A rocket launch begins long before the engines ignite. It takes months—sometimes years—of preparation to ensure everything is perfect. But what’s happening in the final hours before launch?
A modern launcher is around 60 meters tall (190 feet) and weights around 1065 metric tons or 2.34 million pounds, with more than 85% of this mass being the highly flammable liquid propellants.
Launching a rocket is one of the most difficult things, it requires attention to details, making sure that everything is working precisely and without any errors. Not all rocket launches follow the same path, but more or less it is always the same. So, let’s see together what the different steps are.
Rocket Transported to Launchpad
T-24h. Once the various stages, or parts, of the rockets are made, they are transported to the launchpad. Some rockets are already assembled and transported vertically, others horizontally. If the rocket is a big rocket, it is assembled at the Launchpad, stage after stage.
Launch Area Evacuation
T-24h. If the trajectory of the rocket being launched is particularly close to inhabited places, there might be the need to evacuate the surrounding areas. For instance, an evacuation notice is issued to the residents of Boca Chica, Texas when a SpaceX Starship launch is scheduled to take place to inform them of the possibility of falling debris and to instruct them to evacuate. The first evacuation notice is given around 24 hours before the launch, although this can vary based on different conditions, such as weather.
Vehicle Power Up
T-12h. Once the rocket is ready in position, it is powered up to allow system checks on all equipment. Rocket engineers, or technicians, perform tests on the electrical and electronics components, and make sure all other equipment is working properly. At this stage, they also check screws, nuts and bolts.
Weather Briefing
T-12h. Weather plays a significant role when launching a rocket into space. High winds and intense lightning can influence the launch and sometimes even destroy the rocket. Although the first official weather report is given at T-12 hours, more weather reports are given throughout the pre-launch and launch windows.
Propellant Loading
T-3h. Now, one of the most critical steps during the preparation phases.
Unlike solid-fueled rockets, which are pre-filled at the factory, liquid-fueled rockets are fueled directly at the launch site. The most common fuels used today are RP-1 (a refined kerosene), liquid hydrogen (LH2), or liquid methane (CH4), paired with liquid oxygen (LOX) as the oxidizer.
Fueling typically starts 1 to 3 hours before launch, depending on the rocket. For example, SpaceX’s Falcon 9 begins fueling about an hour and 10 minutes before liftoff, while the Delta IV starts much earlier, nearly five hours before launch.
During fueling, you might notice white smoke or vapor forming around the rocket. This isn't actual smoke but rather condensed water vapor caused by the super-cold cryogenic fuels. As the cryogenic liquids evaporate, they release extremely cold gas that chills the surrounding air, condensing moisture into what looks like white smoke.
Flight Readiness Poll
T-10m. As you might imagine, building and operating a rocket requires lots of people. During the launch window, all people involved in the launch sequence will start a status report for each subsystem. This is when you start hearing “propulsion?” “go”, “electrical?”, “go”. Honestly, this is one of the most exciting parts.
Rocket Launch
T-1m. At this point, the onboard computer takes full control of the rocket and its subsystems. The computer manages all critical processes including engine activation, system checks and getting ready to launch.
T-0s. LIFTOFF! During liftoff, the rocket’s engines ignite, creating bright flames and sometimes sparkles from the combustion process. These sparkles occur due to unburned fuel particles reacting with the atmosphere. The engines generate massive thrust, overcoming gravity and atmospheric drag, pushing the rocket upwards.
Roll and Pitch Maneuvers
T+10s. Just moments after clearing the launch tower, the onboard computer makes precise adjustments to the rocket's trajectory. Instead of continuing straight upward, the rocket tilts slightly to follow a more optimal path, ensuring it's heading in the correct direction for its mission. This maneuver, known as a "gravity turn," helps the rocket gain the necessary horizontal velocity for orbit.
Vehicle Supersonic
T+80s. At this point the rocket is gaining more and more speed and becoming supersonic (meaning it goes faster than the speed of sound!).
Max Q
T+90s. At this stage, the rocket enters the region of maximum dynamic pressure, where it faces the highest gravitational forces and drag while producing maximum thrust. This intense phase places significant stress on the vehicle's structure. To mitigate this, the launch vehicle adjusts its thrusters slightly downward to reduce the strain on its frame.
MECO
T+3m. During this phase, the boosters of the rocket are exhausted and are separated from the body of the rocket. This helps the rocket becoming lighter and reaching higher speeds. This phase is called MECO or Main Engine Cut Off.
First Stage Separation
T+4m. Shortly after MECO, the First Stage is also detached from the rocket and falls back on Earth. Some companies, like SpaceX, are working on making rockets reusable, so that the first stage comes back on Earth without burning in the atmosphere.
Second Stage Ignition
T+4m. As soon as the first stage is gone, the rocket’s onboard computer ignites the second stage, this gives even more thrust and allows the rocket to reach incredibly high speeds, around 28000 kph or 17500 mph.
SECO
T+Variable. Once the rocket has reached its destination and speed, it performs a second engine cut off. This can time a few minutes if the orbit is close to Earth, or several hours or days if the orbit is further away, for example in GEO at 36000 km.
Payload Deployment
The final part of the launch is the payload deployment. This phase can last a few hours of a few minutes, depending on where the payload needs to be deployed. To save money, rocket companies sell space on their rockets to multiple companies at the same time, and release payloads through the first or second orbit.
Conclusions
As you can see there are many steps involved in the launch of a rocket, and every single step is equally important to ensure it successfully launches. Launching something into space costs a lot of money, and a rocket failure could be catastrophic, this is why rocket companies do everything they can to ensure rockets work properly.