Stratospheric balloons are high-altitude balloons that are released and operated into the stratosphere ( region of the atmosphere (15 to 45 km in altitude). Stratospheric provide platform to test and advance space science for far less than the cost of a satellite (up to 40 times less). The original stratospheric balloons were flown by NASA in the 1950s, and the agency still uses them for science missions. The Canadian Space Agency uses stratospheric balloons to test and validate new technologies developed for long-duration space missions and to perform scientific experiments in a near-space environment.
In July 2020, Google sister company Loon launched a service providing 4G internet to remote parts of Kenya from stratospheric balloons at 65,000 feet. Project Loon is a network of balloons traveling on the edge of space, designed to connect people in rural and remote areas, help fill coverage gaps, and bring people back online after disasters, says Google. Google is using weather balloons operating as an airborne Wi-Fi provider under Project Loon, and plans to launch as a trial over Sri Lanka, Indonesia and possibly India. Project Loon balloons travel approximately 20 km above the Earth’s surface in the stratosphere. Project Loon, successfully deployed such balloons to provide mobile communications in the aftermath of Hurricane Maria in Puerto Rico.
Early service quality testing has shown very positive results. In one late-June field testing session within the service region, we saw an uplink speed of 4.74Mpbs, a downlink speed of 18.9Mbps, and latency of 19 milliseconds (ms). In that and subsequent tests, the Loon and Telkom teams have used the service for all sorts of applications, including voice calls, video calls, YouTube, WhatsApp, email, texting, web browsing, and more, says Loon CEO Alastair Westgarth.
The commercial launch shows the steerable balloon technology, which Loon has been working with since 2011, is now reliable enough for everyday use. This is a powerful new capability that the Pentagon is keen to exploit. Military has been employing various platforms like Balloons, Aerostats, Airships, Satellites, and UAVs for communications and persistent, wide area, real time Intelligence, Surveillance, and Reconnaissance (ISR) of battle space.
Challenges : Rough Stratospheric conditions and Wind
Near space, which begins at about 20km above sea level, has until now been regarded a “death zone” for drones – thin air at this altitude makes it hard to generate lift, while extremely low temperatures mean electronic components like batteries are prone to fail. Near space has long been seen as a promising frontier for intelligence services, but has remained relatively untapped because it is too high for most aeroplanes to operate, and too low for satellites. Until now, the Northrop Grumman RQ-4 Global Hawk, limited to an altitude of about 19km, has been the highest flying drone in use.
Yang Chunxin, a professor at the school of aeronautic science and engineering at Beihang University in Beijing, said there were still many challenges in developing high altitude drones. “One of the biggest headaches is the near-vacuum environment, where electric currents can produce a spark. This can lead to shortages and damage electronic equipment,” he said. “This is why high altitude drones are more difficult to build than lower-flying variants. Whether they can play a practical role in military operations remains an open question,” he said.
The goal of scientists is to develop a durable near space vehicle capable of observing large areas for weeks, months or even years on end. Drones, which would cost just a fraction of what a satellite with comparable abilities would cost, are seen as one of the best ways of reaching that goal. Depending on the mission, the platform may be required to satisfy a wide range of performance characteristics. While in the stratosphere, balloons can encounter 150°C temperature swings, with temperatures reaching as low as -90°C ( at altitudes of 35 km (22 miles)). Extremely low temperatures mean electronic components like batteries are prone to fail
Winds in the stratosphere are stratified, which means they’re comprised of layers that travel in different directions and speeds. While one layer may cause the balloon to drift far from its target location, another nearby layer might allow the balloon to blow in the right direction. Depending on winds, a balloon can drift more than 200 km (125 miles) from the place it was released.
The higher the balloon travels, the more it expands – from 2 meters (6.5 ft) to up to 8 meters (26 ft) across – because air pressure decreases as the balloon climbs higher in the atmosphere. Eventually the balloon bursts. The latex or neoprene balloon is flexible and can expand a lot, but eventually it breaks – usually when the balloon reaches an altitude where air pressure is only small fraction (a few thousandths) of what is found at Earth’s surface.
