Author Topic: Reusability of BFS Heat Shield  (Read 17403 times)

Offline JonathanD

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Reusability of BFS Heat Shield
« on: 04/02/2018 03:02 pm »

Sorry if I missed a topic on this elsewhere, but it seems like the heat shield on BFS is sure going to take a beating, especially at interplanetary velocities and especially coming back from Moon/Mars and landing on Earth.  The heat shield on Dragon is relatively small, but still looks pretty complicated (https://www.nasa.gov/images/content/215574main_spacex_heatshield_226x170.jpg) in terms of # of tiles and fitment.  And we know from Shuttle the complicated nature of maintaining the integrity of a large thermal management system.  Even at LEO velocities it's no joke.  I'm curious how reusable this portion of BFS is realistically, and how that may impact the design architecture of using multiple tanker trips to orbit for refilling.  Seems like it would take extensive inspection at the least, if not frequent maintenance.  Are my concerns overstated?

Offline Elmar Moelzer

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Re: Reusability of BFS Heat Shield
« Reply #1 on: 04/02/2018 04:02 pm »
For LEO it should be fine, but for interplanetary velocities, it will need frequent refurbishment. I think Musk talked about 12 mars launches between major refurbishments. The tanker will have 100 reuses, since that only goes to LEO. So that should give you an estimate of the capability of the TPS.

Offline Alkan

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Re: Reusability of BFS Heat Shield
« Reply #2 on: 04/03/2018 08:53 am »
For LEO it should be fine, but for interplanetary velocities, it will need frequent refurbishment. I think Musk talked about 12 mars launches between major refurbishments. The tanker will have 100 reuses, since that only goes to LEO. So that should give you an estimate of the capability of the TPS.

I think you should try to find out where that is, because I feel like I've heard it all about ITS and BFR, scouring everything, and I never heard reuse numbers. I just heard roughly "there will be some ablation of the heat shield on Mars."

Online niwax

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Re: Reusability of BFS Heat Shield
« Reply #3 on: 04/03/2018 09:00 am »
For LEO it should be fine, but for interplanetary velocities, it will need frequent refurbishment. I think Musk talked about 12 mars launches between major refurbishments. The tanker will have 100 reuses, since that only goes to LEO. So that should give you an estimate of the capability of the TPS.

I think you should try to find out where that is, because I feel like I've heard it all about ITS and BFR, scouring everything, and I never heard reuse numbers. I just heard roughly "there will be some ablation of the heat shield on Mars."

Well, 12 reuses to Mars and back is a timeframe of over 25 years when using every minimum energy opportunity. Even traditional airframes have a lifetime on the same order of magnitude, so the heat shield won't be the only thing that needs refurbishing.
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Offline JonathanD

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Re: Reusability of BFS Heat Shield
« Reply #4 on: 04/03/2018 02:00 pm »
Well, 12 reuses to Mars and back is a timeframe of over 25 years when using every minimum energy opportunity. Even traditional airframes have a lifetime on the same order of magnitude, so the heat shield won't be the only thing that needs refurbishing.

I've got to think they are going to do a very thorough inspection/refurbishment after every Mars trip before they send it "there and back again" with more kerbals on board.

Offline speedevil

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Re: Reusability of BFS Heat Shield
« Reply #5 on: 04/03/2018 04:28 pm »
For LEO it should be fine, but for interplanetary velocities, it will need frequent refurbishment. I think Musk talked about 12 mars launches between major refurbishments. The tanker will have 100 reuses, since that only goes to LEO. So that should give you an estimate of the capability of the TPS.

I think you should try to find out where that is, because I feel like I've heard it all about ITS and BFR, scouring everything, and I never heard reuse numbers. I just heard roughly "there will be some ablation of the heat shield on Mars."

From memory, the 100 reuses comes from numbers from IAC2016, where it was in the context of tanker reuse, and 'we are aiming at 100 reuses before major refurbishment'.
This is because for ITS as it was then, 100 reuses is all that was needed for Mars ambitions, before it impacted cost.

Recent statements have not made comment more than 'minimal wear', with the wear implied to be during reentry to earth from Mars transit if you read carefully.

P2P of course means you want to get rework of the heatsheild averaging well below $50K/flight or so, or it starts to become a noticable line item.

Offline Elmar Moelzer

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Re: Reusability of BFS Heat Shield
« Reply #6 on: 04/03/2018 04:49 pm »
Well, 12 reuses to Mars and back is a timeframe of over 25 years when using every minimum energy opportunity. Even traditional airframes have a lifetime on the same order of magnitude, so the heat shield won't be the only thing that needs refurbishing.
Unless they use it for something else between mars launch opportunities.

Offline KelvinZero

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Re: Reusability of BFS Heat Shield
« Reply #7 on: 04/07/2018 09:59 am »
I have wondered if they will produce some highly automated refurbishment method, eg scanning each inch, repairing cracks and 3d printing shielding back on where it is needed. (if that makes any sense for something like pica-x)

With enough automation refurbishing the shield might be just another mundane operation between each flight like refilling the tanks.

Offline speedevil

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Re: Reusability of BFS Heat Shield
« Reply #8 on: 04/07/2018 06:04 pm »
I have wondered if they will produce some highly automated refurbishment method, eg scanning each inch, repairing cracks and 3d printing shielding back on where it is needed. (if that makes any sense for something like pica-x)

With enough automation refurbishing the shield might be just another mundane operation between each flight like refilling the tanks.

