# Can a space station settlement orbit the sun?

Is it possible to create a large space station orbiting the sun around 10 million kilometers away from the sun? It would be a large settlement which houses around 200 people. Energy would not be a problem provided they bring solar panels with them. So is this possible and would 10 million kilometers be too small? Could they create sustainability? Humans would have 10 years to build it and our current technology plus any new tech they develop in the next 10 years.

• 10M km is about a quarter of the distance from Mercury to the Sun at closest approach (Mercury's perihelion, point of closest approach in its orbit, is almost exactly 46M km, but that's orbital radius so you should subtract the Sun's radius for about 45.3M km from the sun's perimeter). Hint hint, Mercury's sunlit side is kinda warm, and heat rejection is non-trivial in space.
– user
Commented Jul 7, 2016 at 11:14

Solar radiation increases/decreases according to an inverse-squared principle, much like sound on Earth. The closer you get, the exponentially higher the energy of the sun will become. To put it in perspective, check out http://www.pveducation.org/pvcdrom/properties-of-sunlight/solar-radiation-in-space

According to those calculations, if you are 10 million km from the sun, you will get something like 290,000 watts per square meter. That's ~200 times more intense than the sunlight on Earth. Things will get rather toasty in our space station.

So how can we prevent this heat from cooking our intrepid stationkeepers? A reflector can help in a major way (there are reflectors designed to reflect gigawatt lasers, so they can handle the sun), but even the best mirrors are about 99.9% efficient, so our station will receive about 2.5x the energy of the earth even behind a giant mirror. There are better options, though. A reflector paired with a heat shield, or layered reflectors and heat shields, can do wonders. Certain high-temperature ceramics can exist up to temperatures in the thousands of degrees C. These could shield the station (hopefully from behind a reflector) and keep the inhabitants relatively cool.

The real issue is that the leading edge of the station (the side facing the sun) will erode eventually. Space is an inhospitable place, and even if the station isn't baked to a crisp, micrometer strikes will bring the reflector plate down eventually, and the ceramics will chip away. Once this shield is gone, the station will literally be toast. Hope your folks have a backup plan.

• O(N^2) is not equal to O(2^n). Commented Jul 7, 2016 at 10:07
• @Taemyr I don't think I understand what you mean. Where do I use either of those formulae? Commented Jul 7, 2016 at 14:41
• inverse-squared principle and exponentially higher. Commented Jul 7, 2016 at 15:03
• Ah yes. Semantics. My apologies, everyone, "Exponential" implies an e^x style formulation, while "Polynomial" implies x^n. So sorry for wasting everyone's valuable time with my slight semantic error. It's a good thing you caught that mistake @Taemyr or else everyone might have been seriously confused. Commented Jul 7, 2016 at 15:26
• The part facing the sun is not the leading edge, it's the side. The leading edge (facing the direction of motion) is 90' around from the sunward direction Commented Dec 2, 2016 at 6:02

http://www.popsci.com/science/article/2010-07/how-close-could-person-get-sun-and-survive

Riding in the space shuttle, though, someone could get much closer to our star. The ship's reinforced carbon-carbon heat shield is designed to withstand temperatures of up to 4,700° to ensure that the spacecraft and its passengers can survive the friction heat generated when it reenters the atmosphere from orbit. If the shield wrapped the entire shuttle, McNutt says, astronauts could fly to within 1.3 million miles of the sun (roughly the two-yard line). But the integrity of the shield degrades rapidly above 4,700°, and the cockpit would begin to cook. "I would advise turning away from the sun well before that point," McNutt says. Much hotter than that, the shields would fail altogether, and the vehicle would combust in less than a minute.

Of course, just getting that close to the sun would be quite an accomplishment, says NASA radiation-health officer Eddie Semones. The constant exposure to cosmic radiation during the voyage would most likely prove fatal before the astronauts crossed the 50-yard line.

So the answer seems to be YES, if you can survive the insane amount of crazy radiation. In KM 1.3m milion is 2,092,147km so being 5x further away would be good. You would probably have to generate a large magnetic fields with backup generators to block the radiation. If they ever failed even for a short time everyone dies.

• Instead of a magnetic shield, perhaps there is a second rotating structure orbiting between the settlement and the Sun. Aside from maneuvering, it wouldn't require power to operate. And, if it's transparent, it could be used to control the day-night cycle of the colony (like in Lary Niven's Ringworld series) Commented Jul 7, 2016 at 5:20

It is technically feasible so long as the temperature can be controlled, as suggested by MozerShmozer. Indeed his answer suggests why anyone would want to do such a thing; they will be able to accommodate a very high energy lifestyle.

