The control aspects of the ITS BFR aren't much different from F9. If the BFR is expected to be legless and land directly back on the launch pad, wouldn't it make sense to work this out first with F9?Obviously it wouldn't have to land at the launch pad, just on a structure built on one of the LZ pads. Perhaps they'd try a sort of legless grasshopper first.If F9 could lose its legs and still be recovered (at least on land) it would drop a couple thousand kilos of dead weight that would go right to its lift capability.
I was also under the impression that the F9 couldn't throttle down enough to hover in the way that would be needed to align with a landing mount.
On the other hand the only rocket that Spacex made that can't hover is the F9; Dragon2, Grasshopper 1&2 could.There is nothing to suggest that a rocket that lands in a cradle can't hover or descend from a hover.
Quote from: cppetrie on 07/11/2017 05:11 pmI was also under the impression that the F9 couldn't throttle down enough to hover in the way that would be needed to align with a landing mount.nothing i've seen suggests a hover. it'll still be a suicide burn, just with greater accuracy because of the extra, stronger thrusters.
If F9 could lose its legs and still be recovered (at least on land) it would drop a couple thousand kilos of dead weight that would go right to its lift capability.
Modifying F9B5 to learn pinpoint landing does not contradict F9B5 being the "end if the line", since such a mode is part of BFR development.Removed legs, attach cold thrusters and pressure tanks on same mount points, and that's all there is to the modification.Fail cheaply.
Quote from: meekGee on 07/12/2017 03:38 amModifying F9B5 to learn pinpoint landing does not contradict F9B5 being the "end if the line", since such a mode is part of BFR development.Removed legs, attach cold thrusters and pressure tanks on same mount points, and that's all there is to the modification.Fail cheaply.My thinking is that legless Falcon 9 development would compete for the same resources that are needed for the BFR/BFS - both capital and people. And I don't yet understand what value such a capability would provide?- Is this is supposed to address a market for Falcon 9 that is not currently served by planned Falcon 9 pricing, or not served by the upcoming Falcon Heavy capabilities? If so then today it must be pretty niche, so one would think it would be a gamble to go after this market.- Is this supposed to help with BFR/BFS development? Not sure why Falcon 9 would be the best vehicle to test this since.I've been known to be wrong, but I'm having trouble believing such a thing would make a lot of sense in the near term...
I have no idea if it will be done. But it would secure the stage on the barge, better than the Roomba/Octocrab can. It would make turn around easier than with legs. They could be on the way back an hour or two after landing. It would save some weight. But can they come down precisely enough that the thrusters can do the fine tuning? The last two landings at the limits of what can be done, were not that precise. We will see if they can improve at the limits with practice.I wonder if they could modify the He-pressurization for the legs for at least initial tests, before they install cold gas thruster in the thrust structure area.
My thinking is that legless Falcon 9 development would compete for the same resources that are needed for the BFR/BFS - both capital and people. And I don't yet understand what value such a capability would provide?- Is this is supposed to address a market for Falcon 9 that is not currently served by planned Falcon 9 pricing, or not served by the upcoming Falcon Heavy capabilities? If so then today it must be pretty niche, so one would think it would be a gamble to go after this market.- Is this supposed to help with BFR/BFS development? Not sure why Falcon 9 would be the best vehicle to test this since.I've been known to be wrong, but I'm having trouble believing such a thing would make a lot of sense in the near term...
Better idea (?): it should be easy enough to create a "cradle" for the second stage that could be temporarily installed on a the Vandenberg ASDS for Falcon Heavy launches from the Cape. It would catch the second stage using the same attachments that the booster stage uses. If you then install a pair/quartet of grid fins on any second stage where you have the margin, you could then practice cradle landings on a smaller scale.From a bit of googling, I can see the F9 landing legs (collectively) are estimated at just under 2100kg, where as the grid fins are estimated at only 41kg each. Even if that's off by an order of magnitude, it seems far more feasible to use grid fins on the second stage than landing legs. A grid fin plus cradle arrangement seems like a likely "hail mary" attempt that they could perform on the Falcon heavy demo.