The Science behind the "RE"-usable Rockets.

Most of the people think a rocket is a thin cylindrical round object that goes to space. Well, it is but, that's not just it. By definition, Rocket can mean, "A type of engine or a vehicle that uses the engine".

Now that we've defined what a rocket is, Let's jump into the history of rockets,

The first rocket was probably made in China in the 1200's. They Used it for Fireworks. Fast forwarding to the 1900's, In the early 1900's rockets were crazily experimented. Like, 

• A German scientist, Fritz Von Opel's rocket car which was named "The OPEL-RAK 1"
• They made Manned Rocket Glider!! (Whoa! Iron man in the 1900's right? That rocket was destroyed in the second flight though :-p)
• Rocket powered Aeroplanes

and the list goes on....

And later on July 16 1969,  US sent two men(Neil Armstrong & Buzz Aldrin) to the moon! on the rocket, "Saturn V" and the mission was called, Apollo 11.

Saturn V(Apollo 11)

 And today, Rockets are used by the Military, Astronomy(by launching telescopes to space), Communication(Satellites), Space exploration, conducting experiments in space(sending scientists to the ISS) and a lot.

Now, coming to the RE-launchable rockets, The first rocket(Booster) that was re-used was done by the Elon Musk's (If you don't know who he is, I already wrote an article on him. I'll put a link in the comments below) private rocket company, SpaceX. I want you to have a look at this data,

CRS-8: -                                                                              

• Date:- 8th April 2016                                                
• Location: - Cape Canaveral SLC-40
• Mission Type: - ISS resupply
• Contractor: - SpaceX 

     SES- 10: -

• Date:- 30th March 2017                                                
• Location: - Kennedy LC-39A
• Mission Type: - Communications
• Contractor: - SpaceX 

Now if I ask you what are the similarities between the two missions, you'd say, "They both had the same contractor". But, there's one more thing too! They both had the same Booster(technically, rocket). Now, to make you understand what a booster is, Let me explain the stages of a rocket launch.

Most of the modern rockets have three major stages. Have a look at this image,

The stage 1, which is the booster of the Launch Vehicle fires to propel the entire rocket upwards. But the sad part is when the booster runs out of fuel, they are detached from the Launch Vehicle and they fall somewhere in the Oceans. The booster makes up most of the rocket and also makes up most of the amount spent to build the Vehicle.

The stage 2, which fires just before the detachment of Stage 1(booster)  to propel the Payload(example: Satellite, Cargo, Spacecraft carrying humans etc.,) to the orbit. 

The stage 3, is making use of the payload that has just entered the Earth's orbit.

Yeah, now that you know how a rocket goes to space, Let me tell you  How did SpaceX manage to bring it's booster(Stage 1) back to earth,

Before SpaceX, most of the Boosters have needed to use all of their fuel to send Payloads into orbit. But SpaceX makes rockets with reusability in their mind. The process with which SpaceX bring their boosters back to Earth is called "Supersonic RetroPropulsion". Let me define it,

"It is defined as a method of landing a space vehicle 'softly',

 on a planet using the thrust of its engines to reduce the descent velocity to an acceptable, non-destructive speed."

Simplified, Using thruster(technically, Retro-thrusters) to land a Vehicle on a planet.

To land a booster(Stage 1) back to Earth SpaceX adds these additional features to their booster,

1. Grid fins: - Have a look at these images,
   
    

These grid fins rotate clockwise and anti-clockwise to steer the booster back down to earth.

   2. Cold gas thrusters: - Cold gas thrusters are located at the top of the booster and are used to flip the rocket.

Source: - SpaceX.

       3.Landing Legs: - There are four landing legs located at the bottom of the booster that helps to land the booster on the surface. You can find them on the image above.

     4.Navigational Sensors: - They use the LIDAR(Laser Image Detection And Ranging) technique to land their boosters. They call their LIDAR sensor "The Dragon Eye". It provides a 3d image based on the amount of time it takes for a single laser pulse to reach the target and bounce back.

Source: - SpaceX.com

Here's what Elon Musk said after the RE-launch of one of the Falcon 9s

“If one can figure out how to effectively reuse rockets just like aeroplanes,
the cost of access to space will be reduced by as much as a factor of a hundred.
 A fully reusable vehicle has never been done before.
That really is the fundamental breakthrough needed to revolutionise access to space.”

Well, That's how boosters come back to Earth. this is Anirudh Dasari signing off. And, if you have come this far reading the article.... Thankyou! and here's a video of all SpaceX's landings,