KSK Posted September 22, 2017 Share Posted September 22, 2017 (edited) 3 hours ago, Northstar1989 said: SpaceX doesn't have remotely near the capital available to it to develop the ITSy upper stage just yet. It's not just a matter of focus or logistics- they simply don't have enough available funding to finish the ITSy design if they begin it right now. If they are SUCCESSFUL in not only launching a Falcon Heavy, but in eventually learning to recover all its stages, then I think there will be a lot more government and investor-confidence to invest in the ITSy. I don't see why investors would care too much to be honest. SpaceX have already demonstrated the ability to bring a complex product to market, handily beating their competitors on price along the way. They've demonstrated persistence and ability to execute once they have confidence in a technology (F9 first stage propulsive landing) and, more importantly a willingness to ditch technologies that either don't work (F9 first stage parachute landing) can't be made to work in a commercially realistic timeframe (propellant crossfeed), or are no longer required (Dragon 2 propulsive landing). It's also worth noting that Elon has no ego when it comes to ditching concepts, that he's been publically gung-ho about (Dragon 2 propulsive landing). Given all that, I don't see that successful launch and 100% of a Falcon Heavy is going to tell investors much at all about SpaceX's ability to develop a completely different launch vehicle running on a completely different engine/propellant combination and with significant structural components built (if I remember rightly) from completely different material. Edited September 22, 2017 by KSK Quote Link to comment Share on other sites More sharing options...
KSK Posted September 22, 2017 Share Posted September 22, 2017 (edited) 3 hours ago, Northstar1989 said: The Merlin engine is already throttleable down to 60%, but I suspect they will also need the 20% throttling that the Raptor is supposed to be capable of (which will also require a re-design of the upper stage to run on Liquid Methane and LOX instead of RP-1 and LOX...) That's for the Merlin 1C. The 1D vacuum can be throttled down to 40%. From figures I've seen quoted for dry masses of the two Falcon stages (if anyone has any good numbers, please share them) the first stage is about 5.5 times heavier than the second stage. We know that 3 Merlin propulsive landings are possible for the first stage (and I'm not sure if the 1D can be as deeply throttled as the 1D vacuum), so single Merlin landings for the second stage don't seem completely implausible, especially since the 1D vacuum is optimised for - well, vacuum and may not be as efficient at sea level. Admittedly there are a lot of 'maybes' in there but I don't see a compelling reason why Raptor is needed for a recoverable second stage. Edited September 22, 2017 by KSK Quote Link to comment Share on other sites More sharing options...
tater Posted September 22, 2017 Share Posted September 22, 2017 The vac engine would not survive. When they put t in the test stand, they don't put the bell extension on it. Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted September 22, 2017 Share Posted September 22, 2017 6 minutes ago, tater said: The vac engine would not survive. When they put t in the test stand, they don't put the bell extension on it. How is the bell extension attached? I'm guessing it would not be as simple as swapping regular bolts for pyros to ditch it... Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 22, 2017 Share Posted September 22, 2017 6 minutes ago, CatastrophicFailure said: How is the bell extension attached? I'm guessing it would not be as simple as swapping regular bolts for pyros to ditch it... Correct. It would not be simple. It would, in fact, be prohibitively-not-simple. 26 minutes ago, KSK said: That's for the Merlin 1C. The 1D vacuum can be throttled down to 40%. From figures I've seen quoted for dry masses of the two Falcon stages (if anyone has any good numbers, please share them) the first stage is about 5.5 times heavier than the second stage. We know that 3 Merlin propulsive landings are possible for the first stage (and I'm not sure if the 1D can be as deeply throttled as the 1D vacuum), so single Merlin landings for the second stage don't seem completely implausible, especially since the 1D vacuum is optimised for - well, vacuum and may not be as efficient at sea level. Admittedly there are a lot of 'maybes' in there but I don't see a compelling reason why Raptor is needed for a recoverable second stage. Propulsive landings on the Merlin 1D Vacuum are a non-starter, 100%. Quote Link to comment Share on other sites More sharing options...
Nibb31 Posted September 23, 2017 Share Posted September 23, 2017 (edited) The RL10 has an extendible nozzle. It might be possible to design a retractable one too. Or you can do an aerospike version of Merlin. Edited September 23, 2017 by Nibb31 Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted September 23, 2017 Share Posted September 23, 2017 42 minutes ago, Nibb31 said: The RL10 has an extendible nozzle. It might be possible to design a retractable one too. Or you can do an aerospike version of Merlin. Like @sevenperforce said, possible but 8 hours ago, sevenperforce said: prohibitively-not-simple I'm wondering what they can possibly do for the "experimental" recovery on the maiden FH launch. If that's even still on the table. Quote Link to comment Share on other sites More sharing options...
