Author Topic: Will SpaceX experiment with legless F9 Booster landing on a structure?  (Read 10529 times)

Offline Ludus

  • Full Member
  • ****
  • Posts: 726
  • Liked: 250
  • Likes Given: 112
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.

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 3294
  • California
  • Liked: 2561
  • Likes Given: 1569
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.

Maybe... But several years down the road IMO. Once F9 has shown the required precision repeatedly. (and it is nowhere close at the moment) But F9 also lacks bottom mounted thrusters that the BFR/ITS booster will have that will give it extra aiming ability.

But that extra leg weight doesn't really add much extra capability. (I seem to recall reading that taking off 1 ton of mass from the first stage would only add 100kg of payload, but don't quote me on it)

Online Semmel

  • Full Member
  • ****
  • Posts: 1006
  • Germany
  • Liked: 697
  • Likes Given: 2068
I think the consensus to the question was that F9 would require thrusters at the bottom to achieve the landing precision. That would be a major redesign which they dont do. Also, it would require stronger thrusters than the cold gas thrusters which are used at the top of the stage at moment. Lots of no-goes all around.

@edit: Lars-J ninjad me ;)
« Last Edit: 07/11/2017 07:22 AM by Semmel »

Offline AncientU

  • Senior Member
  • *****
  • Posts: 4551
  • Liked: 2676
  • Likes Given: 3772
More likely would be to use a spare F9 core and modify it for landing practice, maybe at Spaceport (unless they've completely given up on that site).  Modifying the F9 line at this point is a non-starter.  Block 5 is supposed to be the end of evolution for now.
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Online cppetrie

  • Full Member
  • ***
  • Posts: 307
  • Liked: 146
  • Likes Given: 3
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.

Offline RoboGoofers

  • Full Member
  • *
  • Posts: 183
  • NJ
  • Liked: 69
  • Likes Given: 144
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 imagine they will do the bolded part. They are, seemingly, spread a bit thin with all their projects and goals, but it would make sense to do this before they go too far down the path of engineering cradle landing into ITS.

The only reason they wouldn't is if they can't make ITS work without it and therefore it's do-or-die (unlikely), or if they are so confident in their simulations and F9 data so far that they don't feel it necessary, or they don't feel F9 scale will be illuminating enough.

Offline RoboGoofers

  • Full Member
  • *
  • Posts: 183
  • NJ
  • Liked: 69
  • Likes Given: 144
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.

nothing i've seen suggests a hover. it'll still be a suicide burn, just with greater accuracy because of the extra, stronger thrusters.

Offline Doesitfloat

  • Full Member
  • **
  • Posts: 217
  • Detroit MI
  • Liked: 303
  • Likes Given: 124
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.
« Last Edit: 07/11/2017 05:52 PM by Doesitfloat »

Offline RoboGoofers

  • Full Member
  • *
  • Posts: 183
  • NJ
  • Liked: 69
  • Likes Given: 144
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.

GH1&2 had specific fuel loads and ballast for the test flights they were flying, and could only "hover" in a specific window.

Dragon 2 did a hover test, but was suspended from a crane. it wasn't a free flight test, and there's no indication they'll hover to land it's when operational.

You could say "the only operational rocket SpaceX had made doesn't hover, so there's nothing to suggest a production rocket that lands in a cradle will hover."
« Last Edit: 07/11/2017 06:10 PM by RoboGoofers »

Offline rpapo

  • Cybernetic Mole
  • Full Member
  • ****
  • Posts: 1029
  • Michigan, USA
  • Liked: 461
  • Likes Given: 375
Not only that, but hovering is incredibly expensive in fuel.  The more hover margin you build into a rocket, the less it can boost towards orbit.
An Apollo fanboy . . . fifty years ago.

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 3294
  • California
  • Liked: 2561
  • Likes Given: 1569
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.

nothing i've seen suggests a hover. it'll still be a suicide burn, just with greater accuracy because of the extra, stronger thrusters.

Exactly! One has nothing to do with the other. (hover != increased accuracy)

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.

Sure, but they are limited by the engines they use and basic physics... The M1D can only throttle down to 40% of its full thrust. And a leg-less stage is going to be ~2 tons lighter (no legs), which makes hovering even harder.

