Author Topic: What will the BFS tanker look like?  (Read 12000 times)

Offline meekGee

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Re: What will the BFS tanker look like?
« Reply #40 on: 06/23/2018 10:29 PM »
My $0.02

We've heard from Musk that the initial tanker will be a BFS cargo, and logic dictates it'll likely be gutted to educe mass & increasd margins. We also heard from Musk that a dedicated Tanker will look “kind of weird”.

Starting from those items, I checked the below linked NASA patent PDF documenting potential aeroshell shapes,

https://patents.google.com/patent/US8725470B1/en

#14888 is circular in cross section and with more parallel sides than BFS's foreward section. Given this additional forward tanks seem simpler. Perhaps it could also form the basis of an improved Chomper satellite dispenser - one without the tapered payload bay & door.

Perhaps larger winglets, though I didn't depict them.

OK, pick it apart :)

Even if the nose cone is not quite right, yeah, maybe.  But it will be shorter.  With this length, IMO the tanker will be too heavy.

Since for the tanker doesn't have boil-off issues, the landing tanks can be taken out of the main tanks and placed anywhere on the ship, helping with control of c.g. for reentry.  Since re-entry is always on earth, the back-side "canard" might be different. Since they hold the flapperons (which replace the grid fins in functionality) then I doubt they can eliminate them altogether.

This last consideration applies to the p2p variant as well.
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Offline guckyfan

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Re: What will the BFS tanker look like?
« Reply #41 on: 06/24/2018 08:31 AM »
Since for the tanker doesn't have boil-off issues, the landing tanks can be taken out of the main tanks and placed anywhere on the ship, helping with control of c.g. for reentry. 

Possible, but it would have to bring major advantages. I think they will keep the propulsion part of BFS as similar as possible, just tank stretches.. Moving the landing tanks elsewhere would be a major redesign.

Offline meekGee

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Re: What will the BFS tanker look like?
« Reply #42 on: 06/24/2018 09:33 AM »
Since for the tanker doesn't have boil-off issues, the landing tanks can be taken out of the main tanks and placed anywhere on the ship, helping with control of c.g. for reentry. 

Possible, but it would have to bring major advantages. I think they will keep the propulsion part of BFS as similar as possible, just tank stretches.. Moving the landing tanks elsewhere would be a major redesign.
Yup, agreed. 

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Offline tea monster

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Re: What will the BFS tanker look like?
« Reply #43 on: 06/24/2018 10:55 AM »
Remember that a lot of the standard ITS payload area is empty (living quarters). A dedicated tanker version will be full of liquid. I'm assuming that will take up a lot less room for the same weight of fuel.


Offline nacnud

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Re: What will the BFS tanker look like?
« Reply #44 on: 06/24/2018 11:07 AM »
Remember that a lot of the standard ITS payload area is empty (living quarters). A dedicated tanker version will be full of liquid. I'm assuming that will take up a lot less room for the same weight of fuel.

Yep

BFS propellant load = 1,100 Tonne
BFS payload = 150 Tonne
BFT payload = 200 Tonne (swag)

So you'd need a 10 to 20% tank stretch. As it's only ever going to LEO and back you can position the landing tanks so you don't need the wings. The whole thing would probably be about 3/5 the length of the BFS and be shaped like a bullet.

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #45 on: 06/24/2018 11:48 AM »
Remember that a lot of the standard ITS payload area is empty (living quarters). A dedicated tanker version will be full of liquid. I'm assuming that will take up a lot less room for the same weight of fuel.
Assuming for the moment that BFS/tanker cost $150M, and launch does in fact cost (to spacex) $5M, and the tanker gets 20% more for that launch, this all ends up as tankers being quite a way in the future.

Assuming you place no benefit at all on having spare BFS, a tanker will pay for itself in around 150 launches - around 30 launches to the Moon/Mars.
So, there is no real point until we have many, many thousands of tons of stuff on Mars or Moon.

Other side benefits as well as having spare BFS may be significant - more testing per BFS 'free', higher production volume, ...

Of course, if for some reason reuse is very, very expensive - these numbers all change, in a way that might make the tanker come sooner.
« Last Edit: 06/24/2018 11:49 AM by speedevil »

Offline nacnud

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Re: What will the BFS tanker look like?
« Reply #46 on: 06/24/2018 12:31 PM »
^ what speedevil said

Offline meekGee

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Re: What will the BFS tanker look like?
« Reply #47 on: 06/24/2018 06:04 PM »
Remember that a lot of the standard ITS payload area is empty (living quarters). A dedicated tanker version will be full of liquid. I'm assuming that will take up a lot less room for the same weight of fuel.
Assuming for the moment that BFS/tanker cost $150M, and launch does in fact cost (to spacex) $5M, and the tanker gets 20% more for that launch, this all ends up as tankers being quite a way in the future.

