darthgently Posted June 25 Share Posted June 25 (edited) 5 hours ago, Exoscientist said: I say again SpaceX is desperately in need of a true Chief Engineer, not someone who dabbles in the field. Oh stop being so coy. Just Do It! https://www.spacex.com/careers Edited June 25 by darthgently Quote Link to comment Share on other sites More sharing options...
darthgently Posted June 25 Share Posted June 25 3 hours ago, Terwin said: Using cryogenics is a choice, it is entirely possible to get to orbit using compressed oxidizer and non-cryogenic fuel, but compressed o2 does not seem to be the best choice. Dumping oxygen rich exhaust into the LOX tank my or may not prove to be the superior choice, but we do know that on previous launches the draw-backs of doing so were not properly accounted for. Probably because it is something new which may or may not prove to be superior to the old preferred choices once everything has been accounted for. We also know that the refurbishment requirement of using the standard choice of compressed He for pressurization would preclude the stated design goal of rapid reusability. Perhaps that design goal is not possible, but until it has been discarded as such, autogenous pressurization is the only viable option, and pumping oxygen rich exhaust into the LOX tank still looks like a lower-mass and lower failure-rate option than adding a heat exchanger. Just because trying new things also introduces new problems does not mean we should never try anything new. If there were cargo or passengers, then new failure modes would be a concern, but as the only launch product for these test-launches is data, this is the best time to try out new things that may have new failure modes. Think of it as 'unlocking new rocket parts by trial and error' or 'exchanging funds for science' It is also important to remember that preheating was not the only reason to explore dumping exhaust directly. They also wanted to pressurized the tanks with as little hardware as possible. If they succeed in solving the ice issue without doing away with the entire exhaust dump approach they will have pulled another "landing a booster" class advance in rocketry. It is worth exploring even if they do end up going a different direction. All the whinging is coming people with zero skin in the game and least motivated by SpaceX's mission statement Quote Link to comment Share on other sites More sharing options...
Brotoro Posted June 25 Share Posted June 25 How much LOX needs to be vaporized to pressurize the tank? Instead of a fancy heat exchanger, couldn't they have a smaller LOX tank at the bottom of the main tank (where they already have one…the header tank) and dump the turbo exhaust gas into that? Trap the water and carbon dioxide ice in the small tank and let out the gaseous oxygen. Quote Link to comment Share on other sites More sharing options...
Deddly Posted June 25 Share Posted June 25 1 hour ago, Brotoro said: How much LOX needs to be vaporized to pressurize the tank? Instead of a fancy heat exchanger, couldn't they have a smaller LOX tank at the bottom of the main tank (where they already have one…the header tank) and dump the turbo exhaust gas into that? Trap the water and carbon dioxide ice in the small tank and let out the gaseous oxygen. Would that be different from just filtering it on the way in? Quote Link to comment Share on other sites More sharing options...
tater Posted June 25 Share Posted June 25 Quote Link to comment Share on other sites More sharing options...
RCgothic Posted June 25 Share Posted June 25 (edited) Although I have many, many criticisms of Musk, as a chartered engineer myself "not being a proper engineer" isn't one of them. By all appearances he has as much of a grasp of technical details as top engineers for a nuclear power plant. There are many decisions that get made during the design process of any system, and they're not always good ones. Iteration is part of the process. The only difference with SpaceX is that we see the iterations happen publicly in hardware rather than purely in private sim. Edited June 26 by RCgothic Quote Link to comment Share on other sites More sharing options...
Brotoro Posted June 25 Share Posted June 25 (edited) 18 minutes ago, Deddly said: Would that be different from just filtering it on the way in? If you are filtering at the LOX inlet pipes, you are separating solid ice from the LOX which is coming through at a high flow rate. If you filter through this special tank, you are filtering out gas from liquids/solids, and dealing with a smaller mass. The tank would not need to contain high pressures (it's at about the same pressure as the rest of the main tank that it’s embedded in… more like a sectioned off part of the main tank), so this tank need not be heavy. Go Falcon Heavy! Falcon Heavy boosters separated… Staging good. Edited June 25 by Brotoro Quote Link to comment Share on other sites More sharing options...
mikegarrison Posted June 25 Share Posted June 25 2 hours ago, darthgently said: It is also important to remember that preheating was not the only reason to explore dumping exhaust directly. They also wanted to pressurized the tanks with as little hardware as possible. If they succeed in solving the ice issue without doing away with the entire exhaust dump approach they will have pulled another "landing a booster" class advance in rocketry. It is worth exploring even if they do end up going a different direction. All the whinging is coming people with zero skin in the game and least motivated by SpaceX's mission statement There is an easy solution for "the ice issue". Just don't introduce water and CO2 into the tank like that. Of course, now you have a different issue. Engineering is like that. I can't say this approach they are taking is the wrong one. I assume they have done the trades. But it's a bad sign when they have to add more and more screens for the ice, and also have to start adding more redundant thrusters to backup any that get shut down by the ice. It's obvious that this is turning out to a bigger problem than they realized when they did their trades originally. Quote Link to comment Share on other sites More sharing options...
