Raptor SN56 was loaded into the Raptor van and taken away.
I've been thinking about longevity of a Raptor engine. I would expect that, with time, they would settle into a maintenance schedule of some sort for an engine (similar to the inspection/maintenance schedule that an airline adheres to for a jet aircraft).I've sort of been assuming that a start/stop cycle probably places more stress on an engine than a period of steady state thrust (similar to how they weigh takeoff/landings more heavily that flight hours when determining maintenance schedules for a jet). Can someone with more knowledge than I confirm that is the case (or explain why it isn't)?
Looking at the photos of the 3 engines for the SN15, we can see the great advance already achieved. Began to look more like a product, and less like a prototype. And that's not an easy thing.
Quote from: copper8 on 04/16/2021 05:22 amI've been thinking about longevity of a Raptor engine. I would expect that, with time, they would settle into a maintenance schedule of some sort for an engine (similar to the inspection/maintenance schedule that an airline adheres to for a jet aircraft).I've sort of been assuming that a start/stop cycle probably places more stress on an engine than a period of steady state thrust (similar to how they weigh takeoff/landings more heavily that flight hours when determining maintenance schedules for a jet). Can someone with more knowledge than I confirm that is the case (or explain why it isn't)?Transient issues can include:-Hydrodynamic bearings that work fine at operational speeds but sometimes suffer from rubbing contact at lower speeds or at resonance frequencies.-Fluid transients that lead to reactions and hot spots occurring in places that they don't during steady state operation. Potentially a killer when one of the fluids is hot high pressure oxygen.-Thermal transients as cold things heat up or cool down through their thickness leading to big temperature gradients that induce large thermal strains. These strains can exceed the elastic limits of the materials (particularly at high temperatures where those elastic strain limits reduce) and lead to dimensional changes and low cycle fatigue (an everyday example of this is gradual belling out of initially flat fry-pans and saucepans with repeated thermal cycles ). In large power stations this problem leads to very slow gentle ramps in operating powers that can take 10's of minutes to preserve life. In rocket engines such mitigations are not possible and you get spool up from zero to max power in a second or two with construction from horribly low thermal conductivity materials like titanium, inconels and stainless steels that lead to large thermal gradients, exacerbating the issue. Thick flanges and anywhere else you get big thickness of material are a particular weakness in this regard.-Combustion chamber and nozzle wall heat fluxes. Same thermal strain issue - huge heat fluxes of 10's of MW/mē (maybe as high as 160MW/mē in SSME according to linked paper) lead to large temperature gradients through the walls that cause elastic and then plastic strain due to differential expansion of different layers if the heat fluxes are to high and the walls too thick. Exacerbated by material weakening and reduction in elastic limits at higher operating temperatures. This issue - the heat fluxes encountered are linked strongly to chamber pressure. https://www.sciencedirect.com/science/article/pii/S1000936117301024It is not clear to me that these thermal fatigue problems have any viable solutions - engines may be inherently limited to quite low numbers of thermal cycles, and it could be that the only path to low cost is making them in large numbers to make them cheap to regularly replace.
Quote from: Alberto-Girardi on 04/15/2021 07:06 pmQuote from: capoman on 04/15/2021 06:25 pmYeah, I think there is still a lot of flux in the design. They won't ramp up production until they get a mature design. Higher production means automation, and there no sense putting all that automation effort and cost in until you get to a reasonably fixed design. It's possible that they are doing batches of iterations right now, testing the entire batch to get good handle on data and performance, then tweaking and making another batch. I'm sure there are certain components that are reasonably settled on, but Raptor output really won't ramp up until all or most components are mature.I agree, since they plan the full stack for NET July (if this is true this summer will be simply beautiful) they have enough time to have 28 engines, only making production a bit faster, which IMO is happening now. Maybe with no payload they need less engine on SH, but I don't think a few engine will be the proble, since the production is probably in batches.I would just like to point out that according to the information Chris received, the target for an orbital flight is by July 1st, not NET July 1st.
Quote from: capoman on 04/15/2021 06:25 pmYeah, I think there is still a lot of flux in the design. They won't ramp up production until they get a mature design. Higher production means automation, and there no sense putting all that automation effort and cost in until you get to a reasonably fixed design. It's possible that they are doing batches of iterations right now, testing the entire batch to get good handle on data and performance, then tweaking and making another batch. I'm sure there are certain components that are reasonably settled on, but Raptor output really won't ramp up until all or most components are mature.I agree, since they plan the full stack for NET July (if this is true this summer will be simply beautiful) they have enough time to have 28 engines, only making production a bit faster, which IMO is happening now. Maybe with no payload they need less engine on SH, but I don't think a few engine will be the proble, since the production is probably in batches.
Yeah, I think there is still a lot of flux in the design. They won't ramp up production until they get a mature design. Higher production means automation, and there no sense putting all that automation effort and cost in until you get to a reasonably fixed design. It's possible that they are doing batches of iterations right now, testing the entire batch to get good handle on data and performance, then tweaking and making another batch. I'm sure there are certain components that are reasonably settled on, but Raptor output really won't ramp up until all or most components are mature.
[...] In rocket engines such mitigations are not possible and you get spool up from zero to max power in a second or two with construction from horribly low thermal conductivity materials like titanium, inconels and stainless steels that lead to large thermal gradients, exacerbating the issue. Thick flanges and anywhere else you get big thickness of material are a particular weakness in this regard.-Combustion chamber and nozzle wall heat fluxes. Same thermal strain issue - huge heat fluxes of 10's of MW/mē (maybe as high as 160MW/mē in SSME according to linked paper) lead to large temperature gradients through the walls that cause elastic and then plastic strain due to differential expansion of different layers if the heat fluxes are to high and the walls too thick. Exacerbated by material weakening and reduction in elastic limits at higher operating temperatures. This issue - the heat fluxes encountered are linked strongly to chamber pressure. https://www.sciencedirect.com/science/article/pii/S1000936117301024It is not clear to me that these thermal fatigue problems have any viable solutions - engines may be inherently limited to quite low numbers of thermal cycles, and it could be that the only path to low cost is making them in large numbers to make them cheap to regularly replace.
Quote from: RobLynn on 04/16/2021 10:36 am[...] In rocket engines such mitigations are not possible and you get spool up from zero to max power in a second or two with construction from horribly low thermal conductivity materials like titanium, inconels and stainless steels that lead to large thermal gradients, exacerbating the issue. Thick flanges and anywhere else you get big thickness of material are a particular weakness in this regard.-Combustion chamber and nozzle wall heat fluxes. Same thermal strain issue - huge heat fluxes of 10's of MW/mē (maybe as high as 160MW/mē in SSME according to linked paper) lead to large temperature gradients through the walls that cause elastic and then plastic strain due to differential expansion of different layers if the heat fluxes are to high and the walls too thick. Exacerbated by material weakening and reduction in elastic limits at higher operating temperatures. This issue - the heat fluxes encountered are linked strongly to chamber pressure. https://www.sciencedirect.com/science/article/pii/S1000936117301024It is not clear to me that these thermal fatigue problems have any viable solutions - engines may be inherently limited to quite low numbers of thermal cycles, and it could be that the only path to low cost is making them in large numbers to make them cheap to regularly replace.From what you say (thanks, very informative!) it seems that lifetimes may be shorter for some of the big, simple, solid parts (the combustion chamber, etc.) than for some of the complex subsystems with moving parts (turbopumps, etc.). If so, then what gets replaced and what gets kept during refurbishment could be a bit counterintuitive.
Brief history of Starship development from SpaceX's HLS award announcement:QuoteSpaceX has manufactured and tested more than 60 of Starships Raptor engines, accumulating nearly 30,000 seconds of total test time over 567 engine starts, including on multiple Starship static fires and flight tests.https://www.spacex.com/updates/starship-moon-announcement/index.html
SpaceX has manufactured and tested more than 60 of Starships Raptor engines, accumulating nearly 30,000 seconds of total test time over 567 engine starts, including on multiple Starship static fires and flight tests.