The point remains that landing accuracy is a separate thing from hover ability. One does not require the other. Would it be nice to do both? Sure... ITS will have more engines and should be able to hover more easily, but for an F9 it will be tricky.

« Last Edit: 07/11/2017 06:11 PM by Lars-J »

Offline Coastal Ron

  • Senior Member
  • *****
  • Posts: 3225
  • I live... along the coast
  • Liked: 2054
  • Likes Given: 2446
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.

From what we know the Block 5 Falcon 9 is supposed to be the last iteration before they stop product development on the Falcon 9, and when they do that they are shifting a major amount of their engineering resources to the BFR/BFS.

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.

So maybe in a decade, but at that point the market may have changed to just using the BFR/BFS architecture, which is supposed to be completely reusable, whereas the Falcon 9 architecture at this point is still dumping the 2nd stage. Which means we may be more likely to see a Falcon 9 retirement than a Falcon 9 re-engineering effort that provides little benefit.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline rakaydos

  • Full Member
  • **
  • Posts: 203
  • Liked: 72
  • Likes Given: 2
More likely, they'll build a "Grasshopper 2" test vehical for Raptor and the hot methane RCS, to test cradle landings using  the hardware they'll be using on the actual vehical.

Offline dorkmo

  • Full Member
  • ****
  • Posts: 641
  • Liked: 292
  • Likes Given: 757
i think it would actually be pretty straight forward to design this. It would need to be big to accomidate current f9 abilites and have some massive hydraulic systems for agility and power. Maybe tweak the hooks on the falcon itself to be more forgivable.
maybe the roomba team will do this next.

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7494
  • N. California
  • Liked: 3822
  • Likes Given: 803
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.
ABCD - Always Be Counting Down

Offline Coastal Ron

  • Senior Member
  • *****
  • Posts: 3225
  • I live... along the coast
  • Liked: 2054
  • Likes Given: 2446
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.

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...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7494
  • N. California
  • Liked: 3822
  • Likes Given: 803
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.

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 don't think it will help with commercial F9.
- I am on the fence on whether it will be good use for BFR development.

See if F9 wasn't already a working platform where "everything else" has checked out, then it would be wasted time and resources to build a small, incompatible, unrelated test platform.  It would be like making Grasshopper using different engines, fuel, and structure from F9.

But - F9 exists, flies, has flight rules that are well characterized, and there's plenty of them to spare.  So if they can learn anything from it - it's a small investment, and will cost less than "one more failure" at BFR scale.

So I don't think it's a non-starter.  It's a reasonable option, and they can go either way.
« Last Edit: 07/12/2017 05:00 AM by meekGee »
ABCD - Always Be Counting Down

Online guckyfan

  • Senior Member
  • *****
  • Posts: 6246
  • Germany
  • Liked: 1547
  • Likes Given: 1325
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.

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7494
  • N. California
  • Liked: 3822
  • Likes Given: 803
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.

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.
ABCD - Always Be Counting Down

Offline mikelepage

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 doubt we'll see a legless F9 booster anytime soon, but what about second stage?
To shamelessly quote myself (and also so you can reply in the appropriate thread):

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.

Offline Oersted

  • Member
  • Full Member
  • ****
  • Posts: 659
  • Liked: 302
  • Likes Given: 174
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.

However, at landing the F9 first stage is very bottom-heavy due to carrying almost no fuel. We have seen it tilt very much after landing without toppling over. I don't think its slenderness is such an important factor.

Offline RoboGoofers

  • Full Member
  • *
  • Posts: 183
  • NJ
  • Liked: 69
  • Likes Given: 144
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.

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.
« Last Edit: 07/12/2017 04:45 PM by RoboGoofers »

Offline Norm38

  • Full Member
  • ****
  • Posts: 912
  • Liked: 304
  • Likes Given: 443
I vote for the Grasshopper 2 approach. Raptors, methane and BFR diameter.

Offline Ludus

  • Full Member
  • ****
  • Posts: 726
  • Liked: 250
  • Likes Given: 112
I vote for the Grasshopper 2 approach. Raptors, methane and BFR diameter.

That seems more likely to be necessary. With F9 it's just cheaper, in the sense that they have a lot of earlier run flight proven boosters laying around. With Block 5 coming out better suited to reuse, they may not get used for orbital missions. It wouldn't take very much to use a couple of them to play with legless landing designs.

As far as extra capability it would be the mass of the legs minus any thrusters that have to be bolted on in their place. Extra would apply to mass in the S2 at separation so it could be extra propellant and/or payload. Whether it matters would be a mission by mission issue but it might prove useful.

Offline Ludus

  • Full Member
  • ****
  • Posts: 726
  • Liked: 250
  • Likes Given: 112
They 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.

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 3294
  • California
  • Liked: 2561
  • Likes Given: 1569
They 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.

No, no, no. What would be the point if it doesn't match the BFR landing system? Only one part will move, and the booster already does, so...

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31144
  • Cape Canaveral Spaceport
  • Liked: 9396
  • Likes Given: 297
They 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.

How does that work over a launch duct and then how does it hold on for launch?

Offline Space Ghost 1962

  • Senior Member
  • *****
  • Posts: 2268
  • Whatcha gonna do when the Ghost zaps you?
  • Liked: 2032
  • Likes Given: 1496
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.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 5722
  • Everyplaceelse
  • Liked: 712
  • Likes Given: 4121
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.
Of those probably 2 is the easiest, with differential GPS capable of giving location to within cm.
Getting the stage to physically move to where you want it to be is going to be harder.  :(

AFAIK the other 3 points are completely unexplored territory.

I keep seeing the Soyuz takeoff, with all those arms swinging away from it and (sort of) imagining it happening in reverse. Completely unrealistic, given the massive change in configuration between T/O and landing but it's that idea that I can't get out of my head.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline garidan

  • Member
  • Posts: 93
  • Italy
  • Liked: 14
  • Likes Given: 19
I'm too for a legless grasshopper based on a reused end-of-life first stage, with only one engine and some ballast to simulate a BFR as for thrust to weight ratio.
It would be ready in a short time and help a lot to refine a scaled down cradle, and tweak the problems with no fear to loose much.
Once that is set, they could refine it using a 1 mini raptor legless grasshopper to practice with throttle and test near to actual use, a scaled down BFR - true raptor.
Slowing down and almost hovering gives you more time to adjust the horizontal position, and minimize the energy on impact (to avoid damage to stage), but can damage the cradle and costs fuel, if done too long.
BFR could hover because of its thrust to weight ratio, using only 1 or few engines throttled down.
Falcon without ballast could not.
I guess something similar could be done to test carbon fiber for the rocket, they need to build up experience before going full scale.
Divide et impera complex problems is better than all or nothing approach, in my opinion.
Remeber tic toc  Intel approach to CPU development ?


Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 953
  • Liked: 355
  • Likes Given: 326
I'd use some old - and current - passive technology to land the BFR.

The Soviet 1960s 'Kontakt' LOK/LK docking system used a stinger on one spacecraft and a grid target on the other to allow a robust encounter between both spacecraft after the LK returned to Lunar orbit. There's no reason to doubt this would have worked.

The current Augusta-Westland AW101 'Merlin' helicopter (no relation) also uses a stinger system to land on the UK RN's five new River Class Offshore Patrol Vessels. A 3.5m x 3.5m titanium alloy honeycomb plate is located on the aft flight deck, and locks down the aircraft as it lands. The Merlin is about the same size as a Sea King, and was the cancelled VXX POTUS VVIP transport vehicle.

On a *very* old front, the early 1950s Collier's Monship used a central fifth leg to sense touchdown and control the final landing thrust of the giant Von Braun craft - so nothing new there, either!

An almost 'ball and joint' construction using fearsomly strong materials and an RCS mounted high on the rocket would do the job for Grasshopper 2 or BFR!
« Last Edit: 09/10/2017 12:53 AM by Bob Shaw »

Offline alang

  • Full Member
  • *
  • Posts: 169
  • Liked: 42
  • Likes Given: 2
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.

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.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 5722
  • Everyplaceelse
  • Liked: 712
  • Likes Given: 4121

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.
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.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Mader Levap

  • Full Member
  • ****
  • Posts: 913
  • Liked: 367
  • Likes Given: 359
..or simply land in different place. ::)
Be successful.  Then tell the haters to (BLEEP) off. - deruch
...and if you have failure, tell it anyway.