Current balloons shift with the wind and can only stay in one area for a few days at a time. Winds in the stratosphere are stratified, and each layer of wind varies in speed and direction. Project Loon uses software algorithms to determine where its balloons need to go, then moves each one into a layer of wind blowing in the right direction. By moving with the wind, the balloons can be arranged to form one large communications network.
“By flying higher we hope to take advantage of a larger range of winds,” says ALTA project manager Alex Walan. ALTA will operate even higher than Loon at 75,000 to 90,000 feet (22,900 to 27,400 meters or 14 to 17 miles), where the winds are less predictable. That shouldn’t be a problem if the balloon can see exactly where the favorable winds are. But while machine learning and better data are improving navigation, the progress is gradual. In theory it should be possible to find a wind blowing in any desired direction simply by changing altitude.
Stratospheric balloons technology
Stratospheric balloons provide a platfom from which a variety of scientific research efforts may be conducted. Stratospheric balloons are typically made out of ultra-thin plastic filled with helium and can stretch into a gigantic upside-down “teardrop” shape more about the height of the Eiffel Tower. They are equipped with several gondolas suspended on the flight chain. The gondolas can carry science, astronomy, atmospheric chemistry, weather forecasting and technological demonstration payloads weighing up to 1.1 tons altogether.
Some balloons are bigger than a football field and able to lift payloads of 2 tonnes to altitudes of 40 km. They can reach altitudes of up to 42 km, holding their instrument packages aloft for several hours. Some balloons can even conduct long-duration flights, lasting days, weeks and even months. These balloons require no engine and no fuel and are fully recovered after each flight. It relies exclusively on natural forces: buoyancy for lift, winds for direction and gravity to descend.
The stratosphere is divided into many different layers, with winds blowing in different directions at different altitudes. In principle, a stratospheric balloon can go in any desired direction simply by rising or falling to the right layer and riding the wind. Companies like Raven Aerostar have developed the technology, which Loon use to hover their balloon over one spot to provide service to a specific area.
Balloons went from lasting hours to days to weeks to months to over half a year. Launching, once done by hand, is now done by twin, 90-foot tall automated machines that can send a balloon to 60,000 feet once every 30 minutes, says Loon CEO Alastair Westgarth.
Balloons that once floated freely around the world are now directed by machine-learning algorithms that have developed their own interesting and complex navigational maneuvers to achieve the mission of providing sustained service to users below. Communications equipment that could have once been made in a college dorm room (literally: beer coolers and WiFi routers were used in the early days) now deliver a coverage footprint of over 11,000 square kilometers — a whopping 200x that of an average cell tower. And a company that began building a commercial business just two years ago now has contracts to serve on multiple continents, partnerships with some of the largest mobile network operators in the world, is leading the commercial exploration and development of the stratosphere, and is helping the global aviation community develop the next generation of high-altitude operations, regulations, and policy.
Two kinds of balloons zero pressure and super pressure
There are two kinds of balloons the Open stratospheric balloons or zero pressure balloons. They are gas filled balloons (hydrogen or helium) having one or several openings which enable the balance between atmospheric pressure and the gas inside the balloon. They stay aloft for no more than a week. They can carry Payload up to 2700 kg at Flight altitude up to 45 000 meters.
These balloons are made from very thin polymeric films which provide an effective gas barrier between the lifting gas and the atmosphere that provides the buoyant force. The film needs to exhibit a number of properties including low permeability, high toughness at low temperatures, a wide range of sealing temperatures, and a relatively low weight per unit area. The structural design of a zero pressure balloon is such that transverse stresses are minimized and meridional loads are carried by high strength fibers sealed into the seams, and thereby structural analysis is relatively simple and only requires some minimal estimate of stress or strength.
Some science missions require longer duration flights in the stratosphere than can be accomplished by zero pressure balloons. This is accomplished with very light weight pressurized spheres which do not require the use of ballast to maintain altitude at night. Superpressure balloons are sealed and their envelope is stable enough for long-duration flights upto 6 months. They can carry payoad of 50 kg at Flight altitude up to 20 000 meters .The materials are extremely thin, high modulus, high strength elastic films with adequate permeability for the life of the mission. Polyester films, such as Mylar, are extensively used for this application.
