Author Topic: What will the BFS tanker look like?  (Read 13166 times)

Online Slarty1080

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What will the BFS tanker look like?
« on: 03/24/2018 11:42 AM »
BFS tanker variant – I would be interested in people’s views of what this might look like. We know that it will be optimised for maximum fuel transfer, will be reusable, be based on the BFS design and according to Elon will look “kind of weird”. So what options are there?

From a weight saving angle it should resemble an elongated sphere with a diameter of 9 meters. But it will also need to re-enter the atmosphere and land so will need the BFS engine layout and heat shield. But how much of the rest of the BFS structure will it use? Will it just be a cut down BFS shell? Or a standard BFS shell with empty space in it? What might count as kind of weird?
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Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #1 on: 03/24/2018 12:35 PM »
BFS tanker variant – I would be interested in people’s views of what this might look like.

I would not be surprised if it is not considerably delayed.
BFS in the minimum Mars capable form - no windows, passenger door, ... is quite capable of lifting fuel, and at best you're going to get another 20-30 tons fuel from a tanker, due to lowering structural weight.

This means a tanker flies 10-20% less, for bulk fuel deliveries - while still being a large slice as expensive to construct as a 'normal' BFS.

A spare BFS may be operationally more valuable at this point.

Addressing the 'it's gonna look wierd' comment.
In principle, thermal protection may be moderately easier in some ways with a 15m tanker, that launches mostly dry, and has great ability to act as a depot.

This is inconsistent with the IAC2017 presentation showing similar OML though.

Offline Archibald

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Re: What will the BFS tanker look like?
« Reply #2 on: 03/24/2018 03:18 PM »
Interestingly enough, while the KC-135 was Boeing main aerial tanker, there were also a lot of converted civilian 707 tankers, less efficient but cheaper to operate. Same dilema here !

On top of my head, bar USAF of course, in fact few other air forces ever bought KC-135s: perhaps France and Turkey. Everybody else, from Israel to Canada to Australia, got converted 707s.
« Last Edit: 03/25/2018 09:34 AM by Archibald »
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Online Elmar Moelzer

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Re: What will the BFS tanker look like?
« Reply #3 on: 03/25/2018 03:01 PM »
This is inconsistent with the IAC2017 presentation showing similar OML though.
I saw that quote from Musk and I believe that the tanker shown in the 2017 presentation is essentially the cargo version of BFS without cargo bay doors. Musk however indicated on Reddit that there will be a dedicated tanker version that will look "kind of weird". So what ways are there to cut down the outer mold line without losing aerodynamic properties for launch and re- entry? Maybe they will also move (or remove) the wings?

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #4 on: 03/25/2018 03:44 PM »
This is inconsistent with the IAC2017 presentation showing similar OML though.
I saw that quote from Musk and I believe that the tanker shown in the 2017 presentation is essentially the cargo version of BFS without cargo bay doors. Musk however indicated on Reddit that there will be a dedicated tanker version that will look "kind of weird". So what ways are there to cut down the outer mold line without losing aerodynamic properties for launch and re- entry? Maybe they will also move (or remove) the wings?

I guess there are several kinds of weird.
It looks like a chicken. (it is clear to the general public that is confused if Voyager is a real science show it looks weird).
It looks very different to IAC2017 BFS.
It looks very odd to people who understand rockets at first glance.

The last one might almost be 'lol - we did nothing other than remove the windows', from the perspective of the third.
Those who have 'it must be as light as possible' baked in as a mantra, when easy reusability trumps it so far as to make lightness irrelevant mostly.
But that's a bit of a cop-out.

Significantly oversized/diameter tanks, compared to BFS.
I think this is possibly the most plausible.
Once experience is gained by operating BFR, the stresses on the interface during normal launch will be well known, and allow for reasonable safe extrapolation to rather more draggy and heavy payloads.
This is not going to look very weird to someone in the general public.

The only sort-of-sane 'really weird' suggestion I can think of that makes some degree of sense would be a very large tank, capable of storing 4000 tons or so of propellant, which normally lifts off with 2000ish tons, with the normal BFS raptors supplemented by four raptors on the outside diameter, several degrees out so as to parallel stage with S1 at liftoff to get the launch acceleration reasonable.

This would look weird and sort-of-work, and be a really, really awesome moon lander basis, as the jets from the top would not impinge on the legs.

However, as above, I'm not sure we're seeing tankers soon - unless they are cutdown BFS.

Online Elmar Moelzer

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Re: What will the BFS tanker look like?
« Reply #5 on: 03/25/2018 08:52 PM »
The exact quote by Musk is:
Quote
At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).

Offline Archibald

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Re: What will the BFS tanker look like?
« Reply #6 on: 03/26/2018 05:57 AM »
Just a simple question. We know that at least five tankers will be needed to fill the tanks of a single BFS. So every single tanker will have to dock back-to-back with the BFS, rince, repeat.
I wonder instead about a true, permanent  propellant depot with 2200 mt or 3300 mt of methalox, enough to refuel 2 or 3 BFS with a single docking. Kind of space gas station, really.
I suppose Musk thought about it but don't want permanent orbital infrastructures with their maintenance cost...
« Last Edit: 03/26/2018 05:59 AM by Archibald »
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Online niwax

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Re: What will the BFS tanker look like?
« Reply #7 on: 03/26/2018 08:08 AM »
Just a simple question. We know that at least five tankers will be needed to fill the tanks of a single BFS. So every single tanker will have to dock back-to-back with the BFS, rince, repeat.
I wonder instead about a true, permanent  propellant depot with 2200 mt or 3300 mt of methalox, enough to refuel 2 or 3 BFS with a single docking. Kind of space gas station, really.
I suppose Musk thought about it but don't want permanent orbital infrastructures with their maintenance cost...

I'm not sure what the advantage of that would be. The only difference is slightly looser scheduling regarding resupply launches as compared to direct tanking for significantly higher cost. If BFR is really meant to fly every few days, I doubt they'd gain much by being able to store fuel beforehand.

Offline MikeAtkinson

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Re: What will the BFS tanker look like?
« Reply #8 on: 03/26/2018 11:59 AM »
Just a simple question. We know that at least five tankers will be needed to fill the tanks of a single BFS. So every single tanker will have to dock back-to-back with the BFS, rince, repeat.
I wonder instead about a true, permanent  propellant depot with 2200 mt or 3300 mt of methalox, enough to refuel 2 or 3 BFS with a single docking. Kind of space gas station, really.
I suppose Musk thought about it but don't want permanent orbital infrastructures with their maintenance cost...

I'm not sure what the advantage of that would be. The only difference is slightly looser scheduling regarding resupply launches as compared to direct tanking for significantly higher cost. If BFR is really meant to fly every few days, I doubt they'd gain much by being able to store fuel beforehand.

For Mars a "fleet" is supposed to leave Earth orbit at the same time (where at the same time might be weeks for cargo, but instantaneous for crew). Being able to decouple launching the fleet in a few days (and then refueling them almost immediately) from launching the tankers over 6 months is a major advantage.

A small fleet of 2 crew and 4 cargo ships would require 30+ tanker flights. At a launch cadence of 1 per day some of the ships would have to hang around in LEO for a month. A disruption in tanker flights, e.g. by a hurricane, anywhere in that month could lead to the optimum TMI window being missed. Boil-off from the fueled ships in LEO would also be an issue.

This issue only gets worse as the size of the fleet grows.

Some form of propellant depot(s) has major advantages, whether those advantages are enough to cause SpaceX to use a propellant depot for early synods is debatable. I tend to think not, but only SpaceX have all the information.

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #9 on: 03/26/2018 03:19 PM »
A small fleet of 2 crew and 4 cargo ships would require 30+ tanker flights. At a launch cadence of 1 per day some of the ships would have to hang around in LEO for a month. A disruption in tanker flights, e.g. by a hurricane, anywhere in that month could lead to the optimum TMI window being missed. Boil-off from the fueled ships in LEO would also be an issue.

