Skip to main content
shopping_basket Basket 0

The Science and Engineering Behind the Falcon 9 Rocket


The SpaceX Falcon 9 is a reusable rocket

The SpaceX Falcon 9 is a reusable rocket capturing attention for how it’s moving space exploration forward. Company founder Elon Musk hopes to eventually land people on Mars. Here’s a closer look at the science and engineering that makes the Falcon 9 function as expected.

The Engines

The Falcon 9 is a two-stage rocket that uses nine engines during its first stage. The idea is that if one fails, the others can safely take over. The engines are inside a metal structure SpaceX calls Octoweb, placed in an orientation with one in the centre and the other eight engines circling it. Installing them that way cuts the length and weight of the rocket’s thrust structure so it’s easier to design and put together.

The second stage only requires one engine. SpaceX built Merlin rocket engines for the Falcon 9. They use liquid oxygen and rocket-grade kerosene for the propellants during the gas generator’s power cycle.

Water’s Contribution to a Trouble-Free Launch

Together, the engines generate more than 1.7 million pounds of thrust. Although they play a significant part in a successful launch, so does water. Temperatures can reach around 5,800 F, so water helps cool the launch pad. More importantly, though, sheets of water shield the rocket from acoustical energy that could reflect and interfere with its performance.

How the Falcon 9 Handles Stage Separation

Once the Falcon 9 gets beyond the Earth’s atmosphere, it uses a pneumatic stage-separation system to release the rocket’s first stage from the second. The interstage connects the first and second stages and houses the engine necessary for the second stage. Most rockets use explosive bolts and pyrotechnics for separation. However, SpaceX’s approach minimizes the associated shock and allows on-ground testing before launch.

The second stage’s single-engine then fires, sending it into orbit. After the separation happens, the rocket’s first stage returns to Earth.

The second stage delivers the Falcon 9’s payload to the desired orbit. The engine can restart numerous times if there are multiple payloads. In any case, the Merlin engine has several igniters for increased reliability.

The second-stage payloads are ordinarily satellites or supplies for the International Space Station. However, in 2020, the Falcon 9 made history by launching a Crew Dragon spacecraft into orbit. It’s an autonomous capsule with touch-sensitive controls passengers can use during emergencies. The Crew Dragon can carry up to seven people, though it typically accommodates four.

The First-Stage Landing

The first stage of this reusable rocket has four landing legs made of carbon fibre. They fold flat against the fuselage until use. Onboard cold gas thrusters flip the rocket to position it with its engines facing forward.

The Falcon 9 also has lattice-structured grid fins. They make tiny movements to steer stage one as it enters the Earth’s atmosphere, allowing it to have a more precise landing location.

As the grid fins deploy, three engines reignite to help slow the first stage’s velocity before landing. That action has a dramatic effect. The first stage reaches a top speed of 4,700 kilometres per hour and slows to just 20 kilometres per hour for landing. The landing legs come down, and the engines light once more before the first-stage rocket comes to rest on a platform.

The SpaceX team also figured out how to land stage-one rockets on a floating platform, which made a major difference in lift capacity. If a Falcon 9 rocket lands at sea, it can lift approximately 5.5 tons to geostationary transfer orbit. However, that figure falls to 3.5 tons if the rocket comes home to a launch site.

Why Isn’t the SpaceX Falcon 9 Fully Reusable?

SpaceX initially hoped to reuse both stages. However, by 2014, it became clear that such attempts would cause prohibitive performance sacrifices. So, the second stage falls back to Earth and burns up in the atmosphere after depositing its payload.

Sometimes, things go wrong, however. In one instance, a second-stage Falcon 9 rocket caused fireballs in the sky and dropped debris on land in Oregon and Washington. One 200-pound tank landed 50 feet from someone’s trailer residence.

The way the reusable stage looked after a May 2021 return from sending dozens of Starlink internet satellites into orbit showed that the company is still making the most of its reusability, though. A Falcon 9 rocket that went into space a record-setting 10 times had a sooty exterior upon returning. Since SpaceX debuted its upgraded Falcon in 2018, it has worked toward this 10-trip milestone.

The Hardware and Software

The first-stage landing mentioned above is entirely automated, and the various components respond in real-time to changing conditions. The launch vehicles also have autonomous flight termination systems. They abort the vehicle’s flight if systems detect something’s wrong that breaks mission rules and puts the rockets at risk of damage. Computers make these operations possible.

The Falcon 9 has a Linux onboard operating system running on a trio of dual-core x86 processors. Programmers wrote the flight software in the C and C++ programming languages. The Falcon 9 needs three processors because it uses an actor-judge system that bolsters safety through redundancy.

Every decision made is compared with the results of the other two cores. Any disagreement between the three restarts the process. However, when they match, the initial decision is sent to PowerPC microcontrollers responsible for how the rocket engines and grid fins behave. In all other cases, the microcontrollers carry out the last command verified by this triple-redundancy process.

The SpaceX team also performs regular hardware-in-the-loop testing to verify the whole mission profile works as expected before the reusable rocket takes flight. Doing that allows engineers and computer scientists to fix any problems early, reducing the chances they’ll lose a rocket after it launches.

The Falcon 9 Contributes to Space Exploration Achievements

The Falcon 9 helps scientists learn more about space, particularly when its payloads include communications and Earth observation satellites. SpaceX also has a “ridesharing” program where interested parties can reserve the Falcon X to transport their payloads into space. Through these efforts and others, the reusable rocket could help researchers learn previously unknown outer space insights.

Emily Newton is the Editor-in-Chief of Revolutionized Magazine. She has over three years experience writing articles for the tech and industrial sectors. Subscribe to the Revolutionized newsletter for more content from Emily at

Recommended Articles

DesignSpark Electrical Logolinkedin