Author Topic: Landing legs design : SpaceX vs Blue Origins  (Read 15250 times)

Offline b0objunior

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Landing legs design : SpaceX vs Blue Origins
« on: 01/24/2016 04:00 AM »
Hello,

Ok, I want to know what is the feedback from you on the design differences of the landing legs from SpaceX and Blue Origins. Why would they be so different and which is better in your opinion?

Thanks.

Offline JBF

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #1 on: 01/24/2016 04:54 AM »
Hello,

Ok, I want to know what is the feedback from you on the design differences of the landing legs from SpaceX and Blue Origins. Why would they be so different and which is better in your opinion?

Thanks.

Based on what I've seen, it all comes down to size.  The falcon 9 is a much taller rocket and it needs a wider stance to be stable.  With a wider stance and a heavier rocket the legs must be more substantial.  The weight penalty to make them as articulate as New Shepard's legs would be high.
"In principle, rocket engines are simple, but that’s the last place rocket engines are ever simple." Jeff Bezos

Offline cambrianera

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #2 on: 01/24/2016 12:24 PM »
Layout of SpaceX landing gear is simple, but execution has been complicate:
-Telescopic cylinder, with a swing movement of over 140°, many seals and locking rings.
-"A" frame, big, complex and heavy, but effectively carrying no load.

Personally I prefer the general layout of New Shepard landing gear, at the cost of more joints you get simpler struts, with reliable deployment and steady open position.
That said I don't know much of it other than the general layout, therefore no way to say better or worse.
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Offline funkyjive

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #3 on: 01/24/2016 02:46 PM »
New Shepard also does a preflight check by extending, locking, then retracting the gear giving some extra confidence prior to a flight commit. The f9 legs are one way.

Online kevinof

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Landing legs design : SpaceX vs Blue Origins
« Reply #4 on: 01/24/2016 04:05 PM »
Remember that blue Shepard is about the size of one falcon 9 leg. It's all to do with weight and forces. I've no doubt that if BO ever build a reusable orbital stage it's leg design will be more like SpaceX.
« Last Edit: 01/24/2016 05:56 PM by kevinof »

Offline John Alan

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #5 on: 01/24/2016 05:17 PM »
It's like comparing a car tire... a semi truck tire... and a 747 tire...
Each is designed to the need at hand...

Both leg designs have their pluses and minuses... from an engineering standpoint... IMHO
I think SpaceX worked off their 'in use' rocket structure and weigh savings as key items...
It was an "add on" in other words... but it fit the need at hand...

Both may have design flaws still...
Only using them and time passing will find out...
IMHO...

Offline meekGee

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #6 on: 01/24/2016 06:56 PM »
Layout of SpaceX landing gear is simple, but execution has been complicate:
-Telescopic cylinder, with a swing movement of over 140°, many seals and locking rings.
-"A" frame, big, complex and heavy, but effectively carrying no load.

Personally I prefer the general layout of New Shepard landing gear, at the cost of more joints you get simpler struts, with reliable deployment and steady open position.
That said I don't know much of it other than the general layout, therefore no way to say better or worse.

SpaceX's design is motivated by mass.   The main compression strut, when extended, is a cylinder, which is the lightest possible compression beam.    I also initially disliked the multiple slip joints in each leg, but I came to understand where they're coming from.
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Offline Robotbeat

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #7 on: 01/24/2016 07:19 PM »
SpaceX will no doubt eventually use a different leg design for their rockets (post-Falcon). I doubt Blue Origin's is perfect, either. And it is a suborbital craft, so yeah, very different story.
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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #8 on: 01/26/2016 08:12 AM »
It would seem to me that the BO landing system provides a lot less stability once they would be 'forced' to start barge landings as well on future rockets. The wide base of SpaceX's landing gear combined with the very low center of mass is what would keep the rocket from tipping over on a barge after landing, especially with the barge rolling around in de waves. BO's current system on a larger rocket would probably mean a lot of tipped over rockets before a crew can get aboard to secure it.

Online sanman

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #9 on: 01/27/2016 02:23 AM »
It would seem to me that the BO landing system provides a lot less stability once they would be 'forced' to start barge landings as well on future rockets. The wide base of SpaceX's landing gear combined with the very low center of mass is what would keep the rocket from tipping over on a barge after landing, especially with the barge rolling around in de waves. BO's current system on a larger rocket would probably mean a lot of tipped over rockets before a crew can get aboard to secure it.

Surely Blue won't keep those same legs for larger rockets. Their orbital vehicle will probably have lighter and longer legs - but maybe they'll have their own original look that's different from F9R's legs. Hoping there'll be some more one-upsmanship.

Offline guckyfan

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #10 on: 01/27/2016 06:36 AM »
Surely Blue won't keep those same legs for larger rockets. Their orbital vehicle will probably have lighter and longer legs - but maybe they'll have their own original look that's different from F9R's legs. Hoping there'll be some more one-upsmanship.

A Blue rocket won't be as long and slender as Falcon 9. The legs can be very different than the wide spreading legs of Falcon.

Offline Elmar Moelzer

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #11 on: 01/27/2016 11:45 AM »
A Blue rocket won't be as long and slender as Falcon 9. The legs can be very different than the wide spreading legs of Falcon.
Would that mean that they wont do road transport?

Offline rpapo

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #12 on: 01/27/2016 12:15 PM »
A Blue rocket won't be as long and slender as Falcon 9. The legs can be very different than the wide spreading legs of Falcon.
Would that mean that they wont do road transport?
Does it matter?  I thought they intended to build the factory a couple of miles away.
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Offline guckyfan

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #13 on: 01/27/2016 12:43 PM »
A Blue rocket won't be as long and slender as Falcon 9. The legs can be very different than the wide spreading legs of Falcon.
Would that mean that they wont do road transport?
Does it matter?  I thought they intended to build the factory a couple of miles away.

This. Most, initially all launches, would be from the production site. Plus they are reusable, which means less transport and there is a harbour nearby, so quite easily transportable anywhere.

Edit. The first launch vehicle is supposed to be one engine. It might even be road transportable. The next generation larger vehicle won't.
« Last Edit: 01/27/2016 12:44 PM by guckyfan »

Online sanman

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #14 on: 01/27/2016 01:24 PM »
So was the decision to locate factory and launch site together done with the road transport constraint particularly in mind?

Offline leaflion

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #15 on: 01/27/2016 02:39 PM »
Has anyone calculated the tipover radius/height for NS vs F9?  I would bet that NS is has a larger tipover radius than F9 per unit height, which would make it more stable (assuming similar CG height/height, which I think is hard to know)...

Does anyone have these numbers?
« Last Edit: 01/27/2016 02:40 PM by leaflion »

Offline mvpel

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #16 on: 01/29/2016 12:09 PM »
Has anyone calculated the tipover radius/height for NS vs F9?  I would bet that NS is has a larger tipover radius than F9 per unit height, which would make it more stable (assuming similar CG height/height, which I think is hard to know)...

Does anyone have these numbers?
A post on another site which I can't seem to find at the moment estimated using mass and CG numbers for Falcon 9 that it would take a 23 degree tilt to move the center of mass past the end of the legs.
"Ugly programs are like ugly suspension bridges: they're much more liable to collapse than pretty ones, because the way humans (especially engineer-humans) perceive beauty is intimately related to our ability to process and understand complexity. A language that makes it hard to write elegant code makes it hard to write good code." - Eric S. Raymond

Offline rpapo

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #17 on: 01/29/2016 01:01 PM »
Has anyone calculated the tipover radius/height for NS vs F9?  I would bet that NS is has a larger tipover radius than F9 per unit height, which would make it more stable (assuming similar CG height/height, which I think is hard to know)...

Does anyone have these numbers?
A post on another site which I can't seem to find at the moment estimated using mass and CG numbers for Falcon 9 that it would take a 23 degree tilt to move the center of mass past the end of the legs.
Don't forget the dynamics of the problem, though: on the barge there will be a sinusoidal side-to-side rocking motion, which motion will impart a momentum to the entire rocket, and the legs have to not only absorb that energy, but do so quickly enough that the momentum doesn't result in overshooting that critical tilt angle.

In other words, if the barge tilted all the way between +23 and -23 degrees, even slowly, I don't think the rocket would remain upright for long.

Also consider another worst case: the rocket is tilted directly in line with one of its legs.  In that case, the leg in that direction may take a load far higher than any of the other three, the most extreme being right before tipping, when that leg is taking nearly 100% of the tilted rocket's weight.  How much can one of these legs take before they give?
« Last Edit: 01/29/2016 01:50 PM by rpapo »
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Online alang

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #18 on: 01/29/2016 02:08 PM »
Does the Spacex approach lend itself, with modification, more to using the legs as an airbrake at partial extension than the blue origin approach

Offline mvpel

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Re: Landing legs design : SpaceX vs Blue Origins
« Reply #19 on: 01/30/2016 09:42 PM »
In other words, if the barge tilted all the way between +23 and -23 degrees, even slowly, I don't think the rocket would remain upright for long.

Also consider another worst case: the rocket is tilted directly in line with one of its legs.  In that case, the leg in that direction may take a load far higher than any of the other three, the most extreme being right before tipping, when that leg is taking nearly 100% of the tilted rocket's weight.  How much can one of these legs take before they give?

Nobody seems to grasp that the ASDS is the size of a football field, and for it to be tilted at 23 degrees bow to stern the bow would be about 120 feet higher than the stern, and port to starbord it would be 40 feet higher. In that kind of sea state, a previously-flown rocket tipping over would be the least of their concerns.

"Ugly programs are like ugly suspension bridges: they're much more liable to collapse than pretty ones, because the way humans (especially engineer-humans) perceive beauty is intimately related to our ability to process and understand complexity. A language that makes it hard to write elegant code makes it hard to write good code." - Eric S. Raymond

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