First Stage
The Falcon 9 tank walls and domes are made from aluminum lithium alloy. SpaceX uses an all friction stir welded tank, the highest strength and most reliable welding technique available. Like Falcon 1, the interstage, which connects the upper and lower stage for Falcon 9, is a carbon fiber aluminum core composite structure. The separation system is a larger version of the pneumatic pushers used on Falcon 1.
Nine SpaceX Merlin engines power the Falcon 9 first stage with 147,000 lbs-f sea level thrust per engine for a total thrust on liftoff of just over 1.3 Million lbs-f. After engine start, Falcon is held down until all vehicle systems are verified to be functioning normally before release for liftoff.
Spacex Merlin Engine
The main engine, called Merlin, was developed internally at SpaceX, but draws upon a long heritage of space proven engines. The pintle style injector at the heart of Merlin was first used in the Apollo Moon program for the lunar module landing engine, one of the most critical phases of the mission.
Propellant is fed via a single shaft, dual impeller turbo-pump operating on a gas generator cycle. The turbo-pump also provides the high pressure kerosene for the hydraulic actuators, which then recycles into the low pressure inlet. This eliminates the need for a separate hydraulic power system and means that thrust vector control failure by running out of hydraulic fluid is not possible. A third use of the turbo-pump is to provide roll control by actuating the turbine exhaust nozzle (on the second stage engine).
Combining the above three functions into one device that we know is functioning before the vehicle is allowed to lift off means a significant improvement in system level reliability.
Designed for Maximum Reliability
The vast majority of launch vehicle failures in the past two decades can be attributed to three causes: engine, stage separation and, to a much lesser degree, avionics failures. An analysis (p. 23) of launch failure history between 1980 and 1999 by Aerospace Corporation showed that 91% of known failures can be attributed to those subsystems.
Engine Reliability
Falcon 9 has nine Merlin engines clustered together. This vehicle will be capable of sustaining an engine failure at any point in flight and still successfully completing its mission. This actually results in an even higher level of reliability than a single engine stage. The SpaceX nine engine architecture is an improved version of the architecture employed by the Saturn V and Saturn I rockets of the Apollo Program, which had flawless flight records despite losing engines on a number of missions.
Another notable point is the SpaceX hold-before-release system — a capability required by commercial airplanes, but not implemented on many launch vehicles. After first stage engine start, the Falcon is held down and not released for flight until all propulsion and vehicle systems are confirmed to be operating normally. An automatic safe shut-down and unloading of propellant occurs if any off nominal conditions are detected.
NASA'S CHOICE TO RESUPPLY THE SPACE STATION
In December 2008, NASA announced the selection of SpaceX's Falcon 9 launch vehicle and Dragon Spacecraft to resupply the International Space Station (ISS). The $1.6 billion contract represents a minimum of 12 flights, with an option to order additional missions for a cumulative total contract value of up to $3.1 billion.
NASA CITED SPACEX'S SIGNIFICANT STRENGTHS AS FOLLOWS:
First stage engine-out capability
Dual redundant avionics system
Structural safety factor in excess of industry standards
Enhanced schedule efficiencies
Reduced overall technical risk to ISS cargo supply
