Author Topic: Reusability of BFS Heat Shield  (Read 17398 times)

Offline biosehnsucht

  • Full Member
  • ***
  • Posts: 322
  • Liked: 112
  • Likes Given: 258
Re: Reusability of BFS Heat Shield
« Reply #20 on: 05/09/2018 10:38 pm »
With modern drone tech (to remove old tile and install new one), combined with space versions of all of the above (laser, printing, etc), you might even be able to do all that on-orbit without another flight sent up.

Ideally you'd have a system that has no need for this, but that doesn't mean knowing how might not be useful ...

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #21 on: 05/10/2018 08:43 am »
Low priority work on solutions that seem non-favoured can result in the ability to rapidly pivot if things change.
Or you could go with Occams razor that they've accepted PICAX can't hack it for upper stage recovery without unacceptable loss of payload and are going with another solution.

I reckon the ratio of energy loss from LEO compared to 1st stage separation for F9 is about 20:1 and there's a lot more surface to protect to begin with.

One of the other lessons of Shuttle maintenance was that while the acreage TPS was annoying the detail  stuff, around doors and joints was an enormous PITA. Aerosurfaces especially, requiring +/- 45deg from their centreline while stopping the ingress of very hot air. Seals and bearings were a serious pain to mfg and maintain.

OTOH the BFS shape seems much  simpler for most of its area. IIRC NASA said Shuttle had 24 000 different shaped tiles. The ability to mfg them all was viewed as a mfg triumph, rather than a design failure given the logistics of testing and repairing them.  :(

BFS's much simpler overall shape suggests a lot of it could be done as "staves," like a barrel. the joker will remain the differential thermal expansion coefficient between the integral CRFP tank structure and the selected TPS material, although NASA solved (and patented) fasteners to cope with large differential CTE's in the early 80's and I'd guess the technology is long out of patent.

An interesting development strategy for the TPS would be to cover the whole vehicle with a uniform layer of ablator, add whatever mass you could and still make orbit, then fly the re entry and see what thickness had been ablated away. Knowing the material properties of PICAX would give you a pretty good idea of how much enthalpy it had been exposed to.  This would give you a map as accurate as the positioning accuracy of the coordinate measuring hardware would allow.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3213
  • Fife
  • Liked: 1663
  • Likes Given: 1973
Re: Reusability of BFS Heat Shield
« Reply #22 on: 05/10/2018 10:11 am »
Or you could go with Occams razor that they've accepted PICAX can't hack it for upper stage recovery without unacceptable loss of payload and are going with another solution.
See the 'party balloon' tweet.
F9S2 seems headed in a different direction entirely.

Offline Patchouli

  • Senior Member
  • *****
  • Posts: 4425
  • Liked: 195
  • Likes Given: 396
Re: Reusability of BFS Heat Shield
« Reply #23 on: 05/10/2018 02:45 pm »
Or you could go with Occams razor that they've accepted PICAX can't hack it for upper stage recovery without unacceptable loss of payload and are going with another solution.

I think a possible solution for BFS since it should have a fairly low ballistic co efficient might be the metallic thermal protection system from the X-33.
For interplanetary return it would need an abalator or some form of actively cooled TPS on the hottest parts of the vehicle.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040086762.pdf

The X-33s TPS requires fewer panels and was supposed to be much lower maintenance than the Shuttle's TPS.
« Last Edit: 05/10/2018 02:46 pm by Patchouli »

Offline Elmar Moelzer

  • Senior Member
  • *****
  • Posts: 3266
  • Liked: 654
  • Likes Given: 931
Re: Reusability of BFS Heat Shield
« Reply #24 on: 05/10/2018 06:43 pm »
PICA-X is really light weight. So unless they assume it would ablate too much for rapid reusability, it should be fine.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #25 on: 05/10/2018 10:24 pm »
PICA-X is really light weight. So unless they assume it would ablate too much for rapid reusability, it should be fine.
Depends. The NASA original was tested over a rang of specific gravities (relative to water) of 0.22-1.0.

Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Elmar Moelzer

  • Senior Member
  • *****
  • Posts: 3266
  • Liked: 654
  • Likes Given: 931
Re: Reusability of BFS Heat Shield
« Reply #26 on: 05/11/2018 12:02 am »
Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
It is only 48 meters long and tapered towards the front. In return we have a small amount of wing surface that also needs to be protected. PICA-X is a little lighter than the original PICA at 0.2 grams per cm3.
I am assuming an average thickness of 4 cm. The whole ship wont need the full 4 cm of thickness. In return one can probably assume a thicker layer around the bottom half of the ship.
With all this in mind, I am estimating a very conservative 9.5 tonnes for the whole spaceship covered in PICA-X with an average thickness of 4 cm. I think that is pretty decent at 12% of the dry mass. I normally would assume about 20% of the dry mass to go to TPS. So there is still some margin there.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #27 on: 05/12/2018 05:18 pm »
Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
It is only 48 meters long and tapered towards the front. In return we have a small amount of wing surface that also needs to be protected. PICA-X is a little lighter than the original PICA at 0.2 grams per cm3.
I am assuming an average thickness of 4 cm. The whole ship wont need the full 4 cm of thickness. In return one can probably assume a thicker layer around the bottom half of the ship.
With all this in mind, I am estimating a very conservative 9.5 tonnes for the whole spaceship covered in PICA-X with an average thickness of 4 cm. I think that is pretty decent at 12% of the dry mass. I normally would assume about 20% of the dry mass to go to TPS. So there is still some margin there.
So about 11.1% of the structural mass of the BFS.

Again the question is wheather it's good enough to cope with dissipating a combined kinetic and potential energy per Kg of structure that's about 20x the F9 booster copes with.

And AFAIK it can't.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline envy887

  • Senior Member
  • *****
  • Posts: 5180
  • Liked: 3073
  • Likes Given: 1547
Re: Reusability of BFS Heat Shield
« Reply #28 on: 05/12/2018 06:05 pm »
Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
It is only 48 meters long and tapered towards the front. In return we have a small amount of wing surface that also needs to be protected. PICA-X is a little lighter than the original PICA at 0.2 grams per cm3.
I am assuming an average thickness of 4 cm. The whole ship wont need the full 4 cm of thickness. In return one can probably assume a thicker layer around the bottom half of the ship.
With all this in mind, I am estimating a very conservative 9.5 tonnes for the whole spaceship covered in PICA-X with an average thickness of 4 cm. I think that is pretty decent at 12% of the dry mass. I normally would assume about 20% of the dry mass to go to TPS. So there is still some margin there.
So about 11.1% of the structural mass of the BFS.

Again the question is wheather it's good enough to cope with dissipating a combined kinetic and potential energy per Kg of structure that's about 20x the F9 booster copes with.

And AFAIK it can't.

PICA-X works fine for Dragon which has much higher heat flux and peak temperature than BFS will have, due to Dragon's higher ballistic coefficient and lower hypersonic L/D.

Offline Eerie

  • Member
  • Full Member
  • ****
  • Posts: 780
  • Liked: 128
  • Likes Given: 7
Re: Reusability of BFS Heat Shield
« Reply #29 on: 05/12/2018 06:23 pm »
Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
It is only 48 meters long and tapered towards the front. In return we have a small amount of wing surface that also needs to be protected. PICA-X is a little lighter than the original PICA at 0.2 grams per cm3.
I am assuming an average thickness of 4 cm. The whole ship wont need the full 4 cm of thickness. In return one can probably assume a thicker layer around the bottom half of the ship.
With all this in mind, I am estimating a very conservative 9.5 tonnes for the whole spaceship covered in PICA-X with an average thickness of 4 cm. I think that is pretty decent at 12% of the dry mass. I normally would assume about 20% of the dry mass to go to TPS. So there is still some margin there.
So about 11.1% of the structural mass of the BFS.

Again the question is wheather it's good enough to cope with dissipating a combined kinetic and potential energy per Kg of structure that's about 20x the F9 booster copes with.

And AFAIK it can't.

Why are you comparing it with F9 booster at all? You should compare it with Dragon.

