Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3  (Read 718996 times)

Offline Kabloona

  • Senior Member
  • *****
  • Posts: 4227
  • Velocitas Eradico
  • Fortress of Solitude
  • Liked: 2447
  • Likes Given: 506
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #700 on: 04/28/2016 01:04 PM »
So we're expecting OCISLY to depart sometime tomorrow (Friday), correct?


Yes, late Friday night if they follow the same script as SES-9.
« Last Edit: 04/28/2016 01:09 PM by Kabloona »

Offline cscott

  • Senior Member
  • *****
  • Posts: 2848
  • Liked: 1970
  • Likes Given: 664
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #701 on: 04/28/2016 01:08 PM »
I always expect to see the ASDS leave port around the time of a successful static fire, although I think they left port shortly before the successful static fire of ses-9 (but after the start of the scheduled static fire window, IIRC; the static fire came late on the window).  I haven't heard anything about static fire timing for this one.

Offline Kabloona

  • Senior Member
  • *****
  • Posts: 4227
  • Velocitas Eradico
  • Fortress of Solitude
  • Liked: 2447
  • Likes Given: 506
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #702 on: 04/28/2016 01:15 PM »
I always expect to see the ASDS leave port around the time of a successful static fire, although I think they left port shortly before the successful static fire of ses-9 (but after the start of the scheduled static fire window, IIRC; the static fire came late on the window).  I haven't heard anything about static fire timing for this one.

Probably will have to leave before static fire, again.

Offline John Alan

  • Full Member
  • ****
  • Posts: 667
  • Central IL - USA - Earth
  • Liked: 350
  • Likes Given: 1565
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #703 on: 04/28/2016 01:31 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


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

How about call it upward boost... loft it a bit to add some downrange to the ballistic arc it's on...
Once the S2 has gone on... adding some loft to S1 to increase downrange should use little fuel margin...
Lofting burn...
Reentry burn...
Landing burn...

Think RTLS... but going the wrong way on the first burn...  :o

Again just thinking out loud...  ;)

On edit...
To clarify my original thought...
Two barges at Port Canaveral implies you now have flexibility and a spare on hand...
Worst case is one down south catching one from Texas and one out east catching one from the Cape at the same time...
Otherwise you have just built in some flexibility to fix or unload one while the other is busy... into your process...
Having them based together gives you options that splitting them up takes away...
Since SpaceX has indicated IIRC Texas is to be mostly Geo orbits... then my suggestion fits the need...
Just saying...  ;)

More edit...
Sure... your going for about 1100 miles downrange to catch S1 out of Texas... bit of a loft ok
BUT, your only dragging a barge less then 400 miles south to pull it off...
Just suggesting one idea... and a cheap and flexible one...  ;)

Even more edit...
Go catch two stages going two directions from 39A and 40 from the Cape same day even...
Catch a FH booster close in and the core far downrange... with the other booster to LZ1...
Like I said... lots of cheap options basing two barges at the Cape and none in Texas...
« Last Edit: 04/28/2016 02:46 PM by John Alan »

Offline OxCartMark

  • Full Member
  • ****
  • Posts: 1054
  • Michigan
  • Liked: 820
  • Likes Given: 884
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #704 on: 04/28/2016 04:18 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.

Regarding the proposals for deep sea anchoring -
Perhaps that scheme would benefit from having the anchor lines connected to 4 autonomous drone winches?

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32006
  • Cape Canaveral Spaceport
  • Liked: 10632
  • Likes Given: 317
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #705 on: 04/28/2016 04:37 PM »
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.


Bingo

Offline CJ

  • Full Member
  • ****
  • Posts: 848
  • Liked: 620
  • Likes Given: 180
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #706 on: 04/28/2016 07:37 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.

Regarding the proposals for deep sea anchoring -
Perhaps that scheme would benefit from having the anchor lines connected to 4 autonomous drone winches?

Mark, IMHO that's an excellent point on ballasting; taking the ASDS out ballasted absolutely increases drag, and thus reduces speed.

