Some people ask: Which will come sooner, controlled nuclear fusion or the use of solar energy in near-solar orbit?
Problem description: I've always been pessimistic about controlled fusion, let alone eternal fifty years, and with some information now, there is no reactor device with a Q greater than one. And greater than one is only the beginning, and it can really achieve commercial purposes, at least greater than 10.
The sun itself is also a super-large reactor energy, if a space solar power station similar to the Dyson sphere can be built in near-solar orbit to harness the sun's energy. As long as you can use one-ten-thousandth of the energy output of the theoretical sun, or one hundred thousandth. It is still a very large amount of energy for human beings.
From a purely technical point of view, which of the two is more difficult to implement and technical?
The space solar power plant envisaged by the subject is completely locked in theory.
It takes 1/310 of the mass of the earth's crust, 10 trillion years to build, and more than 7,000 cosmic ages.
Here is the calculation and derivation process:
The radiant power density (illuminance) of the sun's surface is as high as 60 million W/m^2, producing a temperature of 5700K, enough to plasmonize any material.
In the orbit on the surface of the sun, to achieve one hundred thousandth of energy, even the trisolarans dare not think so.
For a material to be able to generate electricity, it must be far enough away from the sun.
How far should that be?
Through the relationship between radius and circular surface area (4πr^2), it is easy to know that the illuminance attenuates with the increase of distance, and the attenuation factor is proportional to the square r^2 of the radius.
- Illuminance, that is, the density of radiant power, is the luminous flux per unit area (E=dΦ/dS).
- The luminous flux Φ is equivalent to the radiant energy of 1 second.
When 10 solar radii away from the center of the sun, the illuminance attenuation is 600,000 W/m^2.
This illumination is still very high.
The sun is directly regarded as blackbody radiation, and its illuminance is equivalent to the radiation flux per unit area of the blackbody.
E=B(T)=σT^4(W/m^2)
- σ is the Stefan–Boltzmann constant 5.67×10-8W/(m^2· K^4), the energy formula for blackbody radiation is a special case of the Stefan-Boltzmann law when the radiation coefficient is 1 (blackbody).
From the above energy relationship, it can be seen that the illuminance is proportional to the fourth power T^4 of the thermodynamic temperature.
Since the illuminance decays with the irradiation radius r^2.
The thermodynamic temperature T then decays with the square root r of the irradiation radius.
Easy to get:
At 10 solar radii away from the center of the sun, when a material absorbs all the energy, the resulting temperature is still as high as:
5700÷10=1802K
- The melting point of silicon is 1414 °C, which is equivalent to 1687K
This temperature is still much higher than the melting point of silicon, even taking into account the 20% reflectivity of silicon wafers, the temperature is as high as 1700K, which is enough to melt silicon crystals.
Below 1414 ° C, is it feasible.
Actually, it's not.
In addition to silicon wafers, there are tempered glass (protection), aluminum alloy (sealing support), silicone (sealing), EVA (fixed paste), TPT (back film, corrosion resistance) on photovoltaic panels.
The maximum temperature that these materials can withstand is in the range of 200~600 °C.
In space, you can make rough points, try to use metal materials, do not consider life loss, we try to estimate as high as possible:
It can achieve the limit of more than 700 °C, that is, about 1000K.
This temperature is 5.7 times lower than the surface temperature of the sun.
Bringing in the above formula, we can get the irradiation radius, which increases by multiples compared to the solar radius:
5.7^2=32.5 times.
The solar radius is 6.955×10^8 m
Then, when the temperature of the solar space power station is 1000K, the closest distance between the power station and the sun is: 2.26×10^10 m
To use one hundredth,000th of the solar energy, considering the loss of photovoltaic power generation, effective electromagnetic wave conversion, emission and absorption. The energy used by the strength reaches 5% of the light energy is already very high.
Then the area that needs to be covered by one hundred thousand needs to be increased by 20 times, that is, it reaches one 5,000th of the area of the solar photosphere.
The total area that needs to be covered is:
S=1.28×18 m^2
Common photovoltaic material modules are 12kg per square meter, and monocrystalline silicon modules are 17kg/m^2.
Then the total weight of the photovoltaic material required can reach 2.2×19 kg.
Crustal mass 2.6×10^22kg.
