The Space Launch Process: From Countdown to Orbit

Launching a rocket to orbit is one of the most complex engineering operations humans perform. A modern launch campaign involves months of preparation, thousands of checkpoints, and a countdown sequence measured in hours that culminates in a few minutes of controlled violence: millions of pounds of thrust hurling a payload from zero to 28,000 km/h. Here is what actually happens, step by step, from weeks before launch to successful orbital insertion.

The Pre-Launch Campaign (Weeks to Months Before)

Long before the countdown clock starts, the launch campaign begins with vehicle integration. The rocket stages arrive at the launch site, are inspected, and assembled: either vertically on the pad (as with ULA's Atlas V and Vulcan) or horizontally in a processing facility before being transported to the pad (SpaceX's Falcon 9, Rocket Lab's Electron).

The payload, whether it's a satellite, a crew capsule, or a batch of Starlink satellites, undergoes its own preparation in a cleanroom facility near the launch site. This includes final testing, fueling (if the satellite has its own propulsion), and integration into the payload fairing (the protective nose cone). The fairing halves are sealed in a cleanroom environment to prevent contamination.

Once the payload is mated to the rocket, the integrated vehicle undergoes a series of combined tests verifying that the rocket and payload communicate correctly, that the flight computer has the correct trajectory parameters, and that all mechanical and electrical connections are nominal.

Launch Readiness Reviews (Days Before)

Before any countdown begins, a series of readiness reviews bring together engineers, range safety officers, weather forecasters, and mission managers:

• Launch Readiness Review (LRR): Typically held 2-3 days before launch. Each subsystem team reports their status, and the mission director polls for a Go/No-Go decision. Any team can call a hold.
• Range safety certification: The Eastern Range (Cape Canaveral) or Western Range (Vandenberg) confirms that the flight safety systems, including the flight termination system (FTS) that can destroy the rocket if it deviates off course, are certified and operational.
• Weather briefing: The 45th Weather Squadron (for Cape launches) provides forecasts for launch day, evaluating lightning risk, upper-level winds, cumulus cloud rules, and recovery weather for booster landing zones.

The Countdown Sequence

The countdown is a precisely choreographed sequence of events. Using SpaceX's Falcon 9 as a representative example:

T-38 hours: Countdown begins

The launch team initializes countdown procedures and begins configuring ground systems. Weather monitoring begins. The rocket sits on the pad, unfueled.

T-7 hours: Terminal count begins

The intensive final phase of countdown begins. The launch team transitions to the terminal count timeline where every minute is scripted.

T-35 minutes: Propellant loading (RP-1 kerosene)

The first stage begins loading RP-1 kerosene, a refined jet fuel. RP-1 is stored at ambient temperature, so this is straightforward. Falcon 9 carries approximately 123,000 kg of RP-1 across both stages.

T-35 minutes: LOX loading begins

Liquid oxygen (LOX) loading begins simultaneously. LOX is cryogenic at -183°C and continuously boils off, so loading continues right up to launch. SpaceX sub-cools their LOX to -207°C (denser than normal, allowing more propellant in the same tank volume), which is one reason Falcon 9 performs better than competitors with similar-sized vehicles.

T-16 minutes: Range confirms Go for launch

The range safety officer confirms that the flight safety corridor is clear, tracking stations are operational, and all range constraints are met.

T-7 minutes: Engine chill sequence

A small amount of LOX is circulated through the engine turbopumps and combustion chambers to bring them to cryogenic temperatures. Pumping -207°C liquid through room-temperature metal would cause thermal shock and pump cavitation without this conditioning step.

T-1 minute: Final computer checks

The flight computer runs a final automated check of all vehicle systems. The strongback (the launch tower arm that supports the rocket) begins retracting. The propellant loading system switches to flight-pressure mode.

T-45 seconds: Autonomous launch sequence

The launch director gives the final Go, and the onboard flight computer takes over. From this point, the computer controls the sequence autonomously. Any anomaly detected by the computer will trigger an automatic abort.

T-3 seconds: Engine ignition

The nine Merlin 1D engines ignite in a carefully sequenced pattern over approximately 0.5 seconds, ramping up to full thrust. Sensors verify that all engines are operating nominally: if any engine shows off-nominal performance, the computer can abort before the hold-down clamps release.

T-0: Liftoff

The hold-down clamps release and the rocket lifts off. Falcon 9 produces approximately 7.6 million newtons (1.7 million pounds) of thrust at liftoff, about 1.3 times the vehicle's weight, giving a thrust-to-weight ratio of 1.3. The rocket accelerates relatively slowly at first, clearing the tower in about 7 seconds.

Ascent to Orbit

Max-Q (T+60-80 seconds)

Approximately one minute after liftoff, the rocket reaches Maximum Dynamic Pressure (Max-Q), the point where the combination of increasing speed and decreasing air density creates the greatest aerodynamic stress on the vehicle. The engines may throttle down slightly to reduce structural loads. This is one of the most critical moments of flight.

MECO: Main Engine Cutoff (T+2:30)

After approximately 2.5 minutes of powered flight, the first stage has exhausted its propellant and the nine engines shut down. The vehicle is now traveling at roughly 6,000 km/h at an altitude of 60-80 km.

Stage Separation

Pneumatic pushers separate the first and second stages. The second stage's single Merlin Vacuum engine ignites within seconds, continuing the climb to orbit. The first stage begins its journey back to Earth (on reusable missions), flipping around with cold gas thrusters, performing a boostback burn to reverse direction, a reentry burn to slow down in the upper atmosphere, and a final landing burn to touch down on a drone ship or landing pad.

Fairing Separation (T+3:00-3:30)

Once the rocket is above the dense atmosphere (typically above 100 km), the payload fairing splits apart and falls away, exposing the payload. The fairings are no longer needed: they only protect the payload from aerodynamic forces during the lower atmosphere portion of flight. SpaceX recovers fairings for reuse.

Second Engine Cutoff: SECO (T+8:00-9:00)

The second stage engine burns for approximately 6 minutes, accelerating the payload to orbital velocity, approximately 7.8 km/s (28,000 km/h) for a typical low Earth orbit. When the engine cuts off, the payload is in orbit.

Payload Deployment (T+15:00-60:00)

After coasting to the precise deployment point, the second stage orients itself and releases the payload. For Starlink missions, the 20-60 satellites deploy from a dispenser in a flat-stack configuration, gradually separating and raising their orbits using onboard ion thrusters. For single-satellite missions, springs or clamp-band systems push the satellite away from the second stage.

When Things Go Wrong

Despite the precision of modern launch operations, failures still occur at a rate of roughly 2-5% depending on the vehicle:

• Scrubs and holds: The most common outcome of an anomaly during countdown is a scrub, where the launch is postponed to a future date. Scrubs are caused by weather violations, ground equipment issues, range conflicts, or vehicle anomalies detected during automated checks. Scrubs are expensive (propellant must be offloaded and reloaded) but are always the right call.
• Aborts after ignition: Rare but possible. If the flight computer detects an engine anomaly between ignition and clamp release, it can command an engine shutdown while the rocket is still on the pad. This happened once with Falcon 9 in 2016 during a static fire.
• In-flight failures: Engine failures, structural breakups, guidance errors, or stage separation malfunctions can cause loss of mission. Modern rockets carry flight termination systems that range safety can activate if the vehicle deviates from its planned corridor toward populated areas.

Track Every Launch

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