Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3  (Read 807419 times)

Offline Ohsin

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #680 on: 04/26/2016 11:48 PM »
Go Sisters are near Droneship. When it all nears departure we should tweet to PTZtv folks.
« Last Edit: 04/26/2016 11:50 PM by Ohsin »
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Offline Alastor

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #681 on: 04/27/2016 09:47 AM »
That's amazing. However their target is a fixed platform. Transferring a stage from one barge to another would require a different sort of compensation...

When hooking the stage, the crane has to move in concert with the tip of the stage, but when setting the stage down the crane has to avoid penduluming but also get the stage to actually set down when the deck isn't moving under it a lot. Doable but a fun motion control problem to program.

Well, if the crane is compensated for six degrees of freedom, you can theoretically keep the hook immobile in the referential of the barge ship, with proper instrumentation (I don't say its easy, but after all, they manage to land a stick on top of a single booster). Even in the referential of the top of the stage, it's not that much harder (since the stage is immobile on the ASDS).

Now, if they have a lifting fixture on the end of this hook, as we have seen before, that is a problem, since the fixture will try to stay more or less vertical when the stage is not. So the fixture has to be changed, and now, you need something that also controls its motion at the end of the crane (2 to 3 additional degrees of freedom : the rotations), to match the axis of the fixture with the ones of the stage. That's pretty complicated, but I think it would be still doable.

Then (once you have lifted it), you can use this same system to slowly dampen the pendulum effect and bring the stage back to a stop relative to the transporting ship.

I do like this idea. although it would certainly not be cheap, it might be cheaper than operating another ASDS, to have an integrated support ship capable of starting work on reconditioning the stage while still at sea.

But still. As long as there is no consistent need of a second ASDS, I say they probably will try to catch every stage they can with JRtI in order to get the maximum amount of data on returned stages. Then if they start having too many stages in storage, either they start to put older ones in museums or scrap them. And if the ASDS is not available, because of repairs or because it's busy with an other stage, no big deal just go expandable.
« Last Edit: 04/27/2016 09:50 AM by Alastor »

Online speedevil

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #682 on: 04/27/2016 01:47 PM »
I don't see any need to know the precise wind speed in the final moments before touchdown except for after-the-fact analysis (which IMHO they would need) because there's no way to make use of the data in real time.

With adequate measurement upwind, you can get a complete picture of the wind and gusts in the next 5 seconds.
This means that there are never any unexpected gusts, or winds in the last 5 seconds. (Or more strictly, the unknown magnitude is vastly smaller)
You measure the wind environment in a shell around the craft, and build in these expected forces into your landing model, instead of assuming a simple constant wind field at the same value you measured 5s before landing.

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #683 on: 04/27/2016 02:07 PM »
using a ship-carrier to get the ASDS out on station a fair bit quicker than any "fast tug" could tow it.
Once the ASDS was on that ship carrier then there would be no ship to ship motion so a crane mounted on the ship carrier could pluck the stage off the ASDS then return the empty ASDS to the water to catch another.  BUT a) would still have pendulum motion to deal with while its hanging from the crane, b) initial contact between the ASDS and ship carrier would be hellatious since they'd be moving in the waves differently (vs.normal loading in a calm harbor), c) this is the max $$$$$ solution.

Offline Jim

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #684 on: 04/27/2016 02:24 PM »
Why are we making a big of this?
A.  The flight rate isn't going to be that high (for ASDS missions) to need the transfer.
b.  The problem was fixed long ago (it was designed for the open sea)
« Last Edit: 04/27/2016 02:25 PM by Jim »

Offline Kabloona

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #685 on: 04/27/2016 03:47 PM »
No activity visible on OCISLY.

Ready for Friday night departure?

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #686 on: 04/27/2016 04:07 PM »
Why are we making a big of this?
A.  The flight rate isn't going to be that high (for ASDS missions) to need the transfer.
b.  The problem was fixed long ago (it was designed for the open sea)
That looks like a really expensive solution.  I'll bet if someone tried it using such fancy and expensive equipment they'd go out of business.  Needs to be a SpaceX budget(able) solution.

Online John Alan

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #687 on: 04/27/2016 04:44 PM »
My humble opinion...  ???
The cheapest solution here... is start the ball rolling on the OCISLY barge copy to be built for the upcoming Texas need...
And charter much more powerful tugs to do "fast drags" of barges to where they are needed...  as needed...
Base whole east coast fleet out of Port Canaveral...
For Texas launches... drag one down south of Miami and do a small boost forward if need be to reach it...
Mix in some RTLS at both pad sites...
Job Done...
Just my opinion...  ;)

edit... spelling
« Last Edit: 04/27/2016 04:47 PM by John Alan »

Offline CJ

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #688 on: 04/27/2016 05:09 PM »
I don't see any need to know the precise wind speed in the final moments before touchdown except for after-the-fact analysis (which IMHO they would need) because there's no way to make use of the data in real time.

With adequate measurement upwind, you can get a complete picture of the wind and gusts in the next 5 seconds.
This means that there are never any unexpected gusts, or winds in the last 5 seconds. (Or more strictly, the unknown magnitude is vastly smaller)
You measure the wind environment in a shell around the craft, and build in these expected forces into your landing model, instead of assuming a simple constant wind field at the same value you measured 5s before landing.

True, they theoretically might be able to generate something like that with enough data points, but being able to put it to use (other than for later analysis) is another matter; there isn't currently a way to do so, because there's no way to uplink the data to the F9, and no way for the F9's flight control program to make use of it.

It's also worth bearing in mind that gusts are less of an issue at sea than on land (on average, there's far less variance between maximum and minimum wind speeds except in major storms). It's the same dynamic that gives us far steadier winds on flat plains than in the mountains; a flat surface vs. an uneven one.

Offline CJ

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #689 on: 04/27/2016 06:39 PM »
Why are we making a big of this?
A.  The flight rate isn't going to be that high (for ASDS missions) to need the transfer.

Sorry, Jim, but that's just too rational for this thread.  :)

By my way of figuring, one ASDS means a capability to handle launches a week apart - less, if a faster tug is used. So, if we assume 50% ASDS landings, one ASDS could handle a flight rate approaching 80 launches a year (40 to ASDS) - and thus worrying about it now is rather akin to worrying about the demise of the sun in a few billion years. If there are launches scheduled too close together, say two days apart, IMHO it'd be easier and far cheaper to adjust the schedule slightly than to create a transfer capability or expand the ASDS fleet. 

The spirit of Rube Goldberg does not merely walk through this thread, it parades in grand style.   ;)

Offline Lar

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #690 on: 04/27/2016 06:53 PM »
The spirit of Rube Goldberg does not merely walk through this thread, it parades in grand style.   ;)
Fanciful stuff has always been unwelcome... Jim's example, and the example of the crane that can handle movement of the ship it's mounted on... are real things that real people built and put into service to solve real problems.  I'm inclined to let those slide, but fanciful stuff? No. there are other threads for that.
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Offline cuddihy

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #691 on: 04/27/2016 09:43 PM »
Also, what US Navy does, for example, to crane on/ off missiles from one ship to another is just separate the crane platform from either ship... i.e. use an aircraft. For missiles, a helicopter works.

I'm not sure a helicopter big enough for F9 exists, but there are airships in planning that would be big enough.

You'd really need a substantial flight rate to justify it, and at that point the economics probably point to it being more effective to either take them straight off the barge and fly to the hangar at the launch pad, or build a refueling/ sea launch platform to fly themselves back to the pad.

Offline Brian45

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #692 on: 04/27/2016 10:29 PM »
Given the inherently dangerous act of landing a rocket on a moving platform, I would think that the risk of having a barge get taken out and have no sea landing capability for a few weeks/months while it is repaired/replaced would motivate SpaceX to have at least some sort of contingency barge plan on stand-by that could be rapidly put into service.

Offline CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #693 on: 04/27/2016 11:37 PM »
using a ship-carrier to get the ASDS out on station a fair bit quicker than any "fast tug" could tow it.
Once the ASDS was on that ship carrier then there would be no ship to ship motion so a crane mounted on the ship carrier could pluck the stage off the ASDS then return the empty ASDS to the water to catch another.  BUT a) would still have pendulum motion to deal with while its hanging from the crane,

I wouldn't suggest doing this.. but that doesn't stop you from doing so. :)

b) initial contact between the ASDS and ship carrier would be hellatious since they'd be moving in the waves differently (vs.normal loading in a calm harbor),

Wrong.  Obviously they don't load in a typhoon, but there are plenty of videos on-line of ship loading at sea so I won't try to post one here (Dockwise are the biggest in this game, so start there).  Essentially the ship-carrier submerges and moves slowly (1-5 kts depending on conditions) to windward whilst the barge/ship comes in behind.  The wide front of the carrier creates a calm essentially wave-free area behind and once the barge/ship is tied off they blow ballast tanks and increase speed.. 

c) this is the max $$$$$ solution.

I'm not so sure about that.  It's certainly cheaper than Jim's solution and you pay per trip.  There aren't many crew required either since it's a straightforward operation.  If they didn't need the support ships for other reasons, I expect it would be far cheaper than having the ASDS towed out there the way they currently do. Heck, if they were really concerned about there-and-back man/hour costs (and they may not be) they could carry the support tugs out also.  8)

 
« Last Edit: 04/27/2016 11:41 PM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline CJ

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #694 on: 04/28/2016 01:29 AM »
Given the inherently dangerous act of landing a rocket on a moving platform, I would think that the risk of having a barge get taken out and have no sea landing capability for a few weeks/months while it is repaired/replaced would motivate SpaceX to have at least some sort of contingency barge plan on stand-by that could be rapidly put into service.

