Catching a Rocket Mid-Fall

There are many strange ideas that have helped bring spaceflight to where it is today. Some of these ideas include making massive engines, such as the F-1, which stood almost 20 feet wide or using explosives to separate different parts of the rocket. There are currently two space companies working on catching rockets while they are still falling. SpaceX is planning on using a robot arm to catch their Super Heavy booster and place it back on the launchpad for refueling. Rocket Lab has plans to deploy a steerable parachute (a ram-air parachute), and then use a hook suspended from a helicopter to snag the parachute and fly the rocket back to a large boat.

SpaceX has not released much information about how they plan to catch a rocket on the launchpad. This plan only became public knowledge when Elon Musk, the founder of SpaceX, tweeted, “We’re going to try to catch the Super Heavy Booster with the launch tower arm, using the grid fins to take the load.” Super Heavy is the lower stage of SpaceX’s Starship rocket. The grid fins are waffle-patterned pieces of forged steel that control the ship during its descent. The joints that the grid fins are held on with are designed to withstand very large and sudden stresses and could be upgraded to be even stronger. As a result of this information and no news from SpaceX or Elon Musk about how the catching mechanism will work, the space community has started coming up with their own ideas. Some of these designs are created as jokes. One design concept created by Julius Bruton is an excellent example. This video rendering of the design shows two robotic arms mounted to a tower grabbing onto the rocket and slowly lowering it to the ground before giving it a pat on the ‘head’. The design that seems to be favored by many is a claw on the launch tower that can spin around the tower. This claw also has a mechanism to absorb some of the impact from the grid fin mounts. The ability to spin allows the claw to account for imprecise landings. The benefits of catching the rocket instead of propulsively landing (firing a few engines at a low throttle level to slow down the rocket for landing) in the launch clamps is that the forces exerted by the engines are reflected off of the launch pad and can damage the engines. If the distance between the engines and the ground is larger, then there is a much lower risk of damage to the engines.

Rocket Lab currently does not have the capability to recover its first stage boosters. Their plan for recovering boosters is to deploy a rectangular parachute that will allow them to control the path that the rocket falls in. To catch the booster, a helicopter will fly over the falling rocket with a hook dangling below it. The hook will snag the parachute, allowing the helicopter to fly back to a large boat nearby to lower the rocket onto the deck then land on a helipad. The reason Rocket Lab is pursuing this idea is to lower the cost of their rockets. When a booster can be used multiple times, the manufacturing cost can be divided among multiple launches, lowering the price. When SpaceX began to reliably land their Falcon 9 rocket the price dropped by $52.7 million. Rocket Lab has full carbon composite small satellite launch vehicles, which are much smaller and cheaper to manufacture than Falcon 9s, so their price will be very low for each launch once they can be reliably caught for reuse.

There is an increasing number of rocket companies and space agencies that are developing reusable rockets. One day there may be many more methods for catching rockets for reuse. Maybe catching a rocket will even become the most common way to reuse a first stage booster.

Freshmen Sean Harren is a staff writer for the 2020-2021 Colonel. He plays soccer and lacrosse. In his free time, he enjoys sailing and CAD modeling/3D printing.

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