Assuming you place no benefit at all on having spare BFS, a tanker will pay for itself in around 150 launches - around 30 launches to the Moon/Mars.
So, there is no real point until we have many, many thousands of tons of stuff on Mars or Moon.

Other side benefits as well as having spare BFS may be significant - more testing per BFS 'free', higher production volume, ...

Of course, if for some reason reuse is very, very expensive - these numbers all change, in a way that might make the tanker come sooner.
Well that's true if the tanker is "extra".  But if you need a certain (large) number of tanking launches, you need the vehicles for that.  They can be either BFSs, or tankers.  Either way you have to build them.  And if he tankers carry more, then so much the better.

You'll never be at the point where you are left with a tanker that you wish was a BFS, because you could have launched it to Mars.

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« Last Edit: 06/24/2018 06:15 PM by meekGee »
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Offline hkultala

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Re: What will the BFS tanker look like?
« Reply #48 on: 06/24/2018 07:11 PM »
Quote

Moving them to the wings would mean they could not be used for landing.

So, makes no sense.
Why not? Center of thrust is still aligned with center of mass, it just needs the same pitch-up maneuver the regular BFR needs.

Aligning center of mass with thrust vector of wing mounted engines would mean that

1) the engines would be greatly canted outwards.

This would also mean that
1A) some considerable cosine losses would occur.
1B) single-engine failure would affect the direction of vector greatly and causing big problems.

2) the engines would be greatly canted downwards.

This would mean that the landing position would be far from vertical.


Practically: It does not work.


« Last Edit: 06/24/2018 07:11 PM by hkultala »

Offline rakaydos

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Re: What will the BFS tanker look like?
« Reply #49 on: 06/25/2018 04:35 AM »
Quote

Moving them to the wings would mean they could not be used for landing.

So, makes no sense.
Why not? Center of thrust is still aligned with center of mass, it just needs the same pitch-up maneuver the regular BFR needs.

Aligning center of mass with thrust vector of wing mounted engines would mean that

1) the engines would be greatly canted outwards.

This would also mean that
1A) some considerable cosine losses would occur.
1B) single-engine failure would affect the direction of vector greatly and causing big problems.

2) the engines would be greatly canted downwards.

This would mean that the landing position would be far from vertical.


Practically: It does not work.
Single engine out is indeed a weakness. I do not feel it would be instantly fatal. While a BFT is much larger than a Dragon II, they can handle engine out just fine with outboard engines.

Also, I'm not sure I understand your 2). if the engines are firing vertically, why would the landing position NOT be vertical?

Offline hkultala

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Re: What will the BFS tanker look like?
« Reply #50 on: 06/25/2018 06:10 AM »
Quote

Moving them to the wings would mean they could not be used for landing.

So, makes no sense.
Why not? Center of thrust is still aligned with center of mass, it just needs the same pitch-up maneuver the regular BFR needs.

Aligning center of mass with thrust vector of wing mounted engines would mean that

1) the engines would be greatly canted outwards.

This would also mean that
1A) some considerable cosine losses would occur.
1B) single-engine failure would affect the direction of vector greatly and causing big problems.

2) the engines would be greatly canted downwards.

This would mean that the landing position would be far from vertical.


Practically: It does not work.
Single engine out is indeed a weakness.

I do not feel it would be instantly fatal. While a BFT is much larger than a Dragon II, they can handle engine out just fine with outboard engines.

Dragon II has EIGHT engines. It can survive engine-out by shutting the opposite side engines and it still has 75% of the original thrust.

The details are important, and in your proposition they are totally unworkable.

Quote

Also, I'm not sure I understand your 2). if the engines are firing vertically, why would the landing position NOT be vertical?

Landing pitch is what I mean.

In order to engines in wings to fire vertically through the center of mass, the craft has to be pitched considerably (~15 degrees?) away from "vertical attitude".

This would make the legs much more complex to be sure the craft does not tip over, and would mean that after landing, all the loads are in nontrivial directions.