Raptor Engines 1-50 as seen in Boca Chica, Texas.As of, April 16, 2021
Raptor Engines 51-100 as seen in Boca Chica, Texas.As of, April 16, 2021
Quote from: WH2OPaddler on 04/18/2021 02:53 amI'm waiting to see an official look up the skirt of Lunar Starship. To date, every depiction I've seen shows 6 engines: 3 SL Raptors and 3 Vac Raptors. Except that Lunar Starship is a one way vehicle. Once it leaves earth, it will not be coming back. And because Lunar Starship will only ever operate in a vacuum - like the 2nd stage of F9, only vacuum engines are needed after being boosted to altitude - any sea level engines, whether Raptors or otherwise, would be out of their element and quite literally useless. So if there's a reason to send engines that can't function properly in a vacuum all the way to the moon, I'd really like to know what it is.Sea level engines aren't "useless", merely slightly less efficient. Isp of Vacuum Raptor is 375, Isp of SL raptor in a vacuum is 355, the difference of 20 ISP that Elon was referring to as "a lot of hard work". Try running this through the rocket equation, you'll see that the 20 Isp delta helps with one less fueling launch under many scenarios, that's really all it saves.Furthermore, Vacuum raptors don't gimbal, and there probably isn't enough room for their bells at the center. 6 raptors are also needed to boost anything with payload for the first 60 seconds of second stage burn, because thrust/weight ratio is less than one with 6 and less than half with only 3, and thus gravity losses will start to become significant without all 6 Raptors.I doubt SpaceX is going to redesign something as finicky as the puck for Lunar Starship to fit 6 vacuum raptors. It'll be bog standard 3+3.
I'm waiting to see an official look up the skirt of Lunar Starship. To date, every depiction I've seen shows 6 engines: 3 SL Raptors and 3 Vac Raptors. Except that Lunar Starship is a one way vehicle. Once it leaves earth, it will not be coming back. And because Lunar Starship will only ever operate in a vacuum - like the 2nd stage of F9, only vacuum engines are needed after being boosted to altitude - any sea level engines, whether Raptors or otherwise, would be out of their element and quite literally useless. So if there's a reason to send engines that can't function properly in a vacuum all the way to the moon, I'd really like to know what it is.
....Is possible to make Raptors Vac gimbalable? The problem preventing it is the too big nozzle?
Quote from: Alberto-Girardi on 04/18/2021 07:53 am....Is possible to make Raptors Vac gimbalable? The problem preventing it is the too big nozzle?As I remember, the Vac nozzle will be welded to the outer skirt, it was mentioned somwhere (guess that means whatever attachment method not exactly welding). That makes gimballing a bit difficult.But aside the attachment, there arent enogh space there to gimball outward.
Quote from: enbandi on 04/18/2021 01:09 pmQuote from: Alberto-Girardi on 04/18/2021 07:53 am....Is possible to make Raptors Vac gimbalable? The problem preventing it is the too big nozzle?As I remember, the Vac nozzle will be welded to the outer skirt, it was mentioned somwhere (guess that means whatever attachment method not exactly welding). That makes gimballing a bit difficult.But aside the attachment, there arent enogh space there to gimball outward.So gimbaling outward is impossible, but is impossible to gimbal it inwards too? Why they want to weld it to the skirt? What will be the advantage?
So gimbaling outward is impossible, but is impossible to gimbal it inwards too? Why they want to weld it to the skirt? What will be the advantage?
Quote from: Alberto-Girardi on 04/18/2021 02:45 pmSo gimbaling outward is impossible, but is impossible to gimbal it inwards too? Why they want to weld it to the skirt? What will be the advantage?If you watch the SSME(space shuttle) engines when they start up they vibrate in and out in x-y directions. This is because they are over expanded operating at sea level. This is the reason VAC engines that are very over expanded at SL aren't fired at sea level. This is caused by flow separation. This is caused by insufficient exit pressure to move the ambient atmosphere out of the way. So the ambient atmosphere oscillates in and out of the bell.Speculation:So the idea is if you attach the bell at one point you can damp out the flexing from this flow separation.