How Reusable Rockets Work

Author: Abhinav Gorantla

SpaceX is becoming famous in the space exploration industry quite fast. One of the primary reasons for that is their famous Falcon – 9 rockets. The USP of these rockets is their reusable first stage. The first stage of a multistage rocket contains booster engines that propel the rocket to the end of the atmosphere where outer space starts. Reusing this first stage cuts operational costs drastically. It opens the door for space tourism, which may become a reality before the year 2022. 

Falcon – 9 rockets cost $60 Million to build. So with the second stage and the first stage of the rocket successfully landing after separation, 80% of the rocket body safely lands on Earth. This means that only 20% of the rocket body, comprising of the crew capsule or payload compartment, may need re-manufacturing. 

The first stage of the Falcon-9 contains nine Merlin-1 engines. These are responsible for putting the spaceship at the edge of space at an altitude of about 100 km. After this, the first stage separates and lands safely on the ground. The engines used on Falcon – 9 give the rocket 600 tonnes of thrust required for liftoff. After the first stage gets separated, the cold-gas thrusters on the first stage fire up and initiate the “flipping” process to make the rocket ready for re-entry into the earth’s atmosphere. But how does the rapidly accelerating 200-ton iron behemoth land? 

At the time of separation, the first stage is accelerating into outer space at a speed of 4,700 km/h. At the time of landing, the 200-ton giant has a vertical velocity of 20 km/h. Conventional rockets are known to use every drop of fuel they carry to propel the rocket to the edge of space. But, in a Falcon-9 after the cold thrusters vent out Nitrogen gas to flip the first stage, the engines fire up and use the “extra” fuel to make use of the reverse thrust and decelerate. 

After the “flip” happens, the computers, and at least a dozen sophisticated sensors onboard the Falcon-9, kick into action and maneuver the rocket ever so slightly to get a smooth and precise landing. The computers onboard the Falcon – 9 are so precise that they can land the rocket on a 90×50 meter offshore landing site. The landing sites are mostly offshore to ensure safety in case of any mishaps. Remotely controlled from the rocket launch site, drone ships function as “remote landing platforms.” The drone ships, which serve as landing sites, are not exactly completely stationary during the whole touchdown process. 

Using an offshore landing platform comes with its challenges. The computers onboard the drone ship and the rocket need to be synchronized perfectly to achieve a successful touchdown. The time frame for the separation and re-entry and touchdown is just 4 minutes. The process is so complex that it would not be possible for a human to do it without a computer’s aid. 

Landing a 200-ton behemoth traveling in outer space only using computers is nothing short of a beautiful work of art. This shows us how engineers can build such admirable pieces of art. 

“All civilizations become either spacefaring or extinct.” – Carl Sagan


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