Offline tdperk

  • Full Member
  • ***
  • Posts: 340
  • Liked: 136
  • Likes Given: 65
Re: Reusability of BFS Heat Shield
« Reply #30 on: 05/18/2018 11:39 pm »
Over a 58m long 9m wide cylinder that's a bit over 9 tonnes for a 1 inch layer.
It is only 48 meters long and tapered towards the front. In return we have a small amount of wing surface that also needs to be protected. PICA-X is a little lighter than the original PICA at 0.2 grams per cm3.
I am assuming an average thickness of 4 cm. The whole ship wont need the full 4 cm of thickness. In return one can probably assume a thicker layer around the bottom half of the ship.
With all this in mind, I am estimating a very conservative 9.5 tonnes for the whole spaceship covered in PICA-X with an average thickness of 4 cm. I think that is pretty decent at 12% of the dry mass. I normally would assume about 20% of the dry mass to go to TPS. So there is still some margin there.
So about 11.1% of the structural mass of the BFS.

Again the question is wheather it's good enough to cope with dissipating a combined kinetic and potential energy per Kg of structure that's about 20x the F9 booster copes with.

And AFAIK it can't.

I know of no reason even to suspect it can't, since it already has.

No part of the F9 booster even has any PICA-X on it, an the PICA-X v1 thru v3 is in use on the Dragon or, has been thoroughly tested for such usage.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #31 on: 05/19/2018 07:01 am »

Why are you comparing it with F9 booster at all? You should compare it with Dragon.
Did you not know that the BFS is basically a stage with wings (whose nearest resemblance is to the space shuttle) while Dragon is basically a cone which enters base first?

So yes the F9 US is the relevant item to compare BFS with in terms of shape and surface area.

And both have a lot of surface area to protect.

Which is where the mass per unit area (Kg//m^2) starts to become important.
What's acceptable over 14m^2 may not be at 678 m^2.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline JamesH65

  • Full Member
  • ****
  • Posts: 970
  • Liked: 690
  • Likes Given: 8
Re: Reusability of BFS Heat Shield
« Reply #32 on: 05/21/2018 11:54 am »

Why are you comparing it with F9 booster at all? You should compare it with Dragon.
Did you not know that the BFS is basically a stage with wings (whose nearest resemblance is to the space shuttle) while Dragon is basically a cone which enters base first?

So yes the F9 US is the relevant item to compare BFS with in terms of shape and surface area.

And both have a lot of surface area to protect.

Which is where the mass per unit area (Kg//m^2) starts to become important.
What's acceptable over 14m^2 may not be at 678 m^2.

The difference is velocity. This alone makes them incomparable.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #33 on: 05/25/2018 04:40 pm »

Why are you comparing it with F9 booster at all? You should compare it with Dragon.
Did you not know that the BFS is basically a stage with wings (whose nearest resemblance is to the space shuttle) while Dragon is basically a cone which enters base first?

So yes the F9 US is the relevant item to compare BFS with in terms of shape and surface area.

And both have a lot of surface area to protect.

Which is where the mass per unit area (Kg//m^2) starts to become important.
What's acceptable over 14m^2 may not be at 678 m^2.

The difference is velocity. This alone makes them incomparable.
In fact neither is a very good comparison. Dragon is way too small and can protect most of the structure in the lee of the reentry (typcial reentry angles are about 5 deg below local horizontal) while the F9 booster sees nothing like the air velocity of re-entry.

In fact BFS's closest match is either Shuttle or the X37b,with all the issues that implies.

BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline johnfwhitesell

  • Full Member
  • ***
  • Posts: 319
  • Liked: 105
  • Likes Given: 198
Re: Reusability of BFS Heat Shield
« Reply #34 on: 05/25/2018 09:18 pm »
In fact BFS's closest match is either Shuttle or the X37b,with all the issues that implies.

The BFS doesn't have tiles, thanks to PICA/PICA-X, doesn't have solid boosters and doesn't attach on the side.  They learned from the shuttle.
« Last Edit: 05/25/2018 09:20 pm by johnfwhitesell »

Offline guckyfan

  • Senior Member
  • *****
  • Posts: 6873
  • Germany
  • Liked: 1862
  • Likes Given: 1910
Re: Reusability of BFS Heat Shield
« Reply #35 on: 05/26/2018 12:05 pm »
Pica-X comes in tiles. I believe this is one major reason why Pica was was not selected for the Orion heat shield. The tiles are much larger though and should have less issues dropping off. Also with a mostly symmetric shape the number of different tiles will be much smaller than with the Shuttle.

Offline john smith 19

  • Senior Member
  • *****
  • Posts: 7788
  • Everyplaceelse
  • Liked: 1296
  • Likes Given: 8725
Re: Reusability of BFS Heat Shield
« Reply #36 on: 05/29/2018 06:25 am »
Pica-X comes in tiles. I believe this is one major reason why Pica was was not selected for the Orion heat shield. The tiles are much larger though and should have less issues dropping off. Also with a mostly symmetric shape the number of different tiles will be much smaller than with the Shuttle.
Correct.  Although I think NASA have grudgingly admitted that a tiled heat shield is survivable at Lunar reentry (although ARD demonstrated titled heat shield survival from orbit in 1998).

BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP stainless steel structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Online Semmel

  • Full Member
  • ****
  • Posts: 1618
  • Germany
  • Liked: 1495
  • Likes Given: 3868
Re: Reusability of BFS Heat Shield
« Reply #37 on: 05/29/2018 10:59 am »
Pica-X comes in tiles. I believe this is one major reason why Pica was was not selected for the Orion heat shield. The tiles are much larger though and should have less issues dropping off. Also with a mostly symmetric shape the number of different tiles will be much smaller than with the Shuttle.

No, the tiles are not symmetric. Thats because the capsule enters at an angle and the center of influx air is not at the center of the capsule.

Look at the Dragon heat shield:
https://i.imgur.com/s7yORbX.jpg
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1593168#msg1593168

Offline guckyfan

  • Senior Member
  • *****
  • Posts: 6873
  • Germany
  • Liked: 1862
  • Likes Given: 1910
Re: Reusability of BFS Heat Shield
« Reply #38 on: 05/29/2018 12:04 pm »
Pica-X comes in tiles. I believe this is one major reason why Pica was was not selected for the Orion heat shield. The tiles are much larger though and should have less issues dropping off. Also with a mostly symmetric shape the number of different tiles will be much smaller than with the Shuttle.

No, the tiles are not symmetric. Thats because the capsule enters at an angle and the center of influx air is not at the center of the capsule.

Look at the Dragon heat shield:
https://i.imgur.com/s7yORbX.jpg
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1593168#msg1593168

I was talking about the BFS heatshield. Possibly your argumentapplies to that as well. But I would expect that there would be a large number of mostly identical tiles at least on the cylincrical part of the body.

Edit: Maybe that was not quite clear because I mentioned the Orion heatshield.
« Last Edit: 05/29/2018 12:06 pm by guckyfan »

Online Semmel

  • Full Member
  • ****
  • Posts: 1618
  • Germany
  • Liked: 1495
  • Likes Given: 3868
Re: Reusability of BFS Heat Shield
« Reply #39 on: 05/29/2018 01:01 pm »
Pica-X comes in tiles. I believe this is one major reason why Pica was was not selected for the Orion heat shield. The tiles are much larger though and should have less issues dropping off. Also with a mostly symmetric shape the number of different tiles will be much smaller than with the Shuttle.

No, the tiles are not symmetric. Thats because the capsule enters at an angle and the center of influx air is not at the center of the capsule.

Look at the Dragon heat shield:
https://i.imgur.com/s7yORbX.jpg
https://forum.nasaspaceflight.com/index.php?topic=41016.msg1593168#msg1593168

I was talking about the BFS heatshield. Possibly your argumentapplies to that as well. But I would expect that there would be a large number of mostly identical tiles at least on the cylincrical part of the body.

Edit: Maybe that was not quite clear because I mentioned the Orion heatshield.

Ok, in terms of BFS, I agree, there will likely be a large number of identical tiles. The issue with the shuttle tiles was that they had to be completely replaced for each landing. And on top of that, the tiling was impossible to automate. Each tile had to be placed and each gap had to be filled... by hand. This was one of the main reasons shuttle got expensive. For BFS, if they have chance at all, the tiles have to stay on the vehicle for many launches. This reduces the workload compared to shuttle tremendously independent on the shape of the tiles. Then, if they can do the tiling automatically, this becomes feasible. A robot will not care if the tiles are all identical, the manufacturing tolerances are much tighter though. The actual shape of the tiles is less an issue I would imagine, they just need to have a mold for each shape. Identical tiles help but I would think thats not the deciding factor.

Tags: