Falcon-I

Space Exploration Technologies Corporation

The Falcon-I and Falcon-Ie launchers are two-stage semi-reusable small launch vehicles, which is currently under development at Space Exploration Technologies Corp. (SpaceX). Both stages are Kerosene (RP-1)/LOX fueled. The first stage is to be powered by the SpaceX built "Merlin" engine. The Merlin is a turbopump-fed, gas-generator-driven engine with an ablative chamber and nozzle. The second stage will be propelled by a derivative of the Apollo LEM descent engine with a thrust of 31.1 kN ---> "Kestrel". The Kestrel is a high-performance, but simple restartable engine that uses tank-pressure to feed the propellants into the chamber.

First Stage. The primary structure is made of a space grade aluminum alloy in a patent pending, graduated monocoque, common bulkhead, flight pressure stabilized architecture developed by SpaceX. A single SpaceX Merlin-1 engine powers the Falcon -I first stage. After engine start, Falcon is held down until all vehicle systems are verified to be functioning normally before release for liftoff. The first stage returns by parachute to a water landing, where it is picked up by ship in a procedure similar to that of the Space Shuttle solid rocket boosters.
Second Stage. The tank structure is made of aluminum-lithium, an alloy possessing the highest strength to weight ratio of any aluminum and currently used by the Space Shuttle External Tank. A single SpaceX Kestrel engine powers the Falcon -I upper stage. For added reliability of restart, the engine has dual redundant torch igniters. Helium pressurization is again provided by composite over wrapped inconel tanks from Arde. However, in this case the helium is also used in cold gas thrusters for attitude control and propellant settling when a restart is needed.

SpaceX Merlin Engine. The main engine, called Merlin-1, 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.
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. With a vacuum specific impulse of 304s.

Space Exploration Technologies Corp. (SpaceX) announced that it has completed development of its Merlin-1C next generation liquid fueled rocket booster engine.
The Merlin-1C is an improved version of the Merlin-1 ablatively cooled engine, which lofted the Falcon-1 on its first and second. The regeneratively cooled Merlin-1C uses rocket propellant grade kerosene (RP-1), a refined form of jet fuel, to first cool the combustion chamber and nozzle before being combined with the liquid oxygen to create thrust. This cooling allows for higher performance without significantly increasing engine mass.
The Merlin-1C will power SpaceX’s next Falcon-1 mission, scheduled to lift off in early 2008 from the SpaceX launch complex in the Central Pacific atoll of Kwajalein.
 SpaceX’s far larger Falcon-IX rocket, now in development, will employ nine Merlin-1C engines on its first stage, and one on the second stage (Merlin-1V). Merlin-1C in its Falcon-IX first stage configuration has a thrust at sea level of 125,000 lbs, a vacuum thrust of over 138,400 pounds, sea level specific impulse of 275 seconds and vacuum specific impulse of 304 seconds.

SpaceX Kestrel Engine. Kestrel, also built around the pintle architecture, is designed to be a high efficiency, low pressure vacuum engine. It does not have a turbo-pump and is fed only by tank pressure.
Kestrel is ablatively cooled in the chamber and throat and radiatively cooled in the nozzle, which is fabricated from a high strength niobium alloy. As a metal, niobium is highly resistant to cracking compared to carbon-carbon. An impact from orbital debris or during stage separation would simply dent the metal, but have no meaningful effect on engine performance. Helium pressurant efficiency is substantially increased via a titanium heat exchanger on the ablative/niobium boundary.
Thrust vector control is provided by electro-mechanical actuators on the engine dome for pitch and yaw. Roll control (and attitude control during coast phases) is provided by helium cold gas thrusters.
The engine has dual redundant torch igniters, tested in vacuum, to ensure a reliable engine start. Since the igniters use the same propellants as the main engine, they are capable of as many restarts as necessary for a particular mission. In a multi-manifested mission, this allows for drop off at different altitudes and inclinations.