My question is, do we know whether it's salt or fresh water? If it's salt water, there's IMHO no reason why it would be hard to give the ASDS the capability to self-ballast on location (if it does not already have it). If that ballast water is fresh water (and also the source for the deck water cannons) then it becomes a bit harder, depending on the reasons. If the ASDS holds can't handle salt water due to corrosion concerns, then enabling it to do so would be harder (perhaps as hard as painting the interior with the same sort of paint as used on the exterior underwater areas). As for the water cannon, if those are fresh water, perhaps the ASDS could sortie with only one or two compartments ballasted with fresh water, and the rest empty (to be ballasted on location).

Hrmmm. I wonder what the towing speed difference is with an unballasted ASDS vs. a ballasted one? Elsbeth III is small for an oceangoing tug, but not underpowered (5000HP). but the real number we're looking for is bollard pull (the actual amount of force applied via the towline). That varies with tug engine, powertrain, and prop design so it's not a straight conversion from horsepower, but I'm lazy and just looking for a ballpark figure so... turns out Smith Marine has the answer; 50 tons. The tow line is 2 1/4 inch steel, which can easily handle that kind of load.

As for the ASDS... we need to calculate drag. So, I'm going to pretend the ASDS is just a barge (the only parts in the water essentially are). I'm way the heck out of my depth (pun intended) here, because I know how to do this for yachts, not barges, so I may be way the heck off. Okay, the two main factors are skin friction and wave (wake) making. Skin friction increases linearly with wetted area (so doubling the wetted hull area via ballasting or loading doubles skin friction) but speed increases drag by the square of the speed. So, doubling the speed doesn't double the drag, it squares it. Therefor, to go faster, you really, really need smaller wetted area vs. more power - so your point about ballasting is spot on; getting rid of the ballast (and halving the wetted area) would have far more impact on potential speed than getting a larger tug with twice the bollard pull.

I really should give calculating the actual potential speeds a try, but I need to look up some formulas for that, so I'll need some free time and coffee, neither of which are available to me at the moment. If I can, I'll give it a whirl later.
   

 

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 9931
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 6744
  • Likes Given: 4524
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #707 on: 04/28/2016 07:48 PM »
Old small powerboat driver here (in my misspent youth) and I remember the faster you could get on plane[1], the faster you could reach top speed. I also remember  that we got on plane faster if there weren't a lot of people in the bow seats, thus improving the angle of attack.

So if we're talking about manipulating ballast, any merit in having the front of the ASDS ride higher so it would plane easier? I don't know if it's even feasible to speak of getting a barge on plane.. how much more powerful of a tug is needed?

I also remember that the ride was rougher when you're on plane, especially when the waves were certain unfortunate heights/periods, so that there would be a perodic oscillation that would build up. (which you addressed by changing speed slightly) So maybe even if you COULD get on plane you might not WANT to, as it would damage the equipment. (maybe you plane on the way out but return more slowly so as not to damage the stage??)

Note that once you are on plane your wetted area (and thus, drag) goes way down. This is why getting on plane is key for a floatplane that wants to actually take off. As long as it's wallowing it'll never get up enough speed to get airborne. It takes more power to GET on plane than it does to STAY on plane so the excess power then can be used to accelerate further.

1 - https://en.wikipedia.org/wiki/Planing_%28boat%29
« Last Edit: 04/28/2016 07:50 PM by Lar »
"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 Kabloona

  • Senior Member
  • *****
  • Posts: 4227
  • Velocitas Eradico
  • Fortress of Solitude
  • Liked: 2447
  • Likes Given: 506
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #708 on: 04/28/2016 08:06 PM »
Quote
So if we're talking about manipulating ballast, any merit in having the front of the ASDS ride higher so it would plane easier? I don't know if it's even feasible to speak of getting a barge on plane.. how much more powerful of a tug is needed?

A million-pound barge on a plane? Shirley, you jest.  ;)
« Last Edit: 04/28/2016 08:07 PM by Kabloona »

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 9931
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 6744
  • Likes Given: 4524
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #709 on: 04/28/2016 08:23 PM »
Quote
So if we're talking about manipulating ballast, any merit in having the front of the ASDS ride higher so it would plane easier? I don't know if it's even feasible to speak of getting a barge on plane.. how much more powerful of a tug is needed?