It is interesting to note that you can have BFR take off and climb at 100MPH, for most of the ascent through harsh weather, and still get a notable payload to orbit. This is just fine for a fuel launch, if you happen to be constrained somewhat by weather.

You also need several tankers, for redundancy reasons.

Remember, this is 2024, not 2022.
Starlink is launched, and SpaceX at the very least have the additional revenue from operations and launch of a full constellation.
In 2024, it's 5-6 years since BFS first flew.
They will have a very reasonable idea of operations.

If you don't care much about weight, suitable tanks are off the shelf.
https://www.alibaba.com/product-detail/ASME-or-GB-Standard-Liquid-Oxygen_60681993254.html
Contains 50 tons of propellant, boils off at 0.1%/day, weighs 13 tons.
You can in three BFS launches for about $3M buy the tanks for a propellant depot to retank one BFS.

(this is just an example - you may well want to use a larger tank)

« Last Edit: 03/26/2018 03:34 PM by speedevil »

Offline JamesH65

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Re: What will the BFS tanker look like?
« Reply #10 on: 03/26/2018 03:30 PM »
In answer to the original question.

How about a large spherical 2nd stage sitting on a BFB? Would definitely look odd, but best space efficiency. Slow launch, ramp up speed as you get out of the atmosphere. Fuel is cheap so you can afford to do that as long as the BFB can lift it. Can be tank in tank if you want duel fuel, or launch two, one for each fuel.

Online RonM

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Re: What will the BFS tanker look like?
« Reply #11 on: 03/26/2018 04:16 PM »
A small fleet of 2 crew and 4 cargo ships would require 30+ tanker flights. At a launch cadence of 1 per day some of the ships would have to hang around in LEO for a month. A disruption in tanker flights, e.g. by a hurricane, anywhere in that month could lead to the optimum TMI window being missed. Boil-off from the fueled ships in LEO would also be an issue.

It is interesting to note that you can have BFR take off and climb at 100MPH, for most of the ascent through harsh weather, and still get a notable payload to orbit. This is just fine for a fuel launch, if you happen to be constrained somewhat by weather.

No, lightning strikes would still be a problem.

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #12 on: 03/26/2018 04:50 PM »
No, lightning strikes would still be a problem.

For some weather, yes, this will not help at all.

Offline Ludus

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Re: What will the BFS tanker look like?
« Reply #13 on: 03/27/2018 02:05 AM »
The Tanker and Cargo ship are the same ship. As a Tanker it just flies with an empty cargo bay. This isn’t much different from AF tankers for the same reasons. If the OML was filled with topped off propellant tanks it couldn’t take off. This isn’t a bug it’s a feature. It lets SpaceX concentrate on a single simple design that performs all required missions.

Obviously SX did some analysis for a tweaked dedicated Tanker that looks weird. I’m doubtful there’s enough performance advantage to justify building it for a long time.

The Cargo/Tanker really could perform the human passengers to Mars mission too and might be more efficient if less cool. Just put an appropriately sized hab module in the cargo bay. On Mars, you can leave the entire module where it’s more useful and send the ship back empty instead of hauling back all that extra mass as with a dedicated passenger ship. No windows is about the only drawback.

« Last Edit: 03/27/2018 02:09 AM by Ludus »

Online Robotbeat

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Re: What will the BFS tanker look like?
« Reply #14 on: 03/27/2018 02:10 AM »
Are you certain? The 2016 ITS showed differences between the tanker and the ship. The tanker had significantly lower dry mass and significantly greater propellant mass than the ship.

At first, sure, the tanker and the ship might be the same thing.
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Offline Ludus

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Re: What will the BFS tanker look like?
« Reply #15 on: 03/27/2018 02:24 AM »
Are you certain? The 2016 ITS showed differences between the tanker and the ship. The tanker had significantly lower dry mass and significantly greater propellant mass than the ship.

At first, sure, the tanker and the ship might be the same thing.

I have no special knowledge. The 2016 presentation emphasized the Ship as a Buck Rodgers passenger liner. 2017 got around to more emphasis on the Cargo variant that just leaves that whole forward Ship volume empty. I’m inclined to think they got much more practical. It’s been a long time since I did the numbers on it but I became convinced at the time that the volume of full propellant tanks couldn’t be increased very much and that suggested there wasn’t much point in building Cargo and Tanker with different specs.

