Author Topic: Reusability of BFS Heat Shield  (Read 15466 times)

Offline CorvusCorax

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Re: Reusability of BFS Heat Shield
« Reply #60 on: 07/18/2018 10:17 AM »
I remember reading somewhere that PICA/PICAX has an issue with soaking up water and for that reason is initially painted over on Dragon with a silvery paint. (Having water - even in small amounts - in the heatshield during reentry is obviously a bad thing. It would turn to steam, expand drastically and in doing so blows the material apart from within - highly increasing the ablation rate.)

Obviously this paint layer does not survive reentry, it would ablate away.

Dragon currently gets multi-month refurbishment between flights, including - up to now - reapplying a brand new heatshield and new paint.

For BFS this is not an option. It might be an option for in between mars flights, but not for the tanker/cargo variant when going to LEO. Not only needs the ablation of ablative parts of the heatshield be so small that it can go douzends of flights, but the heatshield also needs to remain in a state unaffected by the environment - including moisture, rain, and slightly corrosive coastal winds at the cape.

This would mean, either SpaceX is not using PICAX on BFS but a much more resilent ceramic material which would have to require neither inspection nor refurbishment between LEO flights. Or they have a new version of PICAX which no longer soaks up moisture and is much more resilent to the environment.

Ideally - for maximum ultraquick reuse - a heatshield would not ablate at all during LEO reentries, but dissipate heat radiatively similar to how the shuttle did - but would become ablative when facing much hotter reentries- for example when doing direct interplanetary reentry OR when reentering ballistic in cases of emergency/malfunction. In the latter case the heatshield would have to be replaced.


Offline jpo234

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Re: Reusability of BFS Heat Shield
« Reply #61 on: 07/18/2018 11:16 AM »
I remember reading somewhere that PICA/PICAX has an issue with soaking up water and for that reason is initially painted over on Dragon with a silvery paint. (Having water - even in small amounts - in the heatshield during reentry is obviously a bad thing. It would turn to steam, expand drastically and in doing so blows the material apart from within - highly increasing the ablation rate.)

Obviously this paint layer does not survive reentry, it would ablate away.

Dragon currently gets multi-month refurbishment between flights, including - up to now - reapplying a brand new heatshield and new paint.

For BFS this is not an option. It might be an option for in between mars flights, but not for the tanker/cargo variant when going to LEO. Not only needs the ablation of ablative parts of the heatshield be so small that it can go douzends of flights, but the heatshield also needs to remain in a state unaffected by the environment - including moisture, rain, and slightly corrosive coastal winds at the cape.

This would mean, either SpaceX is not using PICAX on BFS but a much more resilent ceramic material which would have to require neither inspection nor refurbishment between LEO flights. Or they have a new version of PICAX which no longer soaks up moisture and is much more resilent to the environment.

Ideally - for maximum ultraquick reuse - a heatshield would not ablate at all during LEO reentries, but dissipate heat radiatively similar to how the shuttle did - but would become ablative when facing much hotter reentries- for example when doing direct interplanetary reentry OR when reentering ballistic in cases of emergency/malfunction. In the latter case the heatshield would have to be replaced.

Different from Dragon, BFS is not supposed to splash down in the ocean.

That said, we know from job postings that SpaceX investigates ceramic heat shield materials to allow hundreds of reuses.
« Last Edit: 07/18/2018 08:17 PM by jpo234 »
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Offline RoboGoofers

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Re: Reusability of BFS Heat Shield
« Reply #62 on: 07/18/2018 05:27 PM »
I remember reading somewhere that PICA/PICAX has an issue with soaking up water and for that reason is initially painted over on Dragon with a silvery paint. (Having water - even in small amounts - in the heatshield during reentry is obviously a bad thing. It would turn to steam, expand drastically and in doing so blows the material apart from within - highly increasing the ablation rate.)

Obviously this paint layer does not survive reentry, it would ablate away.

Dragon currently gets multi-month refurbishment between flights, including - up to now - reapplying a brand new heatshield and new paint.

For BFS this is not an option. It might be an option for in between mars flights, but not for the tanker/cargo variant when going to LEO. Not only needs the ablation of ablative parts of the heatshield be so small that it can go douzends of flights, but the heatshield also needs to remain in a state unaffected by the environment - including moisture, rain, and slightly corrosive coastal winds at the cape.

