Author Topic: Starship heat shield  (Read 1457436 times)

Offline Vettedrmr

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Re: Starship heat shield
« Reply #4020 on: 06/22/2024 05:31 pm »
Baseballs can generate lift. They just have to be spinning. It's how curveballs and different sink rates for the same speed pitches work.

Yeah, I know.  But it's a different mechanism than lift generated by vehicles.

And yes, I know that aircraft can achieve AoA much higher than their wing's critical angle of attack, (sustained AoA > 60 degrees for F-22 and F-35), but in those conditions the aircraft are either bleeding energy so rapidly they can only hold the condition for a few seconds, or they start descending rapidly.  The airfoils are generating very little lift.
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Offline Spiceman

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Re: Starship heat shield
« Reply #4021 on: 06/22/2024 05:34 pm »
« Last Edit: 06/22/2024 05:35 pm by Spiceman »

Offline OTV Booster

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Re: Starship heat shield
« Reply #4022 on: 06/22/2024 05:43 pm »
[...]
Canard = that bulky structure with glued on tiles that encloses the fin hinge. Fins, as I used the term, are both the front and rear fins.
[...]
Are you perhaps getting "canard" (smaller wing in front of main wing, neither of which Starship has) mixed up with "chine" (longitudinally extended sharp change in fuselage cross section profile)? At least the Great Chine/Strake Debate was more about nomenclature than actual aerodynamic function...

Personally I prefer wordier but less ambiguous descriptions like "flap hinge/root fairing" but we wouldn't have as much back and forth about definitions that way  ;)
Yeah, I got my tang tungled.
Edit to add: I remembered the debate but couldn't remember the terms debated.
« Last Edit: 06/22/2024 05:50 pm by OTV Booster »
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Offline OTV Booster

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Re: Starship heat shield
« Reply #4023 on: 06/22/2024 05:52 pm »
Fowl canard? You mean a duck? Or a foul canard?
Like this?
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Offline alugobi

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Re: Starship heat shield
« Reply #4024 on: 06/22/2024 06:54 pm »
Thread needs a healthy trim.

Offline Dancing Dog

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Re: Starship heat shield
« Reply #4025 on: 06/23/2024 03:55 am »

I understand zero about hypersonics, and only a little about supersonic flow, but we could see the control surfaces moving some during that initial phase of reentry, so we know they contribute *somehow*.  I have no idea what AoA range S29 experienced because I don't know what the flight path was, but I expect it never got much below 40 degrees (even when the pitch attitude went below the horizon), always staying in the deep stall region.

AoA of 70 degrees is what I've seen most often. I don't think characterizing the entry as "deep stall" is accurate, given the amount of lift they were generating to control the descent rate and g-forces.  :)


<for the subsonic region> Don't forget that the vehicle is always in a deep stall, so the stabilizing effect of dihedral is essentially zero.  You get changes in drag by more or less adjusting the flat plate area of the control surface by "tucking" or "extending" the surface.

Here, the ship is presenting belly-first into the relative wind. Having been in this situation myself on numerous occasions, it's less "stall" and more "falling with style."

I think you need to go read up on what an aerodynamic stall is.  NOTHING has an AoA of 70 degrees and not completely stalled, unless maybe a baseball, which doesn't generate lift.  Normal aircraft, roughly 12-15 degrees.  Fighter aircraft, about 25-35 degrees, maybe a touch more.

Since Ship is not a wing, and it would never be able to create lift by an attached airflow, AND it's generating lift on entry, I still think "stall" is a stupid way to characterize the entry path.

Trim away!

Offline alang

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Re: Starship heat shield
« Reply #4026 on: 06/23/2024 04:02 pm »
Even Concorde seemed to have a non-moving  vestigial canard beneath the cockpit windows.
I don't know what it was called.
It can be seen clearly here:
https://www.heritageconcorde.com/yeovilton

Offline InterestedEngineer

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Re: Starship heat shield
« Reply #4027 on: 06/23/2024 10:50 pm »
Falling a distance of 200km at g=10 (very rough value). v^2=2as. v=sqrt(2*10*200,000)=2000m/s.
Thankee. I just asked for this number replying to a post just a bit upstream. I'm a mathematical illiterate. Do we know enough to figure out the ships terminal velocity through that pesky change of atmospheric density on the way down and how much heat would be generated?


Musk is famous for best part, no part, yada yada. Is it possible he just went blindly forth and never looked at this?


I know this is heresy but the propellant would be mostly be burned off and the payload gone. Is there an optimization where some portion of orbital velocity could be killed off enough that they could dispense with the heat shield and save yet another ~10 tons? Or maybe a much diminished heat shield for only the hottest spots? It's a dim hazy memory but IIRC ~800C is the cutoff for the stainless they use and again, IIRC, the heat rises with the square of velocity. Or maybe I'm an idiot. Strong possibility.