A million-pound barge on a plane? Shirley, you jest.  ;)
On plane, not on *A* plane. And don't call me Shirley. :) I trust you did read the WP article I linked...

Although it does seem unlikely, the ASDS does have one thing going for it, the aft end is flat, which helps to achieve planing. But the power required to overcome the hull speed might be immense.
"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 OxCartMark

  • Full Member
  • ****
  • Posts: 1054
  • Michigan
  • Liked: 820
  • Likes Given: 884
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #710 on: 04/28/2016 08:32 PM »
Lar,

Kabloona is right.  It'll be best if you cop to a jesting charge.

There are planing hulls and there are displacement hulls.  Barges and tug boats have displacement hulls.

CJ,

Yes, the fresh vs. salt question is a large question and I don't know the answer.  The other question that figures large into my unballasting suggestion is whether the towing of CRS-8 back to port was done at a reduced speed because they felt the stage couldn't handle more boaty motion than it was getting at the reduced speed....or not.

Online Doesitfloat

  • Full Member
  • **
  • Posts: 224
  • Detroit MI
  • Liked: 311
  • Likes Given: 135
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #711 on: 04/28/2016 08:43 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.

Regarding the proposals for deep sea anchoring -
Perhaps that scheme would benefit from having the anchor lines connected to 4 autonomous drone winches?

Mark, IMHO that's an excellent point on ballasting; taking the ASDS out ballasted absolutely increases drag, and thus reduces speed.

My question is, do we know whether it's salt or fresh water? If it's salt water, there's IMHO no reason why it would be hard to give the ASDS the capability to self-ballast on location (if it does not already have it). If that ballast water is fresh water (and also the source for the deck water cannons) then it becomes a bit harder, depending on the reasons. If the ASDS holds can't handle salt water due to corrosion concerns, then enabling it to do so would be harder (perhaps as hard as painting the interior with the same sort of paint as used on the exterior underwater areas). As for the water cannon, if those are fresh water, perhaps the ASDS could sortie with only one or two compartments ballasted with fresh water, and the rest empty (to be ballasted on location).

Hrmmm. I wonder what the towing speed difference is with an unballasted ASDS vs. a ballasted one? Elsbeth III is small for an oceangoing tug, but not underpowered (5000HP). but the real number we're looking for is bollard pull (the actual amount of force applied via the towline). That varies with tug engine, powertrain, and prop design so it's not a straight conversion from horsepower, but I'm lazy and just looking for a ballpark figure so... turns out Smith Marine has the answer; 50 tons. The tow line is 2 1/4 inch steel, which can easily handle that kind of load.

As for the ASDS... we need to calculate drag. So, I'm going to pretend the ASDS is just a barge (the only parts in the water essentially are). I'm way the heck out of my depth (pun intended) here, because I know how to do this for yachts, not barges, so I may be way the heck off. Okay, the two main factors are skin friction and wave (wake) making. Skin friction increases linearly with wetted area (so doubling the wetted hull area via ballasting or loading doubles skin friction) but speed increases drag by the square of the speed. So, doubling the speed doesn't double the drag, it squares it. Therefor, to go faster, you really, really need smaller wetted area vs. more power - so your point about ballasting is spot on; getting rid of the ballast (and halving the wetted area) would have far more impact on potential speed than getting a larger tug with twice the bollard pull.

I really should give calculating the actual potential speeds a try, but I need to look up some formulas for that, so I'll need some free time and coffee, neither of which are available to me at the moment. If I can, I'll give it a whirl later.
   

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.