Orbiting the sun at that distance will be much like orbiting any other astronomical body, you will essentially be in free fall (unless the station is rotating to create the effect of gravity), and that near the sun you might want to deploy a large "wake shield" ahead of your orbit to protect the station from orbiting particles that would also accumulate due to the Suns's massive gravity, not to mention the particles emitted by the sun itself.

Another trick which would work very well in that region is to deploy a solar sail of sufficient size to counteract the gravitational pull of the Sun and suspend your station under it. This concept (by Robert L Forward) is known as a Statite. The patent drawing shows a statite "hovering" over Earth, with sufficient planning you could build a statute capable of hovering almost anywhere in the Solar System.

• How does making it a statite help? Orbiting debris will be at a high relative velocity! Commented Jul 7, 2016 at 10:47
• @JDługosz at that orbit there will be no debris, everything evaporates, over sun life time - I mean sun already cleaned that region. I guess. Commented Jul 7, 2016 at 12:51
• How would that be different from orbiting at the same distance, if your statement applies to all points at this distance? In any case, stuff falls in and stuff is belched out; we never postulated perminant dust orbiting in close but oddly oriented orbits as being the abrasive hazard. Commented Jul 7, 2016 at 13:00
• @JDługosz do not know, was it to me or not, but if for my comment - there will be no permanent or not permanent, or high electricity orbiting particles. Anything at that orbit will evaporate over time, because of radiation (and vapor pressure in vacuum) and because of particles (H, He and other), because solar flares - in therms of small debris it have to be most clean place in our system. Although I'm not fan of hovering over Sun without no reason, in OP's situation there no obvious reason for that. Looks like just funny fact Thucydides wished to notice. Commented Jul 8, 2016 at 0:50

To steal from Brin's Sundiver (and to a degree, Niven's Ringworld), an hypothetical high-temperature superconductor tied to a very efficient laser could shed whatever excess heat by beaming it back into the sun. (Which is the entire premise of Sundiver)

Naturally, such superconductor materials are made of equal parts science and fiction, …

Yes, a space station settlement could orbit the sun, but, as others pointed out, preferably at a much larger distance. In fact, the earth orbits at about the "perfect" distance of 150 million km, so that it does not get too hot or too cold.

The issue is the energy needed to escape from Earth. It took a lot of energy to bring the international space station at an orbit of just 400 km above sea level. If you look at a (physical) globe of say 30 cm diameter, and at the distance Amsterdam to Paris, you understand that ISS circles just a few millimeters around that globe. To bring that same ISS in a substantially higher orbit, or even to escape velocity, would need unimaginable amounts of energy. And your 200 person space station is much bigger than ISS.

Could this be done? Practically: no. Theoretically: not in 10 years. In your phantasy (phantastically): of course.

My question is: why not use the Earth itself as such space station?

## Yes

• distance from the Sun, 30 light seconds
• visual size of the Sun at 10kk km will be 8° (diameter)
• radius of the Sun, $\approx$ 2.3 light second (diameter 4.6 light second)
• effective temperature of absolute black body, sun side surface, $\small \approx 1500K$
• energy flux, $\small \approx300kW/m^2$

This is not an easy situation, specially for those who do not have much experience in space building, and do not have much stuff to operate in the space ad proven technologies needed for such operation. So this 10year+10year of OP's setup - is source of an uncertainty. We may develop technologies which may make this task an easy task, but will we do it or not in the time, I do not know. Thus I suggest one of possible, but sort of low tech solution, which isn't state of art. And this is not Only solution in any way.

Body with 400m radius will make cone of full shadow, height of that cone will be 5720m (1:14.3 ratio).

Ratio of base area(let it be circle) to side area of that cone in our case where $r \ll h$, is also 1:14.3

full surface area of a cone is ${\pi r^2 + \pi r \sqrt{r^2 + h^2}} = \text{base} + \text{side area}$

$\frac {\pi r \sqrt{h^2+r^2}}{\pi r^2} = \sqrt{\frac{h^2+r^2}{r^2}} = \sqrt{1 + \frac{h^2}{r^2}} = \frac{h}{r} \sqrt{1+\frac{r^2}{h^2}} \approx \frac{h}{r} + \frac{1}{2} \frac{r^2}{h^2}$

$\frac{h}{r} = \cot(4 \deg) \approx 14.30$ , $\frac{1}{2} \frac{h^2}{r^2} \approx 0.00244$ which is less then $\frac{1}{6000} \text{ of } \frac{h}{r}$

• formulas was not totally necessary, but, who knows

This 1:14.30 ratio is actually important for station

Energy from the bottom of the station have to be dissipated by surface which is in the shadow. Near the cone it will be area of half shadow, where flux will change from 0 to full 300kW/m2 solar energy flow, using that gray area we may improve overall energy generation, but consideration of this matter is omitted.

