J-2 (rocket engine)
The J-2 was a rocket engine of Rocketdyne provided with liquid hydrogen (LH 2 ) and liquid oxygen was operated (LOX). It was used in NASA launchers , in particular the Saturn V moon rocket . It was the most powerful liquid hydrogen-powered engine in the United States at the time, but was later surpassed by the Space Shuttle's Rocketdyne RS-25 main engine .
Using the J-2
Five J-2 engines have been in the second stage (S-II) Saturn V used. A J-2 engine was used in the third stage (S-IVB) of the Saturn V and in the structurally identical second stage (also S-IVB) of the Saturn IB . In studies for planned Nova missiles , various configurations have been suggested, the upper stages of which would also have been powered by J-2 engines.
A unique characteristic of the J-2 was that it could be fired multiple times. For example, the J-2 engine of the third stage of the Saturn V was used twice during flight. The first burning period lasted two and a half minutes and was used to put the spacecraft into orbit. After the crew had checked the correct function of the spaceship and the engine was able to ignite again, the J-2 engine was ignited again for 6 minutes and 30 seconds to bring the ship on course to the moon, by NASA TLI ( Trans Lunar Injection ) called.
A longer pause was required to re-ignite the engine in order to allow individual parts to cool down and to have a sufficient amount of gaseous hydrogen available for the turbo pumps to restart them. The break was about 35 minutes. For reignition, the previous technology of ignition using hypergolic ignition media was deviated from, and arc ignition (similar to a spark plug) was introduced.
An improved version, the J-2S, was developed and tested for the planned successor model Nova of the Saturn V. The J-2S provided about 10% more thrust and slightly improved specific impulse, but was never used.
The advanced J-2X
This new variant of this engine was to be used as part of the Constellation program , which was to replace the space shuttle after its decommissioning in 2010. The J-2X engine was supposed to function as an engine in both versions of the Ares rockets , in the Ares I in the upper stage, in the Ares V only in the Earth Departure Stage (EDS). The use of three J-2X was planned in the upper stage of the Space Launch System , but was rejected again.
The new engine is being developed by Whitney Rocketdyne Inc .; the contract for this was signed in July 2007. The first tests with the historic J-2 engine , primarily to obtain comparative data, took place at NASA's Stennis Space Center near St. Louis. In November 2008, the engine passed the Critical Design Review at the Marshall Space Flight Center in Huntsville, Alabama and is thus qualified for flight. It was not used on the Ares IX's first test flight . In 2011, test runs of the new engine in full configuration began at the John C. Stennis Space Center .
Technical specifications
| J-2 | J-2X | |
|---|---|---|
| Mixing ratio LOX / LH2 | 5.0, later 5.5 | 5.5 |
| Burn time | 500 s | 431 s |
| Reignitions | 3 times | |
| Total height | 3.38 m | 4.70 m |
| diameter | 2.01 m | 3.05 m |
| Dry matter | 1400 kg | |
| Mass / thrust ratio (vacuum) | ? kg / kN | |
| Combustion chamber pressure | 3.0 MPa | ? MPa |
| Nozzle throat diameter | ? mm | ? mm |
| Nozzle end diameter | ? mm | ? mm |
| Nozzle end pressure | ? MPa | ? MPa |
| Expansion ratio | 27.5 | 80 |
| Vacuum thrust | 890 kN, later 1000/1030 kN |
1310 kN |
| Specific impulse (vacuum) | 421 s | 448 s |
Usage: Saturn IB / S-IVB, second stage - one engine
Usage: Saturn V / S-II, second stage - five engines
Usage: Saturn V / S-IVB, third stage - one engine
See also
literature
- RE Bilstein: Stages to Saturn. University of Florida Press, Gainesville 2003.
Web links
- J-2 and J-2S in the Encyclopedia Astronautica (English)
- Stages to Saturn . NASA History Office (English)
- NASA to Begin Testing of Engine That Will Power Ares Rockets (English)
- J-2X NASA (English)