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The often overlooked high-altitude balloon (HAB) has proven itself to be a true workhorse of the scientific community. It enables the acquisition of invaluable atmospheric, astronomical and climatic data that would usually be impossible to obtain either from the ground or via aeroplane.
Despite this, many people aren’t even aware that HABs exist, let alone know the ins and outs of how they work. This article will take a peek behind the curtain, demystifying the science and engineering behind their operation in the hopes that HABs will finally get a taste of the stratospheric recognition they deserve.
What is a high-altitude balloon?
A HAB is essentially a scaled-up version of a classic helium balloon you might find at a child’s party, relying on a lifting gas to provide buoyancy. However, as well as HABs generally being orders of magnitude larger than balloons of the party variety, they’re also constructed from stronger, more flexible materials to withstand considerably higher inflation pressures.
Interestingly, they’ve actually been around in one form or another for much longer than many people realise, with the first ever HAB launch taking place in Paris in 1783. Although the balloon only managed to stay airborne for around 40 minutes, it wasn’t long before scientists had perfected the technique and were regularly launching high-altitude flights to transport scientific payloads beyond the clouds.
How do they float?
It all boils down to the fundamental principle that Archimedes laid out circa 246 BC, stating that a body immersed in a fluid – or gas for that matter – is subjected to an upwards force equal to the weight of the fluid displaced. In short, as long as the balloon weighs less than the amount of air it displaces, it will float.
However, things get a little more complicated when taking into account the fact that atmospheric density is not static; it decreases at higher altitudes for two reasons:
gravitational force is greater at lower altitudes, which increases atmospheric pressure by pulling air molecules closer together; and
the atmosphere at lower altitudes is being compressed by the weight of the air above it, increasing pressure even further.
What this means, in practice, is that the mass of air displaced by an HAB will decrease with increasing altitude due to declining atmospheric pressure, causing its buoyancy to reduce as it ascends. Consequently, the balloon will gradually slow before coming to a stop once the density of the surrounding air becomes equal to that of the lifting gas inside.
However, this is presuming that a balloon even makes it this far; falling pressure also causes dramatic expansion of the lifting gas – accordant with the ideal gas law – often stretching a balloon’s surface to breaking point before reaching its theoretical maximum altitude.
How high do they go?
HABs are generally designed to float within a region of the Earth’s atmosphere called the stratosphere – also known as Near Space – roughly extending between 20 and 50km above the planet’s surface. To put these numbers into context, most commercial flights are subject to service ceilings of between 10.5 and 13.5km, beyond which commercial aircraft struggle to maintain lift due to the thinning of the atmosphere.
HABs aren’t strictly limited to the stratosphere though. In 2013, a team from the Japan Aerospace Exploration Agency set a world record by launching their BS13-08 balloon to an altitude of 53.7km – firmly within the Earth’s mesosphere!
What lifting gases are used?
HABs could theoretically operate if filled with anything lighter than air, which makes for a surprisingly wide range of qualifying substances – including water vapour, hydrogen cyanide, ammonia and even aerogel. However, most of these can be ruled out due to safety, economic, environmental and performance issues.
In reality, most HABs rely on hydrogen or helium to provide buoyancy. Being the lightest elements in the periodic table, their low densities in comparison with that of air make for ideal lifting gases. They aren’t without their downsides though.
While hydrogen is abundant, easy to produce and relatively affordable, it can pose safety risks due to its flammability – harrowingly demonstrated by the Hindenburg airship’s fiery fate. Helium, on the other hand, is much safer to work with since it isn’t flammable. However, it’s a remarkably scarce element on Earth despite its abundance throughout the rest of the universe. It also has vital applications in medicine and other industries, resulting in helium commanding an exorbitantly high price.
What are HABs made of?
Up until the late 1940s, HABs were made from a range of organic and semi-organic materials like rubberised silk, canvas and – remarkably enough – animal intestines. These days, however, conventional short-duration HABs are generally constructed from more modern materials that are flexible, lightweight, durable, and capable of withstanding the freezing temperatures, low pressures and increased radiation exposure experienced in Near Space.