It can be obtained that the construction of such a large-scale solar space power station requires a total mass of up to 1/310 of the earth's crust, and most of the earth's crust is below sea level.
To build such a large power station, the surface above sea level has basically been hollowed out (of course, the surface will be accompanied by a large number of geological disasters such as volcanoes and earthquakes, and a new continent will be born).
Of course, if a power station with 100,000th of solar power is built in the orbit of the earth, the mass of the earth's crust required is 1/7 (the orbit is large, and the square multiple of the power station coverage scale is increased).
To build such a large solar space power station, transportation is also a problem.
The rocket with the largest carrying capacity of mankind is Saturn 5, with a carrying capacity of 45 tons to lunar orbit.
After entering the solar orbit, it is also necessary to adjust the direction to form different elliptical orbits, so as to reach different positions in the solar system, and it is estimated that the carrying capacity will be weakened several times, and the final mass ratio is about 20.
Finally, it is sent to the construction track, and the material is about 10 tons.
Well, the total number of times that need to be transported is:
2.2×10^15 times.
At present, the peak of human launches is about 1,000 tons a year, which is equivalent to 20 Saturn 5s.
In other words, for humans, it can be transported 20 times a year.
To build such a space solar power plant, it will take 10^14 years, that is, 100 trillion years.
The age of the universe is only 13.82 billion years, which is equivalent to more than 7,000 times the age of the universe.
Even if humans sacrificed all their industrial production for astronautics, it would take about 50 cosmic ages.
In addition, the fuel consumed is as much as 20 times the weight of the transport, and it needs to consume 1/15 of the mass of the earth's crust. However, there are simply not so many chemical fuels on Earth.
Therefore, to build such a large space solar power plant, it must be based on controlled nuclear fusion.
According to Qian Lao's "Introduction to Interstellar Navigation", the maximum working fluid injection speed of nuclear fusion can reach 15,000km/s, which is equivalent to 3,000 times the current human best engine working fluid injection speed.
According to Aclay's formula (aka the generalized Tsiolkovsky formula):
m0mk=(1+vc1−vc)c2w
It is easy to know that at such a high working fluid injection rate, the fusion fuel required is about 1/1000 of the push mass.
That is, 2.2×16 kg
The total mass of water resources on Earth is 1.66×10^21kg.
Water consumption is about 1 part 75,000 (about 1/4 of the total resources of deuterium and tritium).
If you consider the use of Jupiter's hydrogen resources, the consumption of interstellar hydrogen resources will be lower. Moreover, after mastering controllable nuclear fusion, after being able to travel interstellarly, you can also use interstellar metals, silicon and other resources without consuming motherhood.
In other words, when controlled nuclear fusion is fully mastered, the construction of ultra-large-scale space solar nuclear power plants will be feasible.
The former has instead become a necessary condition for the latter.
But in fact, you can use controllable nuclear fusion, when the solar system is flying, it is very difficult to build and maintain such a large-scale space solar power plant.
In fact, too high energy can not be directly emitted to the earth for use.
Because the earth gets too much heat, it will cause the earth's waste heat to be too high.
Even if the power station envisaged by the subject emits one ten-thousandth of electricity to the earth, the waste heat generated is enough to warm the earth by 100 °C, causing global biological extinction.
However, for spacecraft, there is no need for a power station of this size, and the solar power generation device that comes with the spacecraft is enough. If all spacecraft are combined, it is equivalent to a local Dyson sphere, which is possible, but this is essentially different from building a power station.
Therefore, large-scale space solar power plants can be the icing on the cake for the ultimate energy road of mankind in the future, but they cannot become the right way to the energy road.
Of course, if you reduce the scale of the solar space power station to the level that can be done at present, it is still applicable. For example, both China and Japan now have research directions in this area. Due to the maturity of photovoltaic technology, it is possible that micro-space power stations will appear earlier than controllable nuclear fusion power plants.
In short, as the subject assumes, before mastering controllable nuclear fusion, to create a space solar power station with a total solar energy of one hundred thousandth, human beings currently need more than 7,000 cosmic ages. Considering the molecular thermal movement of the material and the damage of radiation, the entire power station will be built and scrapped in a long time.
In fact, this power station can never be built, and it is completely locked up in theory.