However, as the weight of the scientific instruments is increased, the volume of the sphere must be increased to produce the lift necessary for equilibrium. The resulting stresses in the film increase linearly with the radius of the sphere which places a very definite limit on the size of the balloon and the magnitude of the instrument weight.
Researchers are now designing new type of balloons which will provide the heavy lift capacity of zero pressure balloons and the flight duration of superpressure spheres. This is accomplished with a pumpkin-shaped envelope formed from a high quality polyethylene film and high strength braided cables which support the payload. This concept relies on the formation of lobes with a local radius of curvature to limit the stress in the circumferential, or hoop, direction. This local radius is independent of the balloon volume and does not result in the same limitation as the superpressure sphere.
NASA Mission Will Study the Cosmos With a Stratospheric Balloon
Work has begun on an ambitious new mission that will carry a cutting-edge 8.4-foot (2.5-meter) telescope high into the stratosphere on a balloon. Tentatively planned to launch in December 2023 from Antarctica, ASTHROS (short for Astrophysics Stratospheric Telescope for High Spectral Resolution Observations at Submillimeter-wavelengths) will spend about three weeks drifting on air currents above the icy southern continent and achieve several firsts along the way.
Managed by NASA’s Jet Propulsion Laboratory, ASTHROS observes far-infrared light, or light with wavelengths much longer than what is visible to the human eye. To do that, ASTHROS will need to reach an altitude of about 130,000 feet (24.6 miles, or 40 kilometers) – roughly four times higher than commercial airliners fly. Though still well below the boundary of space (about 62 miles, or 100 kilometers, above Earth’s surface), it will be high enough to observe light wavelengths blocked by Earth’s atmosphere.
ASTHROS will need a big balloon: When fully inflated with helium, it will be about 400 feet (150 meters) wide, or about the size of a football stadium. A gondola beneath the balloon will carry the instrument and the lightweight telescope, which consists of an 8.4-foot (2.5-meter) dish antenna as well as a series of mirrors, lenses, and detectors designed and optimized to capture far-infrared light. Thanks to the dish, ASTHROS tied for the largest telescope to ever fly on a high-altitude balloon. During flight, scientists will be able to precisely control the direction that the telescope points and download the data in real-time using satellite links.
Because far-infrared instruments need to be kept very cold, many missions carry liquid helium to cool them. ASTHROS will instead rely on a cryocooler, which uses electricity (supplied by ASTHROS’ solar panels) to keep the superconducting detectors close to minus 451.3 degrees Fahrenheit (minus 268.5 degrees Celsius) – a little above absolute zero, the coldest temperature matter can reach. The cryocooler weighs much less than the large liquid helium container that ASTHROS would need to keep its instrument cold for the entire mission. That means the payload is considerably lighter and the mission’s lifetime is no longer limited by how much liquid helium is on board.
The team expects the balloon will complete two or three loops around the South Pole in about 21 to 28 days, carried by prevailing stratospheric winds. Once the science mission is complete, operators will send flight termination commands that separate the gondola, which is connected to a parachute, from the balloon. The parachute returns the gondola to the ground so that the telescope can be recovered and refurbished to fly again.
World View sees strong interest in stratospheric balloons despite test incident
World View, a company offering stratospheric balloon flights for research payloads, sees a bright future ahead for a platform that it argues combines the best attributes of satellites and aircraft, despite a recent testing incident at its Arizona headquarters.The company believes that its stratollites can loiter in the stratosphere for extended periods, providing persistence that aircraft cannot offer at costs much lower than satellites. Those flights have carried research payloads, including for NASA’s Flight Opportunities program, as well as commercial users, such as a summer 2017 flight that carried a chicken sandwich as publicity for a fast food restaurant chain.
One new application of World View’s balloons is in remote sensing. At the conference, the company released the first high-resolution images taken from its balloons, using off-the-shelf camera equipment. The images, taken from altitudes of more than 20 kilometers, have a resolution of 50 centimeters, but the company expects it can improve that, with better cameras and observing techniques, to as sharp as 10 to 15 centimeters.