Northstar1989 Posted September 23, 2017 Share Posted September 23, 2017 13 hours ago, tater said: Another important point is that Merlin has been remarkably improved over its versions to the point that possible benefit from Raptor as an US is perhaps not so great, particularly given the need for bigger tanks, which makes any such design completely novel. Raptor should be able to improve over multiple versions too. *Particularly* given what a novel technology Full Flow Staged Combustion is, there should be even more room for optimization than with the Merlin... As for the fuel-density: let's do some math on that, just to see how extreme the difference is... Kerosene has a density of 0.81 g/cm^3, while Liquid CH4 may only have a density of 0.422 g/cm^3. But Meth/LOX also burns with a higher fraction of LOX, which has a density of 1.141 g/cm^3... CH4/LOX burns with a mass-fraction of 80.0% Oxygen, whereas RP-1/LOX (majority C12H26) burns 77.7% Oxygen. This means that RP-1/LOX at stochiometric ratio has an average density of 1.2762 g/cm^3 whereas CH4/LOX is 0.5658 g/cm^3. However the Raptor gets an ISP of 361 seconds, whereas the Merlin gets only 311 seconds. Plugging those into the Rocket Equation, you can see that with a 7:1 mass-fraction the Merlin gets 5935 m/s, whereas with a 3.66 mass-fraction (what you get if you assume only 44.3% as much fuel due to the lower fuel-density in the same-sized tanks) the Raptor gets 4591.6 m/s of Delta-V... Interesting. So a Meth/LOX upper stage only gets 77.4% of the Delta-V as an RP-1/LOX upper stage of the same dimensions if the Kero/LOX upper stage has a 7:1 mass-ratio... Up that to a 6.32:1 mass-ratio for the Meth/LOX upper stage (by a little more than doubling the fuel tank volume) though, and its Delta-V rises to 6528 m/s, already exceeding the Delta-V of the Kero/LOX stage despite having a lower (only 88.7% as much) propellant-mass at that volume... So, the Raptor certainly seems to have a lot more potential, but you're right- it's a very different design that is required to convert the upper stage to Meth/LOX... 11 hours ago, sevenperforce said: Propulsive landings on the Merlin 1D Vacuum are a non-starter, 100%. Why do you believe that to be true? Quote Link to comment Share on other sites More sharing options...
TheEpicSquared Posted September 23, 2017 Share Posted September 23, 2017 15 minutes ago, Northstar1989 said: Why do you believe that to be true? Probably because there’s no way a 0.3mm (I think) thick nozzle would survive reentry and a restart facing downwards... Also, speaking of which, a Merlin would still produce thrust without a nozzle extension, right? It wouldn’t be efficient at all, but it would work, more or less. So theoretically, they could detach the nozzle extension or let it break apart and then fire the bare engine to land...? Its a bit far-fetched though, I do realize. Quote Link to comment Share on other sites More sharing options...
Northstar1989 Posted September 23, 2017 Share Posted September 23, 2017 12 hours ago, KSK said: I don't see why investors would care too much to be honest. SpaceX have already demonstrated the ability to bring a complex product to market, handily beating their competitors on price along the way. They've demonstrated persistence and ability to execute once they have confidence in a technology (F9 first stage propulsive landing) and, more importantly a willingness to ditch technologies that either don't work (F9 first stage parachute landing) can't be made to work in a commercially realistic timeframe (propellant crossfeed), or are no longer required (Dragon 2 propulsive landing). It's also worth noting that Elon has no ego when it comes to ditching concepts, that he's been publically gung-ho about (Dragon 2 propulsive landing). Given all that, I don't see that successful launch and 100% of a Falcon Heavy is going to tell investors much at all about SpaceX's ability to develop a completely different launch vehicle running on a completely different engine/propellant combination and with significant structural components built (if I remember rightly) from completely different material. It will give them more time to grow their business even further for one- making ITS seem more plausible to investors. And Falcon Heavy is a larger and more complex rocket than Falcon 9, and upper stage re-use is a more difficult and complex goal than launch stage re-use. Not to mention achieving it will likely increase their market-share even further, as it makes the Falcon Heavy more cost-efgicient. And as has been pointed out before, it gives Falcon Heavy more potential customers- launching payloads that could be launched on a Falcon 9 with first-stage recovery, but are FAR too heavy to recover all stages on a Falcon 9 with (like I've said before, I'm guessing they would have to slash the Falcon 9's payload down to just a few tons to be able to recover their upper stage). By the way, a tangent, but Falcon Heavy is actually BETTER suited to upper stage recovery than the Falcon 9, as it releases its upper stage later and at a higher altitude- meaning less Delta-V is required of the final stage, and the payload makes up proportionally more of the final stage mass. This means reducing the payload and adding an equal mass of fuel tankage will do a lot more to increase the fuel mass-fraction of the final stage, purchasing more Delta-V that can be used for upper-stage recovery per ton of payload capacity sacrificed (a specialized upper stage designed for recovery, with larger