« Last Edit: 06/25/2018 06:13 AM by hkultala »

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #51 on: 06/25/2018 11:45 AM »
Quote from: SpeedEvil
Assuming you place no benefit at all on having spare BFS, a tanker will pay for itself in around 150 launches - around 30 launches to the Moon/Mars.
Well that's true if the tanker is "extra".  But if you need a certain (large) number of tanking launches, you need the vehicles for that.  They can be either BFSs, or tankers.  Either way you have to build them.  And if he tankers carry more, then so much the better.

You'll never be at the point where you are left with a tanker that you wish was a BFS, because you could have launched it to Mars.
If you are referring to Mars, I think you're implicitly assuming that the fuelling happens once, for two vehicles, with twelve (or so) tankers.

If boiloff happens from the main tanks in a couple of weeks, tanking once a day with a BFS gets you to full quite fast, and your window to do this is quite long.

Even without off-the-shelf tanks which get 0.1% boiloff per dayand take 3 launches to get enough capacity on orbit to wholly refuel.

If you are instead referring to the distant future, where hundreds of flights per airframe are routine, I have no argument that tankers have a role.
« Last Edit: 06/25/2018 04:51 PM by speedevil »

Offline johnfwhitesell

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Re: What will the BFS tanker look like?
« Reply #52 on: 06/25/2018 03:24 PM »
SpaceX has always red-lined some hardware while leaving enormous margins in other places.  They have a one size fits all rocket so most of their payloads are under maximum capacity.  And despite this excess they apply all the gains to every rocket, every rocket gets the cooled fuelling and the titanium gridfins even though some of them wont need them.  They have (correctly IMHO) made the conclusion that you want as little variation as possible because the greater will serve in place of the lesser.

For this reason, I think a tanker version is going to be a very low priority.  Suppose a non-tanker can lift 140 tons of fuel while a tanker can lift 165.  That 25 tons might seem like a lot but it's only saving perhaps one reusable launch and only on missions leaving earth orbit.  Saving one launch here or there isn't nearly as important as getting the launch rate up.

Offline meekGee

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Re: What will the BFS tanker look like?
« Reply #53 on: 06/26/2018 03:20 AM »
SpaceX has always red-lined some hardware while leaving enormous margins in other places.  They have a one size fits all rocket so most of their payloads are under maximum capacity.  And despite this excess they apply all the gains to every rocket, every rocket gets the cooled fuelling and the titanium gridfins even though some of them wont need them.  They have (correctly IMHO) made the conclusion that you want as little variation as possible because the greater will serve in place of the lesser.

For this reason, I think a tanker version is going to be a very low priority.  Suppose a non-tanker can lift 140 tons of fuel while a tanker can lift 165.  That 25 tons might seem like a lot but it's only saving perhaps one reusable launch and only on missions leaving earth orbit.  Saving one launch here or there isn't nearly as important as getting the launch rate up.
Even if the numbers are correct, it's still so much cheaper to make a ship with no windows, airlocks, decks, cabins, ECLS...

Think about a cargo 747..

Except also other advantages such as a shorter barrel.

Since tankers are required anyway, why not build a couple of tankers first, and get basic reliability demonstrated with them?

And if one of them exposes a fatal flaw, at least the images are of a clearly ubmannable ship crashing, not a passenger ship.



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Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #54 on: 06/26/2018 10:03 AM »
SpaceX has always red-lined some hardware while leaving enormous margins in other places.  They have a one size fits all rocket so most of their payloads are under maximum capacity.  And despite this excess they apply all the gains to every rocket, every rocket gets the cooled fuelling and the titanium gridfins even though some of them wont need them.  They have (correctly IMHO) made the conclusion that you want as little variation as possible because the greater will serve in place of the lesser.

For this reason, I think a tanker version is going to be a very low priority.  Suppose a non-tanker can lift 140 tons of fuel while a tanker can lift 165.  That 25 tons might seem like a lot but it's only saving perhaps one reusable launch and only on missions leaving earth orbit.  Saving one launch here or there isn't nearly as important as getting the launch rate up.
Even if the numbers are correct, it's still so much cheaper to make a ship with no windows, airlocks, decks, cabins, ECLS...


This is not clear.
I have doubts about if the windows will materialise.

However, it is reasonable to me that the internals are wholly fittable to a largely bare shell.
The shell is going to need structural stiffener rings anyway, for example.
Bolting decks to them, rather than making the decks integral is likely to make them considerably easier to manufacture.
Similarly, I can see no reason to have the ECLSS not removable, as it adds enormous flexibility and lets your design of it be much less critical as it's not part of the ship.

The pictured BFS hatch of 3.6m is quite adequate for quite large satellite or rover/... deployment, or equipment install.

