Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 819691 times)

Offline ChrML

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3000 on: 01/19/2025 10:10 pm »
Possibly a dumb question, but can't there be some kind of solar powered active cooling system? That radiates the excess heat on the side not pointing towards the sun, to reliquidify the boil-off?

Online InterestedEngineer

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3001 on: 01/19/2025 10:16 pm »
Is there any reason the nose wouldn't be pointed at the sun? I'd always assumed that would be the orientation. The cross sectional area would be more like 70 sq m.

If that were true, and the nose had MLI under a vacuum, wouldn't the heat transfer to the tanks be mainly through the skin and structure connecting the nose to the rest of the 2nd stage? In that case the conduction cross sectional area would be pretty small I'd think. Perhaps some kind of "chomper" opening on the lee side of the nose cone would radiate some of that in addition to decreasing the cross sectional area. Maybe the chomper door actually could be a boom extending forward to put a reflective shield in front of the nose?

In that case, I'd think the Earth's radiation would be the main effect. That's something like a quarter of the Sun's and would vary depending on where the ship was in the orbit with the maximum heat flux being at local noon with the tail pointed at Earth. Obviously at night it would be less.

Earth Flux averages over a 300km orbit about 350W/m2, or 350/1361 = .26 so 1/4 is reasonable.

You make a very good point about conduction.  Stainless Steel is a terrible conductor, and the surface area is pretty small - 28.26m * ~5mm = .141 m2 cross sectional area.  To even get to a fuel tank it has to traverse about 15m of that surface area.

So now we have a cross sectional area, conductivity of stainless steel, a length of 15, Tcold = 90K, and a radiating surface with emissivity of 0.35 to the outside world.  We can solve for the equilibrium temperature at the hot end of the nosecone and then the heat flux to the cold end.

I have the python program to do it, I think but am not sure it's correct.  It gets me an answer of 740K on the hot end and that's ignoring the radiative effects of the cone section that is completely covered by the heat shield.  At that temp heat transfer is a trivial 90W.   It's probably less, as I didn't account for the cone area of the heat shield, just the 15m to the LOX tank.

I did not realize how amazingly well pointing the nosecone at the Sun would work.

NOTE: If I just take the equilibrium temperature of the nose cone area it's around 395K by itself.  The flux to 15m back to the topmost main fuel tank at that temperature is 42W. practically rounding error.



import numpy as np
from scipy.optimize import fsolve

# Constants
q_solar = 1361  # Solar flux in W/m^2
A_radiation = np.pi * 9 * 9  # Surface area for radiation, m^2
k = 14.6  # Thermal conductivity of 304L stainless steel, W/(m·K)
A_cross = np.pi * 9 * 0.005  # Cross-sectional area for conduction, m^2
L = 15  # Length of the cylinder, m
epsilon = 0.35  # Emissivity of the surface
sigma = 5.67e-8  # Stefan-Boltzmann constant, W/m^2/K^4
T_cold = 90  # Temperature at the cold end, K
T_ambient = 90  # Ambient temperature, K

# Integrand for radiative loss
def radiative_integrand(x, T_hot, T_cold):
    # Temperature gradient along the length
    T_x = T_cold + (x / L) * (T_hot - T_cold)
    return T_x**4 - T_ambient**4

# Function to compute the integral of T(x)^4
def average_radiative_loss(T_hot, T_cold):
    x_points = np.linspace(0, L, 1000)  # Discretize the length of the cylinder
    integrand_values = radiative_integrand(x_points, T_hot, T_cold)
    integral = np.trapz(integrand_values, x_points)  # Numerical integration
    return integral / L  # Average over the length

# Heat balance equation considering the corrected length and radiative loss
def heat_balance_corrected(T_hot):
    # Solar input
    Q_solar = q_solar * A_radiation
   