Brotoro Posted June 25 Share Posted June 25 Booster entry burns Quote Link to comment Share on other sites More sharing options...
mikegarrison Posted June 25 Share Posted June 25 21 minutes ago, Deddly said: Would that be different from just filtering it on the way in? It's not ice on the way in. It's water vapor and gaseous CO2. It becomes ice (dry and wet) when it hits that reservoir of cold, cold LOX. Quote Link to comment Share on other sites More sharing options...
CBase Posted June 25 Share Posted June 25 4 minutes ago, Deddly said: Would that be different from just filtering it on the way in? Sounds like that. But actually clogging the autogenous pressure inlet (which is usually smaller) will happen faster than filtering (and potentially clogging) the outlet or tank bottom. Hint to anyone not familiar with filters: Filters operate by collecting the unwanted stuff and eventually get clogged until flow of filtrate is harmed. You can increase lifetime by increasing the surface area (which increases mass and costs), but ultimately you either need to have a recycling mode or service intervals to renew them. Unfortunately so far there is no indictation how starship deals with the ice inside tanks as both options do not align well with rapid reuse. Quote Link to comment Share on other sites More sharing options...
tater Posted June 25 Share Posted June 25 Quote Link to comment Share on other sites More sharing options...
Brotoro Posted June 25 Share Posted June 25 Double booster landing . Sooo cool! Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted June 25 Share Posted June 25 Two boosters back to Terra Firma and one in the drink; GOES-U continuing to orbit. Go Falcon Heavy! Unrelated: is it just me or is the forum site doing REALLY bad? Quote Link to comment Share on other sites More sharing options...
Deddly Posted June 25 Share Posted June 25 3 minutes ago, sevenperforce said: is it just me or is the forum site doing REALLY bad? It's not just you. Quote Link to comment Share on other sites More sharing options...
RCgothic Posted June 25 Share Posted June 25 (edited) Part two of Tim's interview with Musk is up. Notably it was only the front-right flap that really let go, they can tell by the deployment data. That one was fully deploying, the other 3 more nominally. Also where the tiles were missing on the skirt, seems 2 layers of backup ablative didn't burn through, one layer did but not clear that the steel also failed, might have survived. They don't even need infra-red cameras for seeing the hotspots internally, they glow in the visible spectrum. Edited June 26 by RCgothic Quote Link to comment Share on other sites More sharing options...
JoeSchmuckatelli Posted June 25 Share Posted June 25 9 minutes ago, sevenperforce said: forum site doing REALLY bad 502 Bad Gateway all afternoon Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted June 25 Share Posted June 25 2 hours ago, darthgently said: It is also important to remember that preheating was not the only reason to explore dumping exhaust directly. They also wanted to pressurized the tanks with as little hardware as possible. If they succeed in solving the ice issue without doing away with the entire exhaust dump approach they will have pulled another "landing a booster" class advance in rocketry. It is worth exploring even if they do end up going a different direction. All the whinging is coming people with zero skin in the game and least motivated by SpaceX's mission statement Yep, precisely. In a funny sort of twist, part of this whole thing is to make the engines as Kerbal as possible. An engine that just works, no other systems needed, a set dry mass and nothing more, etc etc. -- repressurizes the tank for every bit of propellant it uses, and so forth. 1 hour ago, Brotoro said: How much LOX needs to be vaporized to pressurize the tank? Instead of a fancy heat exchanger, couldn't they have a smaller LOX tank at the bottom of the main tank (where they already have one…the header tank) and dump the turbo exhaust gas into that? Trap the water and carbon dioxide ice in the small tank and let out the gaseous oxygen. I mean, at that point, why not just have a "small helium tank" instead of a smaller LOX tank? Also, how do you propose they "trap" the water and CO2 in the small tank? I'm mildly curious to learn why they didn't use the existing heat exchangers in the engine chamber and bell -- the ones used to preheat the propellant while regeneratively cooling the structure -- and tap off that for autogen repress. I suppose it would tend to decrease overall thrust, while running more volume through the preburners doesn't have that problem. 21 minutes ago, RCgothic said: Although I have many, many criticisms of Musk, as a chartered engineer myself "not being a proper engineer" isn't one of them. While I cannot claim to be an engineer, I do have a degree in physics along with my graduate degree in law, and I concur. Musk may make many stupid decisions, and some of them might even be engineering-related, but that doesn't mean SpaceX has problems surrounding a lack of proper engineers. 17 minutes ago, mikegarrison said: I can't say this approach they are taking is the wrong one. I assume they have done the trades. But it's a bad sign when they have to add more and more screens for the ice, and also have to start adding more redundant thrusters to backup any that get shut down by the ice. It's obvious that this is turning out to a bigger problem than they realized when they did their trades originally. We'll see. They spent a lot of time on deving the hot gas-gas thrusters for Superheavy and then just scrapped them completely when they determined that venting ullage did the same trick with lower dry mass. This is all a pretty fine balance. 4 minutes ago, JoeSchmuckatelli said: 502 Bad Gateway all afternoon Samesies Quote Link to comment Share on other sites More sharing options...