## Bottom

One may use mirrors for the bottom of the station-cone, to reflect the solar energy, but reducing reflective efficiency of this solution have to be expected at this distance from the Sun.

Sun temperature is around 5772K, and spectrum is divided into the following: 5% of the total energy is gamma and UV; 51% 300-800 nm, 41% 800-3300 nm.

The 5% is significant amount of energy at that orbit, and as high energy spectrum it will erode the initially perfect mirror, or layers of reflective materials, specially protective coating if there is such one - more imperfections faster the erosion will develop. It can be solved through constantly refurbishing of the mirror. I do not count solar wind particles erosion, even for perfect reflective mirror we have to protect mirror from them, it can be done by magnetic fields - which can be a challenge by itself.

Thus the mirror isn't an easy option, and sucsess is highly depend on successes in technical development, testings etc - it might fail in 10+10years plan, or do not achieve good enough results, and with necessity to refurbish the surface of the mirror in such not an easy environment is fragile and technologically hungry solutions, so even if it may be a part of a self-sufficient solution, we may choose another approach which requires less maintenance and which is less technologically advanced.

But first of all the energy, how much of it we may produce and use at that distance.

## Energy

Despite abundance of energy at this distance(10 million km) solving the problem of electricity generation may be not so easy, because of energy density of the solar flux, solar wind, it isn't just as simple as plug solar panels and you are in the game, specially as a long therm solution.

It will have the same problems as mirror solution for the bottom of the station, erosion and degradation, and same protection from solar wind plasma needed. Multilayer cells have around 40-50% efficiency (up 64% theoretical, at the moment, according wiki, I heard 70% efficiency)

But as multilayer they may degrade faster then usual cells, specially so close to the Sun which is a strong gamma and neutron source. How much energy they need to be produced, how much energy they may produce in their life time, will it be enough to renew them in this environment, specially with small station production capacities. Who knows. Development of technology isn't so easy to predict.
But those efficiency's are not way too far from electricity generation with steam power, and solar cells just do not work at temperatures where steam generation works. So this way we will go with 40% efficiency, good enough. No need in super duper technologies for to repair and to produce.

Thus as the electricity generation device we choose a steam turbine, was good enough for my grandpa, good enough for the space.

With 300-340K of side surface of the station, it means 460-760W of the waste heat can be dissipated with each square meter of the surface. With above given parameters of the station, we have 5-8 GW in form of electricity. Which we have to spend some where outside of the station(for propulsion as example). More realistically 3.3GW at 300K (waste and electricity(which will become waste after some use) combined, electricity will be something like 1.3GW here)

• there may be another ways to generate energy so close to sun, as example using solar wind(plasma) directly to generate potential, also use photons to accelerate electrons and get energy from them (reverse vacuum tube) and such solutions may work entirely at 1500K (or 1260K actually, because 2 sides irradiate heat). Some materials will form plasma at such circumstances, and just that fact is enough to get energy. These solutions, as they may work in that environment without need for additional cooling, may solve energy and heat problem for station completely(at that orbit). As we have energy, we may cool station, specially in case where energy solution is also heat dissipation-protection solution. But such solutions have to be tested, perfected etc - and how much time it will take, no body knows.(depends). So without smart technologies, like this one Laser Wake Field Acceleration but for our needs at that orbit and without lasers, and and and ....

• But needs to say -- the station may potentially operate with significantly larger amounts of energy then just 1.3GW of electricity. In given situation with steam it can be 15GW, if side surface works as a radiator at about 650K(cold end for steam). Usual hot end for steam is about 823K, so efficiency will be pretty low about 21%, but because of black body emission is proportional to T4 it maximizes electricity generation.

## Heat

• usually people are concerned about that more then it needs actually, and I'm perfect example of that with this kind of answer.

With ratio 1:14.3 we can't just take all energy at bottom and dissipate it, our optimistic dissipation capability with 400K (above boiling point of water, and we still may produce energy at that point) is 10GW in form of heat. Bottom gets $\approx$ 15 times more, so our abilities to dissipate are 6.6% of what we may potentially have to dissipate.

There are good news too

• there are lot of material with melting point above 1500K, Specially Fe, Si, SiC, C, and pure SiO2 with it's almost 2000K.

• zero gravity - we may have just molten ball at bottom of station, as shield(reducing flux) - I mean structural strength of materials is not big issue here.

• we no not need some rare and unique materials

Black body surface, with 0 heat conductivity, will have temperature 1500K on side of sun. But some sheet of material heat conductive, will have temperature 1261K because it emits energy to sun and from sun - so just plain sheet at bottom of station, will reduce energy 2 times.