Offline Ludus

  • Full Member
  • ****
  • Posts: 726
  • Liked: 250
  • Likes Given: 112
..or simply land in different place. ::)

It would be useful to an eventual ITS land on launch pad system to just develop legless landing at the separate LZ. It would also increase F9 lift capability. It would reduce turn around time somewhat. So yeah, first learn to land legless with existing hardware then maybe some of what's learned to can be applied to doing that at the launch pad so turn around is at an absolute minimum.

Offline raketa

  • Full Member
  • *
  • Posts: 199
  • Liked: 34
  • Likes Given: 22

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.
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?

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 5722
  • Everyplaceelse
  • Liked: 712
  • Likes Given: 4121
What about a landing structure that will move in after launch, before landing occur?
It's still extremely large and heavy.

But what I'm wondering about this scheme is How it's going to help steer the booster to landing.

When you look at fasteners on an assembly line the hole exerts force on them to guide them into position.

I doubt the tank structure can survive any forces strong enough to move it's centre line. Likewise a tapered structure implies the first point of contacts would be the engine bells. Again I'm doubtful they can transmit enough load to nudge the stage without being damaged.

I get this idea of lowering ITS costs by testing aspects of the design on the F9 booster or US but I think they are just too different.  :( There ConOps are completely different, their fuel and structure equally so.
Musk has indicated they be showing a downsized ITS 21, not 42 engines. using the 1/4 scale Raptor for that would still be a very formidable vehicle but allow them to test most of this out.
 
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline spacenut

  • Senior Member
  • *****
  • Posts: 2064
  • East Alabama
  • Liked: 284
  • Likes Given: 184
How much payload capability would F9 have without legs?

Offline titusou

  • Member
  • Posts: 30
  • Taiwan
  • Liked: 31
  • Likes Given: 0
In order to do cm-level horizontal accuracy, wasn't that mean extra RCS at the bottom of 1st stage? Instead of just on top of 1st stage? Since CG is closed to bottom, the top RCS is quite useless for horizontal movement.

Or the main engine gimbal is really "that good" ?

Titus

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 3294
  • California
  • Liked: 2561
  • Likes Given: 1569
How 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.

Offline spacenut

  • Senior Member
  • *****
  • Posts: 2064
  • East Alabama
  • Liked: 284
  • Likes Given: 184
Without the legs, if they go that route, could F9 also land on drone ship with the right cradle for slightly larger payloads?

Offline hkultala

  • Full Member
  • ****
  • Posts: 570
  • Liked: 134
  • Likes Given: 67
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.

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.

Your idea does not work. Counterweights are not springs. The counterweight has a huge inertia. The rocket also has huge inertia. In your proposition the stationary counterweight meets a moving rocket in an instant. This causes huge instant force between the rocket and the counterweight.

This is not practically at all better than the rocket just hitting the hard platform.

Springs work because they do not have huge inertia.

Offline wannamoonbase

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 2643
  • Denver, CO
    • U.S. Metric Association
  • Liked: 513
  • Likes Given: 879
I think you still end up with an active cradle that gets you the last 0.5-1 meter.  Whether on sea or land.

A grasshopper like vehicle that starts with baby steps (centimeters or less) then working up to simulate returning boosters is only logical.

One of the biggest advantages, other than weight and leveling the booster, could be having a TEL readily attach to a cradle then lower the stage to horizontal.  Then it can be protected from the elements quickly.

It's a reach and longer term development no doubt, but it's interesting to think about.
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline Ludus

  • Full Member
  • ****
  • Posts: 726
  • Liked: 250
  • Likes Given: 112
How 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.

While the final payload might only increase by ~10% of the removed mass, depending on the orbit, the amount of extra propellant in the S2 could be considerably more. That might be meaningful for S2 recovery and reuse where margins would be very tight.

Online Nibb31

  • Full Member
  • *
  • Posts: 167
  • France
  • Liked: 79
  • Likes Given: 4
I wonder if a system like this would work (forgive the crude drawing):


The idea is to have a set of wires (or solid beams). The wires would move in to catch the booster by using a set of sensors. The booster would have retractable hooks (these could even be combined with grid fins if the ITS has them). Once captured, the booster would hang from the hooks.