Brotoro Posted June 25 Share Posted June 25 (edited) 6 minutes ago, sevenperforce said: I mean, at that point, why not just have a "small helium tank" instead of a smaller LOX tank? Also, how do you propose they "trap" the water and CO2 in the small tank? Because you can't replenish Helium on Mars. And a Helium tank has to be under high pressure, so would be heavy. You trap the the ice in this tank using filters (in this case you are filtering gas from the solids and LOX, which I think would be easier). Edited June 25 by Brotoro Quote Link to comment Share on other sites More sharing options...
magnemoe Posted June 25 Share Posted June 25 1 hour ago, bigyihsuan said: I'd imagine that any byproducts in the tank would either be shot out with the rest of the LOX, and/or drained with leftover LOX when landed. Though, solid ice is a thing, which can be a problem with the "shoot it out with the rest of the LOX" plan. ...Hmm, does water ice float on LOX? Believe LOX has an density below 0.9 kg/L so yes. ice sink in high proof ethanol, its an sign that you should stop drinking, ice does not sink in whiskey. Quote Link to comment Share on other sites More sharing options...
darthgently Posted June 25 Share Posted June 25 (edited) 1 hour ago, mikegarrison said: There is an easy solution for "the ice issue". Just don't introduce water and CO2 into the tank like that. Of course, now you have a different issue. Engineering is like that. I can't say this approach they are taking is the wrong one. I assume they have done the trades. But it's a bad sign when they have to add more and more screens for the ice, and also have to start adding more redundant thrusters to backup any that get shut down by the ice. It's obvious that this is turning out to a bigger problem than they realized when they did their trades originally. No disagreement here. I'm just defending the logic of giving it a try 1 hour ago, sevenperforce said: I'm mildly curious to learn why they didn't use the existing heat exchangers in the engine chamber and bell -- the ones used to preheat the propellant while regeneratively cooling the structure -- and tap off that for autogen repress. Which brings us to Elon's statements in the recent interview about added integral internal "cooling channels" on upcoming Raptors. Anyone else thinking there might be more than just engine cooling going on? Edited June 25 by darthgently Quote Link to comment Share on other sites More sharing options...
mikegarrison Posted June 25 Share Posted June 25 (edited) 47 minutes ago, magnemoe said: Believe LOX has an density below 0.9 kg/L so yes. ice sink in high proof ethanol, its an sign that you should stop drinking, ice does not sink in whiskey. Google says LOX is 1.141 kg/L at the boiling temperature. The "densified" colder liquid oxygen favored by SpaceX is even denser, more like 1.25 kg/L. Edited June 25 by mikegarrison Quote Link to comment Share on other sites More sharing options...
darthgently Posted June 25 Share Posted June 25 2 minutes ago, mikegarrison said: Google says LOX is 1.141 kg/L. Given O will generally be heavier than H2O given the mass of the atoms, ignoring some stuff, and the fact O gets denser as temp drops and water gets less dense when it freezes my gut says Mike and Google win 1 hour ago, CBase said: Sounds like that. But actually clogging the autogenous pressure inlet (which is usually smaller) will happen faster than filtering (and potentially clogging) the outlet or tank bottom. Hint to anyone not familiar with filters: Filters operate by collecting the unwanted stuff and eventually get clogged until flow of filtrate is harmed. You can increase lifetime by increasing the surface area (which increases mass and costs), but ultimately you either need to have a recycling mode or service intervals to renew them. Unfortunately so far there is no indictation how starship deals with the ice inside tanks as both options do not align well with rapid reuse. All I can imagine is a pre chamber where the ice is intentionally formed with some mechanism for ejecting it as it forms. I'm picturing a centrifugal particulate filter as on diesel rigs where the solids fall outward and toward the bottom dropping out and away from the flow, but the gases get pulled from the cleaner center of the vortex. I.e. Dyson vacuum cleaner, lol Quote Link to comment Share on other sites More sharing options...
tater Posted June 25 Share Posted June 25 As for SS/SH? They'll get it sorted, they have some idea what they are doing. ^^^^ Quote Link to comment Share on other sites More sharing options...
tater Posted June 26 Share Posted June 26 Nice John Kraus image: Quote Link to comment Share on other sites More sharing options...
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