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.
The BFR & BFS are supposed to have a more squat profile, which would make them less "tippy" when they land, so it would make sense for SpaceX to investigate legless landing capabilities. But the Falcon 9 is very slender, and I just don't see that it is a good candidate for legless landings. Not until they can perfect it for wider base rockets at least.
Quote from: guckyfan on 07/12/2017 05:30 amI 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.IMO the catching mechanism will have a substantial structure, both for last-inch alignment, and for arresting vertical motion (which the legs kinda do today).That said, there are some advantages for doing it far off shore.
I vote for the Grasshopper 2 approach. Raptors, methane and BFR diameter.
They are already experimenting with a "booster grabber". Wouldn't it be likely to be extended to cover this?
Quote from: Space Ghost 1962 on 07/12/2017 06:04 pmThey are already experimenting with a "booster grabber". Wouldn't it be likely to be extended to cover this?I'd think some sort of roomba version would be in the running. Able to make quick adjustments in its position as the Booster is landing.
Perhaps the development sequence:1. "Auto jack stand" to mechanically constrain freshly landed stage as a part of automated "safeing" at sea.2. GNC improvements to reliably land within a fraction of a meter at sea and land.3. Reversable "launch mount" clamp downs with jack stand's "adjusters" that seat/align vehicle in LZ-1 deployable platform.4. Reconfigured/new pad with above mentioned mount that can be secured, TE/L lowered, booster returned to HIF.
Quote from: meekGee on 07/12/2017 07:29 amQuote from: guckyfan on 07/12/2017 05:30 amI 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.IMO the catching mechanism will have a substantial structure, both for last-inch alignment, and for arresting vertical motion (which the legs kinda do today).That said, there are some advantages for doing it far off shore.I think it could be a substantial, but simple system. I've attached my pet idea of using counterweights on 'see-saws'Getting it out of there without relaunching would require a crane, but so do the legs.F9 doesn't have a frustrum like that on the end, but it's just an example, and any GH type flight would just be for experimentation anyway so there'd be a lot of modifications to get it working.
I'm not going to pretend I can draw, but given the ground structure doesn't have to be small couldn't you extend your cone vertically (or have four arms) and have a series of lightly sprung guide vanes at various points along it.
..or simply land in different place.
Quote from: alang on 09/02/2017 05:10 pmI'm not going to pretend I can draw, but given the ground structure doesn't have to be small couldn't you extend your cone vertically (or have four arms) and have a series of lightly sprung guide vanes at various points along it.I think the phrase you're looking for is "compliant coupling" Holes with rounded corners and tapering the entry area to a hole for a bolt or screw are classic tactics to simplify robot arms locating fasteners to holes. The jokes in this pack is that what you're talking about has to stay in place during takeoff, with 28 million lbs of thrust. Might be possible if the structure is vented, but it's going to be very large and very heavy.
What about a landing structure that will move in after launch, before landing occur?
How much payload capability would F9 have without legs?
Quote from: spacenut on 09/06/2017 02:16 pmHow much payload capability would F9 have without legs?The usual shorthand math for first stage weight reduction is that ~10% of that removed mass is added payload to orbit. So... The 4 legs weigh around 2.5 tons, so removing them would add 250kg to the payload. So not much.Removing legs is more about operational simplicity and rapid turnaround than it is about adding payload capability.
I vote for bees.
Why are people ridiculing this? Landing without legs is an idea that should be taken very seriously, it is based on something that Elon Musk actually showed on stage. It wasn't so very long ago that landing at sea was ridiculed but then SpaceX announced they were going to do it and then did it successfully multiple times.The current F9 landing legs are detachable and optional. It would not be unreasonable to design a separate landing gear that is lighter and designed to be "grabbed" by heavy equipment on the ground instead. Since all of this happens without customer payloads on board it is relatively easy to experiment and SpaceX can easily afford to lose some recoveries.
....If they do a cradle, I expect them to make it the rocket's responsibility to get darn close to the cradle and the cradle to compensate for a meter or two max. No lassos, inflatable catcher's mitts, sky hooks or giant chop sticks.Maybe bees though. The bees have real potential. I'm hearing a lot about bees lately.
Quote from: mme on 09/22/2017 11:40 pm....If they do a cradle, I expect them to make it the rocket's responsibility to get darn close to the cradle and the cradle to compensate for a meter or two max. No lassos, inflatable catcher's mitts, sky hooks or giant chop sticks.Maybe bees though. The bees have real potential. I'm hearing a lot about bees lately.Exactly. The F9 will do it's job and the cradle will be active and will very quickly make up the last distances in 3 axis's. Maybe less than a meter.What technology it would use to sense the stages position through rocket exhaust would/will be interesting.Regarding Bee's people are saying great things about the bees, they are huge bees, the best bees.
Quote from: wannamoonbase on 09/26/2017 06:00 pmQuote from: mme on 09/22/2017 11:40 pm....If they do a cradle, I expect them to make it the rocket's responsibility to get darn close to the cradle and the cradle to compensate for a meter or two max. No lassos, inflatable catcher's mitts, sky hooks or giant chop sticks.Maybe bees though. The bees have real potential. I'm hearing a lot about bees lately.Exactly. The F9 will do it's job and the cradle will be active and will very quickly make up the last distances in 3 axis's. Maybe less than a meter.What technology it would use to sense the stages position through rocket exhaust would/will be interesting.Regarding Bee's people are saying great things about the bees, they are huge bees, the best bees. Well, assuming that they put up some lightening towers around the landing sites, (surprised nobody has considered what kind of a lightening rod a landing stage would be) small radar units could be installed at a far enough distance and height to triangulate the exact position of a stage as it descends. this data would be relayed to the capture device, which would move and elevate to compensate appropriately. Simple solution really.
So, it is not going to happen. Right? He misspoke right?
Maybe I'm crazy, but the following struck me odd from the IAC 2017 presentation.Elon was discussing Falcon 9, Falcon 9 having 16 straight successful landings, and is about to move on to Falcon 9 having 30 planned flights next year. Then, at 8:19 in the video, he starts talking about Falcon 9 landing precision, and says, "In fact, we believe the precision at this point is good enough for propulsive landing that we do not need legs for the next version. It will literally land with so much precision it will land back on its launch mounts."He's talking about Falcon 9. He may have misspoke since BFR was obviously on his mind, but the context says the is saying the next version of Falcon 9 can land on it's launch mounts. BFR is hardly "the next version" when discussing Falcon 9; Block V is.I'll be the first to say that he MUST have misspoke because that is insane. The risk and additional development it would take to have Falcon 9 land its launch mounts would be insane at this stage in the booster's life. If they were planning to roll this out with Block V we would have seen a test. Also, there is no way you could land without legs on the ship due to the imprecision of the ship, and there is no way in hell that Falcon Heavy boosters could all land on their mounts. So, it is not going to happen. Right? He misspoke right?
I guess the first experiment could be to paint four two foot circles on the the concrete at LZ-1. Costs less than a hundred dollars. Important to paint the circles before the landing. Matthew