Rockoons are a hybrid of a rocket and a balloon that split the process of reaching orbit into two parts: First, the balloon rises into the upper atmosphere, then the rocket adds the needed momentum to launch something into orbit or to another planet.

In March of 2017, Zero2Infinity, launched a balloon to about 82,000 feet. At that point, they were above 99 percent of the atmosphere, so they ignited a small solid rocket motor. Another company, ACRA, was using a rockoon-type launch system for its entry into the Google Lunar X Prize competition.

But if using a balloon to lift a rocket seems like old technology, it's because it is... The concept originated in March of 1949 for better, high-altitude atmospheric science.

Rockoons are actually a simple and ingenious approach to spaceflight. Instead of fighting against gravity, they turn gravity into an advantage.

Read More:

Encyclopedia Astronautica: Rockoon

Zero2Infinity: Bloostar - How We Do It

NASA: Development of the First Sounding Rockets