How SpaceX lands its Falcon 9 rocket explained

Dimapur, Oct. 6 (EMN): SpaceX launched its 13^th batch of Starlink satellites on a Falcon 9 on Tuesday, Oct. 6, 2020, from LC-39A at Kennedy Space Centre in Florida. The launch marks SpaceX’s 17th mission so far in 2020, and its 94th Falcon 9 flight to date.

What is Falcon 9?

The Falcon 9 is a two-stage rocket designed and manufactured by SpaceX and is the world’s first orbital-class reusable rocket. The reusability of the Falcon 9 makes it one of the greatest technological developments in the history of rocket engineering. First announced in 2011, Elon Musk’s SpaceX launched a programme to create a new generation of reusable launch vehicles that would drastically reduce the costs of space travel.

To accomplish this, SpaceX needed to create a new rocket that could be launched vertically to deliver a payload into orbit and then return to Earth using controlled descent and land at a pre-determined landing site.   

SpaceX achieved its goal on December 22, 2015, when Falcon 9 flight 20 (also known as Orbcomm OG2 M2) made a successful return and vertical landing. Four years and multiple launches later it is safe to say that SpaceX’s Falcon 9 is now a flight-proven reusable launch vehicle. It also created history when it successfully launched the Crew Dragon spacecraft carrying NASA astronauts Robert Behnken and Douglas Hurley to the International Space Station.

Although we have all seen the videos about the Falcon 9 booster landings and it is nothing new at this point, we can’t help but marvel at the engineering feat that made this possible.

So how do you launch a fourteen-storey piece of aluminium-lithium alloy tube and return it to Earth for a vertical landing?

Here are the technologies that SpaceX incorporated into the Falcon 9 to make vertical landing possible:

Thrust vector control

The Falcon 9’s Merlin engines of the first stage booster are gimballed using hydraulic actuators that enable the Falcon 9 to adjust its thrust direction. The Falcon 9 actively uses thrust vectoring to adjust its orientation both within and outside of the Earth’s atmosphere.

Cold gas thrusters

Falcon 9 is equipped with nitrogen cold gas thrusters that are mounted on top of the first stage. Like the gimballed main engines, these cold gas thrusters are responsible for adjusting the orientation of the rocket. They are particularly used during the ‘flip manoeuvre’ after stage separation. Flip manoeuvre refers to when the cold gas thrusters initiate a controlled blast to ‘flip’ the first stage 180 degrees so that it descends with the bottom facing the Earth.

Re-ignitable first-stage engines

The Falcon 9 first stage needs to perform three separate burns at particular stages of the flight. Hence the main engines must be re-ignitable. The main engines first ignite during the launch, the second burn happens after the ‘flip manoeuvre’ slowing the rocket’s re-entry velocity and finally, the engines must fire again when the rocket nears the landing platform.

For stability, the engines are arranged in what SpaceX calls an ‘octaweb’ configuration – one central engine surrounded by eight more.

Onboard computer

The onboard computer on the Falcon 9 makes flight corrections on the fly to maintain flight trajectory. The Falcon 9 is equipped with an inertial navigation system (INS) that uses several sensors to measure the rocket’s position, orientation and velocity. A global positioning system (GPS) is also used to measure the geo-location of the rocket. The INS and GPS data are then fed to the onboard computer in real-time and the computer checks the information against the pre-programmed flight path. This data on the rocket’s orientation, position, velocity, acceleration and altitude is used by the onboard computer to make necessary flight adjustments to enable the rocket to achieve a smooth vertical landing upon re-entry.

Deployable grid fins

As the booster starts to enter the Earth’s atmosphere, grid fins come out to stabilise the rocket and slow it down as it makes its descent. The grid fins are four small heat-resistant titanium wings mounted at the top of the first stage booster. These fins are deployed for aerodynamic stability during re-entry.

Landing gear

The Falcon 9 is fitted with a four-legged deployable landing gear made of strong, lightweight carbon fibre and aluminium. The legs are deployed using high-pressure helium just before touchdown. Each leg is fitted with a shock-absorbing system to cushion the landing.

Autonomous spaceport drone ship

The Falcon 9 is launched from sites that are near the ocean. So, when the first stage booster falls back to Earth after separation, it is on collision course with the ocean. Although, it is feasible for the Falcon 9 to fly back to its launch pad, it is cheaper and easier to let it touch down at sea.

Autonomous spaceport drone ships are deployed by SpaceX to recover the first stage booster at sea. About the size of a football field, these drone ships enable the Falcon 9 to land at sea especially when it involves a Falcon flight going to geostationary orbit.

SpaceX currently employs two drone ships, ‘Just Read the Instructions’ and ‘Of Course I Still Love You’, both of which operate in the Atlantic for launches from Cape Canaveral.