Author Topic: BFR ASDS  (Read 17103 times)

Online Lars-J

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Re: BFR ASDS
« Reply #60 on: 11/03/2017 08:51 PM »
We've known about the requirement to splash a stage by moving out of the way ever since the first landing attempt - so it's not only a current feature, it's a primary one - and we've all seen what can happen after a bad  (non-emergency) landing.

The IIP is off the Landing Target until they are committed to the attempt.  The booster decides to try to hit the ASDS if things look good.  The ASDS doesn't decide to try to dodge the booster if things look bad.

Are you implying by that that they start off with the ASDS off-target and move it in if all is good??  ???

Better go read https://forum.nasaspaceflight.com/index.php?topic=39766.0 and especially http://forum.nasaspaceflight.com/index.php?topic=36326.0 again..
No, the barge doesn't move at all. The booster changes its landing target to the preset asds coords once it is happy that a safe landing can be attempted.

Right... This is determined when the landing burn starts. If the landing engine(s) starts, it will aim for the landing point. Otherwise the consensus is that it will continue in its trajectory and crash near it. The landing burn starts pretty high so it is able to do that.

Online AC in NC

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Re: BFR ASDS
« Reply #61 on: 11/04/2017 02:33 AM »
The booster decides to try to hit the ASDS if things look good.

Are you implying by that that they start off with the ASDS off-target and move it in if all is good??  ???  Better go read ... [snip] ... again...

How could you POSSIBLY conceive that implication from what I wrote?

In pictures.  Please don't insist that this Land Based diagram doesn't mean anything with respect to ASDS landing profile.  The ASDS doesn't try to dodge the booster in a worst-case scenario anymore than LC-1 does.

« Last Edit: 11/04/2017 02:37 AM by AC in NC »

Offline yokem55

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Re: BFR ASDS
« Reply #62 on: 11/06/2017 04:20 AM »
We've known about the requirement to splash a stage by moving out of the way ever since the first landing attempt - so it's not only a current feature, it's a primary one - and we've all seen what can happen after a bad  (non-emergency) landing.

The IIP is off the Landing Target until they are committed to the attempt.  The booster decides to try to hit the ASDS if things look good.  The ASDS doesn't decide to try to dodge the booster if things look bad.

Are you implying by that that they start off with the ASDS off-target and move it in if all is good??  ???

Better go read https://forum.nasaspaceflight.com/index.php?topic=39766.0 and especially http://forum.nasaspaceflight.com/index.php?topic=36326.0 again..
No, the barge doesn't move at all. The booster changes its landing target to the preset asds coords once it is happy that a safe landing can be attempted.

Right... This is determined when the landing burn starts. If the landing engine(s) starts, it will aim for the landing point. Otherwise the consensus is that it will continue in its trajectory and crash near it. The landing burn starts pretty high so it is able to do that.
Except this didn't work with SES-9. My bet is that the 3-engine burn attempt didn't allow for enough time to retarget after knowing they had 3 good engines, so it was a committed attempt from the get go. When the engine(s?) failed the impact point was already on the ASDS and so poor OCISLY got Falcon-Punched at high speed.

Online guckyfan

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Re: BFR ASDS
« Reply #63 on: 11/06/2017 07:36 AM »
Except this didn't work with SES-9. My bet is that the 3-engine burn attempt didn't allow for enough time to retarget after knowing they had 3 good engines, so it was a committed attempt from the get go. When the engine(s?) failed the impact point was already on the ASDS and so poor OCISLY got Falcon-Punched at high speed.

I see this event as SpaceX willing to risk damage to the ASDS to prove they can hit the target even under extreme conditions. Which would help getting approval for land landing.

Offline JamesH65

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Re: BFR ASDS
« Reply #64 on: 11/06/2017 11:22 AM »
We've known about the requirement to splash a stage by moving out of the way ever since the first landing attempt - so it's not only a current feature, it's a primary one - and we've all seen what can happen after a bad  (non-emergency) landing.

The IIP is off the Landing Target until they are committed to the attempt.  The booster decides to try to hit the ASDS if things look good.  The ASDS doesn't decide to try to dodge the booster if things look bad.

Are you implying by that that they start off with the ASDS off-target and move it in if all is good??  ???

Better go read https://forum.nasaspaceflight.com/index.php?topic=39766.0 and especially http://forum.nasaspaceflight.com/index.php?topic=36326.0 again..
No, the barge doesn't move at all. The booster changes its landing target to the preset asds coords once it is happy that a safe landing can be attempted.

Right... This is determined when the landing burn starts. If the landing engine(s) starts, it will aim for the landing point. Otherwise the consensus is that it will continue in its trajectory and crash near it. The landing burn starts pretty high so it is able to do that.
Except this didn't work with SES-9. My bet is that the 3-engine burn attempt didn't allow for enough time to retarget after knowing they had 3 good engines, so it was a committed attempt from the get go. When the engine(s?) failed the impact point was already on the ASDS and so poor OCISLY got Falcon-Punched at high speed.

Experimental landing. Has it happened since? Not that I am aware of. So the experiment lead to changes to stop is happening again. R&D.

The ASDS doesn't move.

Online envy887

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Re: BFR ASDS
« Reply #65 on: 11/06/2017 01:28 PM »
Right... This is determined when the landing burn starts. If the landing engine(s) starts, it will aim for the landing point. Otherwise the consensus is that it will continue in its trajectory and crash near it. The landing burn starts pretty high so it is able to do that.
Except this didn't work with SES-9. My bet is that the 3-engine burn attempt didn't allow for enough time to retarget after knowing they had 3 good engines, so it was a committed attempt from the get go. When the engine(s?) failed the impact point was already on the ASDS and so poor OCISLY got Falcon-Punched at high speed.

I thought the booster ran out of propellant on that attempt - which would happen after moving the impact point on target.

Online AC in NC

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Re: BFR ASDS
« Reply #66 on: 11/06/2017 07:44 PM »
Except this didn't work with SES-9. My bet is that the 3-engine burn attempt didn't allow for enough time to retarget after knowing they had 3 good engines, so it was a committed attempt from the get go. When the engine(s?) failed the impact point was already on the ASDS and so poor OCISLY got Falcon-Punched at high speed.

Not sure what would lead one to believe that a 3-engine burn wouldn't allow enough time to retarget.  I don't think the details are public knowledge so I guess we're speculating either way, but I just don't know what suggests that the vertical distance involved in a 3-engine burn isn't plenty of room to retarget horizontally the necessary distance.


I see this event as SpaceX willing to risk damage to the ASDS to prove they can hit the target even under extreme conditions. Which would help getting approval for land landing.

SES-9 was after the first successful LZ-1 landing.


Offline UKobserver

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Re: BFR ASDS
« Reply #67 on: 12/24/2017 04:53 PM »
Or SpaceX can build a fleet of BFR sized ASDS floating platforms after where ever they chose as the first BFR pad.
I think a floating platform to launch and land BFR/BFS is highly unlikely.  Way more issues here.  For a rocket that big, a floating platform would probably need to be huge, which would be really expensive.

Fixed launch pads several miles offshore seem much more likely.  These would have legs that physically connect with the ocean floor, with cables and pipelines connecting back to land.  This arrangement is very typical in the oil and gas industry, so it would probably be relatively economical.

Especially if they start the P2P (point to point) service with the BFR.
For this, Elon's presentation showed a small launch platform several miles offshore.  This implies a fixed launch platform that's physically connected to the ocean floor.  A floating platform for a BFR size rocket would probably need to be an order of magnitude larger.

Yes that's true, I hadn't thought about an offshore platform in Florida; if they opted for that then it wouldnít interfere with their current operations and my logic about building BC first wouldnít apply.

I guess Iíd assumed that they would experiment on land first, but in fairness SpaceX have shown they are willing to be bold and jump in with both feet (ASDS was a great example), so maybe they will indeed go straight for the offshore design from the beginning. As you say; it removes a lot of the red tape and removes most of the risk to people/property/wildlife that slows down land-based testing. The initial F9 landing tests and the prototype carbon BFS tank testing were good examples of the freedom the ocean can offer. I guess you could even argue that offshore is the most logical choice for their first prototype; any effort expended designing a land-based pad could have very limited further application, given that most or all of their initial point to point pads will likely need to be offshore for noise/safety/public confidence considerations. For all we know they could already have quietly commissioned a shipyard somewhere to start converting a used jack-up rig into their first prototype BFR pad. Makes you think!

The comments above have also got me thinking about the video images of their future offshore point to point pads; I assumed when I first saw the Adelaide presentation that we weren't meant to take every detail literally and that it was just to give us the basic concept - a vertical booster on a flat platform with tanks. But I'm starting to wonder. If you look closely, we see an elongated rectangular platform, which could be interpreted as a sea-going barge, ie. longer than it is wide. It clearly is sitting on legs resting on the sea bottom, but that could easily make it a jack-up vessel, as I suggested above (and I think others have before). I was originally thinking more like a stationary oil rig, but what if it is a barge/ship and intended to shuttle out to the launch site each time carrying everything it needs? I initially discounted that possibility because I was thinking a fueled, vertical booster would want to topple over at sea, but of course they wouldn't travel with it fueled, and I've only just realised they wouldn't travel with it integrated either. If we assume that for transit all the propellant is in the tanks (keeping most of the mass very close to deck level), and if we assume that the empty (ie. relatively light) BFS is parked on it's haunches on the spot marked X, and the empty (therefore also light) booster is parked on it's launch mount, then transiting out to the launch site wouldn't be any more challenging or any less sea-worthy than bringing a F9 back to shore on an ASDS is currently.

I know that would be too slow an evolution for the eventual point to point model, but for the first few years of experimentation, of Starlink launches, and even fuelling/launching the first few Mars missions, it would be fine. We're only talking a few miles offshore, so not the 24/48hr transits that OCISLY is currently doing, so we're only talking a few hours for them to crane the loaded BFS onto the barge, fill the barge tanks, move to the launch site, lift the BFS onto the BFR, fuel, launch, recover BFR (and maybe BFS too, or if it needs longer in space you instead recover the BFS that launched yesterday/whenever) and return to base. They could easily be back in port 18 hours after leaving, ready to swap the empty BFS for the next one loaded with satellites/fuel for the Mars journey. One launch a day is still an incredibly high launch rate, and removes any near term need to worry about pipelines. Suddenly the offshore option looks extremely simple, easier even than a land pad I would say.

BTW although I think the point to point idea is perfectly feasible and a potentially viable business (at least for long-haul), I don't see it happening overnight. I think it will start with just one or two niche long-distance city pair routes where the massive time-saving will make it attractive to premium customers, enough for some of them to overcome any anxiety they may have about the risk. I'm talking Shanghai to New York types of distance. And I suspect although we will see plenty of scepticism, disbelief and denial (as with booster re-use) and even outright refusal to allow it in some jurisdictions, what I think will win out is that some cities will see it as a way to put themselves on the map, as the place where the future is really happening now. Think how much extra tourism that first pair of cities is going to get.. How many people in the eastern US would fly to New York just so they could experience that flight, rather than using their nearest big airport to fly direct. I think that's how it will start. But I digress, sorry mods.
« Last Edit: 12/24/2017 05:04 PM by UKobserver »

Offline Ludus

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Re: BFR ASDS
« Reply #68 on: 01/01/2018 07:29 AM »
Quote
If you look closely, we see an elongated rectangular platform, which could be interpreted as a sea-going barge, ie. longer than it is wide. It clearly is sitting on legs resting on the sea bottom, but that could easily make it a jack-up vessel, as I suggested above (and I think others have before). ]

I wasnít sure what you were seeing, but when I looked at the posted picture I get it. Itís a pretty poor frame grab. What looks like legs are actually reflections in the water. The platform is at the sea surface like a barge with no legs showing.
« Last Edit: 01/01/2018 03:27 PM by Ludus »

Offline UKobserver

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Re: BFR ASDS
« Reply #69 on: 01/02/2018 04:56 PM »
Quote
If you look closely, we see an elongated rectangular platform, which could be interpreted as a sea-going barge, ie. longer than it is wide. It clearly is sitting on legs resting on the sea bottom, but that could easily make it a jack-up vessel, as I suggested above (and I think others have before). ]

I wasnít sure what you were seeing, but when I looked at the posted picture I get it. Itís a pretty poor frame grab. What looks like legs are actually reflections in the water. The platform is at the sea surface like a barge with no legs showing.

Oh dear, that's embarrassing  :-[ Not sure how I missed that!

Offline IntoTheVoid

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Re: BFR ASDS
« Reply #70 on: 01/03/2018 03:59 AM »
I've read the talk of oil rigs, and barges, and jack-up rigs, but what about it not being a ASDS but a SPP (a SpacePort Pier) With the water as shallow as it is, how do the costs compare if they instead built it like a freestanding bridge pier. It would be the most stable option, and would eliminate the hull inspections, etc. Presumably there could be other inspections, but it's got to be more convenient to have them come to you.

Online Steve D

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Re: BFR ASDS
« Reply #71 on: 01/03/2018 03:53 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by. Not good if they start finding dolphins and endangered sea turtles washing up on the beach cooked......
« Last Edit: 01/03/2018 03:57 PM by Steve D »

Offline JamesH65

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Re: BFR ASDS
« Reply #72 on: 01/03/2018 05:13 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by. Not good if they start finding dolphins and endangered sea turtles washing up on the beach cooked......

Er what? They won't be directing the exhaust straight in to the water, surely?

I'm not a fan of the offshore pad, at least initially anyway. Its expensive just putting in a 5 mile causeway and launch pad....

Offline speedevil

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Re: BFR ASDS
« Reply #73 on: 01/03/2018 05:23 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by.
This is one thing you can pretty much ignore as a concern.
The rocket 'only' burns ten or twenty tons of methane while clearing the tower, this is enough to only heat to boiling 1000 tons of water.
Or 10m*10m*10m - around the same scale as the launchpad. It will heat a 100m*100m*10m patch on average by 1C.
(this assumes that all heat is efficiently transferred to water, which it will not be, and that this is the case for the first several seconds, and no water boils)
Close enough to the rocket to be thermally damaging will be extremely sonically damaging.

Online whitelancer64

Re: BFR ASDS
« Reply #74 on: 01/03/2018 05:53 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by.
This is one thing you can pretty much ignore as a concern.
The rocket 'only' burns ten or twenty tons of methane while clearing the tower, this is enough to only heat to boiling 1000 tons of water.
Or 10m*10m*10m - around the same scale as the launchpad. It will heat a 100m*100m*10m patch on average by 1C.
(this assumes that all heat is efficiently transferred to water, which it will not be, and that this is the case for the first several seconds, and no water boils)
Close enough to the rocket to be thermally damaging will be extremely sonically damaging.

This. It'll be the noise killing wildlife, not the heat.
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Online Steve D

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Re: BFR ASDS
« Reply #75 on: 01/03/2018 06:04 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by.
This is one thing you can pretty much ignore as a concern.
The rocket 'only' burns ten or twenty tons of methane while clearing the tower, this is enough to only heat to boiling 1000 tons of water.
Or 10m*10m*10m - around the same scale as the launchpad. It will heat a 100m*100m*10m patch on average by 1C.
(this assumes that all heat is efficiently transferred to water, which it will not be, and that this is the case for the first several seconds, and no water boils)
Close enough to the rocket to be thermally damaging will be extremely sonically damaging.

This. It'll be the noise killing wildlife, not the heat.

Well, dead is dead. I wonder if they plan on installing blast deflectors to divert the flame off to the side instead of straight down. It may help to minimize the affect of all of the noise and heat. But if endangered sea turtles which do nest in the area get killed you can be sure that the environmentalists will shut them down. Sea life is attracted to structures such as this. I have been diving on quite a few oil rigs off the Texas coast and they all have large amounts of fish and corals growing on them. 

Offline Ludus

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Re: BFR ASDS
« Reply #76 on: 01/03/2018 10:12 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by. Not good if they start finding dolphins and endangered sea turtles washing up on the beach cooked......

Er what? They won't be directing the exhaust straight in to the water, surely?

I'm not a fan of the offshore pad, at least initially anyway. Its expensive just putting in a 5 mile causeway and launch pad....

I havenít seen any mention or reason for a causeway. Whatís shown is like an ASDS but larger and set up for BFR launches as well as landings. That would be MUCH cheaper and more scalable than any land based launchpad where most of limitations, cost and time would be about local impact. Seaplatforms could be built in shipyards and towed into place.

Offline Ludus

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Re: BFR ASDS
« Reply #77 on: 01/03/2018 10:21 PM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by.
This is one thing you can pretty much ignore as a concern.
The rocket 'only' burns ten or twenty tons of methane while clearing the tower, this is enough to only heat to boiling 1000 tons of water.
Or 10m*10m*10m - around the same scale as the launchpad. It will heat a 100m*100m*10m patch on average by 1C.
(this assumes that all heat is efficiently transferred to water, which it will not be, and that this is the case for the first several seconds, and no water boils)
Close enough to the rocket to be thermally damaging will be extremely sonically damaging.

This. It'll be the noise killing wildlife, not the heat.

Well, dead is dead. I wonder if they plan on installing blast deflectors to divert the flame off to the side instead of straight down. It may help to minimize the affect of all of the noise and heat. But if endangered sea turtles which do nest in the area get killed you can be sure that the environmentalists will shut them down. Sea life is attracted to structures such as this. I have been diving on quite a few oil rigs off the Texas coast and they all have large amounts of fish and corals growing on them.

Unless itís a platform thatís elevated quite a bit above the surface, the thrust has to be ducted off to the side across the sea surface rather than directly into it.

There would be a lot of study put in on this issue. Sound is likely to be a bigger problem than any effect from heat. Sea turtles that nest on the beach there are more likely impacted by a launchpad on shore.

Offline JamesH65

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Re: BFR ASDS
« Reply #78 on: 01/04/2018 11:35 AM »
One thing that bothers me about launching from off shore is the impact on marine life in the area of the launch pad. All of that  thrust blasting directly into shallow water is going to cook anything close by. Not good if they start finding dolphins and endangered sea turtles washing up on the beach cooked......

Er what? They won't be directing the exhaust straight in to the water, surely?

I'm not a fan of the offshore pad, at least initially anyway. Its expensive just putting in a 5 mile causeway and launch pad....

I havenít seen any mention or reason for a causeway. Whatís shown is like an ASDS but larger and set up for BFR launches as well as landings. That would be MUCH cheaper and more scalable than any land based launchpad where most of limitations, cost and time would be about local impact. Seaplatforms could be built in shipyards and towed into place.

Cheaper? Running costs would be large - how do you get the BFS to the pad? I'd expect its going to need to come back to dry land for all the initial flights. How do you get the fuel to the pad?

Once BFx is up and running, then maybe. But in the prototyping period, having a floating launch pad will be a PITA. You got to build it first, for starters! Of course, if they started now, they could have it ready in a couple of years I suppose.

Hmm, still not convinced. Just build a pad on the ground at BC or Florida.

Offline Dave G

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Re: BFR ASDS
« Reply #79 on: 01/13/2018 01:38 PM »
how do you get the BFS to the pad? I'd expect its going to need to come back to dry land for all the initial flights.
By ship.  For a fixed launch site 5-10 miles offshore, this wouldn't be very expensive.  After the initial flights, BFS would just stay at the pad.

How do you get the fuel to the pad?
For a fixed launch site 5-10 miles offshore, I'm assuming underwater flexible pipelines.

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