Author Topic: SpaceX Falcon 9 v1.1 - SpX-6/CRS-6 DRAGON - Discussion Thread  (Read 502831 times)

Offline Mapperuo

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Sad to see CNN news article title is 'SpaceX rocket lands, falls over' - did someone tell them it was a successful launch?
- Aaron

Online ugordan

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Sad to see CNN news article title is 'SpaceX rocket lands, falls over' - did someone tell them it was a successful launch?

There was a launch involved???

Ahh, so that's what this thing was...
« Last Edit: 04/14/2015 10:04 pm by ugordan »

Offline Fr4nK

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Based on common sense. You aim for the X or you aim for no lateral motion while landing somewhere on the barge. Bigger barge means more margin

Wrong and neither is it common sense .  The rocket is not aiming for the barge, it is aiming for a spot on the ocean.  The barge happens to be at the spot.
Interresting. I would guess at the last burn it would start to aim for the barge and not leave it to the barge to get exactly at the right spot. I might be wrong.

Offline AJA

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Question: Assuming that they DON'T manage to null out all horizontal velocity, and that the stage still has some tipping motion about the legs, in the instant after touch down.... is this something that they can sense and remedy with another cold gas thruster firing at the top of the stage?


Or are we already in the realm of having to worry about mechanical integrity of load-bearing structures/legs if the stage makes a landing with above-desirable horizontal velocity?


Come to think of it... is there any use of the cold gas thrusters to null the horizontal drift rates - during the landing burn? Or would it be comically ineffective at sea-level? (In terms of response speed, and torque)


This is assuming that they have some left-over after the flip, and after the high altitude re-entry guidance...
« Last Edit: 04/14/2015 10:14 pm by AJA »

Offline sanman

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I'm not a nautical man, but is there any way to reliably anchor the barge - maybe using multiple anchors - to keep the barge from moving at all? Then the barge would truly be a stationary piece of ground.

Offline Kaputnik

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I'm not a nautical man, but is there any way to reliably anchor the barge - maybe using multiple anchors - to keep the barge from moving at all? Then the barge would truly be a stationary piece of ground.

You'd have to 'anchor' it using multiple rigid attachments, preferably at the same time lifting it clear of the water. At which point you've reinvented the jack-up barge...
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline sanman

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Well, oil rigs don't use thrustmasters, and are instead anchored to the ocean floor. If this stage had been landing on something that was more like an oil rig than the current barge, then would this touchdown have had greater chances of success?

Yes, a barge may be cheaper than an oil rig, but if you're going for reusability you may not want to skimp on this cost.

Offline Jim

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Well, oil rigs don't use thrustmasters, and are instead anchored to the ocean floor. If this stage had been landing on something that was more like an oil rig than the current barge, then would this touchdown have had greater chances of success?

Yes, a barge may be cheaper than an oil rig, but if you're going for reusability you may not want to skimp on this cost.

The barge is not going to be the primary landing site, it will be on land. 

Offline sanman

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The barge is not going to be the primary landing site, it will be on land.

But Jim, I thought the barge was still going to be used for recovering stages that were sent too far to bring them back to dry land.

Offline LastWyzard

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This looks to me to strictly be a case of nulling out the horizontal velocity.  I doubt the barge was moving much.  I've done a few simulations and the biggest problem is having to make late (or excessive) targeting corrections and then be left with a very late effort to null out the horizontal velocity.  So I would speculate that the stage was off target by more than was expected and was dealing with the correction and it was just too late.

Also a few posts ago the accuracy of the radar was questioned.  That absolutely shouldn't be a problem.  Check out Curiosity, Mars Phoenix, Viking 1 and 2 and, of course, the Lunar Module.  High precision radar was solved long ago.

Offline AJA

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Yes, a barge may be cheaper than an oil rig, but if you're going for reusability you may not want to skimp on this cost.

But remember that the barge isn't among their operational plan at all. It's only during the testing phase. They'll be landing back at the Cape.
EDIT: But might it be used for the main core on Falcon Heavy?