Although the exact material used will depend on a range of mission-dependent factors – such as maximum altitude, flight duration and payload weight – most modern HABs designed for short-duration flights are constructed from polythene, latex and mylar due to their high elasticity. Latex is proving particularly popular with environmentally-conscious institutions thanks to its inherent biodegradability, meaning that any balloon fragments that manage to escape post-burst recovery will organically decompose.
What happens after the balloon bursts?
HAB flight trains are typically equipped with advanced tracking and recovery systems designed to prevent the loss of valuable payloads and critical data aboard once the balloon bursts. One essential component of these systems is the integrated parachute, which is kept closed via gravity-induced tension during the ascent. This tension is released once the balloon bursts, allowing the parachute to deploy and slow the payload’s descent.
The distance between a HAB’s launch location and its eventual landing site can vary dramatically, from just a few miles to halfway around the world depending on weather conditions and flight durations. GPS and radio telemetry are often used to assist teams in the recovery of the payload after it lands, proving particularly useful in remote or hard-to-reach areas.
Can landing site locations be predicted?
Fortunately, the location of landing sites can be predicted with a high degree of accuracy. Sophisticated modelling tools combine weather forecasting data with key flight parameters like target altitude, payload weight and ascent speed to produce projected flight paths ahead of time.
This information is especially useful for launch teams to have access to when needing to avoid restricted areas and densely populated locations. When operating in remote locations or regions of the world where internet access is restricted, we require the use of a VPN to operate effectively. Cybernews has a great article detailing the benefits of using a VPN, and have reviewed some of the best VPN services for 2025.
Much like weather forecasts, these flight path predictions become more accurate as the launch time approaches. With access to live pre-launch weather data, many flight paths can be forecasted with 99% accuracy before the balloon even leaves the ground. Additionally, live telemetry can be continuously fed into the simulation software throughout the flight, narrowing down the payload’s predicted landing site to within a few metres in some cases.
Are all HABs designed to burst?
While many traditional HABs are designed to expand with altitude until they eventually burst, there are two types of balloon that are engineered to remain intact throughout the flight.
The first variety, known as zero-pressure balloons, incorporate strategic openings within their thin polyethylene envelopes. These venting apertures allow air to enter the balloon as atmospheric pressure drops, as well as letting lifting gas escape in response to pressure spikes, producing a passive pressure regulation system. This results in a HAB that can hover at a certain altitude rather than continuously ascending until reaching its bursting point. However, the cumulative effect of such gas exchanges during daily atmospheric fluctuations is that these balloons will slowly lose buoyancy, limiting their flight duration.
Super-pressure balloons, on the other hand, are engineered to keep internal pressure constant as they ascend by maintaining a rigid, sealed structure. Advanced multi-layered envelope materials are employed to resist lifting gas leakage, as well as to provide enough strength to withstand the high internal pressures required to successfully reach the stratosphere. Consequently, super-pressure balloons can remain at a constant altitude for months or even years, eclipsing the flight durations of their zero-pressure counterparts.
What does the future hold for HABs?
High-altitude balloons have played an instrumental role in many areas of science and technology development over the years. However, with transport to low Earth orbit now being more accessible than ever, do HABS still have a role to play, or has technology simply moved on?
While it’s true that many duties traditionally carried out by HABs are now performed by satellites, they are still carving out a lucrative niche for themselves in a number of key areas like 24/7 fixed-location surveillance, satellite and avionics component testing, and low-cost platforms that can elevate space telescopes above 99.5% of the atmosphere. HAB-powered vehicles are also being developed to give human passengers a first-hand glimpse of Near Space at a much lower cost than the rocket-based alternatives offered by companies like SpaceX and Blue Origin.
The fate of HABs isn’t just confined to Earth either, with many space agencies eyeing up their feasibility for use on other planets. NASA, for example, is planning balloon-based missions destined for Mars, Venus and Titan to enable in-situ measurements at altitudes simply unreachable for technologies like satellites and rovers. With such exciting Earthbound and extra-terrestrial applications in the pipeline, one thing is for sure: the future of HABs is looking brighter than ever.