Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3  (Read 601219 times)

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #720 on: 04/28/2016 09:54 PM »
***Hydrofoil Barge***

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #721 on: 04/28/2016 09:58 PM »
Quote
***Hydrofoil Barge***
Get real.


Does anyone have an app or such that will send (me) a message when a ship that is stationary for a long period of time moves?  Or when an AIS transponder is turned on?  I'm thinking currently of EIII, which is by Fishlips and off the grid, but this functionality would be useful in other cases as well, particularly in monitoring the west coast fleet.

Online CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #722 on: 04/28/2016 10:46 PM »
Regarding the suggestions to get a larger / faster tug to give faster turnaround on 1 ASDS, two thoughts / suggestions for comment -
a) Are multiple tugs an option?  Seems like E3 is already at the large end of the spectrum though certainly not the biggest.
b) It seems to me that the easiest way to speed up the tugging is to have the ASDS unballasted during towing.  IIRC, there is 12' of water in the tanks to enhance stability during landing.  Or was it enough water to cause 12' of draft?  Whichever way, without ballast the ASDS drafts about 3'.  That's a lot less drag and a lot more speed.  Is this ballast needed for towing?  Assuming that the F9 can handle more rocking motion during tow?  If yes to all of the above then fit the ASDS with a built in ballast pumping system.

1.  IIRC from the same discussion we had last thread, the ASDS is ballasted with fresh water and it's the same water that's used to hose down the deck during landing.  There was some talk around them not wanting to hose down the stage with salt..  ::)

2.  For all the reasons recently posted, the only practical way to get the ASDS out there faster than towing it is to pick the whole lot up, tugs and all, and carry it - hence my earlier suggestion re. Dockwise.  With cruising speeds around 15-20kts their entire business model is based around getting barge and tugs (and ships too, I guess) from Point 'A' to Point 'B' as quickly as possible.

https://en.wikipedia.org/wiki/Dockwise




EDIT: ..and, before anyone asks, no, you couldn't land an F9 stage on the deck of the transporter.  They don't use (or need) any kind of active positioning system and, with hulls optimised for speed, roll like pigs when lightly loaded..
« Last Edit: 04/28/2016 10:56 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 Lar

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #723 on: 04/28/2016 11:05 PM »
...ya but can they get on plane to go faster? :)

Actually 15kt is significantly fast.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #724 on: 04/28/2016 11:17 PM »
...ya but can they get on plane to go faster? :)

Actually 15kt is significantly fast.

Remember that to carry another vessel, they're all pretty decent-sized ships.. and displacement hull speed increases proportional to water line length.

Eg.: Without wanting to go too far off-topic, below is a pic of a Pilot boat holding station with a cruise ship we were on last year.  Needless to say, we were plodding slowly along and he was trying his hardest to keep up! :)
« Last Edit: 04/28/2016 11:20 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 #725 on: 04/29/2016 01:15 AM »
@ Cameron D; thanks for the fresh water info; I'd forgotten that, and it makes sense they'd use fresh water.

Won't make any difference you are fighting two facing two large limiting factors:

1) Drag- goes up exponentially till it starts to plane---Not going to happen   ::)
Don't need to do the math typical drag plot attached.

2) Propeller efficiency.  Propellers are designed for specific working limits. See the Wageningen B series curves below. We call these the fishhook curves. (thrust & torque-vertical axis, and speed-horizontal are dimensionless coefficients) Back in the day you could figure out which pitch by looking at you motor torque and drag numbers to match them to the best pitch on this chart. If you have controllable pitch propeller you get all the curves just set you operating point.  Notice how the lines drop sharply after they reach a maximum; these correspond to the torque coefficient.  This is what happens when you over power a propeller;  it cavitates and stops pulling.

The fastest we have seen the tugs is about 7 Kts(J=1.0). So Assuming these curves and controllable pitch propeller ( we get all the pitch lines) J / speed maxes out at 1.2 or 8.4 Kts.  Less than a knot and a half.
That's if you have enough power to overcome the drag.

Thanks, you saved me from some research and math.

The props on Elsebeth III are 3 Bird-Johnson props in Kort nozzles (in other words, ducted props, not variable pitch, and that type of nozzle is often used on low speed craft, as it loses its usefulness at about 9 knots).

