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Blue Origin Thread (merged)

Aethon

By Aethon
in Science & Spaceflight

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Wingman703

Wingman703

Posted
Posted
OK, now for the fun part.

So in looking at this image of the rocket (still airborne) I see the outline of a raised landing leg. Is it just an outline from the sootish stuff or it it the actual landing leg, or an actual leg itself? I can see a sudden stop of the discolored area, likely due to different areas painted with more thermally resistant paint.

Anyone got better eyes than me? I cant tell which in the pic.

- - - Updated - - -

EDIT: thanks for the vid link

I'm going to say that the leg is lowered. Otherwise it would just be more soot, not a fresh surface(as the legs were only just lowered). I think I can also make out one of the 'support lines' running from the leg back to the fuel tank as well.

Besides, the rocket doesn't even seem to fall the right way if that was a leg that didn't deploy, judging from the vid it fell over one of the sides, while the leg in question is towards the front/back(I think anyway, its hard to tell for sure).

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Leszek

Leszek

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Watching the video, it looks like it was over controlling. The engine was gimbaled all the way over until after the rocket was past vertical. This then required another hard correction. It should have eased off as it approached vertical. I wonder if it was trying to hard to get exactly in the center of the barge. It pushed past vertical because it was just a little to far over past the target and because it was close to the barge and moving quickly it needed to do a hard correction to accomplish the adjustment. If this is the case then it would have been better for the rocket to accept being off target but within margins when below a certain height, or it should throttle to hover for a moment to perform last second maneuvers.

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PlonioFludrasco

PlonioFludrasco

Posted
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That was a hell of a last-second correction. I don't remember Grasshopper doing that!

I doubt they have the margins to hover for any length of time, though.

Too much TWR to hover.

However, I think if it was a ground landing, the final correction wouldn't be necessary, both because landing outside the target is not a big trouble and because landing complex 1 is supposed to have secondary pads all around the primary.

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sgt_flyer

sgt_flyer

Posted
Posted (edited)

Looks like they got some 'stiction' problems with the throttle valve (too much friction) - causing a latency in the control, (hence why we see the rocket's slowing down abruptly just before landing) so the rocket had to compensate violently.

https://twitter.com/elonmusk/status/588166157510828033

Edited by sgt_flyer
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Meithan

Meithan

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Posted
That was a hell of a last-second correction. I don't remember Grasshopper doing that!

I doubt they have the margins to hover for any length of time, though.

Too much TWR to hover.

Yep, many people don't consider that even at minimum throttle the Falcon 9 has a TWR > 1, so it can't do a gentle descent but is forced to land with a suicide burn. That's what makes what SpaceX is trying to do so hard.

Their Grasshopper test vehicle was nice but I feel it never did anything as difficult as what Falcon 9 tried yesterday. Grasshopper could hover and never tried a high-g landing nor did they experiment with handling appreciable horizontal velocity components.

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Deutherius

Deutherius

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Yep, many people don't consider that even at minimum throttle the Falcon 9 has a TWR > 1, so it can't do a gentle descent but is forced to land with a suicide burn. That's what makes what SpaceX is trying to do so hard.

Their Grasshopper test vehicle was nice but I feel it never did anything as difficult as what Falcon 9 tried yesterday. Grasshopper could hover and never tried a high-g landing nor did they experiment with handling appreciable horizontal velocity components.

Does anyone have actual numbers? I would assume that 8 of the 9 engines (just the outer gimballed ones - or maybe just 4 engines?) are burning at 70 % (the minimum throttle of the Merlin D1), which gives me thrust, but I have no idea about the almost-dry mass of the stage.

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Meithan

Meithan

Posted
Posted (edited)
Does anyone have actual numbers? I would assume that 8 of the 9 engines (just the outer gimballed ones - or maybe just 4 engines?) are burning at 70 % (the minimum throttle of the Merlin D1), which gives me thrust, but I have no idea about the almost-dry mass of the stage.

For reference, you can find the full specs of the Falcon 9 v1.1 at the SpaceFlight101 website.

They use only the single center Merlin for the final landing suicide burn. With a sea-level thrust of 654 kN, 70% throttle gives 458 kN. The SF101 site reports that the first stage's dry mass is around 18 metric tons. If fully dry, a single Merlin at 70% throttle gives a TWR of 2.6.

Now, in reality it's carrying a residual amount of propellant; how much is hard to tell for sure, but we can ballpark it. With a sea-level Isp of 282 s, the Merlin would be consuming about 170 kg of propellant per second (at 70% thrust). Since the landing burn is a few seconds long, it would need to be carrying at least one or two tons of propellant. Let's make it 2 tons. With that, the TWR comes up as 2.3 - still pretty high.

It would need to be carrying 28 tons of propellant for it to have a TWR of 1, and that's 7% of its load at launch. I think it's unlikely it still has that much propellant on board (I've heard a number as high as 15% of first stage propellant load is saved for the recovery, but I'd guess a large portion of it is used up in the boostback and reentry burns - what's left for landing must be little).

Edited by Meithan
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J.Random

J.Random

Posted
Posted

I think they need a bigger barge. Much bigger, much heavier. Otherwise they get a positive feedback system every time they land a bit off-center or with any lateral velocity: rocket pushes barge, barge tilts and slides away, rocket falls. This wouldn't be a problem if it was a landing intead of "barging".

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J.Random

J.Random

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No it doesn't. The rocket weighs pretty much nothing compared to the barge and doesn't stand the slightest chance of budging it.

What's that movement in the last moments of the video then? To me, it looks like the barge dips a little and then tips the stage to the left.

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Meithan

Meithan

Posted
Posted (edited)
No it doesn't. The rocket weighs pretty much nothing compared to the barge and doesn't stand the slightest chance of budging it.

What's that movement in the last moments of the video then? To me, it looks like the barge dips a little and then tips the stage to the left.

I'm afraid I have to side with Frozen_Heart on this: I don't think a 20 tons rocket will noticeably budge an 1000-tons barge which has a carrying capacity ten times that.

The movement you speak of must be simply that the rocket still did not have full control authority and was fighting to remain vertical. It's hard to judge exactly where the deck is due to the engine exhaust impinging on it. We'll have to wait for the video taken from the barge and see.

Edited by Meithan
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bigdad84

bigdad84

Posted
Posted (edited)
That news anchors cluelessness was cringe worthy.

- 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

Edited by bigdad84
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Dkmdlb

Dkmdlb

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

Every time the news talks about something with which I'm familiar, they get a bunch of stuff wrong, so I assume that they always get a bunch of stuff wrong no matter what they are talking about.

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tater

tater

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

This is sometimes called the "Gell-Mann effect." The story is he was being interviewed by a substantial newspaper about whatever current work in physics he was up to, and then read the article. The reporter managed to get the gist basically 180 degrees from reality. He said he turned the page to the next section, and believed everything he read there.

Reporters are not terribly smart.

Reporters who actually have a background in a field they report on… would not be reporting on it if they were good enough to actually have a job in that field.

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Motokid600

Motokid600

Posted
Posted
- 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

That's why we can't have nice things. You had one job! Lol "news"

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