Option 2 would need new plumbing , thrust structure , and a little more dry mass.
Quote from: RocketmanUS on 01/11/2017 06:03 amOption 2 would need new plumbing , thrust structure , and a little more dry mass.Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146
Quote from: OneSpeed on 01/11/2017 08:43 amQuote from: RocketmanUS on 01/11/2017 06:03 amOption 2 would need new plumbing , thrust structure , and a little more dry mass.Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146What is the expected thrust , ISP ( SL , vac ), and dry mass of the Raptor 80?Looking at that other post it looks like the 12-Raptor 80 BFS could be a little more than 10mt added dry mass.
A plausible mission architecture that requires minimal additional development could based on the development of a SSME-style nozzle for Raptor, with an expansion ratio of 80:1 and diameter of 2.3 m,. This could enable SL trust of 3080 kN at 330 s ISP and vac thrust of 3300 kN at 374 s ISP.
I'm estimating that SL Raptors will mass around 2,500 kg and vac raptors about 3,000 kg, while a 80:1 vac engine would mass ~2,800 kg.
Quote from: RocketmanUS on 01/11/2017 08:30 pmQuote from: OneSpeed on 01/11/2017 08:43 amQuote from: RocketmanUS on 01/11/2017 06:03 amOption 2 would need new plumbing , thrust structure , and a little more dry mass.Yes, I had estimated an extra 10mT for 12 Raptor 80 vs. 3 Raptor 50 + 6 Raptor Vac. That seems to line up pretty well with envy887's assessment here: https://forum.nasaspaceflight.com/index.php?topic=41809.msg1628146#msg1628146What is the expected thrust , ISP ( SL , vac ), and dry mass of the Raptor 80?Looking at that other post it looks like the 12-Raptor 80 BFS could be a little more than 10mt added dry mass.Based on some old RPA simulations (I'll have to re-run these to double check):Quote from: envy887 on 01/06/2017 04:17 pmA plausible mission architecture that requires minimal additional development could based on the development of a SSME-style nozzle for Raptor, with an expansion ratio of 80:1 and diameter of 2.3 m,. This could enable SL trust of 3080 kN at 330 s ISP and vac thrust of 3300 kN at 374 s ISP.And based on some extrapolation from Merlin, using SSME as an extra data point (these are SWAGs, take for what that's worth):Quote from: envy887 on 01/10/2017 01:11 pmI'm estimating that SL Raptors will mass around 2,500 kg and vac raptors about 3,000 kg, while a 80:1 vac engine would mass ~2,800 kg.So by my rough estimates, replacing six vac engines with nine 80:1 engines adds 8,100 kg.
For a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.
Interesting. Wouldn't that be a fully reusable replacement for the Falcon 9? At least the ones going to LEO?
It's kind of a kludge for Dragon launches. Might work, but doesn't seem worthwhile since F9 can already do booster RTLS on those.
Quote from: guckyfan on 01/12/2017 05:11 amFor a minimal design change version, how would a vehicle with only six Raptor 80 work, leaving the 3 central sea level Raptor unchanged? That would work without changing plumbing and thrust structure for maximum commonality with the standard ITS.I've run a quick simulation of your suggestion, and the results look like this:ConfigurationMass to 300 x 300Vehicle massPayload9 x Raptor 400 mT89 mT0mT9 x Raptor 50190 mT90 mT28mT3 x Raptor 50 + 6 x Raptor 80196 mT92 mT32mT12 x Raptor 80240 mT100 mT67mTSo, perhaps an extra 4mT to orbit, but you would have the extra cost of development of the Raptor 80.
The 9 Raptor 40 should get payload to orbit.
There's no point in using a 40:1 nozzle on the BFS. Musk's presentation clearly showed it with only 200:1 and 50:1 nozzles, so there is plenty of room for bigger nozzles.The only point of the 40:1 is packing 42 of them tightly under BFR. That's not an issue on BFS.