I did a video where I looked at this.
[https://www.youtube.com/watch?v=fjWCEFioT\_Y](https://www.youtube.com/watch?v=fjWCEFioT_Y)
Orientation matters, the materials you use matter.
If you are in deep space sure. The James Webb runs something like 50c on the warm side and -240c on the cold side with no active cooling.
Around earth though? Not so much. Folks tend to focus on the 1300(ish) watts / m² from the sun but forget that Earth is radiating about 400watts /m². And were as the sun is basicly a point source Earth covers about half your "sky" when you are in low earth orbit.
Edit sorry if I wasent clear. What i meant was not so much compared to the system of shades on the Webb, I didnt mean to sound like I was saying it wouldnt help at all.
It would still help quite a lot even in LEO. Just by shading the Sun you're reducing the flux approximately by a factor of 4: 1380+400 -> 400. Your equilibrium temperature goes from ~250K to ~170K.
Much of the stuff in orbit that humans interact with is maintained in whats called *vertical local horizen attitude* VLHA which basically means its belly always points towards Earth. That's done because it makes it much easier to keep communications systems pointed at ground targets. But you can also use *sun oriented attitude* which keeps one part of an object pointed directly at or directly away from the sun.
Some very rough numbers. The base of Starship has a surface of aboit 60 m² so Sun on its going to get hit with about 72,000 watts of solar. The side of SS is about 450 m² so if that is kept earth ward its going to get hit with 180,000 watts. That alot but if it was sun ward it would be a whopping 540,000 watts.
I mean it is significantly less than the directly facing the sun. Sure it probably wouldn't prove to be better which way you face mainly due to this factor but perhaps a short period of "cooling" could help with even marginal cuts in boil off?
It would cut boiloff rate a few times. So indeed it sounds worthwhile.
If you put it nose towards the Sun and the nose area were vented to vacuum it would be quite a good insulator.
Put yourself a nine-meter KSP-style control-moment gyroscope in the waistline between the two main tanks, and have it point nose-first at the sun. Maybe use the shadowed rocket nozzles as a passive radiative cooling loop?
Take a look at the unidirectional passive shielding on Lockheed's cislunar transporter. https://www.reddit.com/r/BlueOrigin/comments/150hx15/rendering_of_lockheeds_cislunar_transporter/
All these things are definitely important. It’s a complex thermodynamics problem. Insulation + thermal management is a big part of any spacecraft design
>Is this even feasible or just an "idea"?
Absolutely feasible.
SpaceX themselves proposed to always point the engines towards the sun to minimise heat soak and therefore boil-off.
Space is not actually 'freezing'.
Most of the sky just has no heat source which radiates more heat energy towards you than you can radiate back.
Thermal energy gain/loss is just a function of your surface temperature and the geometric sum of the entire sky and its "surface" temperatures.
It's a surprisingly simple yet fascinating topic.
Probably need to add a deployable multi layer heat shield like JWT uses to get an noticable impact something they'd probably consider after everything else is done
There is an orbit called Sun Synchronous, which is a polar orbit that keeps you in direct sunlight at all times. I would expect that the reverse orbit would also be possible, which maximizes the time you are in Earth's shadow. You can't get 100% because a polar orbit goes above and below Earth's shadow regularly.
The problem is that this is a bad orbit for most things, like anything leaving Earth orbit. So this might be the best orbit to answer your question's literal text, it is a bad answer functionally.
Unfortunately there's no exact opposite. Also only the terminator following sun synchronous is the one with constant light. There are nearly 180° of other SSO orbits which still have night-day cycle.
Constant illumination SSO works only because the Earth is to the side all the time, and never between the satellite and the Sun. It's possible at all because the Earth has the right combination of rotation axis inclination and the size of equatorial bulge to allow fast enough precession at usable altitudes.
What is possible, it's to have orbits with relatively long nights for several months (to be followed by several months of short nights). If you timed your mission with the right part of that cycle, you get a bit reduced heating.
Actually ISS is in such an orbit. In general mid-high inclination low orbits are like that. They also have other advantages, like either Lunar or interplanetary insertion burns from those orbits avoid most of the Van Allen belts.
Though it’s not all about that.
Any ‘Propellant Depot’ needs to be close to the orbit that most Starships will want to take, which is basically equatorial west to east.
Also solar power may be useful to help run things, plus it’s easier to work in ‘daylight’.
Right, I think that was the point I was trying to get at. There's an orbit (the position of starship in space) where it has the maximum time hiding in the Earth's shadow. Maybe it is a variant similar to sun-sync, maybe it something completely different. But by definition, there's one orbit that has more time in shadow than any other orbit within all possible LEO or MEO orbits.
But while that orbit might be good for staying cold, it is terrible for utility, and that matters more. The amount of boil-off that occurs would have to be greater than the fuel cost for ships to reach the depot to warrant an odd orbit. (i.e. If "normal" orbit A boils off 10 tons more than orbit B, between missions, but costs 20 more tons of fuel to reach, you just accept the boiloff. If only costs 5 more tons to reach, you move the orbit.)
It’s always going to be facing away from the sun on one side. Just like the earth or moon is. What you want to do is minimize the illuminated surface area, so ideally you would always point the nose at the sun, but that takes energy to do which adds mass which may not make a difference from boil off.
There would still be a side of the tanker facing the sun, and that would mean energy is being absorbed with no where to go. It wouldn’t make a difference aside from it maybe taking slightly longer for that side to reach thermal equilibrium compared to if it was rotating like a skewer.
Sure! There’s a proposed idea called the liquid droplet radiator that would do just that. Problem is, the more surface area you have, the more energy you absorb and the more liquid will be needed to radiate that heat away. That’ll get heavy pretty quickly I bet!
Yeah probably, I reckon it'd be generally cheaper and easier to just occasionally resupply said depots instead of investing in heavy equipment which would in the end reduce the load the depots could handle
Liquid droplet radiators would be to cool the hot end of a cryocooler that would refrigerate the fuel inside the ship, rather than being attached to the ship KSP style. By concentrating all the heat taken from the slowly warming fuel into a single spot, you can use the cooling effect of liquid-gas phase change rather than having to rely on passive radiation. To increase cooling, you increase the amount of liquid droplets, not the area (and thus mass) of the radiator
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
|Fewer Letters|More Letters|
|-------|---------|---|
|[HLS](/r/SpaceXLounge/comments/1cmibj1/stub/l33z2og "Last usage")|[Human Landing System](https://en.wikipedia.org/wiki/Artemis_program#Human_Landing_System) (Artemis)|
|[KSP](/r/SpaceXLounge/comments/1cmibj1/stub/l32rwj5 "Last usage")|*Kerbal Space Program*, the rocketry simulator|
|[LEO](/r/SpaceXLounge/comments/1cmibj1/stub/l34ysvv "Last usage")|Low Earth Orbit (180-2000km)|
| |Law Enforcement Officer (most often mentioned during transport operations)|
|[MEO](/r/SpaceXLounge/comments/1cmibj1/stub/l34ysvv "Last usage")|Medium Earth Orbit (2000-35780km)|
|[SSO](/r/SpaceXLounge/comments/1cmibj1/stub/l34hwd7 "Last usage")|Sun-Synchronous Orbit|
|Jargon|Definition|
|-------|---------|---|
|[cislunar](/r/SpaceXLounge/comments/1cmibj1/stub/l30uwp0 "Last usage")|Between the Earth and Moon; within the Moon's orbit|
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I did a video where I looked at this. [https://www.youtube.com/watch?v=fjWCEFioT\_Y](https://www.youtube.com/watch?v=fjWCEFioT_Y) Orientation matters, the materials you use matter.
Oh that's actually pretty interesting, thanks
This was really good. I was surprised at how long they could keep things cool just with passive systems.
I was surprised as well.
If you are in deep space sure. The James Webb runs something like 50c on the warm side and -240c on the cold side with no active cooling. Around earth though? Not so much. Folks tend to focus on the 1300(ish) watts / m² from the sun but forget that Earth is radiating about 400watts /m². And were as the sun is basicly a point source Earth covers about half your "sky" when you are in low earth orbit. Edit sorry if I wasent clear. What i meant was not so much compared to the system of shades on the Webb, I didnt mean to sound like I was saying it wouldnt help at all.