Sphere will dissipate energy all around and will have temperature 1060K, 4 times less energy(approximately, visual angle of the sun isn't counted here)

But lets take look at that cone station(r=400m, h=5720m), and If it will be kinda solid, will it have equal temperature on all over it's surface. No, because of heat transfer rate in the material of the cone. So less heat conductivity will be, more will it be the difference between hot part(base of the cone) and cold end(the tip of the cone).

Space Shuttle Thermal Tile Demonstration

This demonstration is good, but eventually any material used for insulation in furnaces will work same way(I mean for needs of the station, not in this kind of demonstrations), just a layer of the material have to be ticker. But we do not need that layer be thin, more then that, we explicitly wish it to be tick enough to stop gamma rays, neutron flux, solar wind, this way thicker it is better is it and for thermal protection and for other types of protection.

So we may take good enough amounts of a material from the mercury, which is near by. SiO2 stuff on top, Fe bars as structure keepers, and heat conductors in perpendicular direction(this way heat conductivity of shield will be more in radial direction and less in axial direction). Ticker it is for longer it lasts, better it is as protection against high energy electromagnetic waves and particles, less energy transfer to "cold" end where people are.

First layer acts as brute force, as heat dissipation system, as filter for spectral energy(cuts everything with short wave length gamma, UV etc). As next layer it may be used something more valuable and suitable for heat protection at lower temperatures, there are lot of solutions to use, they are not space grade(yet), but first layer isolates (if solutions need that) from space - and converts the question: how do you would survive and build station in such hard environment, in to the question: how do you usually protect furnaces and workers.

As example Thermal conductivity of steel is around $92 \frac{W}{m \cdot K}$, SiO2 $8 \frac{W}{m \cdot K}$, basalt-glass $1.2 \frac{W}{m \cdot K}$

We know hot end temperature(1500K), as we steam energy generate, we know cold end temperature 818K(545°С) which is hot end for steam system, we know how much energy we may dissipate 10GW(at boiling point of water and this energy is equivalent to the energy flux from hot end to cold end in the heat shield) and it is something around 20$\small kW/m^2$ at bottom for station (r=400, h=5720), so we may say how tick this bottom have to be for different materials.

$P=-\varkappa\frac{S\Delta T}{l}$, $l=\varkappa\frac{S\Delta T}{P}$

for material with $1 \frac{W}{m \cdot K}$, only 0.034m, or 3.4cm tick - woow that's unexpected.(basalt wool is used for insulation)

For steel it will be 3.15m tick.

If we do not generate energy and just dissipate energy at 300K at side surface of the cone we have to consume less energy from the cold end of the shield, so thickness have to be ticker about 3 times roughly speaking(3 times less energy, 3 times ticker bottom).

Considering the fact we have to have ticker radiation protection layer then for heat protection - heat protection isn't issue after all.

## Conclusion

There are lot of challenges in building such a station, but heat alone is not an issue. For those who thinks about ISS heat dissipation arrays, coolant there is NH3 and temperature at which heat is irradiated is 240-200K. Two times difference in temperature means 16 times difference in power of irradation.

Another big challenge is getting lot of materials to some point where station have to be build, but for 200 peoples station do not have to be so big, all parameters scale well with base surface area. For 200 people at the station it needs something like 20kW per person - for food, technical needs etc, so cone dissipation energy have to be 4MW or roughly 750 times less then the same in the bigger station which was used above as example. It means surface of base have to be 750 times less, so it will be a cone with parameters (r=14.6, h=208m) volume 46406 $m^3$, it is not much a volume per person so it have to be bigger then that, just to be able to place all needed equipment for recycling, maintenance of the station etc. So energy isn't a limiting factor here, and it is more a question about technologies and equipment and sizes and volumes needed for it, for food production, process waste, production lines needed to make repairs in station in- and out- side.

As my opinion we talking at least about 100'000 tonnes of mass (average density 1$\small t/m^3$) and + another 100000 tonnes for shielding, mostly for radiation protection (I think 30m layer may be good enough)

There are ways to solve different parts of the problem, but OP information and 10+10 plan isn't good help here.

But there is nothing which can't be solved by 1000000 launches from Moon or from Earth.

There are other and more reasonable ways to build the station, but looks like OP is about another apocalyptic situation, so one rocket per 7 million peoples each day in next 3 years and station will be done.

7500 m/s delta from earth to mercury, after that solar sails, ION drives with higher ISP and down to 10kk km to the Sun.

Better approach would be establish production base on the Moon, and lift the stuff with Non-rocket spacelaunch.

And the station may be assembled entirely on the moon and be launched from the Moon. Or it may be assembled in L1 point with other constructions we may wish to assemble there.

Is 10+10years possible, with current tech - yes, definitely. And most important tech from them all is our ability to automate tasks.

Will we have such station in 20year, not sure, I do not see any sense at the moment in doing that, but if I do not forget about it for fun or if scientist's will say they need such station - then sure, why not.