    # Conduction heat transfer
    Q_conduct = (k * A_cross / L) * (T_hot - T_cold)
   
    # Average radiative heat loss
    Q_radiation = epsilon * sigma * A_radiation * average_radiative_loss(T_hot, T_cold)
   
    # Total balance
    return Q_solar - (Q_conduct + Q_radiation)

# Solve for T_hot using corrected length and radiative model
T_hot_guess = 300
T_hot_corrected_solution = fsolve(heat_balance_corrected, T_hot_guess)[0]
T_hot_corrected_solution
print(T_hot_corrected_solution)
« Last Edit: 01/19/2025 10:38 pm by InterestedEngineer »

Online InterestedEngineer

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3002 on: 01/19/2025 10:54 pm »
Starship is a cylinder and not a pancake. This only increases the back-side radiation by a factor of pi/2 (ie negligible), but on the illuminated side you probably want to numerically integrate over the curvature, accounting for cosine loss.

When you integrate along the curve with the cosine losses to the irradiance, you find that the net incident radiation is proportional to the cross-section.  So a pancake works fine.

Emissivity is a different story, but to tell it you need to know a whole bunch of stuff about the orbit.  Even the night side of Earth is pretty hot in IR, and the angular width of the Earth from VLEO is large enough that considerably less than πrL will be radiating into cold space.

Assuming 460W/m2 earth shine in the sun, the equilibrium temperature of the tiles is 193K, emissions, 77W/m2, and net 325W/m2 transmitted into the tank through insulation (remainder is reflected).

22*9 = 200m2 * 325W/m2 = 65kW net influx.  I note heat on the nosecone is rounding error.

That is 1t per hour, or roughly 1.25t per orbit in VLEO. 

This assumes you rotate the nose to face the earth on the shady side, and keep nose pointed at the sun and the heat shield facing the earth as much as possible on the sunny side.

I haven't taken into account the absorption capability of the tiles, which will help a lot as the heat builds up and is radiated away on the shady side of the earth.

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3003 on: 01/20/2025 12:33 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

Good discussion, but I haven't seen the math.

Let's take a Starship with heat shield of 6cm thick (including the tiles, the blankets, and the backup ablative), give it an R value of 30 in Imperial units (5.28 in MKS), for an Reffective of 0.32 m2K/W.  We'll give the heat shield and absorption of 1.0 (probably pessimistic) and emissivity of 0.98.

Now for the simplest scenario:  The heat shield is facing the Sun, 1300 W/m2.  What will be the equilibrium temperature and heat flux into the Starship at the boiling point of LOX, 90K?

Now we have two simultaneous equations to solve:

emitted heat = 5.67e-8 * 0.98 * Texternal4
heat flux through insulation = ΔT/R = (Texternal - 90)/0.32

That's a 4th order equation, but fortunately spreadsheets are really good at this kind of thing, and the equilibrium answer is:

outer temp: 320K
inner temp: 90K
heat flux through insulation: 726W/m2

So the heat shield is only dropping the heat flux from the sun by 44%.  Very sad.

However, the other side of the Starship is facing deep space in our simplified scenario.   So we get to solve the equation again, but this time in the other direction:

outer temp: 88K
inner temp: 90K
heat flux: -3 W/m2

So the net heat flux is 723W/m2 into the Starship.  Still very sad.

How much LOX will that heat flux boil?

Q=m⋅L

Q = heat into the system = 723 J/s
L = latent heat of vaporization for LOX = 213kJ/kg. 
m = mass of the LOX being boiled

solving for m, we get 0.00339 kg/sec

Now the fuel tank for LOX is about 20mx9m = 180m2  (this is a square cow, the real one is cylindrical), so every second we are boiling .6kg of LOX.  That's 2.2t per hour.

Is that right?  Someone check my math please.

