J-2 rocket engine specifications |
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| 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 |
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.[1] 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.
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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.
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.
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).[2]
NASA began construction of a new test stand for altitude testing of J-2X engines at Stennis Space Center (SSC) on 23 August 2007.[3] 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.[4]
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).[5] 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.[6] On Sept. 8, 2008 Pratt & Whitney Rocketdyne announced successful testing of the initial J-2X gas generator design.[7] The completion of a second round of successful gas generator tests was announced on September 21, 2010.[8]
Project Constellation was cancelled by President Barack Obama on October 11, 2010,[9] 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.[10]
On November 9, 2011 NASA conducted a successful firing of the J-2X engine of 499.97 seconds in duration. [11]
| J-2[12] | J-2S[13] | J-2X[14] | |
|---|---|---|---|
| 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 -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 |
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