I would agree except for the option of having an ASDS just offshore. Just how close would the asds have to be to muddy the waters and make it an ASDS/RTLS
As I understand it, unless you run all three cores at full thrust and run through them all at the same time (which is not how SpaceX has said they will launch them), the FH center core is going to be higher and faster than any single-stick F9 core has been before recovery was attempted. Regardless of how the throttle the center core down and when they separate the side cores.You would have to leave an awful lot of gas in the core stage's tank to get that back to an RTLS, I would think. And if you run all the cores at full thrust, due to the very high T/W you would get, you would have to leave an awful lot of gas in *all* of the tanks to get all three cores to RTLS.I appreciate the concept that recovering all cores RTLS would be economical, but I'm concerned that, if you leave enough gas in the tanks of the stage(s) to accomplish this, you end up with very little greater performance than the Block 5 F9. In which case, why pay extra for an FH?Also, I seem to recall SpaceX (both Musk himself, and other SpaceX officials) stating rather certainly -- on a number of occasions -- that on FH, the side boosters will always RTLS, and the core stage will always be recovered (when not expendable) on a droneship. Seeing that this has always been the stated operational plan, and that there have been no signs of building a third landing pad to accommodate a change to a three-core RTLS plan, I guess I'm not seeing the argument that three-core RTLS is going to be the obvious way they will go, here...
As I understand it, unless you run all three cores at full thrust and run through them all at the same time (which is not how SpaceX has said they will launch them), the FH center core is going to be higher and faster than any single-stick F9 core has been before recovery was attempted. Regardless of how the throttle the center core down and when they separate the side cores.You would have to leave an awful lot of gas in the core stage's tank to get that back to an RTLS, I would think. And if you run all the cores at full thrust, due to the very high T/W you would get, you would have to leave an awful lot of gas in *all* of the tanks to get all three cores to RTLS.
I appreciate the concept that recovering all cores RTLS would be economical, but I'm concerned that, if you leave enough gas in the tanks of the stage(s) to accomplish this, you end up with very little greater performance than the Block 5 F9. In which case, why pay extra for an FH?
Also, I seem to recall SpaceX (both Musk himself, and other SpaceX officials) stating rather certainly -- on a number of occasions -- that on FH, the side boosters will always RTLS, and the core stage will always be recovered (when not expendable) on a droneship.
Visually at least, the shuttle's SRBSs seemed to be still thrusting a little at sep.Which when you think about it, and you think about the inherent uncertainties of controlling/predicting the thrust rate of a solid, just makes the fact that they made the shuttle work at all even more amazing.
Quote from: Kaputnik on 11/07/2017 11:36 amVisually at least, the shuttle's SRBSs seemed to be still thrusting a little at sep.Which when you think about it, and you think about the inherent uncertainties of controlling/predicting the thrust rate of a solid, just makes the fact that they made the shuttle work at all even more amazing.Thust of the SRBs is about 1% of nominal thrust on separation. IIRC the SRBs are separated when stack acceleration falls below a set value.
From what I can see it looks a bit like the Soyuz booster attachment points. The thrust from the boosters keeps them attached to the middle core which is running at a lower thrust level. The booster are lifting the centre core from the bottom. Once the boosters thrust levels drop then they can fall away. Obviously more going on than that, hopefully someone will provide more clarity.
Quote from: nacnud on 12/21/2017 11:23 pmFrom what I can see it looks a bit like the Soyuz booster attachment points. The thrust from the boosters keeps them attached to the middle core which is running at a lower thrust level. The booster are lifting the centre core from the bottom. Once the boosters thrust levels drop then they can fall away. Obviously more going on than that, hopefully someone will provide more clarity.Does that mean that in the case of engine out on a side booster that the core will have to throttle down further to keep from surpassing the booster and leaving it behind?
Quote from: llanitedave on 12/22/2017 01:17 amQuote from: nacnud on 12/21/2017 11:23 pmFrom what I can see it looks a bit like the Soyuz booster attachment points. The thrust from the boosters keeps them attached to the middle core which is running at a lower thrust level. The booster are lifting the centre core from the bottom. Once the boosters thrust levels drop then they can fall away. Obviously more going on than that, hopefully someone will provide more clarity.Does that mean that in the case of engine out on a side booster that the core will have to throttle down further to keep from surpassing the booster and leaving it behind?No. Remember all of the extra mass on top of the core. In order for the core to surpass the booster, it would need to shoulder all of that mass, less what help the other booster provides. Someone other than me could calculate how many engines the failing booster could loose before being surpassed by the rest of the stack but it is certainly more than one engine and as always, it depends on the time when the failures occur, at lift-off or just before ... what? BECO? (booster engine cut off). It also depends on the gimbol authority of the surviving booster and the core engines. The booster's plus core thrust vector must pass through the center of mass of the stack. That is easy if both boosters are thrusting equally but if thrust from one drops off then boosters and core need to gimbol engines to counter the unequal thrust magnitude and maintain a vector sum that passes through the center of mass of the stack. (Note that I am using "stack" as the descriptor for the complete FH less the burned fuel.)
It also depends on the gimbol authority of the surviving booster and the core engines. The booster's plus core thrust vector must pass through the center of mass of the stack. That is easy if both boosters are thrusting equally but if thrust from one drops off then boosters and core need to gimbol engines to counter the unequal thrust magnitude and maintain a vector sum that passes through the center of mass of the stack. (Note that I am using "stack" as the descriptor for the complete FH less the burned fuel-oops- propellant.)