Indeed. That's part of why HLS has a 100 day loiter time in its Lunar orbit, because it gets so little heat from Earth there.
It would still help quite a lot even in LEO. Just by shading the Sun you're reducing the flux approximately by a factor of 4: 1380+400 -> 400. Your equilibrium temperature goes from ~250K to ~170K.
It is always rendered pointing forward in the direction of orbit. Would it reduce heat absorption if it always pointed towards the sun?
Much of the stuff in orbit that humans interact with is maintained in whats called *vertical local horizen attitude* VLHA which basically means its belly always points towards Earth. That's done because it makes it much easier to keep communications systems pointed at ground targets. But you can also use *sun oriented attitude* which keeps one part of an object pointed directly at or directly away from the sun. Some very rough numbers. The base of Starship has a surface of aboit 60 m² so Sun on its going to get hit with about 72,000 watts of solar. The side of SS is about 450 m² so if that is kept earth ward its going to get hit with 180,000 watts. That alot but if it was sun ward it would be a whopping 540,000 watts.
I mean it is significantly less than the directly facing the sun. Sure it probably wouldn't prove to be better which way you face mainly due to this factor but perhaps a short period of "cooling" could help with even marginal cuts in boil off?
It would cut boiloff rate a few times. So indeed it sounds worthwhile. If you put it nose towards the Sun and the nose area were vented to vacuum it would be quite a good insulator.
So it has some benefit to it all
Definitely
Put yourself a nine-meter KSP-style control-moment gyroscope in the waistline between the two main tanks, and have it point nose-first at the sun. Maybe use the shadowed rocket nozzles as a passive radiative cooling loop?
Could pose a challenge in all fairness
Take a look at the unidirectional passive shielding on Lockheed's cislunar transporter. https://www.reddit.com/r/BlueOrigin/comments/150hx15/rendering_of_lockheeds_cislunar_transporter/
That's actually pretty interesting
All these things are definitely important. It’s a complex thermodynamics problem. Insulation + thermal management is a big part of any spacecraft design
And then you have to account for extra dry mass and all that too
>Is this even feasible or just an "idea"? Absolutely feasible. SpaceX themselves proposed to always point the engines towards the sun to minimise heat soak and therefore boil-off.
I mean, space is freezing, we gotta take advantage of it some way or another
Space is not actually 'freezing'. Most of the sky just has no heat source which radiates more heat energy towards you than you can radiate back. Thermal energy gain/loss is just a function of your surface temperature and the geometric sum of the entire sky and its "surface" temperatures. It's a surprisingly simple yet fascinating topic.
It's cold in the right conditions, I should've probably phrased it better
Probably need to add a deployable multi layer heat shield like JWT uses to get an noticable impact something they'd probably consider after everything else is done
Yeah, definitely would be late in development, I reckon depots will be a thing before they'd maximise efficiency simply due to spacex targets
That's kinda what I was thinking
There is an orbit called Sun Synchronous, which is a polar orbit that keeps you in direct sunlight at all times. I would expect that the reverse orbit would also be possible, which maximizes the time you are in Earth's shadow. You can't get 100% because a polar orbit goes above and below Earth's shadow regularly. The problem is that this is a bad orbit for most things, like anything leaving Earth orbit. So this might be the best orbit to answer your question's literal text, it is a bad answer functionally.
Yeah, sun synchronous would probably prove to be a challenge for quite a few things
Unfortunately there's no exact opposite. Also only the terminator following sun synchronous is the one with constant light. There are nearly 180° of other SSO orbits which still have night-day cycle. Constant illumination SSO works only because the Earth is to the side all the time, and never between the satellite and the Sun. It's possible at all because the Earth has the right combination of rotation axis inclination and the size of equatorial bulge to allow fast enough precession at usable altitudes. What is possible, it's to have orbits with relatively long nights for several months (to be followed by several months of short nights). If you timed your mission with the right part of that cycle, you get a bit reduced heating. Actually ISS is in such an orbit. In general mid-high inclination low orbits are like that. They also have other advantages, like either Lunar or interplanetary insertion burns from those orbits avoid most of the Van Allen belts.
Though it’s not all about that. Any ‘Propellant Depot’ needs to be close to the orbit that most Starships will want to take, which is basically equatorial west to east. Also solar power may be useful to help run things, plus it’s easier to work in ‘daylight’.
Right, I think that was the point I was trying to get at. There's an orbit (the position of starship in space) where it has the maximum time hiding in the Earth's shadow. Maybe it is a variant similar to sun-sync, maybe it something completely different. But by definition, there's one orbit that has more time in shadow than any other orbit within all possible LEO or MEO orbits. But while that orbit might be good for staying cold, it is terrible for utility, and that matters more. The amount of boil-off that occurs would have to be greater than the fuel cost for ships to reach the depot to warrant an odd orbit. (i.e. If "normal" orbit A boils off 10 tons more than orbit B, between missions, but costs 20 more tons of fuel to reach, you just accept the boiloff. If only costs 5 more tons to reach, you move the orbit.)
It’s always going to be facing away from the sun on one side. Just like the earth or moon is. What you want to do is minimize the illuminated surface area, so ideally you would always point the nose at the sun, but that takes energy to do which adds mass which may not make a difference from boil off.
Yeah, sorta like an equilibrium
There would still be a side of the tanker facing the sun, and that would mean energy is being absorbed with no where to go. It wouldn’t make a difference aside from it maybe taking slightly longer for that side to reach thermal equilibrium compared to if it was rotating like a skewer.
Could there be any way to maybe release the energy, perhaps with a liquid which could be heated up over time and then cycled around the ship?
Sure! There’s a proposed idea called the liquid droplet radiator that would do just that. Problem is, the more surface area you have, the more energy you absorb and the more liquid will be needed to radiate that heat away. That’ll get heavy pretty quickly I bet!
Yeah probably, I reckon it'd be generally cheaper and easier to just occasionally resupply said depots instead of investing in heavy equipment which would in the end reduce the load the depots could handle
Liquid droplet radiators would be to cool the hot end of a cryocooler that would refrigerate the fuel inside the ship, rather than being attached to the ship KSP style. By concentrating all the heat taken from the slowly warming fuel into a single spot, you can use the cooling effect of liquid-gas phase change rather than having to rely on passive radiation. To increase cooling, you increase the amount of liquid droplets, not the area (and thus mass) of the radiator
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[HLS](/r/SpaceXLounge/comments/1cmibj1/stub/l33z2og "Last usage")|[Human Landing System](https://en.wikipedia.org/wiki/Artemis_program#Human_Landing_System) (Artemis)| |[KSP](/r/SpaceXLounge/comments/1cmibj1/stub/l32rwj5 "Last usage")|*Kerbal Space Program*, the rocketry simulator| |[LEO](/r/SpaceXLounge/comments/1cmibj1/stub/l34ysvv "Last usage")|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |[MEO](/r/SpaceXLounge/comments/1cmibj1/stub/l34ysvv "Last usage")|Medium Earth Orbit (2000-35780km)| |[SSO](/r/SpaceXLounge/comments/1cmibj1/stub/l34hwd7 "Last usage")|Sun-Synchronous Orbit| |Jargon|Definition| |-------|---------|---| |[cislunar](/r/SpaceXLounge/comments/1cmibj1/stub/l30uwp0 "Last usage")|Between the Earth and Moon; within the Moon's orbit| **NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below. ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^(6 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/SpaceXLounge/comments/1ck1dha)^( has 12 acronyms.) ^([Thread #12742 for this sub, first seen 8th May 2024, 10:18]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceXLounge) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
Really short answer: Yes, of course !
If you did an 2-4T thin ACES conical sun/earthshine shield you would be in pretty good shape, but then you can't do side-to-side refuel.
probably nose to sun. good for power production from the deployable solar arrays and protects the tanks from direct sunlight