fuel tanks, landing-legs, etc. will of course have to be developed...) Anyways, showing mastery over something as complex as 100% reusability with the Falcon Heavy will be EVEN MORE impressive to investors, while growing SpaceX's profit-margins even further. Which is important, as many people consider the ITS (and probably also the ITSy) to be impossible to succeed in- meaning the more other supposedly-impossible tasks SpaceX can accomplish the better they can try to assuage those fears. SpaceX needs to build an unshakeable reputation as the doer's of the impossible if they are to hope to succeed in getting funding for the ITSy- as unfortunately many peoole still don't quite see them that way yet... 5 minutes ago, TheEpicSquared said: Probably because there’s no way a 0.3mm (I think) thick nozzle would survive reentry and a restart facing downwards... Also, speaking of which, a Merlin would still produce thrust without a nozzle extension, right? It wouldn’t be efficient at all, but it would work, more or less. So theoretically, they could detach the nozzle extension or let it break apart and then fire the bare engine to land...? Its a bit far-fetched though, I do realize. They could reinforce the nozzle if the stresses on it are the only conceen. Maybe shorten it a bit (and slightly enlarge the fuel-tanks) if the structural reinforcement makes the extra expansion no longer worth the extra mass... Quote Link to comment Share on other sites More sharing options...
Steel Posted September 23, 2017 Share Posted September 23, 2017 (edited) 52 minutes ago, Northstar1989 said: They could reinforce the nozzle if the stresses on it are the only conceen. Maybe shorten it a bit (and slightly enlarge the fuel-tanks) if the structural reinforcement makes the extra expansion no longer worth the extra mass... Stresses are the main concern, but since the nozzle extension alone for the M1DVac is about the same size as an entire M1D system- and has an exit area about 7 times larger - drag and aerodynamic effects are also a big concern. (see image below for reference) Spoiler Here you have a man with an M1D to his right (our left) and a M1DVac without extension (pictured below) to his left (our right) Shortening it doesn't really work too well, you'll lose so much ISP that you'll end up having to carry a lot more fuel. Obviously the worst case is if you get rid of the whole extension, which adds around 40 s of ISP, so you'd need to carry around 15% more fuel to compensate. This subsequently means the first stage won't push the second stage as far or fast, which in turn means you have to carry even more fuel e.t.c. Edited September 23, 2017 by Steel Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 23, 2017 Share Posted September 23, 2017 5 hours ago, Nibb31 said: Or you can do an aerospike version of Merlin. That would be a completely new engine. The Merlin combustion chamber cannot be modified to accept an aerospike nozzle. The best they could do would be swap out the Merlin turbopump and build an entirely new multichamber aerospike engine. But even that would be suboptimal. The Merlin's turbopump is designed for high chamber pressure; aerospikes typically use lower chamber pressure. 5 hours ago, CatastrophicFailure said: I'm wondering what they can possibly do for the "experimental" recovery on the maiden FH launch. If that's even still on the table. Mount a pair of the new titanium grid fins on either side of the tail of the stage, bolt PICA-X tiles around the perimeter of the payload adapter (the edge of a re-entry surface takes the highest heating, since stagnation pressure protects the center), add a steerable chute, and hope for the best. Maybe aim it at a bouncy castle. Or just do like the early Falcon 9 recovery attempts and just do a controlled splashdown. 2 hours ago, TheEpicSquared said: 2 hours ago, Northstar1989 said: Why do you believe that to be true? Probably because there’s no way a 0.3mm (I think) thick nozzle would survive reentry and a restart facing downwards... Also, speaking of which, a Merlin would still produce thrust without a nozzle extension, right? It wouldn’t be efficient at all, but it would work, more or less. So theoretically, they could detach the nozzle extension or let it break apart and then fire the bare engine to land...? Its a bit far-fetched though, I do realize. Even underexpanded, without the nozzle extension, the Merlin would have WAY too high a TWR at minimum throttle on an empty stage to do a survivable suicide burn. And jettisoning the nozzle extension would require a total redesign, which would defeat the purpose of certifying Falcon Heavy in the first place. Allowing it to break apart wouldn't work, either; the shrapnel would shred the rest of the stage, and even if it didn't, any asymmetry in the breakaway would result in asymmetric thrust which would wreck the whole landing. Plus, the deep throttling of the Merlin Vacuum likely depends on maintaining outlet pressure, which wouldn't be possible without the nozzle extension. 2 hours ago, Northstar1989 said: They could reinforce the nozzle if the stresses on it are the only conceen. Maybe shorten it a bit (and slightly enlarge the fuel-tanks) if the structural reinforcement makes the extra expansion no longer worth the extra mass... Flow separation in the full nozzle at sea level would be so catastrophic that the thrust would be completely uncontrollable and would probably rip the nozzle apart. Quote Link to comment Share on other sites More sharing options...
