Author Topic: What will the BFS tanker look like?  (Read 13134 times)

Offline Zed_Noir

  • Senior Member
  • *****
  • Posts: 2447
  • Canada
  • Liked: 359
  • Likes Given: 568
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.

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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

  • Full Member
  • *
  • Posts: 123
  • Liked: 59
  • Likes Given: 147
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?

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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

  • Full Member
  • *
  • Posts: 123
  • Liked: 59
  • Likes Given: 147
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

  • Full Member
  • ****
  • Posts: 849
  • Liked: 326
  • Likes Given: 276
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

  • Full Member
  • *
  • Posts: 123
  • Liked: 59
  • Likes Given: 147
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.

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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.

Online speedevil

  • Senior Member
  • *****
  • Posts: 2525
  • Fife
  • Liked: 1272
  • Likes Given: 1392
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

  • Full Member
  • *
  • Posts: 123
  • Liked: 59
  • Likes Given: 147
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.

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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

  • Senior Member
  • *****
  • Posts: 3217
  • Boca Chica, Texas
  • Liked: 5316
  • Likes Given: 332
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 »

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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

  • Full Member
  • ****
  • Posts: 613
  • Orlando, FL
  • Liked: 394
  • Likes Given: 238
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.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 28348
  • Minnesota
  • Liked: 8193
  • Likes Given: 5425
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...
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online RotoSequence

  • Full Member
  • ****
  • Posts: 1003
  • Liked: 712
  • Likes Given: 849
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

  • Full Member
  • ****
  • Posts: 849
  • Liked: 326
  • Likes Given: 276
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.

Offline rakaydos

  • Full Member
  • ****
  • Posts: 451
  • Liked: 179
  • Likes Given: 4
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

  • Senior Member
  • *****
  • Posts: 4896
  • Michigan
  • Liked: 2013
  • Likes Given: 1
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 »
DM

Online nacnud

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2287
  • Liked: 445
  • Likes Given: 210
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.

Tags: