Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 335049 times)

Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1280 on: 08/10/2022 08:34 pm »
Well, more than half the nose of any EDL-capable Starship is TPS, which you almost certainly can't paint. 
There's another problem: Whatever you paint, it needs to be reflective, so painting the black TPS isn't going to work in the first place. I think that eliminates this idea--at least for a regular Starship doing depot duty. If the lunar Starship isn't going to have tiles in the first place, though, then maybe it does make sense to paint the stainless steel with Solar White so the propellant will last longer. Assuming it's determined that just pointing the nose at the sun isn't good enough for the time it takes to refuel it.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1281 on: 08/11/2022 12:47 am »
Given that you want to recover that tanker (otherwise, you expend one for every lunar mission), you're probably restricted to bare metal tanks and TPS.  But then that makes it essential minimize transit boiloff without solar white coatings, sunshields, etc. 
Table 1 in the article I linked to above said that applying 5 mils (about 1/8 mm) of Solar White paint on top of stainless steel reduced absorption of solar energy from 53% to 8.5%. That seems like a very fine improvement for very little cost. Especially if you only need to paint the nose.

Well, more than half the nose of any EDL-capable Starship is TPS, which you almost certainly can't paint.  The question would be whether to clean off the solar white after EDL would be worth it, vs. just soaking up the rays.  Remember, the nose for a tanker is kinda like the outside of a dewar.  Only a fraction of the heat that's radiated inward, into the payload bay, will warm the top of the LCH4 tank. 

I'll bet a hunk of MLI in the payload bay to cover the dome would be vastly easier to engineer than figuring out how to paint the nose.  The paint won't survive entry.  I have no clue what scorching it would do to the heat distribution during EDL.  Probably nothing good.
In the solar white article I linked a page or two back, the active ingredient in the paint is yttrium oxide. The outer surface of the tiles is black vitrification. In other words, a glaze, and glazes are routinely pigmented. Is there a chance the black is choice, not chance? It would be very Elon like.


Yttrium oxide is considered to be rare earth like if not actually a rare earth. Rare earths are used as glaze pigments. If yttrium oxide gives solar white properties to the tiles as a glaze (a total unknown - at least to me) and it doesn't do anything wonky, it sounds as if it would be good for the tiles in general, not just for cryo insulation.


I hate when there are that many if's. I know next to nothing about pottery.
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Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1282 on: 08/11/2022 01:41 am »

Just found a paywall Ed paper on Y2O3 that hits on its chromatic behavior when added to Zirconia in varying concentrations. Most of the meat is hidden and what is public strains my level of understanding. The references shown may point to something on point for heat tile glaze for those with the skill and interest.


One takeaway: Y2O3 exhibits infrared photoluminescence when laser pumped which explains its high emissivity in the IR. 


https://www.sciencedirect.com/science/article/abs/pii/S0749603608002760


My search also also hit some Chinese patients using Y2O3 as a low concentration element in powdered glass glazes but nothing specifically as a pigment. The text appeared to be google translated and was a trial to understand.


Edit: paywalled, not paywall Ed.
« Last Edit: 08/11/2022 01:43 am by OTV Booster »
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Offline Paul451

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1283 on: 08/11/2022 06:25 am »
The average albedo OTOH, is not so helpful. VLEO gives such a restricted view of the surface that worst case needs to be explored. It's not impossible that some areas will be so far from the average that mitigation aimed at the average will still allow significant boil off. This may not be, but it should be looked at.

My point was that we're so far away from understanding the thermal properties of Starship, let alone a depot, that the difference between assuming 0.3 global albedo and the specific time-variant radiance from a specific (but unknown) path over the Earth are not even within our rounding-off-errors.

It's like we're booking an appointment 50 years away, somewhere within a random 24-month window, and you're asking whether "Morning or afternoon?" will be better for weather and traffic.

Offline edzieba

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1284 on: 08/11/2022 12:56 pm »
The outer surface of the tiles is black vitrification. In other words, a glaze, and glazes are routinely pigmented. Is there a chance the black is choice, not chance? It would be very Elon like.
The outer borosilciate glass surface is very functional: it's what rejects the majority of re-entry energy via radiation, and what protects the vehicle from chemical attack from the plasma. The sintered silica tile body behind it helps prevent heat conducted from the extremely hot coating from reaching the vehicle skin (and acts as a substrate for the coating) but that coating is the vital component for surviving re-entry.

Online InterestedEngineer

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1285 on: 08/11/2022 03:17 pm »
The outer surface of the tiles is black vitrification. In other words, a glaze, and glazes are routinely pigmented. Is there a chance the black is choice, not chance? It would be very Elon like.

There's a reason they call it "Black Body Radiation"

The black maximizes the Stefan-Boltzmann coefficient, which is the primary method of removing heat from a surface that can reach 1300degC.  The equation has a term where the energy moved is proportional to temperature change to the 4th power, times that coefficient.   Stainless steel is 0.35, the black borosilicate about 0.95 or better.   The black paint they added behind the forward flaps by itself improves the coefficient to above 0.9 (but without all other benefits of the tile)

Maybe this will help you if you your depot spends half time in the shade and half time in the sun in LEO.  The half time in the shade allows the black surface to maximize the emission of the energy gained while being in the sun, while the time in the sun heats up the tiles (which by themselves have about 10MJ / square meter heat capacity, if I'm remembering the math correctly), with the tiles and the mineral fiber mat underneath acting as insulation.

You'd have to do actual math to figure out if this is better or worse than reflecting the energy from the Sun before it is absorbed.  There's a lot of that kind of math on the heat shield thread.

The tiles themselves were designed to be bathed in intense heat for about 30 minutes and are allowed to pass a lot of that heat through to the interior as long as the skin doesn't exceed 800degC or so.  Not exactly what you are looking for, but your scenario has vastly different things happening.

If your depot needs to polar orbit the moon, there is no shade, so I doubt the black surface would be better than a sun shade or white surface.
« Last Edit: 08/11/2022 03:18 pm by InterestedEngineer »

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1286 on: 08/11/2022 04:46 pm »
The outer surface of the tiles is black vitrification. In other words, a glaze, and glazes are routinely pigmented. Is there a chance the black is choice, not chance? It would be very Elon like.

There's a reason they call it "Black Body Radiation"

The black maximizes the Stefan-Boltzmann coefficient, which is the primary method of removing heat from a surface that can reach 1300degC.  The equation has a term where the energy moved is proportional to temperature change to the 4th power, times that coefficient.   Stainless steel is 0.35, the black borosilicate about 0.95 or better.   The black paint they added behind the forward flaps by itself improves the coefficient to above 0.9 (but without all other benefits of the tile)

Maybe this will help you if you your depot spends half time in the shade and half time in the sun in LEO.  The half time in the shade allows the black surface to maximize the emission of the energy gained while being in the sun, while the time in the sun heats up the tiles (which by themselves have about 10MJ / square meter heat capacity, if I'm remembering the math correctly), with the tiles and the mineral fiber mat underneath acting as insulation.

You'd have to do actual math to figure out if this is better or worse than reflecting the energy from the Sun before it is absorbed.  There's a lot of that kind of math on the heat shield thread.

The tiles themselves were designed to be bathed in intense heat for about 30 minutes and are allowed to pass a lot of that heat through to the interior as long as the skin doesn't exceed 800degC or so.  Not exactly what you are looking for, but your scenario has vastly different things happening.

If your depot needs to polar orbit the moon, there is no shade, so I doubt the black surface would be better than a sun shade or white surface.
The whole point of the solar white paint is that it's highly reflective at visible wavelengths and highly emissive in the infrared. Being white in the visible, it rejects much of that input. What it doesn't reject becomes heat. This in turn is emitted in the infrared where, if we could see in the infrared, the paint would normally appear black.


The active component of solar white paint in the 2020 paper is Y2O3. Another paper I linked mentioned Y2O3 as fluorescing in the infrared when pumped by a laser. This makes me suspect that at least part of the infrared emission isn't linked directly to the usual black body considerations.


The energy input/output that follows somewhat more conventional black body considerations would, if examined within a restricted IR range, appear to be much hotter than what a perfect black body would normally exhibit. Within that IR emission range Mr Stefan and Mr Boltzmann become even more your friends than usual.


These are the properties I was noodling for the tile glaze. It would appear white in the visible. Elon likes white.
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Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1287 on: 08/11/2022 06:53 pm »
I did a plot of black-body radiation distribution from 0 to 8 microns for the Starship tiles (1650 K) and the surface of the sun (5778 K). I picked 8μ because Solar White reflects light for shorter wavelengths (down to 0.25μ, below which neither the sun nor the tiles emit much of anything). It's pretty amazing because it reflects all but 0.2% of the sun's light.

Unfortunately, this range is so broad that it's only going to have 5% emissivity for the tiles. That pretty much breaks them completely.

You can't compromise and use something that's a bit less reflective because then it won't keep cryogenics cold. So I think this completely rules out the idea of painting the heat-resistant tiles with something like Solar White. It just won't work.

Note: numbers on the x-axis are meters.
« Last Edit: 08/11/2022 06:54 pm by Greg Hullender »

Online TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1288 on: 08/11/2022 08:12 pm »
One takeaway: Y2O3 exhibits infrared photoluminescence when laser pumped which explains its high emissivity in the IR. 

I wouldn't get too hung up on the details, because I doubt that this is exactly what SpaceX will use on the LSS.

My dumb explanation of solar white:

1) It's really reflective in UV, visible light, and mid-infrared.
2) It's really emissive in low infrared.

It's the combination of these two properties that makes it effective.

Edit:  Hopelessly ninja'd.  That's what happens when you don't pay attention to the "you might want to recheck the thread" warning after leaving something sitting overnight.
« Last Edit: 08/11/2022 08:13 pm by TheRadicalModerate »

Online InterestedEngineer

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1289 on: 08/11/2022 11:07 pm »
I did a plot of black-body radiation distribution from 0 to 8 microns for the Starship tiles (1650 K) and the surface of the sun (5778 K). I picked 8μ because Solar White reflects light for shorter wavelengths (down to 0.25μ, below which neither the sun nor the tiles emit much of anything). It's pretty amazing because it reflects all but 0.2% of the sun's light.

Unfortunately, this range is so broad that it's only going to have 5% emissivity for the tiles. That pretty much breaks them completely.

You can't compromise and use something that's a bit less reflective because then it won't keep cryogenics cold. So I think this completely rules out the idea of painting the heat-resistant tiles with something like Solar White. It just won't work.

Note: numbers on the x-axis are meters.

Nice plot,  Can you include an estimate for the solar white paint?

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1290 on: 08/12/2022 12:50 am »
One takeaway: Y2O3 exhibits infrared photoluminescence when laser pumped which explains its high emissivity in the IR. 

I wouldn't get too hung up on the details, because I doubt that this is exactly what SpaceX will use on the LSS.

My dumb explanation of solar white:

1) It's really reflective in UV, visible light, and mid-infrared.
2) It's really emissive in low infrared.

It's the combination of these two properties that makes it effective.

Edit:  Hopelessly ninja'd.  That's what happens when you don't pay attention to the "you might want to recheck the thread" warning after leaving something sitting overnight.


Ahhh, sometimes getting down in the weeds is fun. You posted this 9 page paper: [size=78%]https://iopscience.iop.org/article/10.1088/1757-899X/1240/1/012001/pdf[/size]


Just finished it. Excellent read. The point that really jumped out at me was that Y2O3 is hydrophobic.


Don't get me wrong. I'm not doing a 'Y2O3 will fix all the problems' type of thing but there are hints that it might be nearly as good as sliced bread. Many unresolved issues too.


On the plus side:
- They are exploring both paint and ceramic tiles with the understanding that the investigation is looking at the tiles for cryo purposes, not EDL.
- Y2O3 has promising thermal properties
- by itself, it's expected to stand up well to atomic Oxygen. Testing is planned.
- it's hydrophobic


On the down side:
- the thermal properties are sensitive to the metallic substrate and stainless (specifics unknown) is a poor performing substrate.
- the KBr binder used in the paint is easily dissolved in water.
- the work is preliminary and many questions specific to use in the real world of rockets are yet to be answered. OTOH, there has been at least one sample mounted outside the ISS and parallel work is planned.


There's more, pro and con. It is intriguing but not a slam dunk. Other binders need to be explored. Investigating the ceramic form as a component of an EDL heat shield isn't mentioned. It's worth a deeper dive to see if there's other research going on. Loves them footnotes.





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Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1291 on: 08/12/2022 02:40 am »
Nice plot,  Can you include an estimate for the solar white paint?
At what temperature? Over what wavelengths? Can you better articulate what you're looking for?

The plots above are for black-body radiation. Solar White isn't black-body from 0.25μ to 8μ, but it pretty much is outside that range. Or, at least, that's what the papers claim.

Offline sebk

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1292 on: 08/12/2022 01:22 pm »
Does anybody have an estimate for how much solar wing and radiator area it would take just to have a depot with bare metal tanks and a brute-force cryocooler that could keep up with VLEO levels of boiloff?

The flux from the Earth day side to ~250m^2 of Starship's stainless tanks side (let's ignore the light falling on the nose cone, skirt or flaps) would be ~35kW. Multiply by 1 - reflectance (0.6) and you have 14kW flux while flying over the day side.

If you point heat shield side towards the Earth, you get 35 * 0.95 ie ~33kW. But this one could be averaged over day-night cycle because of low thermal conductivity of the shield. The day nigt cycle is not 50:50, because Earth shadow intersceting quite a bit less than 50% of the orbit. Also summer/winter time insolation grow with inclination. So the duty cycle is about 70% for low inclinations and get's much worse (>90% for ISS like inclinations). So about 23-30kW if you face the Earth with  heatshield.

So, stainless towards the earth it is. You will have some radiation hitting some heathsield because the earth takes like 1/3 of the sky so it will illuminate the sides, but at a slant angle.

So BOTE result is 15kW to get rid of if you can't average and you have to deal with the momentary peak flux on the day side. If you could average things by for example allowing the pressure to rise on the day side you could get the power to get rid of down to 11-14kW depending on inclination.

I assumed the ship pointing its nose to the Sun and MLI placed in the main bay just above methane tank. I ignored radiative cooling because at 70K the black body power is around 1.25W/m^2 so is negligible. I also ignored night side heating -- the flux would be about 13W per m^2 of Starship side (40W/m^2 from black body at 220K times 1/3 of the sky occupied by it) --  it's be less than 10% of day side light so while not negligible, for BOTE calculations could be ignored.


So it's 11-14kW to get rid of. What's the expected efficiency of practical cryo heat pumps? I suspect it's awful, AFAIR 10-20%. So 55 to 140kW range for the electric power.

Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1293 on: 08/12/2022 03:51 pm »
In The Spacecraft Thermal Control Handbook, Chapter 2: Spacecraft Thermal Environments (Clawson, J.F. & Gilmore, David G., 2002), I think Table 2.2 (p. 27) gives us what we really need to compute the thermal loading caused by the Earth. It gives the "hot case" albedo and IR heating for a hypothetical satellite orbiting just 30 km above the surface. Yeah, that's an impossible altitude, but you can adjust the numbers based on the real orbit of the depot.

Is it safe to assume that we really only care about the average thermal loading over a 24-hour period--given the thermal inertia of the tanks? We don't really care about temporary spikes or anything like that.

In general, this document is rich in information. I think it's well worth a look from anyone who's really interested in this topic.

Online TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1294 on: 08/12/2022 05:49 pm »
So it's 11-14kW to get rid of. What's the expected efficiency of practical cryo heat pumps? I suspect it's awful, AFAIR 10-20%. So 55 to 140kW range for the electric power.

So 150kW would be about 370mē of panels.  That's 15% of an ISS, all to deploy and stow robotically--reliably--if you want to get the Starship back.  Plus, you need the same amount of heat rejection.  Presumably, you deploy that as the back of your solar array.

That's not an easy engineering task.  Not impossible, but not the simplest thing that SpaceX could do (which is what they'll do).  That makes a non-recoverable depot a lot more likely.

PS:

You will have some radiation hitting some heathsield because the earth takes like 1/3 of the sky so it will illuminate the sides, but at a slant angle.

