With the absence of information on recent S2 reusability tests, which of the upcoming missions look to be prime candidates for S2 reusability testing? Which missions look like S2 reusability testing would be off the table?
We have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast. Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"? Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?
Quote from: darkenfast on 08/24/2018 05:04 amWe have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast. Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"? Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?Could well be, but what i have read is that it's for Dragon recovery, being pulled by Mr. Steven. Of course once you have a bouncy castle or a big net, S2 recovery can use that too. I think the most likely candidate for S2 recovery is a CRS mission. They recently deorbited a S2 after a CRS? mission over the middle of the atlantic, a lot of people said it was simply a longevity test for S2, i suspect it was a precursor to S2 recovery.
Okay, but has anybody from SpaceX said the inflatable is for Dragon recovery?
I don’t know, I haven’t seen as careful attention to detail and verification as I have with NSF articles.
Quote from: Robotbeat on 08/25/2018 01:40 pmI don’t know, I haven’t seen as careful attention to detail and verification as I have with NSF articles.By the name, I expect they're car nerds more than rocket nerds. they may be misunderstanding the insider info they get.
Yeah, I know teslarati means well, but NSF has set the bar very high and Teslarati is still relatively new to covering space. Just saying we don't know for certain this giant rubber inflatable kiddie pool is meant for Dragon recovery.
Quote from: ncb1397 on 08/27/2018 04:54 amQuote from: Robotbeat on 08/27/2018 04:28 amQuote from: ncb1397 on 08/25/2018 07:03 pmQuote from: Robotbeat on 08/25/2018 01:51 pmPhysics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg. Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.Delta IV CBC: 8738 m/sAtlas V CCB: 8851 m/sSurprisingly close.Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.(Also, look at falcon 9).IF you want to look at sensitivity to propellant choice, you should control for other variables. Atlas V and Delta IV use similar aluminum isogrid tank construction. Falcon 9 uses Aluminum-Lithium while previous Atlas vehicles used steel balloon tanks that couldn't support their own weight.Another example: S-IVB vs Falcon 9 upper stage: they have comparable wet mass, thrust, wet TWR, engine cycles, and the F9 US has slightly better delta-v with a 6000 kg payload (~8400 m/s vs ~8100). But the F9 US has less than half the dry mass, in a much smaller footprint of 3.7x12 m instead of 6.7x18 m. Both factors would make it much easier to return from space: everything related to control, entry, and landing can be smaller and lighter.Granted, the F9 US is Al-Li alloy instead of Al alloy, and uses FSW instead of arc welding. But the S-IVB is still a good example of a excellent dry mass fraction among restartable LH2 upper stages, so new tech hasn't improved the SOA that much to date.Using LH2 ties up a lot of dry mass in tanks, insulation, engines, and subsystems to support those larger and heavier components.
Quote from: Robotbeat on 08/27/2018 04:28 amQuote from: ncb1397 on 08/25/2018 07:03 pmQuote from: Robotbeat on 08/25/2018 01:51 pmPhysics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg. Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.Delta IV CBC: 8738 m/sAtlas V CCB: 8851 m/sSurprisingly close.Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.(Also, look at falcon 9).IF you want to look at sensitivity to propellant choice, you should control for other variables. Atlas V and Delta IV use similar aluminum isogrid tank construction. Falcon 9 uses Aluminum-Lithium while previous Atlas vehicles used steel balloon tanks that couldn't support their own weight.
Quote from: ncb1397 on 08/25/2018 07:03 pmQuote from: Robotbeat on 08/25/2018 01:51 pmPhysics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg. Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.Delta IV CBC: 8738 m/sAtlas V CCB: 8851 m/sSurprisingly close.Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.(Also, look at falcon 9).
Quote from: Robotbeat on 08/25/2018 01:51 pmPhysics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg. Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.Delta IV CBC: 8738 m/sAtlas V CCB: 8851 m/sSurprisingly close.
Physics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.
Re: 'dry mass of Stage 2' ...Wikipedia (as of May, 2017) indicates the second stage full thrust Falcon 9 ... "Mass (without propellant)" is 4,000 kg (8,800 lbs).Vertical descent velocity is a pertinent question.EDITED punctuation.
S2 can last at least 6 hours, as demonstrated multiple times. First at the FH launch if I remember correctly. 6h is required for direct GSO insertion.