Rockoons: Rocket and Balloon Experiments

The 1950s saw innovation in terms of rocket technology, with engineers working on rockets for many different kinds of purposes—to carry weaponry, to launch atmospheric experiments, and to reach space.

One unusual type of rocket that made its appearance during these years was the rockoon. Rockoons feature a small rocket tied by rope to a high-altitude balloon. Once the balloon carries the rocket through the atmosphere to an altitude of around 15 miles (24 kilometers), an automatic pressure switch or a radio signal sent from the ground causes the rocket to fire its engines, taking it to an even higher altitude.

The rockoon solves a particular problem, especially relevant for rocketry experiments from the 1950s: A rocket launching from the surface of the Earth into space requires a lot of power for its journey. The mass of the rocket, the force of gravity, and the air resistance from the atmosphere mean that a rocket needs to expend a lot of energy during the very earliest part of its journey.

A rockoon has a clear advantage, then. Instead of using fuel to power it through lower altitudes, it starts its flight using a high-altitude balloon. Because the balloon lifted the rocket through the most difficult part of its journey, the rocket can travel much farther than if it had launched from the ground. This way, a relatively small rocket can achieve the same height as a much larger one.

Especially before sounding rockets could regularly travel to the upper atmosphere, rockoons provided one way to allow scientific experiments to reach high altitudes. Space scientist James Van Allen—who later in the decade would become a leading voice for the importance of carrying scientific experiments on satellites—relied on rockoons to launch his experiments in the early 1950s. He received funding from the Office of Naval Research to conduct these experiments via rockoons. The first successful launch occurred in 1952, when Van Allen and his team from the University of Iowa launched a balloon to 70,000 feet (21,336 meters). A pressure switch then fired the rocket, which climbed to nearly 40 miles (64 kilometers) . These experiments represented the beginning of Van Allen’s research on Earth’s radiation belt.

Later in the decade, rockoons were used during the 1957-1958 International Geophysical Year (IGY), a project that gathered scientists from around the globe to pursue research in Earth sciences. U.S.-based projects launched some 60 rockoons as part of the IGY, lifting off from the Arctic, the Antarctic, and off the coast of California. Notable studies included surveying auroral particles for the first time. Deacon, Loki, and Hawk rockets all formed parts of rockoons. The National Air and Space Museum has a Loki rocket of the kind used on rockoons in its collection. And a Loki-Dart rocket is currently on display at the Museum’s Steven F. Udvar-Hazy Center.

File URL

After sounding rockets and satellites became more widely available in the 1960s, the use of rockoons dwindled. The biggest downside to rockoons was that the first part of the flight was affected by changing winds.  Because it was impossible to predict exactly where the balloon would be when the rocket ignited (and therefore where the rocket would eventually land), rockoons had to be launched far away from populated areas.

Today, however, rockoons might be making a comeback. Technological advancements have made their operation more feasible: it is easier to track high-altitude balloons and to have automated systems that remotely launch the rocket at the correct altitude. Within the aerospace community, there is also a growing commitment to lower emissions from rocket launches, and the balloon significantly reduces the fuel that the rocket needs to burn. Companies and researchers are therefore returning to the idea of using rockoons for scientific research and even for launching small satellites into orbit. In 2017, Spanish company Zero 2 Infinity conducted its first test of its satellite launcher Blooster, which it hopes to use to put satellites of up to 220 pounds (100 kilograms) into Low Earth Orbit. The balloon could also take tourists to the edge of space. Colleges have also joined in on the rockoon launch strategy. In 2020, the Stanford Space Initiative at Stanford University attempted to use a rockoon to cross the Kármán Line at an altitude of 62 miles (100 kilometers) and into space.