Those balloon flights use helium, but at the conference Poynter said the company was looking to use hydrogen, which is much less expensive. “It is still on our radar. We have not done it yet, but we are very close to that,” she said. On Dec. 19, World View conducted a test of a hydrogen-filled balloon at its Tucson, Arizona, headquarters. At the end of the test, though, the balloon ruptured. Video of the test obtained by local news media shows the balloon bursting and what appears to be flames, suggesting hydrogen in the balloon combusted.
We have used hydrogen in ground testing, but only helium in flight operations at Spaceport Tucson,” he said, referring to the pad adjacent to the company’s headquarters, near Tucson International Airport, used for balloon flights. “However, to date our use of hydrogen has been limited to ground testing when required by customers or test objectives.” “As of now, we do not have any requirements or future plans for using hydrogen in ground testing or flight at the spaceport,” he added.
Military and Security Applications
The military is already exploring applications for the balloons. U.S. Southern Command has been carrying out a series of test flights with World View’s Stratollite balloons. These are able to ride winds yet stay in a very tight area, keeping a permanent watch over a particular area of interest, unlike low-earth satellites, which only pass overhead at intervals. “We think this has the potential to be a game-changer for us,” Admiral Kurt Tidd, commander of U.S. Southern Command, told New Scientist.
Stratospheric balloons may solve one of the U.S. military’s thorniest problems: gathering intelligence in ‘Anti-Access and Area Denial’ environments, places where the defenses are too dangerous for aircraft to approach. The balloons are stealthy, and can fly at altitudes of 90,000 feet or more, putting them well above the reach of most surface-to-air missiles. They are also extremely hard to shoot down: there are no fuel tanks to puncture or engines to damage. Shrapnel that would destroy an aircraft simply leaves a few small holes in the balloon envelope. When a giant weather balloon drifted off course in 1998, Canadian CF-18 Hornet pilots riddled it with more than a thousand cannon shells and several rockets with no noticeable effect. British and America jets also failed to bring the stray balloon down and it only crashed after several days.
In 2017 Chinese researchers launched two drones from a stratospheric balloon. A research facility in Inner Mongolia successfully tested an experimental drone at an altitude of 25km. The test involved two experimental unmanned aerial vehicles being sent up on a high pressure balloon before being deployed at different altitudes. The second drone was deployed at an altitude of 9km. Each of the drones, which are about the size of a bat, was launched using an electromagnetic pulse that accelerated them from zero to 100km/h within a space about the length of an arm. “It shot out like a bullet,” said Yang Yanchu, lead scientist of the project with the Academy of Optoelectronics at the Chinese Academy of Sciences in Beijing. The drones then glided towards their targets more than 100km away, adjusting course and altitude in flight without human intervention. On-board sensors beamed data back to a ground station.
The drones are small enough to fit in a shoebox and weigh about the same as a soccer ball. They are made with composite materials and are designed to withstand the forces involved in electromagnetic launches. The wings and body are blended into one flat, tailless fuselage to produce sufficient lift in the thin air. The sensors include a terrain mapping device and electromagnetic signal detector to locate military presence or activities. But the drones would not carry cameras, Yang said, as the transmission of photo or video data over long distances requires bulky antenna unsuitable for near space launches.
Novel, Low SWaP-C Unattended Ground Sensors for Relevant SA in A2AD Environments
A new U.S. Army project aims to employ stratospheric balloons to drop a shower of electronic sensors into denied areas. Air-dropped sensors have been used since Project Igloo White covertly monitored traffic moving down the Ho Chi Minh trail during the Vietnam War. The modern versions are tiny electronic devices disguised as rocks with concealed solar cells that can keep sending back data for years.
