A couple of years ago I saw a few North American Aviation studies of uprated S-II stages for the Saturn V. NAA built the S-II and so naturally they were always looking for opportunities to upgrade it and sell more of them. One surprise was that some of the documents listed other upgrades for the J-2 engine. I think there was a J-2T proposal, and also a J-2X proposal. These designations were ca 1966, so they probably bore no correlation to later versions of this engine with similar designations.I don't know if those were NAA designations, or if Rocketdyne had also proposed those variants of the J-2. Anyway, my point is that during Apollo there were proposals to get more performance out of the J-2. Of course, the same is true of the F-1.
While doing research on the J-2S+ from the ESAS report, I ran across a very interesting report put out by Goodyear, which was studying vacuum optimized nozzle extensions for the J-2 series of engines. In it, they had a plethora of data of performance curves, expansion ratios, etc. Studying the nozzle they designed for the J-2S, I realize that the final capability of the J-2S w/ the nozzle extension designed by Goodyear in the 1970's matched almost perfectly with the J-2S+ within the ESAS report, only a few kg of thrust and a half isp difference by my calculations. In addition, the J-2S w/ nozzle extension matches the physical dimensions of the J-2X we have today. So upon request, putting the document on here for everyone to enjoy. I know I have enjoyed this insight into the J-2 evolution.
After going through 33% of the report, I don't understand if this Airmat *extendable* nozzle extension is useable for re-start.Using the search function with "start", "loiter" gives nada.Two issues:1/ Ice forming inside the (4-inch wall thickness) nozzle extension after first cutoff. How to thermaly condition the extension, while loitering in LEO, if the object is a flapping in the ... vacuum. Especially with multiple engines. Is it sensitive to iced wall ?2/ Assymetric loads on the nozzle wall at ingnition = restart. This Airmat thing must be hold in tension, otherwise it collapses under compression loads (it's in the paper). The initial deployment is controled, from a known shape; but a re-start is different. Will read forward to 100%, I promise.edit. Finished. There's nothing about restartability. If anything, this report shows how *not* to build an extendable/deployable nozzle extenson. But cool nontheless.
Did even more digging, and found other information:J-2S in 1972:Chamber Pressure: 1215 psiaThrust: 1,178.8 kNISP: 436 w/o nozzle extension, 452 w/ nozzle extensionJ-2S+ in ESAS report:Chamber Pressure: 1246 psiaThrust: 1,221 kNISP: 451J-2X w/ J-2S tap-off cycle:Chamber Pressure: 1219 psiaThrust: 1,218.8 kNISP: 455sJ-2X w/ RS-68 derived gas generator: (current J-2X calculated)Chamber Pressure: 1380 psiaThrust: 1,307.8ISP: 442
Quote from: Downix on 05/13/2011 12:36 amDid even more digging, and found other information:J-2S in 1972:Chamber Pressure: 1215 psiaThrust: 1,178.8 kNISP: 436 w/o nozzle extension, 452 w/ nozzle extensionJ-2S+ in ESAS report:Chamber Pressure: 1246 psiaThrust: 1,221 kNISP: 451J-2X w/ J-2S tap-off cycle:Chamber Pressure: 1219 psiaThrust: 1,218.8 kNISP: 455sJ-2X w/ RS-68 derived gas generator: (current J-2X calculated)Chamber Pressure: 1380 psiaThrust: 1,307.8ISP: 442Very interesting. Does anybody know if there is any chance that the J-2X contract can be altered toward a higher isp/lower thrust version? Or would this just set the project back too far?
What type of nozzle extention does SpaceX use on the upper stage? It glows in orbit but is simple and works.
A couple of years ago I saw a few North American Aviation studies of uprated S-II stages for the Saturn V. NAA built the S-II and so naturally they were always looking for opportunities to upgrade it and sell more of them. One surprise was that some of the documents listed other upgrades for the J-2 engine. I think there was a J-2T proposal, and also a J-2X proposal. These designations were ca 1966, so they probably bore no correlation to later versions of this engine with similar designations.
Quote from: Blackstar on 05/12/2011 05:27 pmA couple of years ago I saw a few North American Aviation studies of uprated S-II stages for the Saturn V. NAA built the S-II and so naturally they were always looking for opportunities to upgrade it and sell more of them. One surprise was that some of the documents listed other upgrades for the J-2 engine. I think there was a J-2T proposal, and also a J-2X proposal. These designations were ca 1966, so they probably bore no correlation to later versions of this engine with similar designations.The J-2T, by the way, was aerospike version (T = toroidal) of the J-2 intended for growth versions of the Saturn V. It appears to have been desired not for its altitude-compensating characteristics (the S-II being ignited at altitude anyway), but for for its reduced length, which allowed greater tank stretches without raising the roof of the VAB.What I wonder is why the J-2T never appears to have been considered for the ground-launched versions of the S-II (e.g., the INT-17). Then its natural altitude-compensation would have come in handy.
J-2S in 1972:Chamber Pressure: 1215 psiaThrust: 1,178.8 kNISP: 436 w/o nozzle extension, 452 w/ nozzle extension
J-2X w/ J-2S tap-off cycle:Chamber Pressure: 1219 psiaThrust: 1,218.8 kNISP: 455s
Quote from: Downix on 05/13/2011 12:36 amJ-2X w/ J-2S tap-off cycle:Chamber Pressure: 1219 psiaThrust: 1,218.8 kNISP: 455sInteresting, I hadn't realized that the move to RS-68 turbomachinery had made such a difference.Just for comparison that's better Isp than RL-10A-4-2 (@ 451s), but still below the nozzle-extended RL-10B-2 (@ 464s), though all three are pretty darn similar. More to the point, the thrust is equal to 11x RL-10B-2 or 12.3x RL-10A-4-2. If you need the thrust, I can't imagine J-2X being twelve times more expensive than RL-10A-2.