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Questions tagged [j-2]

A liquid hydrogen/oxygen engine, used by the Saturn V's second and third stages.

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1answer
329 views

Was a large-nozzle variant of the J-2 ever considered?

The J-2 engine used on the upper stages of the Saturn launchers has a specific impulse in vacuum of 421 seconds. This is substantially lower than that of the smaller RL10, 440-460 seconds depending on ...
12
votes
2answers
3k views

Why the huge thrust difference between a Sea level and Vacuum J-2 engine?

Looking at the Wikipedia page for the J-2 (one engine was used on the Saturn V third stage, and 5 engines on the second stage) it gets about 232Klbs thrust in vacuum, but at sea level, only 109KLbs ...
3
votes
2answers
485 views

Why were the SSMEs so much more fragile than the J-2 engines?

This answer mentions that the J-2 engines used by the Saturn V's second and third stages were substantially more resilient than the "extremely complex and sensitive" Space Shuttle main engines. What ...
3
votes
1answer
148 views

How would the STS have differed if it used J-2's as the main engine?

In the spirit of counterfactual rocket design questions such as this one - how would the STS have differed from its actual design if it used J-2's as the main engine? What would be the loss in payload ...
1
vote
2answers
824 views

J-2 rocket nozzle length

The total length of the J-2 rocket engine is 133 inches, but what is its nozzle length from throat to exit?