There was a discussion of building a Deep Space Booster variant that could dock nose to tail. THAT version, that SX has said nothing about, might launch with Tanks that filled the whole OML but only partially filled. Then it could take more Tanker loads and be a better Booster.

Offline tea monster

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Re: What will the BFS tanker look like?
« Reply #16 on: 03/27/2018 05:25 PM »
Assuming that it will be "Kind of weird" in a way that disposes of winglets and has a more conical nose, it may look like this:



These were from another thread where it was posited that the tanker wouldn't have winglets like the main ship. Personally, I think it will.

Offline cppetrie

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Re: What will the BFS tanker look like?
« Reply #17 on: 03/27/2018 06:10 PM »
The purpose of the winglets is adapt the aero profile across a variety of payload amounts and atmospheric conditions. Given that the tanker will always land under the same conditions (essentially empty and on earth) the winglets may not be needed.  Or they may be fixed or different shaped.

Online wannamoonbase

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Re: What will the BFS tanker look like?
« Reply #18 on: 03/27/2018 06:31 PM »
The purpose of the winglets is adapt the aero profile across a variety of payload amounts and atmospheric conditions. Given that the tanker will always land under the same conditions (essentially empty and on earth) the winglets may not be needed.  Or they may be fixed or different shaped.

I assume there will be 1 mold line, one set of tooling and 1 way to do things.  Right up to the point they decide if it's Cargo, Crew or Tanker.

Tanker should be the easiest of all of them.

Not expecting to see anything soon.  Lots of development to be done. 

I'll entertain myself with the epic accomplishments of the Falcon family until then.
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Offline cppetrie

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Re: What will the BFS tanker look like?
« Reply #19 on: 03/27/2018 07:47 PM »
The purpose of the winglets is adapt the aero profile across a variety of payload amounts and atmospheric conditions. Given that the tanker will always land under the same conditions (essentially empty and on earth) the winglets may not be needed.  Or they may be fixed or different shaped.

I assume there will be 1 mold line, one set of tooling and 1 way to do things.  Right up to the point they decide if it's Cargo, Crew or Tanker.

Tanker should be the easiest of all of them.

Not expecting to see anything soon.  Lots of development to be done. 

I'll entertain myself with the epic accomplishments of the Falcon family until then.
We’ve already been told by Elon that the dedicated tanker will look “weird”. To me that means the dedicated tanker will probably not share the same OML as the ship and cargo versions. But the dedicated tanker will come (much) later. The early tankers will just be cargo versions with no cargo and so of course will have the same OML.

Online Zed_Noir

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Re: What will the BFS tanker look like?
« Reply #20 on: 03/29/2018 06:30 AM »
The purpose of the winglets is adapt the aero profile across a variety of payload amounts and atmospheric conditions. Given that the tanker will always land under the same conditions (essentially empty and on earth) the winglets may not be needed.  Or they may be fixed or different shaped.

I assume there will be 1 mold line, one set of tooling and 1 way to do things.  Right up to the point they decide if it's Cargo, Crew or Tanker.

Tanker should be the easiest of all of them.

Not expecting to see anything soon.  Lots of development to be done. 

I'll entertain myself with the epic accomplishments of the Falcon family until then.
We’ve already been told by Elon that the dedicated tanker will look “weird”. To me that means the dedicated tanker will probably not share the same OML as the ship and cargo versions. But the dedicated tanker will come (much) later. The early tankers will just be cargo versions with no cargo and so of course will have the same OML.
I think the later unmanned variants of the BFS tanker will have the same OML as the transport variants on the reentry facing portions of the BFS. The other portions could be drastically cut down. In effect asymmetrical airframe cross-sections. Along with parallel vertical propellant tanks.

All the above speculation is due to the fact that the extra 150 to 175 metric tons of propellants for the tanker role doesn't take up much volume. There will be a lot of empty volume if the initial BFS transport OML is utilized.