Radiative flux from a sphere to a cylinder has a computable view factor.  It's horrid, as you can see below, but you can use the pretty graph and see that it's going to be about 45% in VLEO.  So that helps a little.

The other computation that we need is how much heat power a particular boiloff rate gobbles up and expels.  This obviously strays away from full ZBO, but if you have some max amount of electrical power in your budget, it should let you compute the boiloff rate.
« Last Edit: 08/12/2022 08:53 pm by TheRadicalModerate »

Offline Paul451

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1295 on: 08/13/2022 03:31 am »
So BOTE result is 15kW to get rid of if you can't average and you have to deal with the momentary peak flux on the day side. If you could average things by for example allowing the pressure to rise on the day side you could get the power to get rid of down to 11-14kW depending on inclination.

Using 15kW as the worst case, but at 24hr/day. (Ie, 15kJ/second.) And a heat-of-vaporisation figure for methane of 511 kJ/kg, that means boil-off-only cooling would cost 2.5 tonnes of methane per day.

If your refuelling mission cycle takes 30 days from empty, through accumulation, to final target-vehicle transfer and empty again, you lose 75 tonnes of methane. I don't think it's reasonable to assume a faster cycle for a first generation depot.

(Oxygen has worse heat-of-vap (213kJ/kg), so you're only hurting yourself if you let it evaporate. Likewise, proper heat capacity of methane is around 2 kJ/kg per K so ignored at this level of chicken scratchings.)

So, stainless towards the earth it is.

There's no reason to have bare stainless steel. Even if you intend to re-enter the depot-ships, you can paint the dorsal side with something reflective. Just going from your 60% best-case reflectance to a hand-waving 90% for a white coating, and assuming 2/3rds of your 15kW is coming from the bare SS and 1/3rd through the heat-tiles on the sides, that coating alone reduces heat-input by half. And much better if you can also give at least the side-tiles a non-black coating. Between them, coatings alone could get the heat-input down below 4kW. Boil-off-only cooling is thus reduced to below 2/3 tonnes of methane per day, maybe down to half a tonne/day. 30 day mission ops for fuel accumulation costs you 15 tonnes of methane.

And 15 tonnes feels viable for a first generation depot.

Offline Paul451

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1296 on: 08/13/2022 04:16 am »
Re: Above.

Of course this was only the Earth-side heating. It assumes pointing the nose at the sun effectively eliminates heat-xfer to the tanks. IMO, that's not a given, since the nose isn't reflective and isn't designed for the job of being a sun-shield.




You will have some radiation hitting some heathsield because the earth takes like 1/3 of the sky so it will illuminate the sides, but at a slant angle.
Radiative flux from a sphere to a cylinder has a computable view factor.  It's horrid, as you can see below, but you can use the pretty graph and see that it's going to be about 45% in VLEO.  So that helps a little.

It's going to be complicated because the angle of the ship to Earth isn't constant, but rotates 360 degrees each orbit if the nose points to the sun.
« Last Edit: 08/13/2022 04:16 am by Paul451 »

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1297 on: 08/13/2022 12:16 pm »
Re: Above.

Of course this was only the Earth-side heating. It assumes pointing the nose at the sun effectively eliminates heat-xfer to the tanks. IMO, that's not a given, since the nose isn't reflective and isn't designed for the job of being a sun-shield.




You will have some radiation hitting some heathsield because the earth takes like 1/3 of the sky so it will illuminate the sides, but at a slant angle.
Radiative flux from a sphere to a cylinder has a computable view factor.  It's horrid, as you can see below, but you can use the pretty graph and see that it's going to be about 45% in VLEO.  So that helps a little.

It's going to be complicated because the angle of the ship to Earth isn't constant, but rotates 360 degrees each orbit if the nose points to the sun.
Mild confusion on your diagram. It shows the lighter (skin) side towards earth. This works if it's covered with thermal white paint. If not, wouldn't it work better with the tile side earthward?


No, the nose isn't designed as a sun shield but that doesn't mean it can't do less than perfect double duty. Orbit as you show. Much of the nose is already covered in tiles. Top the tank dome in MLI. Not the greatest. An SX first hack to get things working. Improve later.


