CFE - 29/11/2007 4:51 PMMost interesting part of that document, in my view, is the revelation that J-2X uses a similar injector design to RS-68. At least that's what I'm getting from the fact that the same subscale injector plate can support both RS-68 and J-2X.Also interesting is the two-stage improvement program for RS-68: first RS-68A (aimed at improving performance) and RS-68B (chiefly aimed at improving reliability.)
simonbp - 29/11/2007 11:49 PMThe "5-around" arrangement of the RS-68B's is interesting; wouldn't its interaction with the SRBs create a net thrust asymmetry?Simon
Looks like there'd be room for a sixth engine in there. Possible future upgrade or redundancy? -- Saturn V was originally only supposed to have 4x F-1s -- How did they get around constriction with that arrangement?
Might there be room for a J-2X as a sixth engine? Not much good for low altitude Isp, but this would improve markedly once past SRB seperation -- I was thinking in terms of a slight liftoff thrust increase, but a much better boost for later in the ascent. How much would the nominal burn time for the corestage now be, or would the corestage have to be stretched a smidgin to compensate? OR: would an expanded or 2-engined EDS more than compensate?
kraisee - 1/12/2007 2:03 AMThe center engine of a 'cross' pattern arrangement suffers from constriction of it's exhaust plume by the outer engines. This reduces its efficiency by a lot.Conversely though, without a central engine, you get a low pressure region forming above the engine which sucks up some of the exhaust back up onto the vehicle and the engine's mechanicals. A central engine keeps most of the 'blow-back' between the outer engines from coming back at the vehicle. Other wise you need extra TPS.It's tricky striking a good balance either way.Ross.
luke strawwalker - 7/12/2007 10:28 AMQuotekraisee - 1/12/2007 2:03 AMThe center engine of a 'cross' pattern arrangement suffers from constriction of it's exhaust plume by the outer engines. This reduces its efficiency by a lot.Conversely though, without a central engine, you get a low pressure region forming above the engine which sucks up some of the exhaust back up onto the vehicle and the engine's mechanicals. A central engine keeps most of the 'blow-back' between the outer engines from coming back at the vehicle. Other wise you need extra TPS.It's tricky striking a good balance either way.Ross.This 'Five around' configuration looks something similar to a Proton (lot bigger of course). How does the Proton handle this flame impingement on the vehicle base?? Interesting. This five around arrangement would also put 2 RS-68's much closer to the SRB's and their exhaust plumes, so how would they interact?? Some interesting CFD work here I bet... OL JR
luke strawwalker - 9/12/2007 8:02 AMBut while the SRB's are still there, having 3 engines on one side of the centerline between SRB's and 2 on the other would create an imbalance wouldn't it??
Plus I would bet that the plume interaction would rob efficiency from the RS-86's closest to the SRB's, far more than the 75 degree fully symmetrical arrangement would.
JIS - 9/12/2007 3:40 AMQuoteluke strawwalker - 9/12/2007 8:02 AMBut while the SRB's are still there, having 3 engines on one side of the centerline between SRB's and 2 on the other would create an imbalance wouldn't it?? NO. The two engines at one side will produce the same momentum as the three opposite engines. The SRBs won't change it.