Just from LEO. Lunar and Mars return can wait for another day.

We can estimate how much lower the velocity needs to be in order for the SS to handle the heat at 800degC using the T4 emission for dissipating energy using the Stefan-Boltzmann law.

If we assume the tile heat shield can handle 1473K and the SS 1073K, the ratio of emissions is 3.5.

Furthermore SS has less than half the emissivity of the optimized black glass on the tiles, so the ratio is more like 10.

So SS can dissipate 1/10 of the heat of the tile.

Translating that directly into kinetic energy ratio, that comes 0.32 times the velocity. (a possibly wild assumption).

Since the entry speed from orbit is 7.5km/sec, the speed stainless steel can handle without overheating is 2.4km/sec

Which happens to be slightly more than the Booster re-entry speed, which means it sounds reasonable.

It also means the deltaV for braking via propellant would need to be 5.1km/sec, or a mass ratio 4.

So for 150t dry mass 450t of fuel would be required

It's within the realm of possibility of docking with a fuel depot and taking on 450t of fuel, doing the braking, and then not relying on tiles.

I have not accounted for mgh.   A drop from 100km (where the braking burn would happen) to 50km (atmosphere interface) would add another one km/sec.

Offline aporigine

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Re: Starship heat shield
« Reply #4028 on: 06/23/2024 11:03 pm »
Fowl canard? You mean a duck? Or a foul canard?
That might be ducking the issue. Canards are a term generally applied to moving control surfaces well ahead of the center of lift (Viggen or Eurofighter), though some Rutan designs have fixed canards and rely on control authority on moving surfaces aft.

In this instance it makes more sense to apply the term canards to the bits of the forward drag flaps that move. I think it inelegant to repurpose the term for the chines/strakes/roots/blibits that serve as the attachment hardware for the control surfaces.

Offline CMac

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Re: Starship heat shield
« Reply #4029 on: 06/24/2024 08:51 am »
Given that 2024 is all about perfecting the system, in order to test heat shield more fully, they need to do some high energy entries. Will they soon do a lunar fly-by or other high energy manoeuvre to test tiles in this scenario? Should it happen ASAP in the test programme? What could be achieved without need for tanker refill?

Offline Vettedrmr

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Re: Starship heat shield
« Reply #4030 on: 06/24/2024 10:22 am »
Given that 2024 is all about perfecting the system, in order to test heat shield more fully, they need to do some high energy entries. Will they soon do a lunar fly-by or other high energy manoeuvre to test tiles in this scenario? Should it happen ASAP in the test programme? What could be achieved without need for tanker refill?

Crawl, walk, run.  I would say "crawl" was satisfied by IFT-4; lots of lessons learned about how the tiles performed.  IMO, I bet it worked very well except for the flap hinge area, which Musk identified as the primary point of concern.

Walk: Successful orbital flight with an accurate water landing.

(I'll add one here): Jog: Successful orbital flight with a catch landing

Run: High energy reentry from a moon flight, even if it's just a free return trajectory flight.
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Offline dchenevert

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Re: Starship heat shield
« Reply #4031 on: 06/24/2024 10:32 am »
Run: High energy reentry from a moon flight, even if it's just a free return trajectory flight.

Did I not get the memo? I had not thought that "Return from moon" was on the HLS bingo card.
IIUC, conops is:

1. stuff
2. deliver crew to Orion
3. whatevs (not, "return to earth")


Offline Vettedrmr

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Re: Starship heat shield
« Reply #4032 on: 06/24/2024 11:01 am »
Run: High energy reentry from a moon flight, even if it's just a free return trajectory flight.

Did I not get the memo? I had not thought that "Return from moon" was on the HLS bingo card.
IIUC, conops is:

1. stuff
2. deliver crew to Orion
3. whatevs (not, "return to earth")

Well, sure, but my comment was specifically for learning/developing the heat shield.  And, honestly, IDK if an EDL return from the moon *is* part of HLS, since the crew comes back on Orion.
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Offline StraumliBlight

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Re: Starship heat shield
« Reply #4033 on: 06/24/2024 12:54 pm »
Given that 2024 is all about perfecting the system, in order to test heat shield more fully, they need to do some high energy entries. Will they soon do a lunar fly-by or other high energy manoeuvre to test tiles in this scenario? Should it happen ASAP in the test programme? What could be achieved without need for tanker refill?

Once the Propellant Transfer demonstration is completed in 2025, there will be a partially filled up Starship with no payload available for a circumlunar flight.

Offline CMac

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Re: Starship heat shield
« Reply #4034 on: 06/24/2024 07:15 pm »
Since 2024 is about ironing out heat shield among other things, I would think a high E entry is desirable early in dev.

Offline wannamoonbase

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Re: Starship heat shield
« Reply #4035 on: 06/24/2024 08:43 pm »
Given that 2024 is all about perfecting the system, in order to test heat shield more fully, they need to do some high energy entries. Will they soon do a lunar fly-by or other high energy manoeuvre to test tiles in this scenario? Should it happen ASAP in the test programme? What could be achieved without need for tanker refill?