Online rakaydos

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Re: What will the BFS tanker look like?
« Reply #21 on: 03/29/2018 08:35 PM »
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

It would be very fluffy on reentry, with engine mass to the rear, and more reentry surface than a normal BFR. I would think that this would make up for any extra mass for a larger design by saving landing fuel from a softer landing.

Offline octavo

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Re: What will the BFS tanker look like?
« Reply #22 on: 04/01/2018 08:55 AM »
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

It would be very fluffy on reentry, with engine mass to the rear, and more reentry surface than a normal BFR. I would think that this would make up for any extra mass for a larger design by saving landing fuel from a softer landing.
The engines in the wings would not be thrusting through the centre of mass. Gimballing them through the centre would induce a backwards translation. I suppose if you're coming in from orbit, this might actually help do the flip upright and reduce forward velocity?

Online rakaydos

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Re: What will the BFS tanker look like?
« Reply #23 on: 04/02/2018 05:41 PM »
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

It would be very fluffy on reentry, with engine mass to the rear, and more reentry surface than a normal BFR. I would think that this would make up for any extra mass for a larger design by saving landing fuel from a softer landing.
The engines in the wings would not be thrusting through the centre of mass. Gimballing them through the centre would induce a backwards translation. I suppose if you're coming in from orbit, this might actually help do the flip upright and reduce forward velocity?
Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Offline octavo

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Re: What will the BFS tanker look like?
« Reply #24 on: 04/03/2018 07:12 AM »
I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Perhaps I'm misunderstanding you - are you suggesting 4 winglets instead of 2, with an engine in each wing (therefore symmetric thrust) or are you saying the wings should be moved to the centre of the cylinder so that you can have symmetric thust without a second set of wings? Otherwise I'm not following.

Offline hkultala

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Re: What will the BFS tanker look like?
« Reply #25 on: 04/03/2018 07:33 AM »
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

Makes absolutely no sense.

Lifting weight of these engines and their tanks all the way to the orbit.

Heat shielding the first stage tanks from the plume of these engines

All the stability/control trouble of engines whose thrust vector is very far from the center of the gravity.

Better to have more engines in the first stage instead - and oh, it already contains 31 of those.


« Last Edit: 06/17/2018 05:40 PM by hkultala »

Offline octavo

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Re: What will the BFS tanker look like?
« Reply #26 on: 04/03/2018 07:46 AM »
I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Perhaps I'm misunderstanding you - are you suggesting 4 winglets instead of 2, with an engine in each wing (therefore symmetric thrust) or are you saying the wings should be moved to the centre of the cylinder so that you can have symmetric thust without a second set of wings? Otherwise I'm not following.

Online rakaydos

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Re: What will the BFS tanker look like?
« Reply #27 on: 04/03/2018 03:57 PM »
I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Perhaps I'm misunderstanding you - are you suggesting 4 winglets instead of 2, with an engine in each wing (therefore symmetric thrust) or are you saying the wings should be moved to the centre of the cylinder so that you can have symmetric thust without a second set of wings? Otherwise I'm not following.
Moving the wings to parallel the axis of thrust- sorry I thought that was imlied by putting things in them. I was unclear.
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

Makes absolutely no sense.

Lifting weight of these engines and their tanks all the way to the orbit.

Heat shielding the first stage tanks from the plume of these engines

All the stability/control trouble of engines whose thrust vector is very far from the center of the gravity.

Better to have more engines in the first stage instead - and oh, it already contains 31 of those.
In case you didnt notice, the upper stage already includes sea level engines for landing purposes. Moving them to the wings to be used on ascent doesnt actually add mass. Tanks do, but we're adding tanks because it's a tanker.

As far as heat shielding... a properly expanded bell apparetly makes the exaust not so hot. Something about turning heat into movement.

Offline speedevil

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Re: What will the BFS tanker look like?
« Reply #28 on: 04/03/2018 04:04 PM »

As far as heat shielding... a properly expanded bell apparetly makes the exaust not so hot. Something about turning heat into movement.
Only with respect to the moving exhaust.
If you place a thermometer moving along with the exhaust, it may read around 100C.
If you place one sticking into the exhaust stationary, it will read about the same temperature as the combustion chamber.
Plume interaction with structure can heat it a lot.
Plus, if there is residual air, that gets heated lots by turbulence and impact from the jet.

Offline octavo

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Re: What will the BFS tanker look like?
« Reply #29 on: 04/03/2018 07:00 PM »
Apologies for the multiple posts with messed up quotes. I'm not quite sure how that happened.

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Re: What will the BFS tanker look like?
« Reply #30 on: 04/03/2018 08:35 PM »
Apologies for the multiple posts with messed up quotes. I'm not quite sure how that happened.
When you split the quote, you forgot to endquote in the middle.

As far as heat shielding... a properly expanded bell apparetly makes the exaust not so hot. Something about turning heat into movement.
Only with respect to the moving exhaust.
If you place a thermometer moving along with the exhaust, it may read around 100C.
If you place one sticking into the exhaust stationary, it will read about the same temperature as the combustion chamber.
Plume interaction with structure can heat it a lot.
Plus, if there is residual air, that gets heated lots by turbulence and impact from the jet.

And I believe I made a point that any "aerospike-like" effects would have to be properly designed to avoid problems like plume heating. Otherwise the engines would need enough gimbal to avoid plume impingement until stage separation.

Offline Nomadd

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Re: What will the BFS tanker look like?
« Reply #31 on: 04/03/2018 11:40 PM »
 I'm not sure about a 2,000 ton fuel depot, but the idea of what could take advantage of a replenishable, available BFS tank rigged for long term use has to be going through a lot of minds. Or single use tankers rigged for non SpaceX users. 
 NASA or commercial, it would enable entirely new architectures.
« Last Edit: 04/03/2018 11:41 PM by Nomadd »

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Re: What will the BFS tanker look like?
« Reply #32 on: 04/04/2018 12:27 AM »
I'm not sure about a 2,000 ton fuel depot, but the idea of what could take advantage of a replenishable, available BFS tank rigged for long term use has to be going through a lot of minds. Or single use tankers rigged for non SpaceX users. 
 NASA or commercial, it would enable entirely new architectures.
SpaceX is basically going to define the Industry Standard Cryomethane refueling interface. I hope they are planning around future designs being backward compatable.

Offline intrepidpursuit

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Re: What will the BFS tanker look like?
« Reply #33 on: 06/16/2018 06:10 AM »
The tanker will want to share as many parts with BFS as possible, including tooling, but they will want to shed extra weight, complexity and cost. Another difference is that the tanker will go through atmosphere at least an order of magnitude more often than a BFS, so it may use a slightly different TPS strategy.

I think it will just be a stubby BFS with an identical thrust structure and lower cylinder, but minus the winglets since they won't be necessary for simple empty LEO reentry and likely slightly stretched. The upper part that would house payload is just dead weight. IMHO the nose will be simplified to make TPS replacement easier (more identical tiles/segments), perhaps a simple cone or even a half sphere.

If the tanker was going to be identical to a cargo BFS, then it would just be a cargo BFS. And it will be at the beginning so they can focus on a single configuration and build experience. The goal of the dedicated tanker will be to reuse all the expensive stuff from BFS, but leave out unnecessary structure to save weight and cost and optimize it for LEO use.

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Re: What will the BFS tanker look like?
« Reply #34 on: 06/16/2018 06:27 AM »
I'm not sure about a 2,000 ton fuel depot, but the idea of what could take advantage of a replenishable, available BFS tank rigged for long term use has to be going through a lot of minds. Or single use tankers rigged for non SpaceX users. 
 NASA or commercial, it would enable entirely new architectures.
SpaceX is basically going to define the Industry Standard Cryomethane refueling interface. I hope they are planning around future designs being backward compatable.
And then no one else will use it, even though it's clearly better. Instead, they'll develop much larger interfaces that cost more and can't transfer fuel as quickly...
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Re: What will the BFS tanker look like?
« Reply #35 on: 06/16/2018 07:56 AM »
And then no one else will use it, even though it's clearly better. Instead, they'll develop much larger interfaces that cost more and can't transfer fuel as quickly...

The automakers are coasting on the weight of legacy infrastructure, which doesn't exist in Space. Once Government becomes a customer, there's a better chance that they'll start asking for companies to provide services that require SpaceX's refueling interface.

Offline hkultala

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Re: What will the BFS tanker look like?
« Reply #36 on: 06/17/2018 05:42 PM »
I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Perhaps I'm misunderstanding you - are you suggesting 4 winglets instead of 2, with an engine in each wing (therefore symmetric thrust) or are you saying the wings should be moved to the centre of the cylinder so that you can have symmetric thust without a second set of wings? Otherwise I'm not following.
Moving the wings to parallel the axis of thrust- sorry I thought that was imlied by putting things in them. I was unclear.
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

Makes absolutely no sense.

Lifting weight of these engines and their tanks all the way to the orbit.

Heat shielding the first stage tanks from the plume of these engines

All the stability/control trouble of engines whose thrust vector is very far from the center of the gravity.

Better to have more engines in the first stage instead - and oh, it already contains 31 of those.
In case you didnt notice, the upper stage already includes sea level engines for landing purposes. Moving them to the wings to be used on ascent doesnt actually add mass. Tanks do, but we're adding tanks because it's a tanker.

As far as heat shielding... a properly expanded bell apparetly makes the exaust not so hot. Something about turning heat into movement.

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

So, makes no sense.

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Re: What will the BFS tanker look like?
« Reply #37 on: 06/23/2018 02:39 PM »
I'm thinking a rounded diamond or arrowhead shape, outboard SL engines in the "wings" for landing, Vac engines in the circular interface with Stage 1, (up to 7 R-vac with no gimbal, but probably not that many) and the rest of the internal volume is fuel. Exact size is iterated based on how much fuel the rocket can lift to a reference orbit.

Thrusting throught the center of mass is done to avoid a rotation, which is nessisary for asymetric thrust. With symmetric thrusters, however, a tractor arrangement (skycrane?) should be reasonable

Perhaps I'm misunderstanding you - are you suggesting 4 winglets instead of 2, with an engine in each wing (therefore symmetric thrust) or are you saying the wings should be moved to the centre of the cylinder so that you can have symmetric thust without a second set of wings? Otherwise I'm not following.
Moving the wings to parallel the axis of thrust- sorry I thought that was imlied by putting things in them. I was unclear.
Just speculating here...

I like the idea mentioned of improving payload to orbit by having outward gimbaled sea level engines outboard on the second stage, to improve liftoff TWR. Possibly with some aerospike-like effects as the plume interacts with the body, if you have enough balls to design it that way. (note: this very dangerous if not designed correctly)

Makes absolutely no sense.

Lifting weight of these engines and their tanks all the way to the orbit.

Heat shielding the first stage tanks from the plume of these engines

All the stability/control trouble of engines whose thrust vector is very far from the center of the gravity.

Better to have more engines in the first stage instead - and oh, it already contains 31 of those.
In case you didnt notice, the upper stage already includes sea level engines for landing purposes. Moving them to the wings to be used on ascent doesnt actually add mass. Tanks do, but we're adding tanks because it's a tanker.

As far as heat shielding... a properly expanded bell apparetly makes the exaust not so hot. Something about turning heat into movement.

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.

Online docmordrid

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Re: What will the BFS tanker look like?
« Reply #38 on: 06/23/2018 08:00 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 reduce mass & increase 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 :)
« Last Edit: 06/24/2018 09:31 AM by docmordrid »
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Re: What will the BFS tanker look like?
« Reply #39 on: 06/23/2018 10:04 PM »
I don't think that will work aerodynamically, you'll want to have an ogive fairing.

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.


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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 »

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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 »

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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.

Online 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.

Jonesing for a copy of 'Tales of Suspense #39'

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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ABCD: Always Be Counting Down

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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ABCD: Always Be Counting Down

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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ABCD: Always Be Counting Down

ABCD - Always Be Counting Down

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