tater Posted September 23, 2017 Share Posted September 23, 2017 It seems like pyros on a glowing hot engine bell would be a non-starter, as well, but I know nothing about pyros. I can completely see them trying "soft" water landings with stage 2 as a testing regime for various ideas they might have as long as they have excess capacity. Regardless, SpaceX's original vision for S2 recovery included smaller landing engines (dracos?). Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 23, 2017 Share Posted September 23, 2017 25 minutes ago, tater said: It seems like pyros on a glowing hot engine bell would be a non-starter, as well, but I know nothing about pyros. I can completely see them trying "soft" water landings with stage 2 as a testing regime for various ideas they might have as long as they have excess capacity. Regardless, SpaceX's original vision for S2 recovery included smaller landing engines (dracos?). Yeah, but that was predicated on the whole "engine slides in and out" approach, which again would require a complete redesign and would fail to validate FH. Quote Link to comment Share on other sites More sharing options...
Grand Ship Builder Posted September 23, 2017 Share Posted September 23, 2017 1 minute ago, sevenperforce said: Yeah, but that was predicated on the whole "engine slides in and out" approach, which again would require a complete redesign and would fail to validate FH. Landing legs moved too much as well. Quote Link to comment Share on other sites More sharing options...
tater Posted September 23, 2017 Share Posted September 23, 2017 11 minutes ago, sevenperforce said: Yeah, but that was predicated on the whole "engine slides in and out" approach, which again would require a complete redesign and would fail to validate FH. Absolutely. I was merely pointing out that they never intended the vac engine to be used for landing even in their powerpoint version way back when. We should probably skip speculation as we will know more on Friday (!). Quote Link to comment Share on other sites More sharing options...
tater Posted September 25, 2017 Share Posted September 25, 2017 Quote Link to comment Share on other sites More sharing options...
tater Posted September 25, 2017 Share Posted September 25, 2017 (I crossposted the same link in the BO thread) Quote Link to comment Share on other sites More sharing options...
Mitchz95 Posted September 25, 2017 Share Posted September 25, 2017 (edited) https://twitter.com/SpcPlcyOnline/status/912163289102200832 EDIT: Stupid forum doesn't want to embed, here's what it says: "Australia's Science Channel sez SpaceX will broadcst Musk's talk Fri and then it will have live panel disc about it." Edited September 25, 2017 by Mitchz95 Quote Link to comment Share on other sites More sharing options...
Skylon Posted September 25, 2017 Author Share Posted September 25, 2017 He also said he was going to do a Reddit AMA at the weekend Quote Link to comment Share on other sites More sharing options...
Mitchz95 Posted September 25, 2017 Share Posted September 25, 2017 (edited) https://twitter.com/NASASpaceflight/status/912336774575394816 "We expect the Falcon 9 launch with the third set of Iridium NEXT satellites from Vandenberg to be NET Oct. 9. Philip Sloss (NSF) IR-2 photo." Edited September 25, 2017 by Mitchz95 Quote Link to comment Share on other sites More sharing options...
tater Posted September 25, 2017 Share Posted September 25, 2017 (edited) @Mitchz95, when you paste a twitter link, a note appears below with the option to paste as plain text. Counterintuitively, that is what is required for the twitter post to appear (select paste as plain text, if that was unclear). Edited September 25, 2017 by tater Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted September 25, 2017 Share Posted September 25, 2017 3 hours ago, tater said: 43 minutes ago, Skylon said: He also said he was going to do a Reddit AMA at the weekend Sigh. Once again my Monday starts with "just keep it together till Friday, man." SMH. Quote Link to comment Share on other sites More sharing options...
tater Posted September 26, 2017 Share Posted September 26, 2017 Quote Link to comment Share on other sites More sharing options...
Spaceception Posted September 26, 2017 Share Posted September 26, 2017 I'm so excited for this, anyone know the time (EST) of the presentation, I don't think I've seen anything yet. Friday can't come soon enough. Quote Link to comment Share on other sites More sharing options...
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