Once the Propellant Transfer demonstration is completed in 2025, there will be a partially filled up Starship with no payload available for a circumlunar flight.

Except the plan is to deorbit both vehicles after the test. 

Which tells me that SpaceX has doubts or knows Starship can’t spend a lot of time on orbit yet. 

Wouldn’t it be great to do something with it though?
Starship, Vulcan and Ariane 6 have all reached orbit.  New Glenn, well we are waiting!

Online steveleach

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Re: Starship heat shield
« Reply #4036 on: 06/24/2024 09:47 pm »
Given that 2024 is all about perfecting the system, in order to test heat shield more fully, they need to do some high energy entries. Will they soon do a lunar fly-by or other high energy manoeuvre to test tiles in this scenario? Should it happen ASAP in the test programme? What could be achieved without need for tanker refill?

Once the Propellant Transfer demonstration is completed in 2025, there will be a partially filled up Starship with no payload available for a circumlunar flight.

Except the plan is to deorbit both vehicles after the test. 

Which tells me that SpaceX has doubts or knows Starship can’t spend a lot of time on orbit yet. 

Wouldn’t it be great to do something with it though?
While the eventual aim is full and rapid reusability, in the near term I suspect they'll invariably find it easier to build and launch a new vehicle.

Offline OTV Booster

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Re: Starship heat shield
« Reply #4037 on: 06/25/2024 12:41 am »
Falling a distance of 200km at g=10 (very rough value). v^2=2as. v=sqrt(2*10*200,000)=2000m/s.
Thankee. I just asked for this number replying to a post just a bit upstream. I'm a mathematical illiterate. Do we know enough to figure out the ships terminal velocity through that pesky change of atmospheric density on the way down and how much heat would be generated?


Musk is famous for best part, no part, yada yada. Is it possible he just went blindly forth and never looked at this?


I know this is heresy but the propellant would be mostly be burned off and the payload gone. Is there an optimization where some portion of orbital velocity could be killed off enough that they could dispense with the heat shield and save yet another ~10 tons? Or maybe a much diminished heat shield for only the hottest spots? It's a dim hazy memory but IIRC ~800C is the cutoff for the stainless they use and again, IIRC, the heat rises with the square of velocity. Or maybe I'm an idiot. Strong possibility.


Just from LEO. Lunar and Mars return can wait for another day.

We can estimate how much lower the velocity needs to be in order for the SS to handle the heat at 800degC using the T4 emission for dissipating energy using the Stefan-Boltzmann law.

If we assume the tile heat shield can handle 1473K and the SS 1073K, the ratio of emissions is 3.5.

Furthermore SS has less than half the emissivity of the optimized black glass on the tiles, so the ratio is more like 10.

So SS can dissipate 1/10 of the heat of the tile.

Translating that directly into kinetic energy ratio, that comes 0.32 times the velocity. (a possibly wild assumption).

Since the entry speed from orbit is 7.5km/sec, the speed stainless steel can handle without overheating is 2.4km/sec

Which happens to be slightly more than the Booster re-entry speed, which means it sounds reasonable.

It also means the deltaV for braking via propellant would need to be 5.1km/sec, or a mass ratio 4.

So for 150t dry mass 450t of fuel would be required

It's within the realm of possibility of docking with a fuel depot and taking on 450t of fuel, doing the braking, and then not relying on tiles.

I have not accounted for mgh.   A drop from 100km (where the braking burn would happen) to 50km (atmosphere interface) would add another one km/sec.
Well, that settles that. Not impossible to do but not worth it for every day ops.


Thanks for running the numbers.
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Offline OTV Booster

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Re: Starship heat shield
« Reply #4038 on: 06/25/2024 01:11 am »
Artemus doesn't call for SS to do a high energy reentry but return from mars (and maybe mars EDL?) needs it and looking at SS as a general purpose spacecraft, it's reasonable to expect the capability to be tested - when convenient. No big hurry.


Short term they need to demonstrate a relight so full orbital ops are considered safe, then they need to move propellant between ships. Each flight will be an opportunity to improve the heat shield and after a restart demo, an opportunity to launch some starlinks.


AIUI free lunar return reenters ~3km/s faster than from LEO. Cribbing off Interested Engineers numbers a propellant transfer of somewhere around 250t-275t would be about what's needed for a LEO simulation of a lunar free return. Am I looking at this the right way?
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Offline Eer

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Re: Starship heat shield
« Reply #4039 on: 06/25/2024 02:36 pm »
From Tim Dodd's 2nd interview, it seems the missing tile tests returned good results - one tile had two layers of ablative insulation, the other had just one ... the single-layer burned through to at least scorch the underlying steel, while the two layer did not burn through the second layer ...
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