I've noted in the past that the cabins seem plausible to mount on a circumferential and longitudinal rail system, allowing rapid and easy cargo and passenger loading.



Offline CuddlyRocket

Re: What will the BFS tanker look like?
« Reply #55 on: 06/26/2018 08:21 PM »
I have doubts about if the windows will materialise.

Reminds me of the early days of both the Boeing 747 and Airbus A380 when they were promoting the idea that the larger internal volume will mean that passengers got more space and additional facilities. What happened was that the volume was used to pack more passengers in!

The windows are to help sell the dream. The reality is likely to be much more prosaic! :)

Offline alang

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Re: What will the BFS tanker look like?
« Reply #56 on: 06/28/2018 06:01 PM »
I don't get the windows either, except as you say, for marketing.
Have one or two maybe, otherwise use screens.

Offline wannamoonbase

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Re: What will the BFS tanker look like?
« Reply #57 on: 06/28/2018 06:45 PM »
Since tankers are required anyway, why not build a couple of tankers first, and get basic reliability demonstrated with them?

Because SpaceX does not have unlimited funds and like the F9 they will want paying customers to help offset development costs.

Also, like the F9, I expect to many iterations of the BFR/BFS (or BFT).  Each one getting more refined and efficient.  The

BFR is so big the first ones could be built like a battleship and still deliver payloads.

SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

Offline envy887

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Re: What will the BFS tanker look like?
« Reply #58 on: 06/29/2018 01:50 PM »
SpaceX has always red-lined some hardware while leaving enormous margins in other places.  They have a one size fits all rocket so most of their payloads are under maximum capacity.  And despite this excess they apply all the gains to every rocket, every rocket gets the cooled fuelling and the titanium gridfins even though some of them wont need them.  They have (correctly IMHO) made the conclusion that you want as little variation as possible because the greater will serve in place of the lesser.

For this reason, I think a tanker version is going to be a very low priority.  Suppose a non-tanker can lift 140 tons of fuel while a tanker can lift 165.  That 25 tons might seem like a lot but it's only saving perhaps one reusable launch and only on missions leaving earth orbit.  Saving one launch here or there isn't nearly as important as getting the launch rate up.
Even if the numbers are correct, it's still so much cheaper to make a ship with no windows, airlocks, decks, cabins, ECLS...

Think about a cargo 747..

Except also other advantages such as a shorter barrel.

Since tankers are required anyway, why not build a couple of tankers first, and get basic reliability demonstrated with them?

And if one of them exposes a fatal flaw, at least the images are of a clearly ubmannable ship crashing, not a passenger ship.



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Dedicated tankers will carry nothing except fuel. Nobody is buying fuel in orbit today, so how is that supposed to make money?

SpaceX will start with the unmanned cargo version which can deliver satellites to LEO and GTO and can also function as a less efficient tanker. That avoids the complications of crew, while actually earning revenue.

Offline meekGee

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Re: What will the BFS tanker look like?
« Reply #59 on: 06/29/2018 02:42 PM »
SpaceX has always red-lined some hardware while leaving enormous margins in other places.  They have a one size fits all rocket so most of their payloads are under maximum capacity.  And despite this excess they apply all the gains to every rocket, every rocket gets the cooled fuelling and the titanium gridfins even though some of them wont need them.  They have (correctly IMHO) made the conclusion that you want as little variation as possible because the greater will serve in place of the lesser.

For this reason, I think a tanker version is going to be a very low priority.  Suppose a non-tanker can lift 140 tons of fuel while a tanker can lift 165.  That 25 tons might seem like a lot but it's only saving perhaps one reusable launch and only on missions leaving earth orbit.  Saving one launch here or there isn't nearly as important as getting the launch rate up.
Even if the numbers are correct, it's still so much cheaper to make a ship with no windows, airlocks, decks, cabins, ECLS...

Think about a cargo 747..

Except also other advantages such as a shorter barrel.

Since tankers are required anyway, why not build a couple of tankers first, and get basic reliability demonstrated with them?

And if one of them exposes a fatal flaw, at least the images are of a clearly ubmannable ship crashing, not a passenger ship.



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Dedicated tankers will carry nothing except fuel. Nobody is buying fuel in orbit today, so how is that supposed to make money?

SpaceX will start with the unmanned cargo version which can deliver satellites to LEO and GTO and can also function as a less efficient tanker. That avoids the complications of crew, while actually earning revenue.
Yes, a cargo/tanker combo makes sense. 

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