Offline John Alan

  • Full Member
  • ****
  • Posts: 667
  • Central IL - USA - Earth
  • Liked: 350
  • Likes Given: 1565
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #712 on: 04/28/2016 08:50 PM »
Next mod to the ASDS... more power...  :o
Add a 20,000+hp gas turbine stern drive to the hull...
Give the tug a remote control to the powerplant...
Tell em to dial it up till it tries to pass you...  ;D

on edit...
I'm kidding of course...  ;)
« Last Edit: 04/28/2016 08:57 PM by John Alan »

Online acsawdey

  • Full Member
  • ***
  • Posts: 365
  • Minnesota
  • Liked: 215
  • Likes Given: 380
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #713 on: 04/28/2016 08:53 PM »
https://twitter.com/elonmusk/status/565637505811488768?lang=en

Elon mentioned giving it a Merlin. How fast would that go?  ;)

Offline OxCartMark

  • Full Member
  • ****
  • Posts: 1054
  • Michigan
  • Liked: 820
  • Likes Given: 884
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #714 on: 04/28/2016 08:54 PM »
Doesitfloat-

- Is ballasting with sea water OK?
- If the ASDS were easier to tow couldn't the propellers on the tug be changed to be efficient at a higher speed?
- What do you think of towing the ASDS unballasted?
- Built in ballasting / unballasting system feasible?  Rapid?


edit: I don't think a Merlin or a 20,000 hp gas turbine would be a productive modification.  Look at the drag curve.  Need to do something to create a different curve.  Thus my inquiry on unballasting.
« Last Edit: 04/28/2016 08:56 PM by OxCartMark »

Offline rds100

  • Member
  • Posts: 93
  • Liked: 8
  • Likes Given: 21
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #715 on: 04/28/2016 08:54 PM »
It can work, if the stage is towing the ASDS, should have enough power  ;) Just kidding.
I'm still for "pickup the stage with a sufficiently large helicopter and bring it to shore this way, leave the ASDS in place waiting for the next stage". Unfortunately i was told that such a helicopter doesn't exist today.


Online Doesitfloat

  • Full Member
  • **
  • Posts: 224
  • Detroit MI
  • Liked: 311
  • Likes Given: 135
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #716 on: 04/28/2016 08:58 PM »
Next mod to the ASDS... more power...  :o
Add a 20,000+hp gas turbine stern drive to the hull...
Give the tug a remote control to the powerplant...
Tell em to dial it up till it tries to pass you...  ;D

on edit...
I'm kidding of course...  ;)

But You're right it will fit on an LCAC


****Elon---We need a Hovercraft****

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 9931
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 6744
  • Likes Given: 4524
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #717 on: 04/28/2016 09:08 PM »
Kabloona is right.  It'll be best if you cop to a jesting charge.

I'll plead ignorance but not jesting. I never jest. Honest. :)

I bet there's a way to get that barge on plane.  Just not a practical way.
"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 Doesitfloat

  • Full Member
  • **
  • Posts: 224
  • Detroit MI
  • Liked: 311
  • Likes Given: 135
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #718 on: 04/28/2016 09:12 PM »
Doesitfloat-

- Is ballasting with sea water OK?
- If the ASDS were easier to tow couldn't the propellers on the tug be changed to be efficient at a higher speed?
- What do you think of towing the ASDS unballasted?
- Built in ballasting / unballasting system feasible?  Rapid?


edit: I don't think a Merlin or a 20,000 hp gas turbine would be a productive modification.  Look at the drag curve.  Need to do something to create a different curve.  Thus my inquiry on unballasting.

Ballasting with seawater is normal.  Most ports require ships to exchange ballast water 15-20 miles out to limit invasive marine species.

Very difficult to change to high speed propellers.  Whole boat/engine/ gearbox set up to pull/push at slow speed.

Easier to tow ballasted.  Less movement on the end of a long towline.

Built in ballasting is possible not usually done on a deck cargo barge. Just tanks below the deck; no machinery per classification.  We have seen pictures using the Marmac barges as dry-dock equipped with external piping to ballast tanks.

Offline Kabloona

  • Senior Member
  • *****
  • Posts: 4227
  • Velocitas Eradico
  • Fortress of Solitude
  • Liked: 2447
  • Likes Given: 506
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #719 on: 04/28/2016 09:18 PM »
Kabloona is right.  It'll be best if you cop to a jesting charge.

I'll plead ignorance but not jesting. I never jest. Honest. :)

I bet there's a way to get that barge on plane.  Just not a practical way.

To be serious, no. Power requirement for a displacement hull that size to plane approaches infinity, more or less.

Tags: