Using a planet’s atmosphere to secure a satellite’s place in orbit, a process known as “aerocapture”, has been the dream of flight engineers for decades. The only problem? It’s really hard to actually do. It requires control systems, thermal management, and orbital mechanics to all coordinate in a dance that allows a spacecraft to not just slow down while passing by another planet (or moon in some cases) but to start to orbit it without the use of lots of additional propellant. For now, that remains a dream, but a recent NASA contract to a California start-up called Inversion is another step towards making it a reality.