When space launch startup Firefly’s first planned orbital flight takes off in November, it’ll carry an experimental payload developed by engineers from Purdue University: A drag sail that’s designed to haul a rocket back to Earth once it’s fulfilled its mission and deployed its cargo. Safely de-orbiting a spent launch vehicle would mean one less large piece of flotsam circling the globe in an increasingly high-traffic orbital area.
Most launch vehicles do safely de-orbit on their own — eventually. But that can take up to a hundred years for rocket stages. Increasingly, spacecraft like satellites are also building in propulsion systems to actively de-orbit at end-of-life, but any time you put an active propellant system on a craft designed to operate in space, that means you need to make space for both the propulsion system and propellant, both of which take up space, which means added cost for launch, and less room on the satellite for instrumentation and other mission-critical payloads.
As Purdue points out, propellant-based active propulsion systems also require that a spacecraft is operational in order for them to work. A drag parachute, conversely, is effectively a passive measure that can be triggered via fail-safe to de-orbit even a disabled spacecraft.
A drag sail works by creating drag, reducing the orbital velocity of a launch vehicle or spacecraft much more quickly than would occur without any assistance. Objects orbiting Earth in space are only able to maintain those orbits because they’re moving at very high speeds, which in turn means they can counter the effect of Earth’s gravity, which is continually pulling them back down toward the surface, even beyond Earth’s atmosphere.
The experimental drag sail, called Spinnaker3, spans 194 square feet when unfurled, and is a prototype that is designed to eventually form the basis of a line of drag sail products to be commercialized by Vestigo Airspace, a startup company founded by Purdue adjunct associate professor David Spencer. Eventually, small sats and launch craft equipped with drag sails like these could help ensure that despite increased launch activity in Earth’s orbit, the existing traffic problem isn’t exacerbated anywhere near as much as it would be otherwise.