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Blue Origin Thread (merged)


Aethon
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- The Falcon 9 is currently heading to the ISS. *Dragon*

- Attempting to land the second stage. *First*

- Had extra vertical thrust when trying to land. *Lateral*

Makes a guy wonder what else they get wrong with stuff that we don't care about. :P

Der Standard is an Austrian newspaper. And they wrote on derstandard.at (I'm serious, I double-checked!):

- The Falcon 9 has a height of 90 meters and a diameter of 30 meters *68.4 meters & 3.7 meters*

--- They changed it to 90 meters & 3 meters now *closer but still not right*

- It has wings *gridfins*

- It attempted landing on a barge with a size of 91 x 170 meters *91.4 x 51.8 meters*

I'm still investigating what they smoked.

I don't care if you round numbers but almost all of them where made up.

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Elon Musk says on Twitter:

"Droneship is fine. No hull breach and repairs are minor. Impact overpressure is closer to a fast fire than an explosion."

And the Space X music Video is back up in Canada at least.

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Taking this one with a grain of salt. Pretty sure the next attempt (CRS-7) will be on JRTI.

SpaceX To Land Reusable Launcher on Ground

COLORADO SPRINGS, Colo.  SpaceX hopes that the next attempt to land its Falcon 9 reusable launch vehicle will occur on solid ground.

While not providing details of when or where that attempt would occur, Gwynne Shotwell, SpaceX President and COO, told Defense News on Wednesday that the company hopes its next attempted landing will take place on land, not at sea.

All tests of the reusable vehicle have occurred over water as a safety precaution, but the natural instability that occurs when a landing pad floating in the ocean has a very heavy rocket land on top of it has led to a series of near-misses for the technology.

The most recent test of the technology occurred Tuesday, when the rocket appeared to land on target safely before tipping over. The hope is that the added stability of landing on ground would allow a safe landing.

"Just purely the boat moving, even in a low sea state, it's hard to imagine that vehicle is going to stay vertical," Shotwell said. "That vehicle is big and tall, compared to the itty-bity-greater-than-a-football-field-size ship."

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I've been replaying the last moments before touchdown over and over and I'm getting the feeling that when the engine shuts down (you can tell by the shape of the exhaust plume / steam cloud and, if you look closely, by the glow of the engine on the rocket body itself) the F9 is still moving a bit horizontally (to the right/back in the video), then stops and remains momentarily "standing" on one or maybe two legs, but tilted so its CG is outside the leg base, and so it tips over to the left. Do we know the approximate height of the CG? We could estimate the maximum angle that a F9 standing on two legs could make with the vertical and not tip over.

Edited by Meithan
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I've been replaying the last moments before touchdown over and over and I'm getting the feeling that when the engine shuts down (you can tell by the shape of the exhaust plume / steam and, if you look closely, by the glow of the engine on the rocket body itself) the F9 is "standing" on one or maybe two legs, but tilted so its CG is outside the leg base, and so it tips over. Do we know the approximate height of the CG? We could estimate the maximum angle that a F9 standing on two legs could make with the vertical and not tip over.

I expect it will be relatively low but the F9 is a tall skinny booster. However the rocket could have its normal outside its footprint and still right itself. The RCS jets at the top were going full tilt to right it. So you have to figure out what angle it has to be to be not just outside its footprint but also have enough imbalance to overcome the RCS. So we also need to know the strength of the RCS.

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I expect it will be relatively low but the F9 is a tall skinny booster. However the rocket could have its normal outside its footprint and still right itself. The RCS jets at the top were going full tilt to right it. So you have to figure out what angle it has to be to be not just outside its footprint but also have enough imbalance to overcome the RCS. So we also need to know the strength of the RCS.

Yes, that's a good point. But we can still start doing the estimation assuming no RCS, then see how it changes with various levels of RCS. Do you know the exact leg base width?