The US Army Combat Capabilities Development Command (CCDC) C5ISR Center is interested in experimenting with low-cost, very small Size, Weight, and Power (SWaP) unattended ground sensors (UGS) to maintain situational awareness (SA) within a signal dense (e.g. urban centers) and contested (e.g. limited air superiority) area of operations that require a ubiquity of sensors not achievable by conventional means. The objective is to develop and demonstrate novel, very small, inexpensive radio frequency (RF) sensors that can be distributed in mass quantity over an operational zone to gather relevant Situational Awareness (SA) data on millimeter wave signals.
The UGS would be readily distributed within an area of interest to provide the ability to sense the Cyber-Electromagnetic Environment (C-EME) , locating and tracking radio communications from Wi-Fi, cellphones, and military communication systems. This would provide data about the location of enemy units and specific vehicles allowing for the acquisition of data required to achieve Cyberspace Situational Understanding (CYBER SU) and improve network survivability. The collected sensor data would support multiple objectives, to include environment mapping, specific signal of interest detection and geo-referencing, and battle damage assessment. In particular, the sensors will identify and pinpoint targets for “long-range precision fires” by the Army’s new long-range missiles, which can hit targets several hundred miles away — if they know where to aim. Afterwards the sensors will provide battle damage assessment to determine what had been destroyed. In addition, the UGS could be deployed hundreds of miles forward of a Forward Line of Troops (FLOT) from platforms such as high altitude (i.e. >60K feet) balloons to support acquisition of target data for long-range precision fires.
The sensors could leverage emerging Internet of Things (IoT) protocols (or comparable performing waveforms) for data retrieval. Sensors will at a minimum contain the following core functionality: GPS, CPU, non-volatile memory storage, data retrieval waveform and Tx/Rx chain, power management system (to include battery), accelerometer (optional, but highly desirable), and compass (optional, but desirable). As well as various types of electromagnetic detector, the new devices may incorporate seismic sensors to detect passing vehicles. A future development may add sensors for chemical, biological, or nuclear monitoring. Given the small size, weight, power, and cost objectives, it is envisioned that such sensors would only perform a single specific sensing objective. However, the design would ideally allow for the rapid integration of various different types specific EM signals or other modalities (i.e. seismic) of interest within the core sensor package.
DARPA Laser radar can see wind 8.6 miles away and enables permanent balloons
As part of its Adaptable Lighter-Than-Air (ALTA) balloon program, DARPA is tested a wind sensor called Strat-OAWL, which stands for “stratospheric optical autocovariance wind lidar.” The idea is to use lasers to deduce the speed and direction of wind gusting far away from a stratospheric balloon and then make the necessary adjustments to stay in one spot
It does this by shining laser pulses in two directions. Some of that laser light then reflects off the air, returning to the sensor unit, which analyzes its wavelength. The wavelength of the reflected light is changed slightly depending on how fast the air it bounced back from is moving, a change known as doppler shift. Changes in the wavelength allow Strat-OAWL to determine the speed of the air that reflected the light, as well as the direction in which it’s moving.
Previous versions of OAWL flown in aircraft have measured winds more than 14 kilometers (8.6 miles) away with an accuracy of better than a meter per second. The main challenge with Strat-OAWL has been shrinking it to fit the space, weight, and power requirements of the ALTA balloons. Unlike other wind sensors, OAWL looks in two directions at once, giving a better indication of wind speed and direction. “It’s like looking out with two eyes open instead of one,” says Sara Tucker, a lidar systems engineer at Ball Aerospace. The stratospheric balloon can then adjust its altitude to wherever a wind is blowing in the direction it wants to move, ensuring it can remain in one area indefinitely.
Military aircraft have ceilings of 60,000 to 65,000 feet, so they could intercept Loon-type balloons. Because it will fly higher, ALTA will be a much trickier target. The balloon could provide secure communications and navigation or act as a mother ship for drones. The ALTA balloon itself is made by Raven Aerostar, which also makes the Loon balloons. The firm’s general manager, Scott Wickersham, says this sort of technology gets us much closer to balloons that stay aloft indefinitely—and that will make all sort of applications possible. In 2017, U.S. Navy Admiral Kurt Tidd noted during a geospatial intelligence symposium that the military believed stratospheric balloons could have some “interesting applications” if capable of remaining airborne for 180 days or longer.