Edit: added "doesn't"
Edit 2: just reread sbec's  post from 8/7 on stainless vs tiles facing earth. Still scratching my head.
« Last Edit: 08/13/2022 12:46 pm by OTV Booster »
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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1298 on: 08/13/2022 12:31 pm »
So BOTE result is 15kW to get rid of if you can't average and you have to deal with the momentary peak flux on the day side. If you could average things by for example allowing the pressure to rise on the day side you could get the power to get rid of down to 11-14kW depending on inclination.

Using 15kW as the worst case, but at 24hr/day. (Ie, 15kJ/second.) And a heat-of-vaporisation figure for methane of 511 kJ/kg, that means boil-off-only cooling would cost 2.5 tonnes of methane per day.

If your refuelling mission cycle takes 30 days from empty, through accumulation, to final target-vehicle transfer and empty again, you lose 75 tonnes of methane. I don't think it's reasonable to assume a faster cycle for a first generation depot.

(Oxygen has worse heat-of-vap (213kJ/kg), so you're only hurting yourself if you let it evaporate. Likewise, proper heat capacity of methane is around 2 kJ/kg per K so ignored at this level of chicken scratchings.)

So, stainless towards the earth it is.

There's no reason to have bare stainless steel. Even if you intend to re-enter the depot-ships, you can paint the dorsal side with something reflective. Just going from your 60% best-case reflectance to a hand-waving 90% for a white coating, and assuming 2/3rds of your 15kW is coming from the bare SS and 1/3rd through the heat-tiles on the sides, that coating alone reduces heat-input by half. And much better if you can also give at least the side-tiles a non-black coating. Between them, coatings alone could get the heat-input down below 4kW. Boil-off-only cooling is thus reduced to below 2/3 tonnes of methane per day, maybe down to half a tonne/day. 30 day mission ops for fuel accumulation costs you 15 tonnes of methane.

And 15 tonnes feels viable for a first generation depot.
It's all reasonable except the paint gets toasted during EDL. Painting's easy. Prep is the killer. That ship will never relaunch as a depot without a lot of prep. As an alternative, use only virgin tankers w/paint as one time accumulators, then recycle to a tanker only role.
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.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1299 on: 08/13/2022 01:13 pm »
So it's 11-14kW to get rid of. What's the expected efficiency of practical cryo heat pumps? I suspect it's awful, AFAIR 10-20%. So 55 to 140kW range for the electric power.

So 150kW would be about 370mē of panels.  That's 15% of an ISS, all to deploy and stow robotically--reliably--if you want to get the Starship back.  Plus, you need the same amount of heat rejection.  Presumably, you deploy that as the back of your solar array.

That's not an easy engineering task.  Not impossible, but not the simplest thing that SpaceX could do (which is what they'll do).  That makes a non-recoverable depot a lot more likely.

PS:

You will have some radiation hitting some heathsield because the earth takes like 1/3 of the sky so it will illuminate the sides, but at a slant angle.

Radiative flux from a sphere to a cylinder has a computable view factor.  It's horrid, as you can see below, but you can use the pretty graph and see that it's going to be about 45% in VLEO.  So that helps a little.

The other computation that we need is how much heat power a particular boiloff rate gobbles up and expels.  This obviously strays away from full ZBO, but if you have some max amount of electrical power in your budget, it should let you compute the boiloff rate.


A thought.

Quote
That's not an easy engineering task.  Not impossible, but not the simplest thing that SpaceX could do (which is what they'll do).  That makes a non-recoverable depot a lot more likely.


That and radiators and sun shades are why I keep coming back to depot heavy. Deploying stuff is hard and expensive. Tucking it away for redeploy is really, really, hard and expensive.


Here's an alternative for PV. Your numbers assumed state of the art panels with 40% conversion efficiently. What if they use twice as many dirt cheap 20% panels and cut them loose after braking thrust and before encountering significant atmosphere? It rubs against reusability but...


The radiator is quite a bit smaller than the panels and probably easier to refold.
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.

Tags: Starship Depot HLS 
 

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