Talk:RS-68

Early suggestions
Suggesting some details regarding theory of operation. The ratio of LH2 to LOX is 2:1. Fuel is moved via turbopump to the combustion chamber. An EED device starts the ignition. Exhaust is pushed out through the cone. Hot gas is tapped at the combustion chamber. This hot gas is fed to the turbopump. Hot gas is also brought to the top of both the LH2 and LOX tanks used as a press line. LH2 also cools the cone. Statikfire20:00, 5 November 2007 (CST)

This article claims the RS-68 was the first new US engine in 25 years. Well, what about the FASTRAC? Maury 13:08, 19 August 2006 (UTC)

The FASTRAC project was never completed. It was never fired during a test flight, ground tested only. Martin


 * True, but every project that had selected it was canceled out from under it. It was no problem with the engine itself. Maury 13:33, 20 August 2006 (UTC)


 * Nobody is saying it was the engine's fault. Regardless, the fact of the matter is, FASTRAC didn't fly, and it can be argued that to be successfully "developed", a rocket engine needs to fly on something. The RS-68 is the first engine in 25 years to do so. Ergo, first new US engine developed in 25 years. Nick L. 15:36, 20 August 2006 (UTC)

(undent) Sorry, just saw this now... "it can be argued that to be successfully "developed", a rocket engine needs to fly on something" By this remarkable definition, the M-1 was never developed. Nor the J-2T, J-2S, HG-3, KIWI, or literally dozens of other engines. I'm sure the engineers who built them, and the politicians that paid for it, would be absolutely fascinated to hear they were never actually "developed". Having personally witnessed several non-developed engines, I have to admit I'm a little skeptical. If you can find me a single definition in any reputable source that even hints that "developed" in any way remotely requires flew, I'd love to see it. In the meantime my original objection stands. Many engines have been developed in the US over this period, and several of them have even flown. Maury 01:00, 30 October 2007 (UTC)
 * No problem. Sorry about that, I was a bit thick about it that year ago. Nick L. 20:46, 12 November 2007 (UTC)
 * And my apologies too, for being such an ass. Maury (talk) 03:55, 20 November 2007 (UTC)

wrong link cbc/ccb
link to common booster core(cbc) is incorrectly linked to common core booster(ccb) which is a different propulsion system entirely. —Preceding unsigned comment added by Mikedelta12 (talk • contribs) 01:47, 5 October 2007 (UTC)
 * should redirect now to Delta IV. --Duk 06:08, 5 October 2007 (UTC)

Engine Mixture Ratio
Are you sure about the 1:6 ratio? I build 1st Flight Delta IV down in Trinity Alabama, and I quite vividly remember the Hydrogen tank being twice the size of the LOX tank. Jason —Preceding signed but undated comment was added at 18:45, 11 October 2007 (UTC)
 * see

--Duk 19:46, 11 October 2007 (UTC)

Power rating
This seems trivial, but just to be sure it's not some weird technical aberration, it should say that the rocket operates at sea level and in a vacuum both at 100% power, correct?

Alucardtepes 06:20, 27 October 2007 (UTC)


 * Maximum thrust for rocket engines is often stated as greater than 100%. Designers usually set a required minimum thrust, and then during testing it is often found that the engine produces more than this maximum. Rather than change the "100% thrust" value, which could involve a lot of paperwork and other difficulties, they just express it as greater than 100%, for example 102%. Hope this helps, Nick L. 23:12, 29 October 2007 (UTC)


 * Ok, but that's not the only reason that engines are rated higher than 100%, is it? Isn't there something to the effect of "We were happy with the performance and safety limits at 100%, so we decided to push it further?" In any event, it would help to explain in the article just how it got to 102% Piano non troppo (talk) 08:20, 25 May 2009 (UTC)

Maximum Thrust Rating?
This article says the the RS-68 is rated around 3.3MN of thrust, right? However the page for the saturn 5 project (successors - http://en.wikipedia.org/wiki/Saturn_V#Successors) claims the vehicle will be powered by 6 RS-68B's and have a total of 39.6MN of thrust. The Ares V page does not mention a thrust rating for engines or for the whole vehicle. That means the RS-68B is supposed to put out roughly double the thrust of the RS-68A, or is one article wrong?131.107.0.73 (talk) 23:09, 1 July 2009 (UTC)


 * The thrust for the RS-68A is cited in this article. Also, the Ares V will use two longer Solid Rocket Boosters. -Fnlayson (talk) 23:18, 1 July 2009 (UTC)

RS-68 no longer planned for Constellation/Ares?
According to http://www.nasa.gov/mission_pages/constellation/ares/aresl/index.html Ares 1 upper stage will use J-2X engines, not RS-68?

If this is true, should'nt the article be updated? --91.45.214.24 (talk) 20:36, 19 July 2009 (UTC)


 * No this article states the RS-68 will be used on the Ares V launcher, which is correct. See Constellation program for the program overview. -Fnlayson (talk) 20:56, 19 July 2009 (UTC)

Soviet heritage
The page on the RD-0120 engine mentions that Rocketdyne studied that engine (presumably after the USSR collapsed) to find ways of improving the SSME. Then they designed the RS-68 engine, and this article also mentions the adoption of Soviet engineering techniques in order to simplify the design.

This seems to suggest that the design of the RS-68 was derived from the RD-0120 as well as the SSME, which would be worth mentioning if it is the case. Does anyone know more?

GrampaScience (talk) 16:53, 28 September 2010 (UTC)


 * Getting ideas from previous designs may not mean much of a connection. But if someone can find a source for a real connection, please add it. -fnlayson (talk) 17:22, 28 September 2010 (UTC)

Comparison to Vulcain
How about a section on comparison to other engines such as the Vulcain? user:mnw2000 23:15, 21 November 2010 (UTC)


 * Maybe a table or something if the data can be found and properly cited. -fnlayson (talk) 00:07, 22 November 2010 (UTC)

what is this supposed to mean ?
--"The engine's mass is 14,560 pounds (6,600 kg) at 96 inches (2.4 m). "

What does this mean ? Is the 96 inches the size of the engine ? The altitude of the launch site ? Barometric pressure ? Either way it doesn't seem to have anything to do with the mass or the thrust/weight ratio. Eregli bob (talk) 20:13, 8 August 2013 (UTC)

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