So you want to slow down a spacecraft? Well, you’ve got two options–but coming soon, you might have a third. ☄ There are currently two methods for slowing down a spacecraft when landing; which option to choose (or if you use them together) depends primarily on how much atmosphere your landing site has. The first option, retropropulsion, is best used when there is little to no atmosphere to help slow down a spacecraft. Retropropulsion is where you use thrusters pointed down at the surface of the planet to slow yourself down as you're coming in—like those used by the Apollo missions. The second option, heat shields, is used if you do have an atmosphere, which makes slowing down much easier, as the atmosphere acts as a giant brake as you slow down. In this scenario, a heat-resistant shield is on the blunt end of your spacecraft as it travels through the atmosphere. Finally, once the heat shield has sufficiently slowed the spacecraft, parachutes are deployed to slow it down the rest of ...