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Long before we thought about rockets to bring science to space, humans have explored our world in a much gentler way.
But in two new articles published this week, scientists reimagine this nostalgic technology as a way not only to keep an eye on Earth, but also as a means to challenge outer space and even alien worlds.
Today, balloons are largely relegated to party decorations and merry-go-rounds, but hot-air balloons were once the vanguard of transportation technology, capable of transporting people and things to places humans had never ventured before. Now, scientists are once again turning to balloons, this time as a way to create floating space observatories and internet service stations.
Compared to the advanced missile and favorite satellites of Elon Musk and others, balloon technology is beautiful in its simplicity. Using pressurized gas to fuel their journey, these balloons can hover thousands of miles above the ground in the Earth’s stratosphere. But these balloon designs aren’t without obstacles.
In the pair of new articles, scientists think they have solved two of the biggest hurdles for these technologies to take off: one has to do with how they are used, while the other has to do with keeping them usable.
Stand still – For balloons stationed above the Earth, one of the biggest problems blocking their use is keeping the balloons “anchored”, or at least suspended, over a single position. This question of how to “keep the station” accurately and efficiently was what the researchers set out to answer in a new paper published Wednesday in Nature.
Trying to manually correct the course of a wind blown balloon hundreds of feet in the air is not only a tedious task, it can also be impossible depending on the distance. The balloons in the center of the document are Project Loon balloons – they provide internet to remote areas and are from the same parent company of Google, Alphabet.
It would be a big deal if you connected to Loon WiFi to watch a movie and the next minute the ball was thousands of miles away. So the Loon balloons relied on an automatic navigation method called StationSeek to find wind currents that will carry the balloon back to its station when it leaves the path. This approach has worked well enough, but is far from efficient, the authors write.
To accurately return to its station, the balloon must actively test and explore the wind flow options, which uses the balloon’s limited battery power more.
Instead, the researchers propose a reinforcement learning algorithm to allow the balloon to intelligently choose an optimal sequence of wind currents to return to its station. without wasting excess energy.
They trained the algorithm on both historical wind trend data and senseless “noise” to enable it to make these decisions robustly even in an unpredictable environment. This flexibility is the key to the success of ground and extraterrestrial missions, the authors write:
“[S]the maintenance of tations offers an example of a fundamentally continuous and dynamic activity, in which continuous intelligent behavior is a consequence of interacting with a chaotic external world. By reacting to its environment instead of imposing a pattern on it, the reinforcement learning controller gains flexibility that allows it to continue to perform well over time. “
The method fixes balloons above the Earth, but there are no obstacles to the same technology used to fix a balloon above the surface of another world. Clever algorithms like this can help astrometeorologists and astrobiologists explore strange new worlds, such as the atmosphere of Venus, in search of life.
A better telescope – Making space exploration with balloons possible is also at the heart of the second study, published Tuesday in the journal Review of scientific instruments. In this study, researchers from NASA’s Goddard Spaceflight Center solve a very problem cold problem.
Space telescopes generally fall into two categories: ground-based observatories and space observatories. But scientists want to create a third type of telescope: a Goldilocks observatory that hovers in the liminal expanse between the Earth’s stratosphere and outer space. And to hoist these living room-sized telescopes into space, scientists think giant, pressurized balloons may be the best means of transportation.
But to work, this Goldilocks telescope must be super cold. And to be super cold, they also need extremely heavy equipment. That means the balloon has to lift this kit as well, explains Alan Kogut, a Goddard researcher and first author of the study, in a statement.
“Liquid helium can easily cool the telescope, but keeping it cold means putting the entire telescope in a giant thermal bottle called a dewar,” he says.
“A living room-sized thermos would weigh several tons, more than even the largest balloons can carry.”
In the study, the researchers solve this problem by designing an ultralight cooling system called the Balloon-Borne Cryogenic Telescope Testbed (BOBCAT).
“BOBCAT develops the technology for ultralight dewars to reduce their weight enough to allow the really big ones to fly on a balloon,” says Kogut. “The storage tanks are small and don’t weigh much.”
BOBCAT has walls as thin as a soda can and can be cast at room temperature. It cools down when it reaches 130,000 feet, the area that Goldilocks scientists aim for.
A modified version of BOBCAT flew into 2019 to test many of the design systems, but the team has yet to roll out the ultralight system in its entirety.
When they perfect the system, Kogut and his colleagues say it will help scientists peer further back into space and time.
“Now, we have a cold telescope above the atmosphere, capable of seeing faint images from the cold or distant universe,” Kogut says.
By combining this capability with space-bound smart balloons such as those demonstrated by Project Loon, the future of space exploration could be a little lighter.
Extract 1: Efficient navigation of a superpressure balloon in the stratosphere requires the integration of a multitude of signals, such as wind speed and solar elevation, and the process is complicated by prediction errors and poor wind measurements. Together with the need to make decisions in real time, these factors exclude the use of conventional control techniques. Here we describe the use of reinforcement learning to create a high performance combat controller. Our algorithm uses data augmentation and self-correcting design to overcome the key technical challenge of reinforcement learning from imperfect data, which has proved to be a major obstacle to its application to physical systems. We’ve deployed our controller to station Loon super-pressure balloons in multiple locations around the world, including a 39-day controlled Pacific Ocean experiment. Analyzes show that the controller outperforms the previous Loon algorithm and is resistant to the natural diversity of stratospheric winds. These results demonstrate that reinforcement learning is an effective solution to real-world autonomic control problems where neither conventional methods nor human intervention are sufficient, offering clues as to what might be needed to create interacting artificially intelligent agents. continuously with real dynamic environments.
Extract 2: The Balloon-Borne Cryogenic Telescope Testbed (BOBCAT) is a payload of stratospheric balloons to develop the technology for a future cryogenic suborbital observatory. A series of flights is aimed at establishing ultralight dewar performance and open aperture observation techniques for large (3-5 meter diameter) cryogenic telescopes at infrared wavelengths. An initial flight in 2019 demonstrated the mass transfer of liquid nitrogen and liquid helium at stratospheric altitudes. A payload of 827 kg carried 14 liters of liquid nitrogen (LN2) and 268 liters of liquid helium (LHe) in pressurized depots at an altitude of 39.7 km. Once at waterline, the transfer of liquid nitrogen cooled a separate non-pressurized bucket dewar to a temperature of 65 K, followed by the transfer of 32 liters of liquid helium from the storage dewar to the bucket dewar. Calorimetric tests measured the total heat loss in the LHe bath within the dewar bucket. A subsequent flight will replace the receiving bucket dewar with an ultralight dewar of similar size to compare the performance of the ultralight design with conventional super insulated dewars.
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