The risk of rendering an ASDS nonoperational for the next launch via a landing anomaly (one that ends with a kaboom) IMHO increases as the launch tempo increases (less time between sorties to effect repairs). My guesstimate is that SpaceX has, or will have, some sort of near-term contingency plans. My guess as to what they might be would be a kit to make seaworthiness repairs; a slab of deck plate (perhaps thicker than the current deck plate) to be welded over a hole for a temporary but seaworthy repair to damage like we saw recently, and perhaps more importantly, pre approval to do that sort of repair from both the hull owner and the Coast Guard inspector. Also, to speedily replace components such as we see in the modular gear on deck, the thrusters, etc, a written plan to remove those components (whatever is needed) from the ASDS on the opposite coast and air ship them to the one in need. Just having a plan in place would speed the process enormously.

Or, if the hull damage was such that it couldn't be fixed in time, a company that once famously re-purposed a pizza pan as an airborne directional antenna might rush into service a temporary ASDS; any flat-topped barge (or anything else with a large flat area that's strong enough) it could find, and send it out as-is (with the jacks and straps needed to secure the landed F9). The only absolutely necessary thing (IMHO) it couldn't do that an ASDS can is station keep, and that could be addressed via deep sea anchoring (regular anchors with very long anchor line, dropped well off each corner of the barge (about three times the depth) to keep it in place. This can be done in deep water (2000 or so feet is common in the usual recovery zone). It'd be very imperfect and ad-hoc, but might be worth the try vs. certain loss of the stage.   


Offline Jim

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #695 on: 04/28/2016 02:15 AM »
The only absolutely necessary thing (IMHO) it couldn't do that an ASDS can is station keep, and that could be addressed via deep sea anchoring (regular anchors with very long anchor line, dropped well off each corner of the barge (about three times the depth) to keep it in place. This can be done in deep water (2000 or so feet is common in the usual recovery zone). It'd be very imperfect and ad-hoc, but might be worth the try vs. certain loss of the stage.   


Not even enough to work.

Offline CJ

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #696 on: 04/28/2016 03:49 AM »
The only absolutely necessary thing (IMHO) it couldn't do that an ASDS can is station keep, and that could be addressed via deep sea anchoring (regular anchors with very long anchor line, dropped well off each corner of the barge (about three times the depth) to keep it in place. This can be done in deep water (2000 or so feet is common in the usual recovery zone). It'd be very imperfect and ad-hoc, but might be worth the try vs. certain loss of the stage.   

Not even enough to work.

I'm not questioning that it won't work, but I'm curious to know why it won't work?

One big issue even I can see is you'd need approx 5 miles of zero buoyancy anchor line (with enough strength to hold a barge against current and seas), which is both bulky and rather pricy in that quantity, as well as a major job to deploy and recover.

Having personally dropped a lot of anchors for four-point anchoring, I'm moderately sure that four anchors as described could hold a barge in a sufficiently fixed position in fairly calm conditions (assuming the wind and sea direction don't change), BUT, placing it exactly at a per-determined set of coordinates is probably near impossible; it's going to end up fixed by up to a hundred yards off center in any direction (once the anchors are set and the rodes are trimmed) and I have no clue whatsoever if an F9, before launch but on the pad, could be programmed with a new aim point a hundred yards or so from the original one.  EDIT: Just did some calculations and I'm flat out wrong on anchoring; even with weighted rodes well trimmed for slack, that kind of length would have enough play in it to allow the barge to move by a width or more with even slight changes in current wind, and sea and sea.

What else did I miss?
Thanks!
« Last Edit: 04/28/2016 06:05 AM by CJ »

Offline llanitedave

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #697 on: 04/28/2016 03:57 AM »
My humble opinion...  ???
The cheapest solution here... is start the ball rolling on the OCISLY barge copy to be built for the upcoming Texas need...
And charter much more powerful tugs to do "fast drags" of barges to where they are needed...  as needed...
Base whole east coast fleet out of Port Canaveral...
For Texas launches... drag one down south of Miami and do a small boost forward if need be to reach it...
Mix in some RTLS at both pad sites...
Job Done...
Just my opinion...  ;)

edit... spelling


Wouldn't a boost forward increase the re-entry velocity?  Heating is critical enough as it is.
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Offline Kaputnik

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #698 on: 04/28/2016 06:22 AM »
Deep sea anchoring (as used in oceanography buoys) is not like conventional anchoring, you don't want or need 3x scope.
The only realistic way of holding station is if the barge is self propelled, ideally using multiple thrusters. SpaceX have already got this one right.
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Offline Johnnyhinbos

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #699 on: 04/28/2016 10:17 AM »
So we're expecting OCISLY to depart sometime tomorrow (Friday), correct?
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