Inside the telescope is a mirror that can move at an extremely rapid rate of 50 motions per second. When light enters the telescope and appears to be shaking because of the very slight movements of the telescope, the mirror adjusts for that movement so it arrives unshaken at the sensor. The movements that the mirror needs to make are calculated using data from sensors all over the telescope, so the telescope can stabilize entirely autonomously.

And those corrections for small movements aren’t made using thrusters, which would require fuel. Instead, they are made by taking advantage of the size of the balloon itself, Shaaban explained: “The way SuperBIT works is it will sense these motions and it will have motors which torque against the balloon to undo these motions, which means it is basically taking the momentum and dumping it up to the balloon. But the balloon is so big, it’s like pouring a cup of water into the ocean. The level of the ocean won’t rise.” The motors run on electricity, which comes from batteries, which are charged from solar panels, so there’s no fuel to worry about.

The upshot of all of this is a balloon that can lock onto a direction in the sky to observe with a high level of accuracy. “You tell SuperBIT to point and it points,” Shaaban said. “It will look at a thing and it will track it. It will make sure that, from the perspective of the camera, that thing is not moving more than 20 milliarcseconds,” he explained.  This makes SuperBIT the first-ever non-space telescope to be diffraction-limited, because it is both above the atmosphere and the amount of jitter in the readings is essentially zero, making it a powerful scientific tool.

How to fly a telescope strapped to a balloon

So that’s how you aim a telescope from a balloon. But what about moving the balloon itself? When it comes to balloons, getting them exactly where you want them to be can be a challenge. “It’s hard to steer exactly, but it’s relatively easy to kind of steer,” Shaaban explained. That’s because you can make use of weather models to find winds that are blowing in the direction you want to go and move into those currents by adjusting altitude. This lets you move a balloon in roughly the direction you need it to go.

However, steering becomes much harder when the load being carried is very heavy, like a telescope. But fortunately, most scientific applications don’t actually require a balloon to be in a particular position on the Earth — the altitude they reach is far more important. The only concern for these kinds of missions is that the operators must avoid having the balloon traveling over populated areas for public safety.

“The balloon pops, and then you throw out a parachute. It’s kind of like a skydiving mission.”

The balloon heads up to an altitude of between 35 and 40 kilometers (20 to 25 miles), in a region of the atmosphere called the stratosphere. For reference, that’s above where planes fly but below where satellites like SpaceX’s Starconstellations sit in very low Earth orbit. That’s high enough to see the curvature of the planet but not so high that you see the entire Earth. It’s not the most inviting of environments — it’s cold, at between -30 and -40°C (-22 to -40°F), but not as cold as orbital space. And there’s troublesome radiation there too, although again not as bad as in orbit. So the engineering considerations there are not dissimilar to designing for orbital missions, Shaaban said: “It’s space but different when it comes to the challenges we face.”

There’s another challenge that arises from the telescopes being recoverable: If you want to recover a balloon load and reuse it, you wouldn’t want your telescope to be dumped somewhere that’s hard to access. During the test flights of SuperBIT, the team chose their base of operations carefully, launching out of either Palestine, Texas or Timmins, Ontario, both of which are surrounded by large areas of land that are unpopulated but easy to recover the telescope from.

SuperBIT balloon telescope being inflated

As for landing a balloon, it can be a bumpy ride. “We literally pop the balloon,” Shaaban said. “The balloon pops, and then you throw out a parachute. It’s kind of like a skydiving mission.” To cushion the blow of landing when testing the SuperBIT hardware, the team added crash pads to the telescope to absorb some of the momentum. Sometimes they got lucky, and the telescope landed from its dramatic descent relatively unharmed. But other times, the hardware got seriously banged up in the landing.

Even a seriously damaged telescope isn’t the end of the world though, as fixing it up is still cheaper than building a new telescope from scratch. “Refurbishing a destroyed-on-landing mission is significantly cheaper than testing it so it would work the first time,” he explained.

If there’s an overall message to take away from this, it’s that testing space hardware to the degrees of accuracy needed when facing potentially unknown and extreme conditions is really, really expensive. There’s a big advantage to any method which will let you launch missions and iterate as problems arise, instead of facing the impossible task of trying to predict and allow for any possible problem.

“It is really, really, really difficult to simulate [space] environments at a low cost,” Shaaban emphasized. “But it turns out to be cheap and easy to go to these environments, when it comes to ballooning.”

SuperBIT and beyond

SuperBIT has already been through several test flights and is gearing up for science flights, which were unfortunately delayed by the pandemic. But this telescope is just the beginning: The real focus of the project is on its successor, tentatively titled GigaBIT.

“SuperBIT is a pathfinder experiment,” Shaaban said. The long-term aim of the research is to create the highest resolution telescope that can be flown on a super-pressure balloon, to meet the demand from astronomers for high-resolution imaging through visible light and near-ultraviolet wavelengths at a much lower cost.

That’s necessary because telescopes like Hubble are extremely oversubscribed, meaning many more projects want to use them than could possibly be given observing time. So the team is building a more powerful telescope to meet this need. The basic hardware will be similar to SuperBIT, but the telescope will be larger to provide higher-resolution imaging. To maintain the weight while adding a bigger telescope, as SuperBIT is already at the maximum mass that the balloon can carry, GigaBIT will use different materials like carbon fiber in place of aluminum.

SuperBIT’s final preparations for launch.
SuperBIT’s final preparations for launch from Timmins Stratospheric Balloon Base Canada, in September 2019. Steven Benton / Princeton University

If a series of balloons could carry high-resolution telescopes like this one, and be regularly launched and landed as needed, it would be an invaluable aid to astronomers the world over.

That’s not to say that they are looking to make telescopes like Hubble obsolete, Shaaban said: “Hubble has a significantly higher resolution than SuperBIT, but also a significantly smaller field of view. So it’s neither better nor worse, it’s just different. It has a completely different set of scientific questions that it can address.”

With all the potential of balloon-based telescopes, you might expect its advocates to promote them as superior to space-based telescopes like Hubble. But that’s not at all the case with Shaaban — instead, he emphasized the potential for collaborations between ground-based, balloon-based, and space-based instruments.

Getting balloon-based telescopes off the ground means that more research can be done, and that benefits everyone in the astronomical community. “The beauty of astronomy,” Shaaban said, “– in addition to being such a phenomenal, humbling endeavor — is that it is incredibly collaborative.”

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