Author Topic: Falcon 9 1st stage landing accuracy and progress towards ITS landing cradle?  (Read 5446 times)

Offline meekGee

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If they can routinely get 0.7 meters, or even close, it's plenty good enough for landing two boosters on one ship. 

That would result in a big boost in FH payload, at the cost of two ships in one ocean (one to  catch the outside boosters, and one further downrange to catch the central core).

Might want to build the second ship to be larger.

What would happen to boosters that close together?  If one was landed briefly before the other.  What would the affects of the second landing (engine exhaust) be on the first?

A back of the envelope calculation indicates no problem with the second booster blowing over the first.  So it should work if the accuracy is enough.
That would be cool, but I don't think I'll work.  The issue is not one booster toppling the other, but just the backwash ruining the landing accuracy.

Also, the upside is limited. Side boosters cut off low and slow, so RTLS is not so expensive. 
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Offline envy887

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Side boosters cut off low and slow, so RTLS is not so expensive.
FH accelerates faster than F9, so the boosters stage while going faster and further downrange for the same fuel burn.

Offline meekGee

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If that's true, I stand corrected..  but do you have numbers for that? It's payload and orbit dependent, but still.

Initial t/w won't be THAT much higher, since the boosters are much heavier than S2.

Only when the boosters get lighter will the difference begin to grow.  Peak will be just before staging of course, unless thrust is checked.
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Online LouScheffer

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If they can routinely get 0.7 meters, or even close, it's plenty good enough for landing two boosters on one ship. 

That would result in a big boost in FH payload, at the cost of two ships in one ocean (one to  catch the outside boosters, and one further downrange to catch the central core).

Might want to build the second ship to be larger.

What would happen to boosters that close together?  If one was landed briefly before the other.  What would the affects of the second landing (engine exhaust) be on the first?

A back of the envelope calculation indicates no problem with the second booster blowing over the first.  So it should work if the accuracy is enough.
That would be cool, but I don't think I'll work.  The issue is not one booster toppling the other, but just the backwash ruining the landing accuracy.
Should not affect landing accuracy of the second booster much.  The force on the first landed booster is only about 500 kg-force.   The back-reaction on the second landing booster will be much less (something on the order of 10 kg-f, assuming the first booster scatters the wind uniformly.)  Anyway, very much less than the forces available from thrust vectoring, so the closed-loop landing guidance will mostly null out even this small effect.

Offline meekGee

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If they can routinely get 0.7 meters, or even close, it's plenty good enough for landing two boosters on one ship. 

That would result in a big boost in FH payload, at the cost of two ships in one ocean (one to  catch the outside boosters, and one further downrange to catch the central core).

Might want to build the second ship to be larger.

What would happen to boosters that close together?  If one was landed briefly before the other.  What would the affects of the second landing (engine exhaust) be on the first?

A back of the envelope calculation indicates no problem with the second booster blowing over the first.  So it should work if the accuracy is enough.
That would be cool, but I don't think I'll work.  The issue is not one booster toppling the other, but just the backwash ruining the landing accuracy.
Should not affect landing accuracy of the second booster much.  The force on the first landed booster is only about 500 kg-force.   The back-reaction on the second landing booster will be much less (something on the order of 10 kg-f, assuming the first booster scatters the wind uniformly.)  Anyway, very much less than the forces available from thrust vectoring, so the closed-loop landing guidance will mostly null out even this small effect.
Yeah, but the magnitude of the force is a strong function of the precise timing between boosters.

That said, if they come in 10 seconds apart, then there's no issue and only the blow-over consideration remains.

I therefore withdraw that part of the argument....

Still the payback IMO is low, and still I think it'd be the absolute coolest thing to watch
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Offline speedevil

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That said, if they come in 10 seconds apart, then there's no issue and only the blow-over consideration remains.

I therefore withdraw that part of the argument....

Still the payback IMO is low, and still I think it'd be the absolute coolest thing to watch
This was mentioned on the (IIRC) post-launch conference of CRS-12.
Comment was 'the ship looks a lot smaller with a rocket on it' or something.

Offline IRobot

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The wind out at sea is fairly steady (most of the time).  It think some of what we see is the drift that happens right at the end of flight, when the engine starts shutting down.  You can often see a little drift, almost like a skid.  Take a look at where the rocket is when it's 15 feet up and we may get a better idea of what will happen when the vanes enter the guides on the pad.  Pure speculation, etc.
Yes, the wind at high seas is steady (laminar wind) but very close to the ship (last 10-20 meters) it changes a lot.
That is why high performance sailing boats have two wind vanes: one on top of the mast and one lower.

Online AncientU

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Not sure if this is the correct thread... but this will be interesting!

Quote
Putting together SpaceX rocket landing blooper reel. We messed up a lot before it finally worked, but there's some epic explosion footage …

https://twitter.com/elonmusk/status/903333005527093248

Note response from someone named Chris B...;)
Quote
There's an unreleased one from a successful landing. Apparently danced on one leg before landing it. Hope that's included. #EpicLanding.
« Last Edit: 08/31/2017 07:21 PM by AncientU »
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline AC in NC

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Quote
DEIMOS IMAGING‏ @deimosimaging 6m6 minutes ago
Replying to @SpaceX

#DEIMOS2 caught Cape Canaveral's Landing Zone1 at around 15:58 UTC, September 7, less than 2hours after #Falcon9's first stage landed there!



https://twitter.com/deimosimaging/status/907255552153194496




Are they intentionally attempting to land with the legs oriented toward the "hash mark" (breaks) in the landing circle perimeter?  I see similar on the drone ship picture in one of the posts above.  And here on the latest landing, it appears the leg orientation was close to perfect.
« Last Edit: 09/11/2017 03:43 PM by AC in NC »

Online zhangmdev

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Supposedly that has something to do with the orientation of its inertial platform.

Offline oldAtlas_Eguy

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In order for the capture box of 2m on a 9m diameter vehicle the +- rotation angle error must be less than <12.7 degrees.

Are the legs orientation to the marks less than that?

Offline Kabloona

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In order for the capture box of 2m on a 9m diameter vehicle the +- rotation angle error must be less than <12.7 degrees.

Are the legs orientation to the marks less than that?

When I put a straightedge on the photo and line it up with the upper right and lower left hash marks, the lower left leg lies directly on the straightedge, within the resolution of the photo. I'd call it rotationally aligned to within single-digit degrees of angular error, if not better.
« Last Edit: 09/12/2017 11:29 PM by Kabloona »

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