After engine cutoff, the cable supports can easily move the booster onto the launch mount. It can lower or raise the booster by slackening or tightening the cables.

This has several advantages:
- The actual launch cradle is fixed, which allows it to be more robust.
- The system can also be used to load the booster onto a carrier vehicle for moving the booster away for maintenance or storage.
- The same capture system can be used for different sizes of boosters, including F9, and upper stages.
« Last Edit: 09/19/2017 04:41 PM by Nibb31 »

Online Nibb31

  • Full Member
  • *
  • Posts: 167
  • France
  • Liked: 79
  • Likes Given: 4
This is a variant of the above, inspired by the snare grappling system used by Canadarm. The wires are rolled into dispensers that control the tension of the wire. Each wire is attached to a rotating ring. There are 6 wires, 6 dispensers, and six rotating rings.



This system is a bit more complex, as the weight of the booster is supported by the tension control drums. It does offer more redundancy though.
« Last Edit: 09/19/2017 04:54 PM by Nibb31 »

Offline Welsh Dragon

  • Full Member
  • *
  • Posts: 196
  • Liked: 187
  • Likes Given: 25
Not this again....

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 7806
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2099
  • Likes Given: 4888
Hey, it's my old "grapple snare" idea from years ago for securing Falcon on the drone ship! ;D
"The laws of physics are unforgiving"
~Rob, Physics instructor, aviator, vintage auto racer

Offline alang

  • Full Member
  • *
  • Posts: 169
  • Liked: 42
  • Likes Given: 2
I'm sure there's scope for discussion about some Heath Robinson/Rube Goldberg affair using the kind of powerful fans used in skydiving simulators, but to push the sides of the rocket. It would have the advantage of being a 'no  touch system'.
Would be a large structure and  might need a small power station to run it though...
Note to mods: is there room for a sandpit/Rube Goldberg thread for those of us who are engineering challenged.

Online HVM

  • Member
  • Posts: 78
  • Finland
  • Liked: 78
  • Likes Given: 62
My vote is for swarm of tiny drones to push booster sideways.

(No I don't mean unmanned multicopters but gene-engineered bees)

Offline chrisking0997

  • Full Member
  • **
  • Posts: 253
  • NASA Langley
  • Liked: 71
  • Likes Given: 182
fans, arms, cables, bees...we'd be in for a real treat of blooper reels.   Ill throw my guess into the ring: magnets.


as for testing, I gotta think some sort of Grasshopper-like program would be spun up for this.  Too many variables and dependence on launch schedule to just try to tack in on
Tried to tell you, we did.  Listen, you did not.  Now, screwed we all are.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 26609
  • Minnesota
  • Liked: 6483
  • Likes Given: 4703
I vote for bees.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline ZachF

  • Full Member
  • **
  • Posts: 252
  • Park City, UT, USA, Earth
  • Liked: 119
  • Likes Given: 22
I vote for bees.

NASA/SpaceX Rocket Recovery Beekeeper would sound impressive on any resume.

Offline RoboGoofers

  • Full Member
  • *
  • Posts: 183
  • NJ
  • Liked: 69
  • Likes Given: 144

Offline DreamyPickle

  • Member
  • Posts: 45
  • Home
  • Liked: 22
  • Likes Given: 1
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.

Offline mme

  • Full Member
  • ****
  • Posts: 976
  • Santa Barbara, CA, USA, Earth, Solar System, Milky Way Galaxy, Virgo Supercluster
  • Liked: 1201
  • Likes Given: 2942
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.
I think the issue is more the complex Rube Goldbergesque suggestions that get batted around. Whatever SpaceX does, it will start "simple," have as few interdependencies/modes of failure as possible and be refined over time.  Before SX succeeded landing on the ASDS some people were sure that:
1. The ASDS had to communicate with the F9.
2. They should have a swarm of drones to measure and communicate wind speed at various altitudes.
3. They should add complicated flying wire systems or inflatable "catcher's mitts" to help support the rocket.

What SX did was have the ASDS hold station and land where the ASDS should be.  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.
Space is not Highlander.  There can, and will, be more than one.

Tags: