Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3  (Read 827200 times)

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10796
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7720
  • Likes Given: 5560
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #660 on: 04/26/2016 06:04 PM »
Has anyone plotted the location of all ASDS landing attempts so far? Do we have a pattern developing? (perhaps factor out some of the early ones that had high margins and were almost standins for RTLS) My thinking here is that even with two ASDSii[1], you don't need a full complement of support ships IF two successive landings are fairly closeish together... you have a fast tug shoot out bringing an empty ASDS, and turning around to tow one ASDS back with stage, while the flotilla and empty ASDS decamp to the next location. Sucks to be the guys on board the flotilla as they don't get as much shore leave but they can handle it...

(this is a cheaper (temporary??) variant of the "purpose built fast ship with crane to return stages to land leaving the ASDS at sea" idea)

1 - obviously the plural of ASDS is ASDSii ...
« Last Edit: 04/26/2016 06:05 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 IntoTheVoid

  • Full Member
  • **
  • Posts: 296
  • USA
  • Liked: 244
  • Likes Given: 60
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #661 on: 04/26/2016 06:10 PM »
Would you really need a full up 2nd ASDS and host of associated equipment? Or could you possibly use an unmodified crane barge?
Lift the landed stage off the ASDS with the crane barge while on station. Crane barge with possibly it's own tug (or not depending on timing) would lift the S1 off the ASDS and return separately while the ASDS awaited the next landing, moving if necessary.

Edit: Ninja'd by the Mod.
« Last Edit: 04/26/2016 06:14 PM by IntoTheVoid »

Offline OxCartMark

  • Full Member
  • ****
  • Posts: 1109
  • Michigan
  • Liked: 879
  • Likes Given: 908
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #662 on: 04/26/2016 06:19 PM »
I've got this silly picture running through my head that I need to vent out.

One way to land multiple multiple cores on a barge without having to return would be to cover the deck with conveyor belt material.  Conceptually Rexnord tabletop chain.  ...Which would be in constant motion from fore to aft.  The stages would touch down in the center or forward center part of the deck and be conveyed rearward by the conveyor action until coming to a stop against a modified higher blast wall at the rear.  Perhaps with some side guides as well.  You could probably get 50 or so of them to stack up back there before the ASDS would need to come in to be unloaded, assuming the legs nested well.

Check 1:43 of this video for the general concept -

Offline rsdavis9

How about refuel on barge and hop? Maybe in a year?
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline IntoTheVoid

  • Full Member
  • **
  • Posts: 296
  • USA
  • Liked: 244
  • Likes Given: 60
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #664 on: 04/26/2016 06:25 PM »
The stages would touch down in the center or forward center part of the deck and be conveyed rearward by the conveyor action until coming to a stop against a modified higher blast wall at the rear.  Perhaps with some side guides as well.  You could probably get 50 or so of them to stack up back there before the ASDS would need to come in to be unloaded, assuming the legs nested well.

Check 1:43 of this video for the general concept

What I don't understand is... why would you skip the rinse stage at 0:50?

Offline CT Space Guy

  • Member
  • Posts: 45
  • Liked: 16
  • Likes Given: 0

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10796
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7720
  • Likes Given: 5560
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #666 on: 04/26/2016 06:29 PM »
Would you really need a full up 2nd ASDS and host of associated equipment? Or could you possibly use an unmodified crane barge?
Lift the landed stage off the ASDS with the crane barge while on station. Crane barge with possibly it's own tug (or not depending on timing) would lift the S1 off the ASDS and return separately while the ASDS awaited the next landing, moving if necessary.

Edit: Ninja'd by the Mod.
Who me? No, your idea is different... I think more expensive, barge mounted cranes are presumably more expensive than  the whole rest of the ASDS but i could be wrong.
"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 envy887

  • Senior Member
  • *****
  • Posts: 4826
  • Liked: 2712
  • Likes Given: 1446
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #667 on: 04/26/2016 06:31 PM »
I've got this silly picture running through my head that I need to vent out.