Now this is the worst case scenario - deep space, or a highly elliptical orbit.  In VLEO the sun is occluded 1/2 the time, and so now we have to start calculating rates.  The system will heat up for half an orbit, and cool down for half an orbit.  The tiles themselves absorb heat, which we would have to take into account.  Will leave that for another post.



https://docs.google.com/spreadsheets/d/1esN27mUh7s2gFvXzmvM6x1aU_AnVjfvRYwnGs5U2plw/edit?usp=sharing
This would be for a single layer shade? Wouldn't a multi layer shade do much better?


I couldn't follow the math past fourth order equations but I would expect the .98 emissivity would be for each layer in a multi layer, each layer emitting from both sides and each layer inward having less to emit. And wouldn't reflectance play into this?


Or is my model wrong? IAN...
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Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3004 on: 01/20/2025 12:43 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

The Skylab astronauts solved their heat problem with a jury rigged sunshade.
Why is that solution not also appliucable to the depot?

Even if there is need to develop retractable shades to allow refuelling, would it not be sufficient to simply shield the depot from sun and earthshine?
The design I've seen for a depot sun shade was a conical structure a bit like a stiff cape that surrounds the tanks. The wider open end points away from heat sources.


This doesn't work for two belly to belly ships. So it either needs to be able to reliably open up for transfers or go another route entirely. If a sun shade is in the works it will need to be as dynamic or more dynamic than the ISS solar panels and radiators. And it can't get in the way of transfers.


It's one of those 'I wonder how SX will do it' types of things.
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Online DanClemmensen

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3005 on: 01/20/2025 12:59 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

The Skylab astronauts solved their heat problem with a jury rigged sunshade.
Why is that solution not also appliucable to the depot?

Even if there is need to develop retractable shades to allow refuelling, would it not be sufficient to simply shield the depot from sun and earthshine?
The design I've seen for a depot sun shade was a conical structure a bit like a stiff cape that surrounds the tanks. The wider open end points away from heat sources.


This doesn't work for two belly to belly ships. So it either needs to be able to reliably open up for transfers or go another route entirely. If a sun shade is in the works it will need to be as dynamic or more dynamic than the ISS solar panels and radiators. And it can't get in the way of transfers.


It's one of those 'I wonder how SX will do it' types of things.
Such a collar would be a large structure and would probably need to be launched separately before unfolding, much like the JWST. Depot would then dock to it. But if Depot can dock there, it can also undock and emerge to perform transfer operations before re-docking. Depot would also need to be able to boost it to transfer to other orbits.

Offline Greg Hullender

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3006 on: 01/20/2025 01:01 am »
Possibly a dumb question, but can't there be some kind of solar powered active cooling system? That radiates the excess heat on the side not pointing towards the sun, to reliquidify the boil-off?
Not dumb, but there are a lot of challenges to overcome to make this work. Since SpaceX already announced they aren't planning to do this, it hasn't attracted a lot of interest.

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3007 on: 01/20/2025 01:23 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

The Skylab astronauts solved their heat problem with a jury rigged sunshade.
Why is that solution not also appliucable to the depot?

Even if there is need to develop retractable shades to allow refuelling, would it not be sufficient to simply shield the depot from sun and earthshine?
The design I've seen for a depot sun shade was a conical structure a bit like a stiff cape that surrounds the tanks. The wider open end points away from heat sources.


This doesn't work for two belly to belly ships. So it either needs to be able to reliably open up for transfers or go another route entirely. If a sun shade is in the works it will need to be as dynamic or more dynamic than the ISS solar panels and radiators. And it can't get in the way of transfers.


It's one of those 'I wonder how SX will do it' types of things.
Such a collar would be a large structure and would probably need to be launched separately before unfolding, much like the JWST. Depot would then dock to it. But if Depot can dock there, it can also undock and emerge to perform transfer operations before re-docking. Depot would also need to be able to boost it to transfer to other orbits.
The JWST shade launched separately? Didn't know that.


Or maybe the shade stays attached and opens up like Dracula spreading his cape. Ditching the shade when the depot needs ullage acceleration sounds like more of a problem than some reinforcement to handle the low g acceleration.


The side where the heat shield would normally be is available for a ship length structure to house a shade and deployment mechanism during launch.
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Online DanClemmensen

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3008 on: 01/20/2025 01:31 am »
The JWST shade launched separately? Didn't know that.
Sorry, I meant the JWST was a separate spacecraft. Our putative shield could be a separate spacecraft.
« Last Edit: 01/20/2025 02:14 am by DanClemmensen »

Offline aporigine

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3009 on: 01/20/2025 01:40 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

The Skylab astronauts solved their heat problem with a jury rigged sunshade.
Why is that solution not also appliucable to the depot?

Even if there is need to develop retractable shades to allow refuelling, would it not be sufficient to simply shield the depot from sun and earthshine?
The design I've seen for a depot sun shade was a conical structure a bit like a stiff cape that surrounds the tanks. The wider open end points away from heat sources.


This doesn't work for two belly to belly ships. So it either needs to be able to reliably open up for transfers or go another route entirely. If a sun shade is in the works it will need to be as dynamic or more dynamic than the ISS solar panels and radiators. And it can't get in the way of transfers.


It's one of those 'I wonder how SX will do it' types of things.
Such a collar would be a large structure and would probably need to be launched separately before unfolding, much like the JWST. Depot would then dock to it. But if Depot can dock there, it can also undock and emerge to perform transfer operations before re-docking. Depot would also need to be able to boost it to transfer to other orbits.
The JWST shade launched separately? Didn't know that.


Or maybe the shade stays attached and opens up like Dracula spreading his cape. Ditching the shade when the depot needs ullage acceleration sounds like more of a problem than some reinforcement to handle the low g acceleration.


The side where the heat shield would normally be is available for a ship length structure to house a shade and deployment mechanism during launch.

I assume the “like JWST” part was unfolding.

Instrument and folded shield were one launch.

Online InterestedEngineer

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3010 on: 01/20/2025 02:45 am »

Such a collar would be a large structure and would probably need to be launched separately before unfolding, much like the JWST. Depot would then dock to it. But if Depot can dock there, it can also undock and emerge to perform transfer operations before re-docking. Depot would also need to be able to boost it to transfer to other orbits.

We are not trying to cool a telescope to near CMB levels, 90K is sufficient, and no the JWST went in the same package.

It would be pretty trivial to deploy a rollable sun shade out of a cargo bay.  The best thing to do would be to dual purpose it as a flexible solar panel, that way batteries can stay charged while you are in the shade.

You only need to shade the side pointing to the Earth.  As shown in the math  above, facing the nose at the sun by itself is sufficient if you insulate the header tanks well.

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3011 on: 01/20/2025 02:50 am »
This would be for a single layer shade? Wouldn't a multi layer shade do much better?


I couldn't follow the math past fourth order equations but I would expect the .98 emissivity would be for each layer in a multi layer, each layer emitting from both sides and each layer inward having less to emit. And wouldn't reflectance play into this?


Or is my model wrong? IAN...

The math was for no shade at all, going with "best part is no part". 

TL;DR - nose at the sun or hottest source in the sky works extremely well, no shade needed for deep space, for example

In LEO, however, there are two hot sources - the Sun, and 1/4 of that the Earth.  Pointing nose isn't enough.

I'm pretty sure now for long term LEO depots shading from earth-shine will be the most important thing to do, and any lightweight deployable shade would do the job, it only being 460W/m2 on the sun-facing side of the Earth.  Just keep the nose always pointed at the Sun.
« Last Edit: 01/20/2025 02:51 am by InterestedEngineer »

Online DanClemmensen

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3012 on: 01/20/2025 02:54 am »

Such a collar would be a large structure and would probably need to be launched separately before unfolding, much like the JWST. Depot would then dock to it. But if Depot can dock there, it can also undock and emerge to perform transfer operations before re-docking. Depot would also need to be able to boost it to transfer to other orbits.

