Quote from: LouScheffer on 04/26/2018 05:22 pmQuote from: Jim on 04/26/2018 01:49 pmSTAR-48 is too smallTo back up this statement:Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg. With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t. The loss is 348*9.8*ln(13/11) = 570 m/s.So the net gain is only 823-570 = 253 m/s. That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already. What about Star 48GXV tested for the Parker Solar Probe mission as the upper stage on a Atlas V 551 vehicle but was cancelled in favor of DIVH cited Wiki via Orbital ATK
Quote from: Jim on 04/26/2018 01:49 pmSTAR-48 is too smallTo back up this statement:Star 48B masses about 2000kg, and supplies 591,000 kg(force)seconds. So if we add this to a 6000 kg probe, the starting mass will be 8000 kg and the ending about 6000 kg. With an ISP of 292, this gives a delta-V of 292*9.8*ln(8/6) = 823 m/s.But the extra mass takes performance from the second stage, which now ends at 13t, instead of 11t. The loss is 348*9.8*ln(13/11) = 570 m/s.So the net gain is only 823-570 = 253 m/s. That's not enough to erase the shortfall at all launch opportunities, though it would help for some, since the FH is pretty close already.
STAR-48 is too small
Also, 6000kg spacecraft is too large to be supported by a STAR-48. Also, Falcon facilities are not sited for large motors.
Hans' NEAF 2018 talk.... Quote“[Crossfeed] may be introduced a bit later on”
“[Crossfeed] may be introduced a bit later on”
Falcon Heavy having been de-emphasized by SpaceX, I'm surprised there is still talk of cross-feed, which I would think is a pretty big project.
If I recall about wasn't there some concern from the German team about putting Helios-A on the second flight of the Titan IIIE? I thought the first Titan IIIE launch failed or had an issue.
Quote from: vaporcobra on 04/23/2018 11:24 pmHans' NEAF 2018 talk.... Quote“[Crossfeed] may be introduced a bit later on”What's NEAF? Would you have a link for the talk?Falcon Heavy having been de-emphasized by SpaceX, I'm surprised there is still talk of cross-feed, which I would think is a pretty big project.
If SpaceX used the crossfeed method, the only way to recover the side cores would be to land them on two drone ships ("Of Course I Still Love You" and "A Shortfall of Gravitas") while expending the center core.Although the company throws away some money by expending the center core, at least they're bringing back the side cores to either use them again for another Falcon Heavy flight or turn them into Falcon 9 first stages.
If SpaceX used the crossfeed method, the only way to recover the side cores would be to land them on two drone ships ("Of Course I Still Love You" and "A Shortfall of Gravitas") while expending the center core.
2) won't work because rocket will never leave the launch pad.
Something like the current profile but shutdown the center core part way up and then restart center after staging. Alternatively deep throttling could do much of this without stopping and restarting.EDIT: we do know that the throttling of the first FH was VERY conservative. They only ran the engines at 90% thrust? How deep can a M1D throttle? 30% ?Probably a LOT of room for improvement.
Quote from: rsdavis9 on 05/30/2018 11:56 amSomething like the current profile but shutdown the center core part way up and then restart center after staging. Alternatively deep throttling could do much of this without stopping and restarting.EDIT: we do know that the throttling of the first FH was VERY conservative. They only ran the engines at 90% thrust? How deep can a M1D throttle? 30% ?Probably a LOT of room for improvement.(1) Without some changes to the Octoweb, only three of the engines can be started (or restarted) during flight.(2) It is not clear (to me, at least) whether the Merlins can be throttled down from 100% to 60% (40% down), or from 100% to 40% (60% down).
I'm curious about staging strategies but simply don't know enough to fully figure various options out. Irrespective of the economics, business strategy, or likelihood of implementation, what sort of impact on payload and reachable orbits would the following setups result in?1) shortening the center core and elongating the 2nd stage by the same amount for more prop in the US.2) launch using side cores, igniting center core at booster sep. Is this even possible? I presume this would make the core expendable also?3) crossfeed vs the current throttling of the core. Does this result in the same performance as scenario 2?Lastly, can anyone point me to a good resource that compares various parallel vs serial staging strategies? I would have thought this would be easy information to come across but maybe I'm just struggling with right search terms.