Where will F9 flights 14 & 15 attempt "solid surface" landings?

[cambrianera]

In the video you can see how they repeatedly pick the booster up at each end with no center slings (go to 0:13) and how the booster on the right is visibly bent in the middle until the hook it up to the semi truck (0:05).  Now I can see how strong the things are against bending forces and lateral stress.

I don't see any evidence of bending.  With a little bit of pressurization, the stage ought to be incredibly rigid.

I'm a mechanical engineer, not structural, but from the few structural classes I did take I don't think being pressurized is going to make very much difference on how much a stage would sag when lifted at both ends.

http://shellbuckling.com/papers/classicNASAReports/NASASP-8007.pdf figure 6

Pressurization  is going to make a lot of difference in final bending strenght of the tank, but stiffness of the stage (i.e. deflection under a given load) remains the same with or without pressure.

I find that very unlikely and would like a citation. Pressurization makes a huge difference in stiffness.

Stiffness ( http://en.wikipedia.org/wiki/Stiffness ) is the property of an object (due to a combination between material properties and geometry) to resist to deformation under load.
Flexural stiffness of the stage is due to the reaction of the skin; gas inside gives no contribution to resistance to flexing forces.
This must not be confused with strenght (or resistance):
-axial resistance in vertical position -> skin in tension because pressure is actually relieved by applied static load;
-overall resistance to bending -> pressure applied stabilizes shape and avoid local buckling and collapse.
Strenght (or resistance http://en.wikipedia.org/wiki/Strength_of_materials) has no direct reference to deformation, is related to the breaking point of material or objects.
Rubber can be very strong, but for his nature never stiff.
 
Structural classes. as cited by wannamoonbase, are for that: understanding how it works, and ain't always simple.

[cambrianera]

Take a rubber balloon. If it is flat, it is floppy. If it is pressurized, it is stiff. I dont see why that should be different for a rocket.

It is stiffer because his shape changes, this is the effect of pression on your rubber balloon.
Take a sheet of paper, flex it; that's easy.
Roll it forming a tube and try to flex it; suddenly it becames stiffer, much stiffer.
Shape is a very important parameter for stiffness: more distance between members in tension and members in compression means more stiffness.

[gosnold]

From Musk's twitter:
Testing operation of hypersonic grid fins (x-wing config) going on next flight
https://twitter.com/elonmusk/status/536258543675252739

[rpapo]

This isn't Engineering 101, but it isn't post-graduate study either.  The rocket walls are relatively thin metal.  They are somewhat reinforced (with stringers) against losing their shape, but that strength lies mostly along the walls, not through them.  Furthermore, that strength is mostly in tension, not in compression.

When you apply a transverse force to the rocket (for instance, by fixing the bottom end to the ground and then pulling the top sideways (or blowing wind across it)), then in the absence of other forces there will be a compressive force on the rocket wall away from the wind, and a tensile force on the rocket wall that has the wind pushing on it.  If nothing else were done, there would be a tendency for the tube to buckle on the side away from the wind, once the compressive force exceeds the compressive strength of the wall.

But, if you pressurize the tank, then you have a tensile force added uniformly to the all sides of the rocket.  The side away from the wind will not buckle until the compressive force due to the wind exceeds the tensile force due to the internal pressure.  That net compressive force must exceed the rocket's wall strength for buckling to occur.

It is possible, if the pressurization is too high, for the windward side to suffer tensile failure, but that would take some doing...

Another example would be in how concrete is reinforced for use in bridges.  Concrete is the opposite of metal: it is good for compression and poor in tension.  So to make it stronger, you compress it, so you don't have a net tension right away.

Was that clear as mud?  My profession is computer programmer, but my degree was mechanical engineering.

[rpapo]

From Musk's twitter:
Testing operation of hypersonic grid fins (x-wing config) going on next flight

And they're WHITE!

Also notice the leading edge fairings that weren't on Grasshopper.

[rpapo]

While I agree with what you said, remember that F9R Dev 1 spent a lot time in TX upright with no other support than at the base and it can get pretty windy in McGregor.

I wasn't saying that Falcon was doomed to buckle.  I was simply trying to explain how pressurization can help stabilize the rocket's structure.  Too many people here seemed to be having trouble understanding why, so I tried to explain it as simply as I could.  Not that it was "simple"...

But if the rocket can hold its own without internal pressurization, so much the better.  Apparently there have been rockets around that couldn't do it on their own.

[Chris Bergin]

Let's give the cool ship a standalone thread:
http://forum.nasaspaceflight.com/index.php?topic=36140.0

[guckyfan]

Was that clear as mud?  My profession is computer programmer, but my degree was mechanical engineering.

Very clear, thanks.

[guckyfan]

The grid fins are different to the McGregor ones. The new ones have a straigt edge, the old ones had a pointy end. The new ones are also curved, the old ones were flat.

[pippin]

Ah, another design feature of N1 also found on F9. Getting more and more

[Jason1701]

Ah, another design feature of N1 also found on F9. Getting more and more

What are the others?

[pippin]

Engine arrangement. Use of large number of small engines on F9H, all-kerosene design, same engine design for first and second stage,... If I think about it I'll probably find more

[pippin]

Oh, supposed engine-out capability (now that's just a result of the many small engines)

[Robotbeat]

Oh, supposed engine-out capability (now that's just a result of the many small engines)

It actually worked for Falcon 9 v1.0 (and Saturn V).

[pippin]

Yea, but right now I don't remember whether it worked on N1. Pi know there was one engine-failure related failure when KORS failed but I don't remember whether on other flights failed engines at least weren't the cause of failures. Vibrations and lack of control authority were the reasons for the two other failures, weren't they?

[sghill]

Can anyone here make an educated guess about how long it will take the 'huge-ish' barge to transit from Louisiana to the vicinity of Cape Canaveral? Those things are not race boats and the distance substantial. I get anywhere from 4 days to 4 weeks depending on the guesses I make, and if they want to use this thing on CRS-5 then it may need to depart fairly soon.

Not just soon.  Any day now.  They'll need to perform check out work, testing, and operations rehearsals before towing that bad boy out to sea for the big show.  And even that's assuming that this thing doesn't have to make several more stops to finish up the construction and "stuffing out" of all the systems.  December 9 is less than a month away.

My $0.05 bet, is that it's either going to be revealed in a few days (this week IMHO) when they take it out of its bearth in completed, or nearly completed form, or I don't think it's going to be ready for the Dec. 9 flight.  I'm thinking the latter is most likely until I see a picture of this thing in the press.

Booyah! Nailed it!!!

Elon Musk ‏@elonmusk
Autonomous spaceport drone ship. Thrusters repurposed from deep sea oil rigs hold position within 3m even in a storm.

Elon Musk ‏@elonmusk
Base is 300 ft by 100 ft, with wings that extend width to 170 ft. Will allow refuel & rocket flyback in future.

How's that hat tasting this morning fellas? Do you like fedoras with salt or ketchup?

[Kabloona]

Kudos to sghill for correctly predicting wings. I was a doubter, but fortunately did not promise to eat my hat if I was wrong. Will be having my normal tasty breakfast of a glazed doughnut instead. 

[matthewkantar]

The grid fins are different to the McGregor ones. The new ones have a straigt edge, the old ones had a pointy end. The new ones are also curved, the old ones were flat.

I believe the old fins were curved to the shape of the rocket body. The shape is definitely different.

Matthew

[mvpel]

Yes, the Dev1 fins were curved. I got some decent photos when I was there and the flight video makes it pretty evident. These are wider due to the added grid on either side. Nice to see the fairing design - more blunt than I was picturing.

[Rocket Science]

The grid fins are different to the McGregor ones. The new ones have a straigt edge, the old ones had a pointy end. The new ones are also curved, the old ones were flat.

I believe the old fins were curved to the shape of the rocket body. The shape is definitely different.

Matthew

Ha, they’re going with my MOAB idea from a few years ago...

http://forum.nasaspaceflight.com/index.php?topic=21923.msg787784#msg787784