We are not trying to cool a telescope to near CMB levels, 90K is sufficient, and no the JWST went in the same package.

It would be pretty trivial to deploy a rollable sun shade out of a cargo bay.  The best thing to do would be to dual purpose it as a flexible solar panel, that way batteries can stay charged while you are in the shade.

You only need to shade the side pointing to the Earth.  As shown in the math  above, facing the nose at the sun by itself is sufficient if you insulate the header tanks well.
Lots of ways to solve the problem, but adding dry mass to Depot detracts from its primary function, so sending the extra stuff up in a cargo Starship may be a better solution.

Depot is non-EDL, so why does it need header tanks in the nose?

Offline sdsds

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3013 on: 01/20/2025 03:19 am »
Possibly a dumb question, but can't there be some kind of solar powered active cooling system? That radiates the excess heat on the side not pointing towards the sun, to reliquidify the boil-off?
Not dumb, but there are a lot of challenges to overcome to make this work. Since SpaceX already announced they aren't planning to do this, it hasn't attracted a lot of interest.

Has SpaceX said Starship will never have actively cooled depots? Or have they only said they intend to first try passive cooling and/or frequent replenishment of boil-off? I imagine replenishment gets more costly when the depot is located beyond LEO. Also any BLEO depot likely needs to hold propellant longer. So that's where it seems like active cooling will eventually be implemented.
« Last Edit: 01/20/2025 03:19 am by sdsds »
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Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3014 on: 01/20/2025 03:20 am »
Is there any reason the nose wouldn't be pointed at the sun? I'd always assumed that would be the orientation. The cross sectional area would be more like 70 sq m.

If that were true, and the nose had MLI under a vacuum, wouldn't the heat transfer to the tanks be mainly through the skin and structure connecting the nose to the rest of the 2nd stage? In that case the conduction cross sectional area would be pretty small I'd think. Perhaps some kind of "chomper" opening on the lee side of the nose cone would radiate some of that in addition to decreasing the cross sectional area. Maybe the chomper door actually could be a boom extending forward to put a reflective shield in front of the nose?

In that case, I'd think the Earth's radiation would be the main effect. That's something like a quarter of the Sun's and would vary depending on where the ship was in the orbit with the maximum heat flux being at local noon with the tail pointed at Earth. Obviously at night it would be less.

Earth Flux averages over a 300km orbit about 350W/m2, or 350/1361 = .26 so 1/4 is reasonable.

It better be! The Earth is in radiant balance, and (like any sphere) its surface area is 4 times its projected area from the Sun.  :)


Starship is a cylinder and not a pancake. This only increases the back-side radiation by a factor of pi/2 (ie negligible), but on the illuminated side you probably want to numerically integrate over the curvature, accounting for cosine loss.

When you integrate along the curve with the cosine losses to the irradiance, you find that the net incident radiation is proportional to the cross-section.  So a pancake works fine.

Emissivity is a different story, but to tell it you need to know a whole bunch of stuff about the orbit.  Even the night side of Earth is pretty hot in IR, and the angular width of the Earth from VLEO is large enough that considerably less than πrL will be radiating into cold space.

Assuming 460W/m2 earth shine in the sun, the equilibrium temperature of the tiles is 193K, emissions, 77W/m2, and net 325W/m2 transmitted into the tank through insulation (remainder is reflected).

I'm getting an average of 171 W/m 2 (235 W IR and 107 watts reflected, and both these are halved because the Earth takes up half the sky as viewed from the ship).

22*9 = 200m2 * 325W/m2 = 65kW net influx.  I note heat on the nosecone is rounding error.

The surface area here should really be the entire area (not the projected area). If you consider the Starship pointed straight up at solar noon, then the entire ship is exposed to Earthshine and emissions. At other angles it averages out to the same.

If we assume 85% reflectivity and 91% emissivity (Z-93 white coating), this works out to 153.5 W/m2, or a total of 95.5 kW hitting the exterior.

This is why SpaceX needs thick, SOFI insulation (like we've seen in the renderings)

If you plug in 95.5 kW for the incoming heat flux, 0% reflectivity, 91% emissivity, and R-75 (12" SOFI), what do we get for a final heat flux? The spreadsheet isn't working for me for some reason. But I imagine it's still not great, correct?


I'm starting to think SpaceX needs the nuclear option: SOFI-MLI hybrid. A thin layer of SOFI prevents ice formation on the pad, and the MLI on top provides the real insulation value in space. An outer Beta cloth (or similar) quilting supports the MLI during launch, and incidentally the whole stack-up makes a really great whipple shield against MMOD.

https://ntrs.nasa.gov/citations/20110014400
« Last Edit: 01/20/2025 03:23 am by Twark_Main »

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3015 on: 01/20/2025 03:26 am »
This has been a great discussion about absorbance, emissions, and insulation for depots. Thank you everyone for sharing your insights.

Good discussion, but I haven't seen the math.

Let's take a Starship with heat shield of 6cm thick (including the tiles, the blankets, and the backup ablative), give it an R value of 30 in Imperial units (5.28 in MKS), for an Reffective of 0.32 m2K/W.  We'll give the heat shield and absorption of 1.0 (probably pessimistic) and emissivity of 0.98.

Now for the simplest scenario:  The heat shield is facing the Sun, 1300 W/m2.  What will be the equilibrium temperature and heat flux into the Starship at the boiling point of LOX, 90K?

Now we have two simultaneous equations to solve:

emitted heat = 5.67e-8 * 0.98 * Texternal4
heat flux through insulation = ΔT/R = (Texternal - 90)/0.32

That's a 4th order equation, but fortunately spreadsheets are really good at this kind of thing, and the equilibrium answer is:

outer temp: 320K
inner temp: 90K
heat flux through insulation: 726W/m2

So the heat shield is only dropping the heat flux from the sun by 44%.  Very sad.

However, the other side of the Starship is facing deep space in our simplified scenario.   So we get to solve the equation again, but this time in the other direction:

outer temp: 88K
inner temp: 90K
heat flux: -3 W/m2

So the net heat flux is 723W/m2 into the Starship.  Still very sad.

How much LOX will that heat flux boil?

Q=m⋅L

Q = heat into the system = 723 J/s
L = latent heat of vaporization for LOX = 213kJ/kg. 
m = mass of the LOX being boiled

solving for m, we get 0.00339 kg/sec

Now the fuel tank for LOX is about 20mx9m = 180m2  (this is a square cow, the real one is cylindrical), so every second we are boiling .6kg of LOX.  That's 2.2t per hour.

Is that right?  Someone check my math please.

Now this is the worst case scenario - deep space, or a highly elliptical orbit.  In VLEO the sun is occluded 1/2 the time, and so now we have to start calculating rates.  The system will heat up for half an orbit, and cool down for half an orbit.  The tiles themselves absorb heat, which we would have to take into account.  Will leave that for another post.



https://docs.google.com/spreadsheets/d/1esN27mUh7s2gFvXzmvM6x1aU_AnVjfvRYwnGs5U2plw/edit?usp=sharing
This would be for a single layer shade? Wouldn't a multi layer shade do much better?


I couldn't follow the math past fourth order equations but I would expect the .98 emissivity would be for each layer in a multi layer, each layer emitting from both sides and each layer inward having less to emit. And wouldn't reflectance play into this?


Or is my model wrong? IAN...

The math is given on the Wikipedia page for MLI.

https://en.wikipedia.org/wiki/Multi-layer_insulation#Function_and_design

Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3016 on: 01/20/2025 03:30 am »
Personally I doubt all this talk about complex deployables (and especially re-deployables).  This would add a bunch of complexity and failure modes. "The best deployment process is no deployment process."

Hybrid SOFI-MLI can achieve great thermal performance without the complexity.

Online InterestedEngineer

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3017 on: 01/20/2025 04:30 pm »
Personally I doubt all this talk about complex deployables (and especially re-deployables).  This would add a bunch of complexity and failure modes. "The best deployment process is no deployment process."

Hybrid SOFI-MLI can achieve great thermal performance without the complexity.

Personally, I doubt Musk & Co are going to throw away 3.2km/sec of relatively free (20t dry) of deltaV by having a reusable Depot depart LEO without a heat shield and flaps.   It's an order of magnitude more of fuel to do that by propulsion (mass ratio of 2.5, so fuel is 1.5x dry mass or ~225t).  That's 225t that cannot be transferred to another ship.

Of course, if it's NASA, they just throw away things, so maybe they'll just throw away the Depot if it has to leave LEO for Artemis.

Then again, if it's impossible to one-pass aerobrake saving 205t of mass and at the same time not lose 205t of mass to evaporation, then I'm wrong about the heat shield.  I wonder if it is possible to do both.

Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3018 on: 01/20/2025 09:05 pm »
Personally I doubt all this talk about complex deployables (and especially re-deployables).  This would add a bunch of complexity and failure modes. "The best deployment process is no deployment process."

Hybrid SOFI-MLI can achieve great thermal performance without the complexity.

Personally, I doubt Musk & Co are going to throw away 3.2km/sec of relatively free (20t dry) of deltaV by having a reusable Depot depart LEO without a heat shield and flaps.   It's an order of magnitude more of fuel to do that by propulsion (mass ratio of 2.5, so fuel is 1.5x dry mass or ~225t).  That's 225t that cannot be transferred to another ship.

Of course, if it's NASA, they just throw away things, so maybe they'll just throw away the Depot if it has to leave LEO for Artemis.

Then again, if it's impossible to one-pass aerobrake saving 205t of mass and at the same time not lose 205t of mass to evaporation, then I'm wrong about the heat shield.  I wonder if it is possible to do both.

Completely agree. This is exactly the right model for lofting propellant for higher energy missions. The propellant is fully loaded just-in-time into the lofting vehicle, and is only stored for a few hours.

For consolidating a bunch of tanker launches in (V)LEO, there's a need for a large depot with long term storage capability. This de-risks the tanker schedule and minimizes the number of docking with the mission vehicle and lofting vehicle (if any).
« Last Edit: 01/20/2025 09:08 pm by Twark_Main »

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #3019 on: 01/21/2025 03:23 am »
This would be for a single layer shade? Wouldn't a multi layer shade do much better?


I couldn't follow the math past fourth order equations but I would expect the .98 emissivity would be for each layer in a multi layer, each layer emitting from both sides and each layer inward having less to emit. And wouldn't reflectance play into this?


Or is my model wrong? IAN...

The math was for no shade at all, going with "best part is no part". 

TL;DR - nose at the sun or hottest source in the sky works extremely well, no shade needed for deep space, for example

In LEO, however, there are two hot sources - the Sun, and 1/4 of that the Earth.  Pointing nose isn't enough.

I'm pretty sure now for long term LEO depots shading from earth-shine will be the most important thing to do, and any lightweight deployable shade would do the job, it only being 460W/m2 on the sun-facing side of the Earth.  Just keep the nose always pointed at the Sun.
I'm tying to picture a shield big enough to block ~40% of the sky (Earth), mobile enough to keep the ship shielded as the nose targets the sun and the sun-earth angle changes, not get in the way of a mating ship, do it all repeatedly, and still be reasonably light. Almost forgot. It has to withstand cold thruster blasts. I'm coming up blank but hope it's a lack of imagination.


The ISS panels and radiators are simple in comparison.
We are on the cusp of revolutionary access to space. One hallmark of a revolution is that there is a disjuncture through which projections do not work. The thread must be picked up anew and the tapestry of history woven with a fresh pattern.

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