J-2 (rocket engine)

J-2

J-2 rocket engine specifications
Country of origin	United States
Manufacturer	Rocketdyne
Liquid-fuel engine
Propellant	LOX / LH2
Performance
Thrust (Vac.)	232,250 lbf (1,033.100 kN)
Thrust (SL)	109,302 lbf (486.200 kN)
Thrust-to-weight ratio	73.18
Isp (Vac.)	421 sec
Isp (SL)	200sec

Saturn V second stage, with five J-2 engines.

A J2 engine.

Rocketdyne's J-2 rocket engine was a major component of the Saturn V rocket used in the Apollo program to send men to the Moon. Five J-2 engines were used on the S-II second stage, and one J-2 was used on the S-IVB third stage. The S-IVB was also used as the second stage of the smaller Saturn IB rocket used to launch Apollo spacecraft into Earth orbit. There were proposals to use various numbers of J-2 engines in the upper stages of an even larger rocket, the planned Nova.

Unlike most liquid-fueled rocket engines of the time, the J-2 engine used on the Saturn V third stage was designed to be re-started once after shutdown. The first burn, lasting about two minutes, placed the Apollo spacecraft into a low Earth parking orbit. After the crew verified that the spacecraft was operating nominally, the J-2 was re-ignited for translunar injection, a 6.5 minute burn which accelerated the vehicle to a course for the Moon.

The J-2 was America's largest production liquid hydrogen fueled rocket engine before the Space Shuttle Main Engines (SSME), and a derivative (the J-2X) is being studied for potential use in the second stage of the heavy-lift Space Launch System.

J-2S

An experimental program to improve the performance of the J-2 started in 1964 as the J-2X (not to be confused with a later variant by the same name). The main change to the original J-2 design was a change from the gas generator cycle to a tap-off cycle that supplied hot gas from a tap on the combustion chamber instead of a separate burner. In addition to removing parts from the engine, it also reduced the difficulty of starting up the engine and properly timing various combustors.

Additional changes included a throttling system for wider mission flexibility, which also required a variable mixture system to properly mix the fuel and oxygen for a variety of different operating pressures. It also included a new "Idle Mode" that produced little thrust for on-orbit maneuvering or to settle the fuel tanks on-orbit prior to a burn.

During the experimental program, Rocketdyne also produced a small run of six pre-production models for testing, the J-2S. These were test fired many times between 1965 and 1972, for a total of 30,858 seconds burn time. In 1972 it became clear no follow-on orders for Saturn boosters were coming, and the program shut down. NASA did consider using the J-2S on a number of different missions, and for some time a set of five were to power the Space Shuttle, a configuration that can be seen on early diagrams.^{[citation needed]}

J-2T

While work on the J-2S continued, NASA also funded a design effort to use the J-2S turbomachinery and plumbing with a new aerospike nozzle. This would improve performance even further. Two versions were built, the J-2T-200k that provided 200,000 lbf (890 kN) thrust, allowing it to be "dropped in" to the existing S-II and S-IVB stages, and the J-2T-250k of 250,000 lbf (1,100 kN).

Like the J-2S, work on the J-2T had progressed to a lengthy series of ground-based test runs, but further development ended in the post-Apollo draw-down.

J-2X

A new variant of this engine, called the J-2X, was chosen in 2007 for the Project Constellation manned lunar landing program. A single J-2X engine,generating 294,000 lbf (1,310 kN) of thrust, was to be used to power the Earth Departure Stage (EDS).

NASA began construction of a new test stand for altitude testing of J-2X engines at Stennis Space Center (SSC) on 23 August 2007. Between December 2007 and May 2008, nine tests of heritage J-2 engine components were conducted at SSC in preparation for the design of the J-2X engine.

The new J-2X is designed to be more efficient and simpler to build than its Apollo J-2 ancestor, and cost less than the Space Shuttle Main Engine (SSME). Design changes include the removal of beryllium, a redesign of all the electronics, and the use of 21st-century joining techniques.

On July 16, 2007 NASA officially announced the award to Pratt & Whitney Rocketdyne, Inc. of a $1.2 billion dollar contract "for design, development, testing and evaluation of the J-2X engine" intended to power the upper stages of the Ares I and Ares V launch vehicles. On Sept. 8, 2008 Pratt & Whitney Rocketdyne announced successful testing of the initial J-2X gas generator design. The completion of a second round of successful gas generator tests was announced on September 21, 2010.

Project Constellation was cancelled by President Barack Obama on October 11, 2010, but development of the J-2X has continued for its potential as the second stage engine for the new, heavy-lift Space Launch System. The first hot-fire test of the J-2X was scheduled for late June, 2011.

On November 9, 2011 NASA conducted a successful firing of the J-2X engine of 499.97 seconds in duration.

• 

  Concept image of the J-2X engine.

• 

  Test of the J-2X engine 'workhorse' gas generator.

• 

  Cold Flow nozzle testing for the J2X program.

Specifications

	J-2	J-2S	J-2X
Vacuum thrust:	1,033.100 kN (232,250 lbf)	1,138.500 kN (255,945 lbf)	1,310.000 kN (294,490 lbf)
Specific impulse (vacuum) -Isp:	421 sec.	436 sec.	448 sec.
Burn time:	475 sec.	475 sec.	465 sec. (Ares I, upper stage)
Engine weight - dry:	1,438 kg (3,170 lb).	1,400 kg (3,000 lb).	2,472 kg (5,450 lb).
Propellants:	LOX & LH2	LOX & LH2	LOX & LH2
Mixture ratio:	5.50	5.50	5.50
Diameter:	2.01 m (6.60 ft).	2.01 m (6.60 ft).	3.05 m (10.00 ft).
Length:	3.38 m (11.08 ft).	3.38 m (11.08 ft).	4.70 m (15.40 ft).
Thrust to Weight Ratio:	73.18.	85.32	55.04
Contractor:	Rocketdyne	Rocketdyne	PWR
Vehicle application:	Saturn V / S-II 2nd stage - 5-engines, Saturn IB & Saturn V / S-IVB upper stage - 1-engine	Planned replacement for J-2 on Saturn V / S-II 2nd stage / S-IVB upper stage	Proposed for Ares I upper stage - 1 engine / Ares V upper stage - 1 engine

See also

• Comparison of orbital rocket engines

References

• Bilstein, Roger E. (2003). Stages to Saturn: a technological history of the Apollo/Saturn launch vehicles. Gainesville: University Press of Florida. ISBN 0-8130-2691-1. http://history.nasa.gov/SP-4206/sp4206.htm. 

External links

• Boeing History: North American Aviation Rocketdyne J-2 Rocket Engine
• Pratt & Whitney Rocketdyne J-2X site
• Encyclopedia Astronautica link about the J-2
• Encyclopedia Astronautica link about the J-2S