Quote from: LouScheffer on 02/10/2018 04:50 amLooking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core.They only ran the center core 30 more seconds (side cores 2:34, counting early ignition, center core 3:04) so the average throttle down during 3 core operation was 80% (assuming 100% for 30 seconds after separation, they took 2:00 fuel while to side cores took 2:30). They appear to have done this right from the beginning, as the center core plume is about 80% as long right from the start.So it seems they could run a much better (though more complicated) profile. Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more. A back of the envelope calculation indicates this would help a lot. The thrust during the first period would be reduced by about 2.6/2.8 (counting a core as 1.0. The center would give 1.0 for 1/5 of the time, 0.5 for 4/5 of the time, for a total of 2.6, as opposed to the apparent 80% used on this flight). Since staging velocity was about 2634 m/s, this would be reduced by about 200 m/s. This is approximate since there might be additional gravity losses (but that's why I suggested full thrust for the first 0:30) but on the other hand the side boosters have an easier boostback. But judging by Intelsat 35, the last minute of the core stage gives about 700 m/s more than the last 30 seconds alone, for a net gain of 500 m/s at core staging. They would need to reserve some of this for additional core re-entry slowing, but the gain is still significant.This translates into a big gain in payload. If the second stage needs to provide less delta-V, it can loft a heavier satellite. For example, changing the payload from 8 tonnes to 10 tonnes costs about 450 m/s, using the usual assumptions (isp = 348, empty mass 4.5t, fuel = 111.5t). So SpaceX could get about a 20% increase in payload just by changing the throttle profile.Is this likely to have much effect on the timing/magnitude of Max-Q?
Looking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core.They only ran the center core 30 more seconds (side cores 2:34, counting early ignition, center core 3:04) so the average throttle down during 3 core operation was 80% (assuming 100% for 30 seconds after separation, they took 2:00 fuel while to side cores took 2:30). They appear to have done this right from the beginning, as the center core plume is about 80% as long right from the start.So it seems they could run a much better (though more complicated) profile. Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more. A back of the envelope calculation indicates this would help a lot. The thrust during the first period would be reduced by about 2.6/2.8 (counting a core as 1.0. The center would give 1.0 for 1/5 of the time, 0.5 for 4/5 of the time, for a total of 2.6, as opposed to the apparent 80% used on this flight). Since staging velocity was about 2634 m/s, this would be reduced by about 200 m/s. This is approximate since there might be additional gravity losses (but that's why I suggested full thrust for the first 0:30) but on the other hand the side boosters have an easier boostback. But judging by Intelsat 35, the last minute of the core stage gives about 700 m/s more than the last 30 seconds alone, for a net gain of 500 m/s at core staging. They would need to reserve some of this for additional core re-entry slowing, but the gain is still significant.This translates into a big gain in payload. If the second stage needs to provide less delta-V, it can loft a heavier satellite. For example, changing the payload from 8 tonnes to 10 tonnes costs about 450 m/s, using the usual assumptions (isp = 348, empty mass 4.5t, fuel = 111.5t). So SpaceX could get about a 20% increase in payload just by changing the throttle profile.
And I keep bouncing the silly idea around in my head to just leave 4 engines off the FH core and run it full throttle...(except thru Max-Q maybe)... Gravity losses... I know... but the idea haunts me still... I would agree there is something to be gained with a different throttle map schedule on FH...
Enhanced images of the higher res pics posted by SpaceX. Spot the photoshop!
Quote from: LouScheffer on 02/10/2018 04:50 amLooking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core. [...]So it seems they could run a much better (though more complicated) profile. Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more. A back of the envelope calculation indicates this would help a lot. [...]Is this likely to have much effect on the timing/magnitude of Max-Q?
Looking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core. [...]So it seems they could run a much better (though more complicated) profile. Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more. A back of the envelope calculation indicates this would help a lot. [...]
Request to the video creating people out there:The launch was so utterly identical to the animation we've had for the last few years that I think it would be awesome if someone edits together a split screen of actual vs. prediction for the parts that have video for both. That would make for a shorter video that you could show someone less interested to give them an idea of what just happened and it would show how with solid engineering work really far out dreams can come true.
Question - when the side cores separated there seems obvious to my eye the side core exhaust plume impinged along the side of the center core.
Quote from: Johnnyhinbos on 02/10/2018 12:57 pmQuestion - when the side cores separated there seems obvious to my eye the side core exhaust plume impinged along the side of the center core.It was the other way around - center core plume impinged on the side cores.
Quote from: Steven Pietrobon on 02/10/2018 05:52 amEnhanced images of the higher res pics posted by SpaceX. Spot the photoshop!Why care?...
I am spotting a reflected light that would make determining where you should have total darkness hard to determine. ...
Would it be possible for FH to launch a second stage with sufficient fuel to land? A larger second stage to carry the extra fuel would be required, but would full re-use cost savings stack up against the extra complexity / cost of FH for lighter (f9 sized) payloads?
Question - when the side cores separated there seems obvious to my eye the side core exhaust plume impinged along the side of the center core. I wonder if that caused any damage to the center core? Can’t see any direct correlation between that event and the last relight (landing burn) of the center core, but who knows?
Quote from: markhnz on 02/10/2018 05:59 pmWould it be possible for FH to launch a second stage with sufficient fuel to land? A larger second stage to carry the extra fuel would be required, but would full re-use cost savings stack up against the extra complexity / cost of FH for lighter (f9 sized) payloads? Yes.At the most stupid, you can closely approach this nearly with the existing stage 2, if you launch a one or two ton payload, then slow down most of the way before entry, and recover using the fairing recovery boat Mr Steven.However, this is pretty much literally 'one or two' tons. Any significant payload means you need to do atmospheric entry at most of 8km/s, you can't waste the fuel slowing down.This makes everything enormously harder - you basically have to wholly redesign stage 2.At that point, you almost might as well wholly replace the engine, for methane/oxygen.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474659It seems unlikely this will happen, if BFR continues to progress well.At least unless someone comes up with cash for a mission that requires it before then.
QuoteIt seems unlikely this will happen, if BFR continues to progress well.At least unless someone comes up with cash for a mission that requires it before then.I was considering the planned Internet satellite constellation planned for operation by 2019/20 (!!) - and whether the volume would enable a business case; but Elon was clear on no development on FH, focus on BFR / raptor. BFR is early 20's so not going to launch a few 000's of the satellite constellation for Internet, so it would be up to F9 or FH to carry out these launches.
It seems unlikely this will happen, if BFR continues to progress well.At least unless someone comes up with cash for a mission that requires it before then.
