Ripple's design is almost identical to one I tried to kick-off around 2012 as a followup to DIRECT. The only real difference is we managed to delete the need for the outlier thrusters on the outside of Stage 2.The biggest issue that we found with this whole approach is that the performance envelope of a 2-stage pressure-fed launcher - when using KeroLox or MethaLOX first stage - is that the whole architecture is limited to LEO missions only. To get to GTO or anywhere else (which is where the initial low hanging fruit customers are) required an additional stage.That could be solved by switching to HydroLOX for both stages, but the overall vehicle size grows substantially for the equivalent LEO performance, due to the lower density of the S1 fuel. Physically larger doesn't pose much of a problem with the water launch approach though.If a 3rd stage were to be added later, using HydroLOX throughout, you got an interesting, flexible and pretty low-cost launcher able to deliver better than $500kg to LEO!A 3-stage Kerosene/Hydrogen Peroxide variant was also feasible (with acceptable GTO performance), offering room-temp propellants, which solves a major headache of working directly in the ocean. But H2O2 production in the quantities we needed was not a low cost option.Ultimately, these configs essentially use about 2x as much propellant as a more traditional thin-tank turbo-pump fed launcher though. IF you expect the launch business to grow substantially beyond today's market size, at some point the higher cost of the propellants will become a bigger factor in your annual operational costs than the low cost infrastructure can save you. When I was looking at this, the transition point seemed to be somewhere around 30-35 flights per year of a 20-30,000 kg to LEO launcher.Ross.
Ultimately, these configs essentially use about 2x as much propellant as a more traditional thin-tank turbo-pump fed launcher though. IF you expect the launch business to grow substantially beyond today's market size, at some point the higher cost of the propellants will become a bigger factor in your annual operational costs than the low cost infrastructure can save you. When I was looking at this, the transition point seemed to be somewhere around 30-35 flights per year of a 20-30,000 kg to LEO launcher.
The biggest issue that we found with this whole approach is that the performance envelope of a 2-stage pressure-fed launcher - when using KeroLox or MethaLOX first stage - is that the whole architecture is limited to LEO missions only. To get to GTO or anywhere else (which is where the initial low hanging fruit customers are) required an additional stage.That could be solved by switching to HydroLOX for both stages, but the overall vehicle size grows substantially for the equivalent LEO performance, due to the lower density of the S1 fuel. Physically larger doesn't pose much of a problem with the water launch approach though.If a 3rd stage were to be added later, using HydroLOX throughout, you got an interesting, flexible and pretty low-cost launcher able to deliver better than $500kg to LEO!
Expendable flights?
How interesting. Andrew Beal faced similar issues with his BA-2 back in 1999.
Quote from: Archibald on 05/10/2018 05:12 amHow interesting. Andrew Beal faced similar issues with his BA-2 back in 1999. Yeah, another Sea-Dragon style system, "re-imagined" for land operations.I studied Beal's work intensively at the time, and IMHO it's only real weaknesses were the high cost of H2O2 production and the high cost for those massive composite tanks. Even with those, he was still on-target to have a very viable GTO sat launcher at a fraction of the cost of Atlas or Delta.He claimed at the time that he closed because he was cut out of NASA sales, but if he had continued he would have been a few years ahead of everyone when the first COTS contracts came around, and would probably have been flying the BA2 with commercial GEO sats before Elon got Falcon-1 to orbit, so this industry could have been very different.Ross.
these discussions always seem to focus on the rocket...what about the payload? how do you have umbilicals set up? any issues with random wave effects (vs known states on a land based rocket)? problems with making the shroud watertight (or is that already the case)?
From my old notes, the big 140 ton launcher that I linked to above needed about $3.4m of LH2 and about $320K of LOX.Compare that to the BFR's fuel costs at around $200K per flight and you begin to realise how the economic situation today differs quite a bit from when Truax was putting this idea together. His ideas were brilliant, and in his economic environment I believe he was dead on the money.Today though, is a different situation. The costs of the extra fuel needed for these BDB's now represents more money than the cost of the materials needed for these big, heavy tanks, not to mention that the costs to develop a turbopump these days would be recouped on the third or fourth flight.