Questions tagged [j-2]

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

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1 answer
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Why is the value of the Isp of the Rocketdyne J-2 Saturn V engine in my calculation so off?

While calculating the delta V the Saturn V has on its second stage, I wanted to also calculate the Isp of the J2 rockets engines. However, the value difference between my results and the values given ...
The Rocket fan's user avatar
3 votes
1 answer
277 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 ...
DylanSp's user avatar
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5 votes
2 answers
590 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 ...
DylanSp's user avatar
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24 votes
1 answer
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Why is fuel ratio different for upper stage of a rocket?

After reviewing this amazing graphic posted in another question: I noticed that the LH/LOX ratio is slightly different in the Second and Third stages. The mass stoichiometry of the reaction: 2 H2 + ...
MarsJarsGuitars-n-Chars's user avatar
1 vote
2 answers
1k 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?
Kashif Marjan's user avatar
5 votes
1 answer
620 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 ...
Russell Borogove's user avatar
4 votes
0 answers
731 views

If the J-2X is too powerful for SLS, why was it appropriate for Saturn V?

Reading an article about new engines for the SLS (Summary: There is no plan what to do once the current SSME's are expended), they mention that the J-2X is too powerful for the upper stage of SLS. ...
geoffc's user avatar
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7 votes
2 answers
605 views

Was the notion of using an air-started SSME on Ares-1 a reasonable idea?

For whatever reasons, it seems like the standard upper stage engine in the U.S. inventory is the RL-10. A high performance engine with nice specific impulse (Isp = 450-465 s), but very low thrust (25 ...
geoffc's user avatar
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12 votes
2 answers
4k 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 ...
geoffc's user avatar
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