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Quote from: dglow on 10/03/2016 08:42 pmMr. Belluscio, a very nice article – thank you. One note of correction: the 361s ISP you cite for the first stage's Raptors in vacuum is actually the sea level value for the three inner Raptors of the second stage. See pp. 36 of SpaceX's published PDF. It saysRaptor Engines 3 Sea-Level - 361 Isp 6 Vacuum - 382 IspMeaning 3 Sea-Level engines and 6 Vacuum engines, with Isp 361 and 382 seconds in vacuum respectively.It is easy to see that they mean the vacuum Isp for the Sea-Level engines as page 31 gives the sea-level Isp as 334 and the main use of the Sea-Level engines in the Ship will be for Earth ascent, Mars landing and Mars descent all of which are in near vacuum.
Mr. Belluscio, a very nice article – thank you. One note of correction: the 361s ISP you cite for the first stage's Raptors in vacuum is actually the sea level value for the three inner Raptors of the second stage. See pp. 36 of SpaceX's published PDF.
That seems a stretch of interpretation to me. If you state 'Sea-Level' and follow with an ISP value then... what might one suppose you are trying to communicate? Is it possible that, for the three inner Raptors of the second stage, they have a third variant? After all, these engines need never fight Earth's gravity when velocity=0.
If you are not convinced, do 138MN/128MN*334 seconds=360.3seconds. Given the rounding on the MN, it is totally consistent with the 361s vacuum performance for Sea Level optimized Raptor.
The wikipedia edits are getting annoying. A few days ago I saw 382 indicated as the vaccum ISP of the ITS first stage and corrected it to ~360s . Apparently some confused soul changed it back to 382 seconds, looking back at the edit history I saw an edit war between a few other editors between the two values, and then at some point the vaccum isp was deleted outright.The wikipedia article on the ITS seems to be Encyclopedia Astronautica-tier unreliable right now.It would be so much nicer if anyone who edited rocket engine ISP's on any wiki was forced to sanity test said ISP's in RPA before making the edits...
Quote from: baldusi on 10/03/2016 10:04 pmIf you are not convinced, do 138MN/128MN*334 seconds=360.3seconds. Given the rounding on the MN, it is totally consistent with the 361s vacuum performance for Sea Level optimized Raptor.(138*334)/128... yes, that is convincing. When would we expect to see those three engines firing in a vacuum?
Quote from: Nilof on 10/03/2016 10:19 pmThe wikipedia edits are getting annoying. A few days ago I saw 382 indicated as the vaccum ISP of the ITS first stage and corrected it to ~360s . Apparently some confused soul changed it back to 382 seconds, looking back at the edit history I saw an edit war between a few other editors between the two values, and then at some point the vaccum isp was deleted outright.The wikipedia article on the ITS seems to be Encyclopedia Astronautica-tier unreliable right now.It would be so much nicer if anyone who edited rocket engine ISP's on any wiki was forced to sanity test said ISP's in RPA before making the edits...SpaceX have not provided a formal ISP value for the first stage Raptors in vacuum, though Baldusi's math seems fair enough.And yes, Wikipedia changes. Tragic, isn't it?
Quote from: dglow on 10/03/2016 10:23 pmQuote from: baldusi on 10/03/2016 10:04 pmIf you are not convinced, do 138MN/128MN*334 seconds=360.3seconds. Given the rounding on the MN, it is totally consistent with the 361s vacuum performance for Sea Level optimized Raptor.(138*334)/128... yes, that is convincing. When would we expect to see those three engines firing in a vacuum?After staging from the ITS booster, when climbing to LEO. (see the video) Also the martian atmosphere is practically a vacuum.
The 1MN dev. model of Raptor should be mass produced to replace Merlin to do away with the He system on F9 and FH.
This might be a stupid question but that does 1MN mean? some people have said that makes it about 1/3 size i would just like to understand the scaling ect.
SpaceX have not provided a formal ISP value for the first stage Raptors in vacuum, though Baldusi's math seems fair enough.
Quote from: dglow on 10/03/2016 10:26 pmSpaceX have not provided a formal ISP value for the first stage Raptors in vacuum, though Baldusi's math seems fair enough.http://www.spacex.com/sites/spacex/files/mars_presentation.pdfPage 36 gives the vacuum Isp for the SL Raptors.
Quote from: Elmar Moelzer on 10/04/2016 01:01 amQuote from: dglow on 10/03/2016 10:26 pmSpaceX have not provided a formal ISP value for the first stage Raptors in vacuum, though Baldusi's math seems fair enough.http://www.spacex.com/sites/spacex/files/mars_presentation.pdfPage 36 gives the vacuum Isp for the SL Raptors.Actually, that page purports to give the Isp for three sea level Raptors, then the Isp for six vacuum Raptors, all of which belong to the second stage. What exactly this means is the discussion at hand.Moreover, it appears none of these Raptors (on the second stage) are the same as those on the first – smaller nozzles all around on stage one.
Quote from: dglow on 10/04/2016 01:15 amQuote from: Elmar Moelzer on 10/04/2016 01:01 amQuote from: dglow on 10/03/2016 10:26 pmSpaceX have not provided a formal ISP value for the first stage Raptors in vacuum, though Baldusi's math seems fair enough.http://www.spacex.com/sites/spacex/files/mars_presentation.pdfPage 36 gives the vacuum Isp for the SL Raptors.Actually, that page purports to give the Isp for three sea level Raptors, then the Isp for six vacuum Raptors, all of which belong to the second stage. What exactly this means is the discussion at hand.Moreover, it appears none of these Raptors (on the second stage) are the same as those on the first – smaller nozzles all around on stage one.Honestly, the discussion is silly. Try running RPA Lite, and the only way to make any sense of what was given is the simplest explanation:382s is for vac-optimized Raptor at vacuum.~360s is for sl-optimized Raptor at vacuum.332s is for sl-optimized Raptor at sea level.Let's not over-complicate it because the diagram may show slight /apparent differences in nozzle size. Occam's Razor.
382s is for vac-optimized Raptor at vacuum.~360s is for sl-optimized Raptor at vacuum.332s is for sl-optimized Raptor at sea level.
Quote from: Robotbeat on 10/04/2016 01:20 am382s is for vac-optimized Raptor at vacuum.~360s is for sl-optimized Raptor at vacuum.332s is for sl-optimized Raptor at sea level.I agree! Giving anything but the vacuum Isp for a second stage engine makes no sense.
How was it determined that this was a 1MN 1/3 scale engine?I didn't see it any forum posts.Didn't see it in any an announcement.