Not to mention BE-4's much lower chamber pressure gives a lot more confidence in its potential reliability.
Quote from: leaflion on 10/02/2016 11:30 pmNot to mention BE-4's much lower chamber pressure gives a lot more confidence in its potential reliability. I agree. Reliability, not ISP or any other number, will largely determinate if these engines make the history texts or merely the footnotes.
Quote from: edkyle99 on 10/03/2016 12:27 amQuote from: leaflion on 10/02/2016 11:30 pmNot to mention BE-4's much lower chamber pressure gives a lot more confidence in its potential reliability. I agree. Reliability, not ISP or any other number, will largely determinate if these engines make the history texts or merely the footnotes. Reliability has nothing to do with confidence. Reliability is an intrinsic in a manufactured design that is proven on a test stand and confirmed with tear down and measurement. Over and over again. Test history. Flight history. Revisions.Nothing you determine in the short term.
...and there is little test history -and no flight history- of FFSC engines.
BO said it's doing a medium performance version of a high performance architecture. For reliability/reusability. SpaceX does a very high performance version of a very high performance architecture.By the way, do we know why BO chose ORSC? It seems they want to avoid FRSC, which would preclude a FFSC architecture.
Quote from: Space Ghost 1962 on 10/03/2016 12:43 amQuote from: edkyle99 on 10/03/2016 12:27 amQuote from: leaflion on 10/02/2016 11:30 pmNot to mention BE-4's much lower chamber pressure gives a lot more confidence in its potential reliability. I agree. Reliability, not ISP or any other number, will largely determinate if these engines make the history texts or merely the footnotes. Reliability has nothing to do with confidence. Reliability is an intrinsic in a manufactured design that is proven on a test stand and confirmed with tear down and measurement. Over and over again. Test history. Flight history. Revisions.Nothing you determine in the short term. ...and there is little test history -and no flight history- of FFSC engines.
Quote from: Oli on 10/03/2016 05:08 pmBO said it's doing a medium performance version of a high performance architecture. For reliability/reusability. SpaceX does a very high performance version of a very high performance architecture.By the way, do we know why BO chose ORSC? It seems they want to avoid FRSC, which would preclude a FFSC architecture.I think they went for it since it would be a better choice than FRSC, as far as the propellant mix is concerned. FRSC cycles are almost completely devoted to Hydrolox engines.
Well, NK-33 only had half the chamber pressure of Raptor so I'd say Raptors OR loop alone will probably be just as challenging as NK-33's from a materials perspective, especially considering that while the pressure differential and power output in the turbine might be comparable to NK-33 the actual pressure will still be twice as high.
Quote from: Oli on 10/03/2016 05:08 pmBO said it's doing a medium performance version of a high performance architecture. For reliability/reusability. SpaceX does a very high performance version of a very high performance architecture.By the way, do we know why BO chose ORSC? It seems they want to avoid FRSC, which would preclude a FFSC architecture.Well, the decision is very easy from a thermodynamics POV. The power to your turbines is (basically) specific heat * mass flow. Do the numbers for methalox and you get more power with ORSC. They wanted a cheap engine, and so they went with a single turbine.Nothing prevents them from then developing a full flow engine on that base. In fact, it would be "relatively" easy. The FRSC circuit is the easiest.
For staged combustion cycles, the pressure cascadesresulting from thrust chamber cooling and turbopumppower requirements are compared in Figure 8 takingLOX-methane as example. The pumping requirementsare lower for the cycle using a oxidizer-rich preburner,because no fuel is rerouted to the preburner after passingthrough the thrust chamber cooling channels. The smallamount of fuel required for the preburner is delivered bya low-powered kick stage.The fuel-rich cycle results in higher fuel-pumprequirements and requires an additional LOX-kick-stage,while the ox.-rich cycle results in similar lower pumprequirements without a kick-stage. The preburnerpressure is also lower in the ox.-rich cycle. However, theoxygen-rich environment of the preburner gas may causeadditional complexity for the turbines as well as for hot-gas lines and valves.
There is a fuel difference between BE4 and Raptor. BE4 is designed to use LNG while Raptor uses liquid methane (99% ?). How it affects engine design I'm not sure.
Quote from: TrevorMonty on 10/05/2016 01:46 pmThere is a fuel difference between BE4 and Raptor. BE4 is designed to use LNG while Raptor uses liquid methane (99% ?). How it affects engine design I'm not sure.I might be wrong, but SpaceX may need neat methane due to their goal of chilling it more.