Speaking of which. What risks remain to be retired with respect to being given permission to come back to land?

It's probably reckless but I'll ask anyway. The first stage is a nearly (fuel-wise) spent (and therefore a minimal explosive hazard). They've demonstrated accuracy to guiding it within a few hundred meters several times now. How does it affect the FAA if the stage is able to stay on its feet or not? How many flights before they're given permission to fly it back, and have a 'land'ing (attempt)?
« Last Edit: 04/14/2015 10:21 pm by AJA »

Offline Fr4nK

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills
« Last Edit: 04/14/2015 10:21 pm by Fr4nK »

Offline RoboGoofers

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The 1st stage terminal trajectory is to aim for a spot next to the barge, and then once the engines fire up, correct and land on the X, Correct? Perhaps they had too large a safety margin, which required a larger correction, hence the extra lateral motion?

It might just be an issue of tweaking the algorithms.

Offline Jim

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Not the FAA's call but the air force's

Offline GWH

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I posted earlier in jest, but in all seriousness if they can't 100% resolve lateral motion but the rocket body is still aligned vertically then the tendency to tip over is going to be a function of the friction between the foot pads that touch down and deck surface. Reduce the friction at the contact points and you'll reduce the chances of tipping. 

Any skier or snowboarder who's caught an edge landing on an off camber surface can attest to that...

Offline Jim

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills

Not needed.  Too  complex.  The rocket has just to land right

And if the rocket is on the edge, those things will knock it over

Offline AJA

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills


The problem with that is distance. If the arms are long/short enough to support the rocket if it lands at (x1, y1); then what happens when the rocket lands at (x2, y2)? Either your arms, and the support won't be close enough to catch the tipping stage, before it's already fallen over... OR, your arm will nudge an already nicely landed rocket and knock it over.


This, in addition to potentially damaging the stage? (I have contradicting senses for how fragile they are. I mean, I've heard about missile fuel tanks being pierced because someone dropped a wrench in a silo, about how the strongback and supports aren't withdrawn until after the rocket is tanked, and the fuel pressure supports the structure, and self weight. But at the same time, I know that this thing has been through several orders of magnitude of velocity, and aerodynamic stresses...)


Not the FAA's call but the air force's


Ah. My bad. But same question still applies. What's the Air Force looking for, before it deems an overflight/return as safe?

Offline Fr4nK

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills

Not needed.  Too  complex.  The rocket has just to land right

And if the rocket is on the edge, those things will knock it over
It starts like this, then when it goes up, you make it so it stops where the top of the rocket would be if the legs would be right on the edge of the barge. Of course you can add some brain to it so you adjust depending on where it lands. Just need it to be strong and fast. (To prevent tipping)
« Last Edit: 04/14/2015 10:38 pm by Fr4nK »

Offline somepitch

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills

Not needed.  Too  complex.  The rocket has just to land right

And if the rocket is on the edge, those things will knock it over
It start like this, then when it goes up, you make it so it stop where the top of the rocket would be if the legs would be right on the side of the barge. Of course you can add some brain to it so you adjust depending on where it lands. Just need it to be strong and fast. (To prevent tipping)

You realize that as drawn those arms would be like 100' long...

Offline Fr4nK

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Here is what i would add to JRTI ship to help with tipping rocket. It would be folded down until the engine cut off. then spring up to act as a fence for the rocket. Sry for my poor drawing skills

Not needed.  Too  complex.  The rocket has just to land right

And if the rocket is on the edge, those things will knock it over
It start like this, then when it goes up, you make it so it stop where the top of the rocket would be if the legs would be right on the side of the barge. Of course you can add some brain to it so you adjust depending on where it lands. Just need it to be strong and fast. (To prevent tipping)

You realize that as drawn those arms would be like 100' long...
well, im using paint, it is not to scale. And it would be light weight. But strong, It is just to get the idea. SpaceX could figure out how to make it works.  ;)
« Last Edit: 04/14/2015 10:43 pm by Fr4nK »

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