Do Block 4 and 5 leave the merlin unchanged?If the iteration period is shortened (with higher flight rates), can a smaller vehicle be fielded and matured faster? I get all the stuff about isp, coking, density, but I'm wondering if programmatically there is an opportunity cost of taking bigger slower steps. And, also added risks. What about lost revenue derived from more capable in-space hardware (like constellations, space stations, ..) that would be enabled by an earlier, but less dramatic, reduction in cost/lb to orbit that intermediate steps might offer.
The optimum no. of engines on a booster is 7-9. More than that increases the risk of a catastrophic engine failure destroying the LV.
...If the iteration period is shortened (with higher flight rates), can a smaller vehicle be fielded and matured faster?
Quote from: gin455res on 08/01/2017 02:21 pmDo Block 4 and 5 leave the merlin unchanged?If the iteration period is shortened (with higher flight rates), can a smaller vehicle be fielded and matured faster? I get all the stuff about isp, coking, density, but I'm wondering if programmatically there is an opportunity cost of taking bigger slower steps. And, also added risks. What about lost revenue derived from more capable in-space hardware (like constellations, space stations, ..) that would be enabled by an earlier, but less dramatic, reduction in cost/lb to orbit that intermediate steps might offer.Yes, there might be a rationale for taking a 'halfway' step to increased performance while not impacting operations and infrastructure very much, but the only one that makes sense is the opposite of what you've proposed. That is, a new Raptor based ITS-like upper stage atop a Falcon Heavy. This at least puts the ISP/Density fuel tradeoff in the right stages. But I no longer think this is anywhere in their plans. I expect an 8+ meter 'ITSy' full bore. A Merlin based upper stage atop an ITSy booster is a non-starter, for all the reasons above.
Quote from: GORDAP on 08/01/2017 02:37 pmQuote from: gin455res on 08/01/2017 02:21 pmDo Block 4 and 5 leave the merlin unchanged?If the iteration period is shortened (with higher flight rates), can a smaller vehicle be fielded and matured faster? I get all the stuff about isp, coking, density, but I'm wondering if programmatically there is an opportunity cost of taking bigger slower steps. And, also added risks. What about lost revenue derived from more capable in-space hardware (like constellations, space stations, ..) that would be enabled by an earlier, but less dramatic, reduction in cost/lb to orbit that intermediate steps might offer.Yes, there might be a rationale for taking a 'halfway' step to increased performance while not impacting operations and infrastructure very much, but the only one that makes sense is the opposite of what you've proposed. That is, a new Raptor based ITS-like upper stage atop a Falcon Heavy. This at least puts the ISP/Density fuel tradeoff in the right stages. But I no longer think this is anywhere in their plans. I expect an 8+ meter 'ITSy' full bore. A Merlin based upper stage atop an ITSy booster is a non-starter, for all the reasons above.Falcon Heavy hasn't flown yet and is much more complicated.How would this upper-stage land with only one vacuum optimised engine?
Quote from: GORDAP on 08/01/2017 02:37 pmQuote from: gin455res on 08/01/2017 02:21 pmDo Block 4 and 5 leave the merlin unchanged?If the iteration period is shortened (with higher flight rates), can a smaller vehicle be fielded and matured faster? I get all the stuff about isp, coking, density, but I'm wondering if programmatically there is an opportunity cost of taking bigger slower steps. And, also added risks. What about lost revenue derived from more capable in-space hardware (like constellations, space stations, ..) that would be enabled by an earlier, but less dramatic, reduction in cost/lb to orbit that intermediate steps might offer.Yes, there might be a rationale for taking a 'halfway' step to increased performance while not impacting operations and infrastructure very much, but the only one that makes sense is the opposite of what you've proposed. That is, a new Raptor based ITS-like upper stage atop a Falcon Heavy. This at least puts the ISP/Density fuel tradeoff in the right stages. But I no longer think this is anywhere in their plans. I expect an 8+ meter 'ITSy' full bore. A Merlin based upper stage atop an ITSy booster is a non-starter, for all the reasons above.Falcon Heavy hasn't flown yet and is much more complicated.How would this upper-stage land with only one vacuum optimised engine?If system performance is a function of payload AND no. of reuses; might it be better to make the booster more reusable with Raptors? It is 70% of the cost of an F9. A single stick Raptor-7 or Raptor-9 booster that requires reduced maintenance and can be reused 100 times could be a money saver. And if constellations are the primary payload, does their lower orbit counter-act some of the advantage that is gained from methane's improved vacuum isp?Sea-Level -> Vacuum ISP (from Wikipedia)Raptor: 334 -> 361Merlin: 282 -> 31118%-> 16% differenceVacuumRaptor: 382Merlin: 34810% difference - improved mass fraction for merlin
Raptor upper stage has its own thread and is off-topic for this one. Please consider that thanks.
Do Block 4 and 5 leave the merlin unchanged?
Has the merlin reached its final version yet? No.