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37 minutes ago, mikegarrison said:

The point is that this guy LunarCaveman seems to have completely not realized that the available catching span is nowhere near as big as he is imagining.

Let's say they have perfect roll control, and bring it down in the exact alignment they intended. In that case, they can only move off the target far enough to create a 15 degree angle, or else they will miss that 15 degree window you refer to.

This whole maneuver is going to be extremely dynamic, and they are going to need very precise landings. We have seen that Falcon 9 usually lands inside that painted circle on the deck, and if they can get that same precision then that should be good enough. But the stakes are a lot higher, because it's not just a barge in the ocean that is at risk -- it's your whole launch tower.

I'm not sure if I understood correctly, but the booster should definitely be able to compensate for that. The starship control software appears to be quite advanced, being able to compensate for the autogenous pressurization problems in the initial flight tests by either landing (SN10) or at least reaching the pad (SN8) which shouldn't repeat in Superheavy (or at least nor in the same way since no sloshing). Roll can be controlled with the RCS thrusters on the booster, or alternatively by a slight change of angle of the engines; either case, that is not impeded by a booster going off center.  The limit does appear to be the one shown in the graphic provided the RCS is still working at least partially

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6 hours ago, mikegarrison said:

Hmm. Look at this picture.

FIWjRPNXEAgXtsN?format=jpg&name=large

 

Do you see the issue there?

Look at how on one edge of the arc the image shows the SH clocked one way, and on the other edge of the arc it is clocked the other way.

That would be super convenient, but if they had enough control to get that kind of precision then they wouldn't be landing out on the edge anyway.

What does it look like if you have the roll controlled and bring in in like it is in the middle, but it drifts laterally?  It looks like at the very least the arm might catch only one grid fin on each side.

The one weird thing for me is that it looks like they will try to catch over the launch mount.   
Yes you can catch to the sides but then the  left (lower) arm will be almost fully folded out while the right will probably be folded a bit to the left to and be over the launch mount and it will have to hurry up and catch it. 
 

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5 hours ago, mikegarrison said:

This whole maneuver is going to be extremely dynamic, and they are going to need very precise landings. We have seen that Falcon 9 usually lands inside that painted circle on the deck, and if they can get that same precision then that should be good enough. But the stakes are a lot higher, because it's not just a barge in the ocean that is at risk -- it's your whole launch tower.

Falcon 9 usually lands inside the rings on the barge using a margin of error of less than a second to get the hover-slam correct(margin provided by the throttle range of the engines in use.  I have not done the math, but I would not be surprised by a margin of 0.1 seconds or less).

Super Heavy and Starship can both hover.  This provides a margin of error in the range of multiple seconds, possibly even a minute or longer when testing and there is plenty of fuel available.

I'm not sure about you, but if I can generally do a job in X time, and I am given 10x or 100x to do the same job, it gets a whole lot easier.

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55 minutes ago, Terwin said:

Falcon 9 usually lands inside the rings on the barge using a margin of error of less than a second to get the hover-slam correct(margin provided by the throttle range of the engines in use.  I have not done the math, but I would not be surprised by a margin of 0.1 seconds or less).

Super Heavy and Starship can both hover.  This provides a margin of error in the range of multiple seconds, possibly even a minute or longer when testing and there is plenty of fuel available.

I'm not sure about you, but if I can generally do a job in X time, and I am given 10x or 100x to do the same job, it gets a whole lot easier.

Hover for an minute, yes if you take off go a couple of hundred meter up and then decent you can, now its an weight limit on the arms but this probably also depend on how hard you land. 
This has the benefit that something coming in hot will be low on fuel and therefore light. 
They will also get pretty powerful thrusters down the line, perhaps for the first catch attempt. 
You could put these thrusters on the tip of the arms if you need them to move faster :) Musk talked about using cold gas thrusters on the roadster 

One thing you will not catch is Starship as the arms point the wrong way, you will also be overflying Mexico coming in, last is also true for landing on legs. 
Who make me suspect the point of the oil platform conversions is to catch Starship out in the gulf, refuel it and have it fly west towards starbase and land or get grabbed there. 
This will require much less fuel and oxidizer than the full launch stack.

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8 minutes ago, magnemoe said:

you will also be overflying Mexico coming in, last is also true for landing on legs. 

Overflying is not a problem - some Atlas V and F9 overflew some islands in the past during a few launches, and Shuttle obviously overflew most of the US when landing. What matters is the area where the debris would spread and the zone affected by the sonic booms during landing, which does not have to be over Mexico necessarily

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24 minutes ago, RCgothic said:

I don't think they'll catch over the mount. They'll almost certainly catch to one side.

But its not designed to catch at the side, for that ) would rotate it 90 degree against the clock. Add an extension to let the right arm having some freedom, say the distance to the first bend in the QD arm. 
But again if you need right arm to move fast put rocket engines on it 

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8 minutes ago, magnemoe said:

But its not designed to catch at the side, for that ) would rotate it 90 degree against the clock. Add an extension to let the right arm having some freedom, say the distance to the first bend in the QD arm. 
But again if you need right arm to move fast put rocket engines on it 

Nope, looks like @RCgothic is right

I imagine this spot is to be more or less halfaway between the OLM and the arm rotation limit - so like @mikegarrison said before the range is actually going to be smaller than the one shown in the graphic, even if for different reasons

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I saw that guy!

Spoiler

tumblr_inline_ohbek52BaI1r5jgg0_640.jpgTMnLiUrh.jpgMichael-Winslow-in-Spaceballs.jpg?q=50&f


Arms!.. The catching arms.

The stupid me didn't recognize the source of idea.

Spoiler

c7edd8c24927f5822401c070c95b9f35.jpg

 

And now we can see the name of the first Starship.

Absolutely in SpaceX traditions.

Spoiler

3afb4c6d-3998-433e-a616-b65c34106ca3

 

Upd.
And look!

Spoiler

4hg3cm.pngllopatto_180609_2658_0068.jpg

 

Edited by kerbiloid
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1 minute ago, caecilliusinhorto said:

If the catching arms miss the hardpoints, could it do a sort of backup catch using the gridfins?

Yes. The bottom of the grid fins will be damaged, but the current plan is that the grid fins will still be able do hold the booster's weight

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The more I know about this landing scheme, the more I ensure that a giant pogo stick would be better choice...

No need even to launch it. Just the rocket could land on it with the bottom opening, undock from ground and start jumping.

(Also a precursor of a pusher plate scheme.)

Edited by kerbiloid
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36 minutes ago, kerbiloid said:

The more I know about this landing scheme, the more I ensure that a giant pogo stick would be better choice...

No need even to launch it. Just the rocket could land on it with the bottom opening, undock from ground and start jumping.

(Also a precursor of a pusher plate scheme.)

3.28991.fp.png_v03

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That was some pretty sweet footage of stage separation, SES and boostback burn.  That's a nice perk of RTLS!

I noticed that the entry burn has a pretty high TWR--my rough timing-it-with-a-stopwatch estimate is something like 30m/s^2 deceleration, which means its actual TWR is about 4.  I suppose that shouldn't be a surprise, since the thing is almost empty at that point, and you want to minimize gravity losses, but still...

Edited by zolotiyeruki
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1 minute ago, Beccab said:

Another happy landing

But seriously, that was amazing to see. I think it's the first RTLS I watch live

First (F9, I watched the FH test flight) RTLS I watched live was B1050's first and only flight (CRS-16).  Definitely the most... interesting landing I've seen.

This one was just beautiful.  The shot of stage sep and the start of the boostback is amazing.

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Bear in mind that whilst they splash actual SS booster cores, they can feed altered telemetry to the chopsticks *as if* the booster is trying to land within their grip (i.e. with just adjusted coordinates). They can then compare actual vs expected performance and not switch to actual catching attempts until confident. Heck, once they have one SS core ditch they can replay it multiple times.

I'm not saying they will do this, just a simple, obvious, thing they can do before actual catch attempts, if they're not certain.

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2 hours ago, Damien_The_Unbeliever said:

I'm not saying they will do this, just a simple, obvious, thing they can do before actual catch attempts, if they're not certain.

I'm sure they are already doing this at some level via simulations.

Like anything else though, there are some things you can't simulate, and thus a real-life test is the only way to find the unknowns. 

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