One way to land multiple multiple cores on a barge without having to return would be to cover the deck with conveyor belt material.  Conceptually Rexnord tabletop chain.  ...Which would be in constant motion from fore to aft.  The stages would touch down in the center or forward center part of the deck and be conveyed rearward by the conveyor action until coming to a stop against a modified higher blast wall at the rear.  Perhaps with some side guides as well.  You could probably get 50 or so of them to stack up back there before the ASDS would need to come in to be unloaded, assuming the legs nested well.

That's $2 billion worth of rockets sitting out on a barge in the Atlantic for many weeks...  :o

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10796
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7720
  • Likes Given: 5560
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #668 on: 04/26/2016 06:36 PM »
That canning line thing was amusing but let's stick to halfway realistic ideas for how to handle increased cadence.... Or the thread might be canned.
"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 IntoTheVoid

  • Full Member
  • **
  • Posts: 296
  • USA
  • Liked: 244
  • Likes Given: 60
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #669 on: 04/26/2016 06:38 PM »
Would you really need a full up 2nd ASDS and host of associated equipment? Or could you possibly use an unmodified crane barge?
Lift the landed stage off the ASDS with the crane barge while on station. Crane barge with possibly it's own tug (or not depending on timing) would lift the S1 off the ASDS and return separately while the ASDS awaited the next landing, moving if necessary.

Edit: Ninja'd by the Mod.
Who me? No, your idea is different... I think more expensive, barge mounted cranes are presumably more expensive than  the whole rest of the ASDS but i could be wrong.

I'm thinking standard COTS stuff. 14 day rental or whatever it needs. No long term lease, no wing mods, no thrustmasters, no mm precision automated positioning, etc. Rent it, go pick up the stage, fill the gas tank, and return it. Hertz/Avis style. I don't see how it would be more expensive than modifying and maintaining a 2nd ASDS. (All uninformed opinion, I could easily be wrong.) Something like...
https://www.dnlsalvage.com/services/crane-barges/

Offline Arb

  • Full Member
  • ***
  • Posts: 345
  • London
  • Liked: 224
  • Likes Given: 208
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #670 on: 04/26/2016 07:44 PM »
Occasional sailor here.

There's a huge difference between craning from ship to ship in the calm sheltered waters of a harbour and out in the open ocean where there are significant waves almost all the time. Consider what happens if a hoisted first stage starts to pendulum...

Not saying it couldn't be done (the USN have researched crane designs that counteract wave motion for according to Google) but not going to be easy or cheap, IMO.

Offline CJ

  • Full Member
  • ****
  • Posts: 887
  • Liked: 649
  • Likes Given: 180
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #671 on: 04/26/2016 08:39 PM »
Thank you!

That rohn tower does indeed have a combined anemometer/direction indicator, and it's ultrasonic.
.......
I'd also be willing to bet that somewhere aboard is an accelerometer/tiltmeter, to give them data on the exact attitude and motion of the ASDS at the moment of touchdown (for later analysis, not realtime use).  Might also be useful to know before launch if conditions are marginal (assuming they'd delay a launch for a landing issue). 

The high-res photos aren't quite high-res enough to work out exactly what they're using, but for completeness it is probably what is technically known as a "marine weather station", similar to this one:



These units use on-board GPS and gyros to compensate for movement of the platform giving precise true wind speed and direction - something I presume they'd need to know in the final seconds before touchdown - and the gyro outputs can be useful for motion recording also.  They're extraordinarily accurate.. to tenths of a knot!


PS:  Apologies for the viewing angle mix-up.  I've edited my original post accordingly.

I think you've hit the nail on the head; that sort of data station would provide a lot that they need.

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.


Online launchwatcher

  • Full Member
  • ***
  • Posts: 376
  • Liked: 258
  • Likes Given: 362
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #672 on: 04/26/2016 09:01 PM »
Not saying it couldn't be done (the USN have researched crane designs that counteract wave motion for according to Google) but not going to be easy or cheap, IMO.
Motion-compensating technology is apparently deployed in production in the North Sea for the offshore energy industry (oil/gas/wind).

Here's video of a motion-compensated crane in operation:



(see 37 minutes 10 seconds in; I attempted to link directly there but the embed is losing the time offset somehow).

They also have a motion-compensated walkway allowing workers to "walk to work" across the North Sea.   This video shows it compensating for ship-to-fixed-platform motion but other videos show it doing ship-to-ship adjustments.

I agree that it's not going to be cheap, but it might be cheaper than maintaining a large fleet of ASDS's and continuously towing them back & forth between the port and the landing zones.
« Last Edit: 04/26/2016 09:05 PM by launchwatcher »

Offline LastStarFighter

  • Full Member
  • **
  • Posts: 232
  • Europa
  • Liked: 71
  • Likes Given: 11
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #673 on: 04/26/2016 09:16 PM »
That canning line thing was amusing but let's stick to halfway realistic ideas for how to handle increased cadence.... Or the thread might be canned.

My vote (if they need more east coast help) would be to bring JRtI back from the west coast once VAFB RTLS is approved. I don't see anything on the manifest for the West Coast that would really require a barge landing. Maybe I'm over looking some larger payload missions though.

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 10796
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 7720
  • Likes Given: 5560
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #674 on: 04/26/2016 09:19 PM »
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.
"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 acsawdey

  • Full Member
  • ****
  • Posts: 402
  • Minnesota
  • Liked: 244
  • Likes Given: 478
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #675 on: 04/26/2016 10:03 PM »
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.

A fun motion control problem indeed -- reminds me of how a double-pendulum is a classic chaotic physical system. If you squint at it right, you could convince yourself a stage hanging from a crane boom would behave this way too.

Online launchwatcher

  • Full Member
  • ***
  • Posts: 376
  • Liked: 258
  • Likes Given: 362
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #676 on: 04/26/2016 10:49 PM »
That's amazing. However their target is a fixed platform.

Not always!  Ship-to-ship motion compensation is demonstrated here:



(skip ahead to 3:00 or so).   They do mention "constant force" so they're likely using force-feedback control; they'd clearly need to integrate other sensors to do more general ship-to-ship motion compensation. 

Quote
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.
No doubt!  Though if deck motion on the destination was a problem they could put the stage stand onto another motion-compensated platform.


Online llanitedave

  • Senior Member
  • *****
  • Posts: 2157
  • Nevada Desert
  • Liked: 1332
  • Likes Given: 1569
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #677 on: 04/26/2016 11:02 PM »
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.


If they were going to do a ship to ship transfer, I believe they'd be better off with, rather than craning from one barge to another, creating a system that can lay the stage horizontal and set it on a faster, narrower boat with proper cradling.  Maybe that would allow them to remove the legs in transit, and they'd have much of the reprocessing one by the time they offloaded the stage in port.
"I've just abducted an alien -- now what?"

Offline CameronD

  • Full Member
  • ****
  • Posts: 1441
  • Melbourne, Australia
    • Norton Consultants
  • Liked: 469
  • Likes Given: 337
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #678 on: 04/26/2016 11:17 PM »
That's amazing. However their target is a fixed platform.

Not always!  Ship-to-ship motion compensation is demonstrated here:

Makes you sea-sick just watching it.  :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 CameronD

  • Full Member
  • ****
  • Posts: 1441
  • Melbourne, Australia
    • Norton Consultants
  • Liked: 469
  • Likes Given: 337
Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3
« Reply #679 on: 04/26/2016 11:22 PM »
Has anyone plotted the location of all ASDS landing attempts so far? Do we have a pattern developing? (perhaps factor out some of the early ones that had high margins and were almost standins for RTLS) My thinking here is that even with two ASDSii[1], you don't need a full complement of support ships IF two successive landings are fairly closeish together... you have a fast tug shoot out bringing an empty ASDS, and turning around to tow one ASDS back with stage, while the flotilla and empty ASDS decamp to the next location. Sucks to be the guys on board the flotilla as they don't get as much shore leave but they can handle it...

Note that, if money is no object, there's nothing stopping them using a ship-carrier to get the ASDS out on station a fair bit quicker than any "fast tug" could tow it.



Float-on, float-off..

EDIT:  If they sent a maintenance crew along with it, they could clean the barnacles off of the hull and refresh the anti-foul whilst they're on the way out.  ;D


« Last Edit: 04/26/2016 11:26 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.

Tags: