Returning a rocket safely back to the launch site involves a series of complex steps which begin on the edge of space, when it’s still traveling at over 3,500 miles per hour.
How Do You Get a Rocket to Land Back on Earth?
Published: February 20, 2019
Narrator: Returning a rocket safely back to the launch site involves a series of complex steps which begin on the edge of space, when still traveling at over 3,500 miles per hour.
Tim Fernholtz: First the rocket does what’s called a boost-back burn, it fires its engines, slows itself down and starts returning in the opposite direction.
Narrator: Now on a trajectory that’s taking it back towards the launch site, this giant 14-story tower must turn itself around once more to point the engines forward, as it starts to reenter the top of the atmosphere. And that’s when things begin to get tricky.
John Garvey: A rocket is an unstable vehicle. You have to deal with the control elements, so how do you keep it stable on the way down?
Fernholtz: It has maneuvering jets at the top that shoot out bursts of compressed air to keep it aligned, but it’s main way to keep going in the right direction are something called grid fins.
Narrator: These fins, the size of dining tables, act as paddles to steer and slow the falling booster rocket as it enters the denser lower atmosphere.
Fernholtz: As the rocket gets closer and closer to land, it does more controlled burns with its engines to slow down and align itself with the landing pad.
Narrator: As the engine ignites into a hypersonic headwind, the 33-ton rocket suddenly becomes even more unstable.
Fernholtz: It’s like balancing a pencil on the end of your finger. And think of how much effort and work you need to do that yourself.
Narrator: An array of sensors is now constantly relaying the rocket’s orientation to the engine at the base that swings left and right to keep the vehicle upright as it slows down.
Garvey: Landing on a pillar of fire, that last five feet can be critical, if you don’t know where the ground is.
Narrator: Approaching the landing pad, the onboard autopilot now deploys legs and throttles back the engine, so that velocity and altitude both equal zero, together.
Fernholtz: All of these different variables just show how much has to go right every time the rocket comes back to Earth, for it to land.
Rise of the Rockets
Directed by: Christopher Riley
Digital Producer: Ana Aceves
© WGBH Educational Foundation 2019