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I don't, I was able to find that the span is about 18 meters. For CG estimation I have the following data: Mass Legs is 2,100 kilograms. Each engine has a dry weight of 450 to 490kg. The hole booster has a dry weight of 18kg. The booster is 43m high.

source: http://www.spaceflight101.com/falcon-9-v11.html

Alright, that should be enough info to get us started. Assuming the engines+legs mass (490*9+2100) ~ 6500 kg is located at the lower end of the cylindrical section, I get a CG about 15.2 m from the base level of the legs (when deployed). Sounds a bit too high. I think our estimated tank section mass (18000 - 6500 = 11500 kg) is too big. I'm betting the engine cluster weighs considerably more than 4.4 tons when including structural supports and other parts.

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Well there is also the RCS and Fins at the top, they have machinery that supports them as well. The fuel tanks one of which is on top will still have fuel in them.

If the rocket legs has an 18 meter span, then a 9 meter CG would break even with the footprint at 45 degrees. The rocket was not that steep when it fell over. So the CG has to be higher than that.

Also the height of the rocket will change when the legs are deployed a bit. How high off the barge is the rocket suspended?

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Well there is also the RCS and Fins at the top, they have machinery that supports them as well. The fuel tanks one of which is on top will still have fuel in them.

If the rocket legs has an 18 meter span, then a 9 meter CG would break even with the footprint at 45 degrees. The rocket was not that steep when it fell over. So the CG has to be higher than that.

Also the height of the rocket will change when the legs are deployed a bit. How high off the barge is the rocket suspended?

From this picture of F9R I estimated that the rocket body-leg angle is about 115° when deployed, so the angle the legs make with the ground is about 35°. The legs extend about 3.3 m vertically from the base of the cylinder, and they extend about 7.2 m horizontally from the rocket body (so that 7.2 + 3.6 + 7.2 ~ 18 m).

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OK, I'm a bit tired but I could produce a plot of Maximum tilt angle vs. center of gravity height, based on the leg figures we found. The CG height is measured here vertically from the base of the legs (i.e. ground). Click for larger image. It's hard to conclude anything without better CG height info. But if it's above about 25 m from the leg base, the maximum tilt is about 20°. It's not a lot.

VDxg6kNm.png

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I wonder if they need to change the centre engine to one with lower thrust, it seems if it was able to come in just a little slower and hover it would make the whole thing a lot easier and introduce a larger margin of error. I remember hearing that Falcon is capable of completing a launch if as many as two engines die so they've possibly got enough TWR to have one weaker engine without impacting the launch too much.

Presumably whatever engine they were using on Grasshopper would be suitable as that thing could hover.

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I wonder if they need to change the centre engine to one with lower thrust, it seems if it was able to come in just a little slower and hover it would make the whole thing a lot easier and introduce a larger margin of error. I remember hearing that Falcon is capable of completing a launch if as many as two engines die so they've possibly got enough TWR to have one weaker engine without impacting the launch too much.

Presumably whatever engine they were using on Grasshopper would be suitable as that thing could hover.

It's the same engines.

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I guess grasshopper must have been heavier then as that thing seemed to have much finer control than the suicide burning Falcon.

Well, they could load Grasshoppper full if they wanted to, just to decrease TWR and provide more flight time. Plus, it was built form a Falcon 1.0, so it's Merlin was like... ¿25%, was it? less powerful than the 1D. In any case, all the overcorrecting is consistent with the induced lag due to a sticky valve Elon talked about yesterday, and that should be easy to fix, and/or upgrade the control software to handle that case better. I mean, 10º more vertical, and Musk would have had to build a volcano lair to celebrate...

Rune. Nothing to fix here other than the thing that actually broke.

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Just Read the Instructions spotted being towed! Still too far to see the extense of the damage.

It's going south though, not towards the river mouth where JAX port is. Where are they taking it?

VOWfFI0.png

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I wonder if they need to change the centre engine to one with lower thrust, it seems if it was able to come in just a little slower and hover it would make the whole thing a lot easier and introduce a larger margin of error. I remember hearing that Falcon is capable of completing a launch if as many as two engines die so they've possibly got enough TWR to have one weaker engine without impacting the launch too much.

Presumably whatever engine they were using on Grasshopper would be suitable as that thing could hover.

This would just add complexity to the whole rocket, which in turn would increase costs, which SpaceX is trying to lower.

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