This would mean, either SpaceX is not using PICAX on BFS but a much more resilent ceramic material which would have to require neither inspection nor refurbishment between LEO flights. Or they have a new version of PICAX which no longer soaks up moisture and is much more resilent to the environment.

Ideally - for maximum ultraquick reuse - a heatshield would not ablate at all during LEO reentries, but dissipate heat radiatively similar to how the shuttle did - but would become ablative when facing much hotter reentries- for example when doing direct interplanetary reentry OR when reentering ballistic in cases of emergency/malfunction. In the latter case the heatshield would have to be replaced.

I was wondering the same, mainly about P2P. there's no structures shown in any of the renderings as BFS hangers to keep them out of the rain.

I suspect that P2P BFS will evolve away from the interplanetary version, and vice versa, with the interplanetary ships preferring weight and the P2P extreme reusability.

Offline cppetrie

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Re: Reusability of BFS Heat Shield
« Reply #63 on: 07/18/2018 07:38 PM »
I remember reading somewhere that PICA/PICAX has an issue with soaking up water and for that reason is initially painted over on Dragon with a silvery paint. (Having water - even in small amounts - in the heatshield during reentry is obviously a bad thing. It would turn to steam, expand drastically and in doing so blows the material apart from within - highly increasing the ablation rate.)

Obviously this paint layer does not survive reentry, it would ablate away.

Dragon currently gets multi-month refurbishment between flights, including - up to now - reapplying a brand new heatshield and new paint.

For BFS this is not an option. It might be an option for in between mars flights, but not for the tanker/cargo variant when going to LEO. Not only needs the ablation of ablative parts of the heatshield be so small that it can go douzends of flights, but the heatshield also needs to remain in a state unaffected by the environment - including moisture, rain, and slightly corrosive coastal winds at the cape.

This would mean, either SpaceX is not using PICAX on BFS but a much more resilent ceramic material which would have to require neither inspection nor refurbishment between LEO flights. Or they have a new version of PICAX which no longer soaks up moisture and is much more resilent to the environment.

Ideally - for maximum ultraquick reuse - a heatshield would not ablate at all during LEO reentries, but dissipate heat radiatively similar to how the shuttle did - but would become ablative when facing much hotter reentries- for example when doing direct interplanetary reentry OR when reentering ballistic in cases of emergency/malfunction. In the latter case the heatshield would have to be replaced.

Different from Dragon, BFS is not supposed to splash down in the ocean.

That said, we know from job postings that SpaceX investigates ceramic head shield materials to allow hundreds of reuses.
Water from the ocean isnít the primary issue.   Itís water vapor from the air being absorbed into the material while itís being processed and sitting on the pad.

Offline Robotbeat

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Re: Reusability of BFS Heat Shield
« Reply #64 on: 07/19/2018 12:49 AM »
I remember reading somewhere that PICA/PICAX has an issue with soaking up water and for that reason is initially painted over on Dragon with a silvery paint. (Having water - even in small amounts - in the heatshield during reentry is obviously a bad thing. It would turn to steam, expand drastically and in doing so blows the material apart from within - highly increasing the ablation rate.)

Obviously this paint layer does not survive reentry, it would ablate away.

Dragon currently gets multi-month refurbishment between flights, including - up to now - reapplying a brand new heatshield and new paint.

For BFS this is not an option. It might be an option for in between mars flights, but not for the tanker/cargo variant when going to LEO. Not only needs the ablation of ablative parts of the heatshield be so small that it can go douzends of flights, but the heatshield also needs to remain in a state unaffected by the environment - including moisture, rain, and slightly corrosive coastal winds at the cape.

This would mean, either SpaceX is not using PICAX on BFS but a much more resilent ceramic material which would have to require neither inspection nor refurbishment between LEO flights. Or they have a new version of PICAX which no longer soaks up moisture and is much more resilent to the environment.

Ideally - for maximum ultraquick reuse - a heatshield would not ablate at all during LEO reentries, but dissipate heat radiatively similar to how the shuttle did - but would become ablative when facing much hotter reentries- for example when doing direct interplanetary reentry OR when reentering ballistic in cases of emergency/malfunction. In the latter case the heatshield would have to be replaced.
Inspection may be acceptable if it can be done quickly and cheaply. Actually a good spot for computer vision systems. High resolution scans (via crane or drone). Problem areas are identified and sent to humans for detailed analysis.
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