Author Topic: Will SpaceX experiment with legless F9 Booster landing on a structure?  (Read 16982 times)

Offline Oersted

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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

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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

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I vote for the Grasshopper 2 approach. Raptors, methane and BFR diameter.

Offline Ludus

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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

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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.

Online Lars-J

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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

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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

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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

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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

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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

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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 Moonship 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: 09/29/2017 11:13 PM by Bob Shaw »

Offline alang

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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

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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

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..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

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..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

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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

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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.

Online spacenut

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How much payload capability would F9 have without legs?

Offline titusou

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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

Online Lars-J

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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.

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