tater Posted August 20 Share Posted August 20 16 hours ago, Brotoro said: Why increase LOX tank by one ring and Methane tank by two rings? Unsure why, & I can only assume an NSF diagram was made by observing tanked being moved and counting rings (albeit harder now that everything is inside). Quote Link to comment Share on other sites More sharing options...
tater Posted August 20 Share Posted August 20 Quote Link to comment Share on other sites More sharing options...
tater Posted August 21 Share Posted August 21 Quote Link to comment Share on other sites More sharing options...
darthgently Posted August 21 Share Posted August 21 2 hours ago, tater said: I have a forming theory about these. I wonder if they all can actually feed all lit engines during landing even if one is not used and if non-liquid is detected in any one of them its flow is deferred and the others get it done. Maybe an anti-bubble ingestion strategy via redundant downcomers somehow? I do know that the smaller the diameter of a "vertical" pipe, the harder it is for sloshing to make bubbles Hey, I didn't say it was a fully formed theory Quote Link to comment Share on other sites More sharing options...
tater Posted August 21 Share Posted August 21 The RVacs are only used in space, so perhaps less spaghetti-piping at the bottom is more reliable for the gimbal engines on restart for landing? Quote Link to comment Share on other sites More sharing options...
tater Posted August 22 Share Posted August 22 mechazilla Quote Link to comment Share on other sites More sharing options...
softweir Posted August 22 Share Posted August 22 On 8/19/2024 at 9:03 PM, Brotoro said: Why increase LOX tank by one ring and Methane tank by two rings? Because a suitable volumetric LOX/Methane combustion ratio (for this rocket) is approximately 2 parts Methane to 1 part LOX by volume. The two tanks have to be stretched proportionately, so the Methane tank gets two added rings, the LOX gets one added ring, to keep that 2:1 volumetric ratio. Quote Link to comment Share on other sites More sharing options...
tater Posted August 23 Share Posted August 23 Quote Link to comment Share on other sites More sharing options...
magnemoe Posted August 23 Share Posted August 23 I assume space lasers at starlink is an new way to get high speed communication for satellites especially they who generate a lot of data. Down the line we want dedicated satellites for this purpose, ping is not important and an higher orbit let them service more and they can have more lasers and receivers, primary purpose for starlink lasers is to relay data if over water. Quote Link to comment Share on other sites More sharing options...
mikegarrison Posted August 23 Share Posted August 23 2 hours ago, magnemoe said: I assume space lasers at starlink is an new way to get high speed communication for satellites especially they who generate a lot of data. Down the line we want dedicated satellites for this purpose, ping is not important and an higher orbit let them service more and they can have more lasers and receivers, primary purpose for starlink lasers is to relay data if over water. Ping *is* important. That is the main reason for Starlink. The speed of light issues with geostationary satellites are significant for computers. Quote Link to comment Share on other sites More sharing options...
Brotoro Posted August 23 Share Posted August 23 19 hours ago, softweir said: Because a suitable volumetric LOX/Methane combustion ratio (for this rocket) is approximately 2 parts Methane to 1 part LOX by volume. The two tanks have to be stretched proportionately, so the Methane tank gets two added rings, the LOX gets one added ring, to keep that 2:1 volumetric ratio. Is that correct? The LOX tank of V1 Starship is larger in volume than the Methane tank. Quote Link to comment Share on other sites More sharing options...
softweir Posted August 23 Share Posted August 23 (edited) 26 minutes ago, Brotoro said: Is that correct? The LOX tank of V1 Starship is larger in volume than the Methane tank. Hmm... OK, I'm a bit less sure of myself. Have you got a reference I can look at? A lot of fully cryogenic engines (NEVER kerolox!) produce best ISP with a rich mixture, causing some part of the exhaust to be super-heated propellant rather than combusted products - the lighter the molecule, the higher its velocity when heated, and the better the ISP. This is most apparent when burning H2, as H2 molecules are vastly lighter than H20! Even methane (CH4) is a lot lighter than the H20 and CO2 combustion products, so a rich mix leading to a proportion of CH4 in the exhaust provides better ISP. Of course, this has to be a carefully judged balance:- make the exhaust too rich and the reduced energy leads to excessively reduced exhaust temperature, thrust and ISP! Edited August 23 by softweir punctuation Quote Link to comment Share on other sites More sharing options...
Ultimate Steve Posted August 23 Share Posted August 23 Raptor uses about 3.6 kg of oxygen per kg of methane. I think they subcool both of them for increased density but I'm going to ignore that because that's more math than I'm willing to do right now. Liquid oxygen has a density of 1141 kg per cubic meter and liquid methane has a density of 424 kg per cubic meter. 1000 kg of methane would take up about 2.358 cubic meters, and 3600 kg of oxygen would take up about 3.155 cubic meters. Thus we can infer that for every volume of methane added, 1.34 volumes of oxygen should be added. There's stuff I haven't accounted for that will shift that number around. But spacex is in a position where it can only easily add volumes in discrete rings. The ratio is pretty close to 3 rings of methane for 4 rings of oxygen. The thought of taking the analysis any further than this hurts my brain. There isn't an immediately obvious reason why they would add 2 methane rings and 1 oxygen ring. Maybe the new downcomer is more space efficient, maybe the header tanks are getting moved, maybe the old design was suboptimal, maybe the new domes have significantly less volume. I don't know. Or maybe NSF got the rings wrong. Quote Link to comment Share on other sites More sharing options...
Brotoro Posted August 23 Share Posted August 23 (edited) 40 minutes ago, softweir said: Hmm... OK, I'm a bit less sure of myself. Have you got a reference I can look at? A lot of fully cryogenic engines (NEVER kerolox!) produce best ISP with a rich mixture, causing some part of the exhaust to be super-heated propellant rather than combusted products - the lighter the molecule, the higher its velocity when heated, and the better the ISP. This is most apparent when burning H2, as H2 molecules are vastly lighter than H20! Even methane (CH4) is a lot lighter than the H20 and CO2 combustion products, so a rich mix leading to a proportion of CH4 in the exhaust provides better ISP. Of course, this has to be a carefully judged balance:- make the exhaust too rich and the reduced energy leads to excessively reduced exhaust temperature, thrust and ISP! The diagram posted earlier in this discussion shows the LOX tank in blue and the Methane tank in red. The volume of the V1 LOX tank appears to be about 7 rings (counting the space of the bottom dome and the space around the upper common dome as one ring), while the Methane tank is less than 5 rings (three full rings and two dome rings). The V2 diagram shows the larger LOX tank increased by one ring, and the smaller Methane tank increased by two rings? Are these accurate diagrams? I don't know. I also Googled "Starship tank volumes" and found a diagram where somebody calculated Starship tank volumes and got LOX tank volume of 793.48 m^3 and Methane tank volume of 604.93 m^3 (with header tank volumes of 14.65 m^3 for LOX and 13.14 m^3 for Methane...not counting amounts in downcomers). Are these accurate? I don't know, but the ratios look to be about correct from the diagrams. On 8/19/2024 at 9:31 AM, tater said: From NSF vid showing ring counts for the current V1 vs the V2 version (the V2 ship in question already being stacked). 1 ring added, payload section reduced by 2 rings (not counting any ring section with even part of a dome in it). Useful for spitballing variant capabilities. Edited August 23 by Brotoro arrrgh, typos Quote Link to comment Share on other sites More sharing options...
darthgently Posted August 23 Share Posted August 23 (edited) 1 hour ago, Ultimate Steve said: Raptor uses about 3.6 kg of oxygen per kg of methane. I think they subcool both of them for increased density but I'm going to ignore that because that's more math than I'm willing to do right now. Liquid oxygen has a density of 1141 kg per cubic meter and liquid methane has a density of 424 kg per cubic meter. 1000 kg of methane would take up about 2.358 cubic meters, and 3600 kg of oxygen would take up about 3.155 cubic meters. Thus we can infer that for every volume of methane added, 1.34 volumes of oxygen should be added. There's stuff I haven't accounted for that will shift that number around. But spacex is in a position where it can only easily add volumes in discrete rings. The ratio is pretty close to 3 rings of methane for 4 rings of oxygen. The thought of taking the analysis any further than this hurts my brain. There isn't an immediately obvious reason why they would add 2 methane rings and 1 oxygen ring. Maybe the new downcomer is more space efficient, maybe the header tanks are getting moved, maybe the old design was suboptimal, maybe the new domes have significantly less volume. I don't know. Or maybe NSF got the rings wrong. At first I was thinking that the lower tank losing volume to the upper tank's downcomer might explain, but yeah, that makes it more confusing if only stoichiometry is considered. All I can think of is they need extra oxygen beyond fuel use. Like for HLS. Or the LOX tank needs more headroom for some reason Edited August 23 by darthgently Quote Link to comment Share on other sites More sharing options...
magnemoe Posted August 24 Share Posted August 24 6 hours ago, mikegarrison said: Ping *is* important. That is the main reason for Starlink. The speed of light issues with geostationary satellites are significant for computers. Ping is important for stuff who has to be real time: games, drone control, short time trading. It does not matter for streaming, Most live TV streams has couple of seconds as an buffer anyway. Watch sport on cable and streamed on your phone or laptop. at the same time, no it does not matter much here outside of edge cases. For science data time is pretty irrelevant, same for streams. Quote Link to comment Share on other sites More sharing options...
tater Posted August 24 Share Posted August 24 Regarding ring counts, there's also the header tanks to consider. Quote Link to comment Share on other sites More sharing options...
softweir Posted August 24 Share Posted August 24 18 hours ago, Brotoro said: LOX tank in blue and the Methane tank in red Ah. Very-well, my information is emphatically out-informed! Quote Link to comment Share on other sites More sharing options...
tater Posted August 24 Share Posted August 24 Ship 33: Quote Link to comment Share on other sites More sharing options...
Minmus Taster Posted August 24 Share Posted August 24 1 hour ago, tater said: Ship 33: Very interesting look, like a steampunk airship sliced in half, is it a V2 Starship? Probably known to you all by now but: Quote Link to comment Share on other sites More sharing options...
JoeSchmuckatelli Posted August 24 Share Posted August 24 I'm calling some BS here. If I was an astronaut and getting a trip to the ISS... I'd be pretty excited. But if I was an astronaut getting a trip to the ISS and then unexpectedly stuck on the tin can until sometime next year? I mean, thank god for them having an alternative way to come back dirtside alive but more months of diapers and being an unplanned guest? Zheesh. Also - why next year? SX can throw rocks at space every few days - why not a Crew Dragon in the next 2 weeks? Quote Link to comment Share on other sites More sharing options...
Nuke Posted August 24 Share Posted August 24 (edited) id not be too surprised if one or both astronauts dont file a lawsuit with boeing the day they get home. and really they aren't allowed to use the station facilities? and im not going to blame sx for boeings worthless tin can not working. Edited August 24 by Nuke Quote Link to comment Share on other sites More sharing options...
tater Posted August 24 Share Posted August 24 (edited) 20 minutes ago, JoeSchmuckatelli said: I'm calling some BS here. If I was an astronaut and getting a trip to the ISS... I'd be pretty excited. But if I was an astronaut getting a trip to the ISS and then unexpectedly stuck on the tin can until sometime next year? I mean, thank god for them having an alternative way to come back dirtside alive but more months of diapers and being an unplanned guest? Zheesh. Also - why next year? SX can throw rocks at space every few days - why not a Crew Dragon in the next 2 weeks? Years ago I gave Senator Jake Garn a ride to the airport from a conference here (I was a student involved in conf, and had the best car). Famous (among space nerds, anyway) for being given a ride on Shuttle. He was so space sick, they now (only half jokingly) use "1 Garn" as the most spacesick someone can get. Asked in the car about just his personal take on spaceflight he said to us (buddy in back seat, me driving, Garn front passenger), he said the worst thing was knowing he could never do it again. He specifically mentioned (considering for family friendly forum), um, being told after first engaging in the physical act of love that you'd never be allowed to do it again. In short, spending more time at ISS is probably not pretty awesome for them. Edited August 24 by tater Quote Link to comment Share on other sites More sharing options...
JoeSchmuckatelli Posted August 24 Share Posted August 24 Oh - not blaming the rescue crew at all - just curious as to why it needs to be so far down the line Quote Link to comment Share on other sites More sharing options...
tater Posted August 24 Share Posted August 24 1 minute ago, JoeSchmuckatelli said: Oh - not blaming the rescue crew at all - just curious as to why it needs to be so far down the line It would be really expensive, and disrupts crew vehicle flow for SpaceX? 18 minutes ago, Nuke said: and really they aren't allowed to use the station facilities? ? Quote Link to comment Share on other sites More sharing options...
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