You probably don't want to re-do the whole thing if you can possibly avoid it.

Scanning the whole surface was developed for shuttle after the incident, but at that time was lots more expensive.

How repairable any defects are is a fun question, as is the tolerance for any hidden defects, never mind scanning for damage in orbit and repair.

Online Slarty1080

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Re: Reusability of BFS Heat Shield
« Reply #9 on: 04/07/2018 06:42 pm »
How easy would it be to accurately test or simulate the wear on a BFR heat shield?
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Offline Elmar Moelzer

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Re: Reusability of BFS Heat Shield
« Reply #10 on: 04/07/2018 08:34 pm »
How easy would it be to accurately test or simulate the wear on a BFR heat shield?
I think the BFS- grasshopper flights planned for next year are meant to test that out (among other things).

Offline Robotbeat

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Re: Reusability of BFS Heat Shield
« Reply #11 on: 04/08/2018 12:16 am »
How easy would it be to accurately test or simulate the wear on a BFR heat shield?
Easy, just use an arcjet. Ames has a bunch.
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Offline the_other_Doug

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Re: Reusability of BFS Heat Shield
« Reply #12 on: 04/08/2018 03:36 am »
At the FH Demo post-launch briefing, Musk discussed the heating profiles that are coming up in the computer simulations for BFS entries, at both Mars and Earth.

He was discussing it in such a detailed fashion that I can't imagine SpaceX isn't pretty solidly aware of what their TPS is going to have to deal with.  As it's supposed to be PICA-X based, and SpaceX is already familiar with that material, again I would imagine they have the various specifications for its application and refurbishment pretty well patted into shape already... ;)
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Online Slarty1080

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Re: Reusability of BFS Heat Shield
« Reply #13 on: 04/08/2018 10:10 am »
How easy would it be to accurately test or simulate the wear on a BFR heat shield?
I think the BFS- grasshopper flights planned for next year are meant to test that out (among other things).
So it would appear difficult to test as it needs to be tested in situ high in the atmosphere with a special vehicle (grasshopper flights). What about simulation? How good is that likely to be?
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Online Cheapchips

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Re: Reusability of BFS Heat Shield
« Reply #14 on: 04/08/2018 11:50 am »

SpaxeX have sophisticated simulation software.  Like any model, they'll still need to refine with actual test data..  This video from a while ago is mostly engine simulation. There are some Dragon bits in the video too though.


Offline Elmar Moelzer

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Re: Reusability of BFS Heat Shield
« Reply #15 on: 04/08/2018 04:33 pm »
So it would appear difficult to test as it needs to be tested in situ high in the atmosphere with a special vehicle (grasshopper flights). What about simulation? How good is that likely to be?
They are going to gradually increase altitude and speed over multiple flights all the way to orbit. BFS without BFR can go all the way to orbit. So they can and will test that.

Offline mgfitter

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Re: Reusability of BFS Heat Shield
« Reply #16 on: 04/20/2018 10:23 pm »
Will BFS's winglets have control surfaces?

-MG

Offline Lars-J

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Re: Reusability of BFS Heat Shield
« Reply #17 on: 04/20/2018 10:47 pm »
Will BFS's winglets have control surfaces?

-MG

Yes, the renderings we have seen from behind show two body flaps.
« Last Edit: 04/20/2018 10:48 pm by Lars-J »

Offline john smith 19

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Re: Reusability of BFS Heat Shield
« Reply #18 on: 05/09/2018 08:54 am »
At the FH Demo post-launch briefing, Musk discussed the heating profiles that are coming up in the computer simulations for BFS entries, at both Mars and Earth.

He was discussing it in such a detailed fashion that I can't imagine SpaceX isn't pretty solidly aware of what their TPS is going to have to deal with.  As it's supposed to be PICA-X based, and SpaceX is already familiar with that material, again I would imagine they have the various specifications for its application and refurbishment pretty well patted into shape already... ;)
If so then why are they advertising for someone with "heritage" tile TPS experience?

Run the numbers.

Check what the KE and PE for a Kg of mass at full orbital speed WRT to that at which the F9 booster separates. IE 1/2 x 1 x V(orbital m/s)^2 + 1 x h(metres) x g(proper g, with altitude variation factored in)

Orbital is not a little bit more energy to dissipate, it's a lot more energy to dissipate.
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Offline speedevil

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Re: Reusability of BFS Heat Shield
« Reply #19 on: 05/09/2018 10:24 am »
If so then why are they advertising for someone with "heritage" tile TPS experience?
Low priority work on solutions that seem non-favoured can result in the ability to rapidly pivot if things change.

As a stupid example, perhaps it turns out that with 3d printing, accurate milling of tile blanks on demand, rapid automated scanning enabled by the explosion in LASER metrology and better cameras and computers, maybe you can repair defects in a vehicles shuttle-like tiles in a couple of hours.

Lack of hiring in an area you think they should be hiring in can also mean they think they've nailed it internally, rather than a move in an unexpected direction.

Perhaps this job is even far down the road, and they're working on how to make a $20 reentry package to throw a million of at Mars.

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