The tugs have been seen towing an ASDS at 7 knots? Any idea where? If it's in a strong favoring current, that's not a true speed, but if that's actual speed through the water, that's actually quite an improvement from 5 knots. To go out 400 standard miles, 69 hours at 5 knots, 49 hours at 7kt. Shaving off 20 hours each way might be quite useful in case of a scheduling bottleneck necessitating a fast ASDS turnaround.


Online CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #726 on: 04/29/2016 02:29 AM »
The tugs have been seen towing an ASDS at 7 knots? Any idea where? If it's in a strong favoring current, that's not a true speed, but if that's actual speed through the water, that's actually quite an improvement from 5 knots. To go out 400 standard miles, 69 hours at 5 knots, 49 hours at 7kt. Shaving off 20 hours each way might be quite useful in case of a scheduling bottleneck necessitating a fast ASDS turnaround.

Nope.  The issue, pure an simply, is fuel economy.

From Doesitfloat's graphs we see drag increases exponentially with speed and, generally speaking, fuel consumption follows a similar curve.  There is a limit to the amount of fuel each of the Support Tugs can carry (ASDS on-station duration is similarly constrained), so whether or not they can do the tow at 7kts becomes kinda irrelevant if they'll run out of fuel when they get there and need to call the USCG to tow them back.

I wonder how fast a Coast Guard Cutter could tow an ASDS??  ;D
 
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 Zed_Noir

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #727 on: 04/29/2016 05:22 AM »
I wonder how fast a Coast Guard Cutter could tow an ASDS??  ;D
 

USCG cutters are just frigate size units that can keep pace with Amphibious units.

A lot more interesting is how fast a Burke class Destroyer can towed the ASDS. Considering they are fitted to tow an active sonar array.  ;D

Offline The Amazing Catstronaut

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #728 on: 04/29/2016 06:15 AM »

A lot more interesting is how fast a Burke class Destroyer can towed the ASDS. Considering they are fitted to tow an active sonar array.  ;D

Don't destroyers create a lot of wake for their size when moving at speed?  The sonar array is suspended under the waterline whilst towed so it's not all that vulnerable to wave action. The barge doesn't have that luxury.
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Offline CJ

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #729 on: 04/29/2016 07:57 AM »
The tugs have been seen towing an ASDS at 7 knots? Any idea where? If it's in a strong favoring current, that's not a true speed, but if that's actual speed through the water, that's actually quite an improvement from 5 knots. To go out 400 standard miles, 69 hours at 5 knots, 49 hours at 7kt. Shaving off 20 hours each way might be quite useful in case of a scheduling bottleneck necessitating a fast ASDS turnaround.

Nope.  The issue, pure an simply, is fuel economy.

From Doesitfloat's graphs we see drag increases exponentially with speed and, generally speaking, fuel consumption follows a similar curve.  There is a limit to the amount of fuel each of the Support Tugs can carry (ASDS on-station duration is similarly constrained), so whether or not they can do the tow at 7kts becomes kinda irrelevant if they'll run out of fuel when they get there and need to call the USCG to tow them back.

I wonder how fast a Coast Guard Cutter could tow an ASDS??  ;D
 

Going from 5 to 7 knots looks like it increases drag by a factor of 3. So, let's factor in some guesses at reduced efficiency and say that it'll increase fuel consumption by a factor of 4, which is probably too high, but let's use it. That's not a problem (except for cost, so they'd only do it in case of need); Elsbeth III carries 80,000 gallons of diesel, and has towed a (on a normal speed run, not 7 knots) a 400 foot barge from Norfolk, Virginia, to Seattle, Washington (via Panama) on 70,000 gallons. That's about 7000 miles, so even if we divide that by 4 for a 7 knot tow, it's still a lot more than an ASDS sortie (max about 400 out, 400 back, plus some use on station). 

Uhoh, I feel a bit of a Rube Goldberg mood coming on, which is compelling me to ponder using one ASDS to recover two Falcon Heavy side cores... can it be done? The ideal way was one Lar came up with; land the cores on towards the opposite ends. But, if that's not viable (not enough accuracy) then... could an ASDS be joined by a deck barge, lashed stern to stern once on station  and the ASDS positioning system keep both of them on station? I'm assuming light seas here... so the ASDS thrusters should have the capacity, and the ASDS bow will be into the wind. I'm betting the ASDS positioning software would need some changes - but are there other reasons this wouldn't work?

 If there isn't a way to make an ASDS do double duty, they may need 3 ASDS for a non-RTLS FH launch; one for each side core and one further downrange for the center core.   

Offline RobLynn

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #730 on: 04/29/2016 10:37 AM »
Pitch and roll stabilisation can be done with a heavy concrete weight suspended 100's of meters below the barge by 4 equal length cables from each corner of the barge.  Because the cables are always in tension it behaves like an enormously long keel to transfer weight to whichever side is highest.

And for convenience you can leave it on the seabed between missions, only winching it up and attaching it to the barge when a mission with rough weather happens (though likely just as easy to fit a winch in middle of barge to haul it up on a 5th central cable).

Taken to the limit the concrete weight could be transported while the ASDS has no ballast water then lowered and rested on the bottom (which takes some of the weight) before pumping in water ballast so that you could also use the keel to eliminate heave and so have a perfectly stable platform.

Might save a bit on leg loads/mass.  And might also reduce the required leg length slightly.
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Offline Jet Black

I expect that if the reuse stuff works (we still don't know if those stages are reusable many times or not) and they get a decent launch cadence, they'll have to go for something much more custom than a jury rigged marmac barge, perhaps with separate landing/shipping elements so the large, unweildy landing element doesn't have to move far. What they have at the moment is ok for eperimentation, but not terribly efficient.
« Last Edit: 04/29/2016 10:58 AM by Jet Black »
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Offline Semmel

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #732 on: 04/29/2016 12:29 PM »
OK spacefans...er, barge fans...get ready for OCISLY to head out tonight.

So soon?

Anyway, I sincerely hope that this will bring back this thread to the quality of the old one. Since resetting, this thread has become way worse than the old one. First time I see that happening on this forum, usually its the other way around.

Offline MarekCyzio

OK spacefans...er, barge fans...get ready for OCISLY to head out tonight.

I will be in the port this afternoon, will check what's going on.

Offline Kabloona

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #734 on: 04/29/2016 12:34 PM »
OK spacefans...er, barge fans...get ready for OCISLY to head out tonight.

So soon?

Correction:

I'm expecting OCISLY to depart almost exactly 5 days (120-ish hours) before launch time based on SES-9 operations.

But the latest published launch NET was early morning hours of May 4th, and we've already passed that L-120 hours mark, with OCISlY still in port and no sign of activity. (Sorry, my math was off about expected departure tonight).

So this make me wonder if the launch date is slipping again and we just haven't heard yet. I expect we may hear a new NET today...
« Last Edit: 04/29/2016 12:59 PM by Kabloona »

Offline cscott

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #735 on: 04/29/2016 01:16 PM »
As I mentioned earlier, usually we have a static fire schedule (even if only in L2) before the ASDS leaves port.

Offline Kabloona

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #736 on: 04/29/2016 01:24 PM »
As I mentioned earlier, usually we have a static fire schedule (even if only in L2) before the ASDS leaves port.

There is one scheduled in L2. Don't know why it's not also on the public side.
« Last Edit: 04/29/2016 01:29 PM by Kabloona »

Offline Lar

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #737 on: 04/29/2016 01:33 PM »
OK spacefans...er, barge fans...get ready for OCISLY to head out tonight.

So soon?

Anyway, I sincerely hope that this will bring back this thread to the quality of the old one. Since resetting, this thread has become way worse than the old one. First time I see that happening on this forum, usually its the other way around.

Maybe we need to split into operational, with no future speculation at all (not even capacity calculations) and future speculation? I will ponder and then ask the big boss what he thinks. (says the guy who's part of the problem)
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline John Alan

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #738 on: 04/29/2016 01:37 PM »
Question... to steer this thread back to topic...  ;D

What would be the estimated cost (we think) to replicate OCISLY class ship as a new build...???

Right now... it's a leased asset with all kinds of add on (but removable) items...

Cost (all in) to build a clone to own...  ???

My WAG... $25 mil... I may be way off however...  :P
Those here with a better number based on experience... your thoughts?

Offline kevinof

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #739 on: 04/29/2016 01:51 PM »
Divide by 10!  The barge itself is not a complicated build and therefore not a very high cost. Doesn't have a powerplant, rudders or anything fancy.

Not sure about the cost of the add-ons.

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