It doesn't need to be totally pressurized and if assembled in orbit, it can be assembled in orbits with very low debris density like MEO.
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A kilometer scale spacecraft would be some sort of ginormous space station. So, there would be an operational requirement to sustain many hundreds and possibly 1000+ taikonauts. A MEO orbit wouldn't be practical for something having this much entry-exit traffic, aside from crossing the radiation belts. However, a high LEO orbit in the 500km+ range or a little higher than the Tiangong and ISS orbits, would be a good balance between operations and a relatively lower orbital debris density. In any case, any spacecraft in the kilometer range would be impacted A LOT whether it was from orbital debris or meteor showers. They need to account for this inevitable and frequent situation. My recommendation would be to create double hulls along with large kevlar netting. We could reduce cabin pressure by using something like an 65/35 oxygen nitrogen mix at 8psi, which would help. Better yet, they shouldn't build kilometer scale spacecraft until materials technology allows something as tough as titanium, while costing and weighing as much as aluminum.
I believe the plan is that the first model is going to be an unmanned power station in MEO or high LEO beaming power back.
Even a manned station will not require full pressurization throughout, only inhabitable zones pressurized and with pressurizable bulkheads in between. It's a waste of resources trying to armor against debris that has relative velocity in km/s range. Such debris will penetrate anything thinner than tank armor.
Arming the spacecraft with lasers for small debris, along with highly resilient architectures like modular sections that are connected by elevators with most of the structure being unpressurized, is the way to go AND will be far cheaper than trying to build a monolithic spacecraft fully pressurized throughout. An armed modular design is more robust against failure due to lower debris impact cross section, the possibility of active defense against debris, and much lower cost than full pressurization while retaining much of the function.
Agreed only to the extent that they shouldn't be designing to stop everything. I was thinking along the lines of stopping objects larger than what frequently impacts the ISS. These small objects have never penetrated the hull but they have caused spalling. With larger mass, the spalling would be full penetration into the cabin. I think they should be designing to stop penetration up to say object masses of a 50 caliber bullet. This kind of catastrophic failure is highly likely to happen with something in the kilometer size range. Better to be proactive than be complacent and decades later an explosive decompression or even full hull rupture kills a bunch of taikonauts.
Speaking of beaming power back to Earth. China has plans to launch a space mirror for shining sunlight to illuminate Chengdu. This is to save on energy costs and turn Chengdu into a nightlife city. It was announced back in 2018 and supposedly still in the works.
By
10th June 2020
The Four Great Inventions of paper, gunpowder, printing and the compass are the four most amazing and revolutionising innovations that came from ancient China. In the modern world, creative innovations include the first AI teaching assistant, making a house out of 3D-printed parts and clones of monkeys.
All illustrate cutting edge innovation. But one idea really takes the biscuit; plans for an artificial moon for Chengdu, capital of China’s Sichuan Province.
Chengdu’s artificial moon is a satellite that will be launched into space to orbit above Chengdu and reflect the sun’s light at night on to the city to replace streetlights. According to officials, it will be able to shine eight times brighter than the moon and save huge sums of money.
The idea has been around for a while; China released plans for it back in October, 2018. According to Wu Chungfeng, Chairman of Chengdu Aerospace Science and Technology Microelectronics System Research Institute, the moon would focus its reflected light only onto the city of Chengdu itself..
Such a concept of reflecting the sun’s light at night was inspired by a French artist who thought that if there was a necklace of mirrors above the earth it would reflect the sun’s light all year round in Paris. While the plan for this innovation is to save electricity and money it has both advantages and disadvantages.
As previously mentioned one of the main benefits of the artificial moon will be the money it saves. Since it replaces streetlights at night it is estimated to save US$170 million a year which would have been otherwise used for electricity. It would also be reflecting the sun so if there was any emergency and a blackout happened, there would still be light. However, Mr. Wu did say that the fake moon’s light would only amount to a fifth that of streetlights.
There are also theories that the light would affect animals and their monthly rhythms and biological processes. John Barentine, Director of Public Policy at the International Dark-Sky Association, said, “This potentially creates significant new environmental problems with what, at first, seems like a novel approach to an already solved problem”.
All of the benefits or disadvantages of the fake moon cannot be 100 percent accurate, not until it is actually launched and its effects are analysed. However, the biggest question is whether or not Chengdu’s fake moon will be a success or will it fail?
China has often flourished where other countries have floundered. In 1994, Vladimir Syromyatnikov, a Russian engineer tried to launch an artificial moon for this purpose. The satellite was called Znamya which means “banner” in Russian and it did work, at least partially. Astronauts on the International Space Station could see it reflecting a beam of light towards earth. However, those on Earth in the beam’s path only saw it for a moment. The issue was that the satellite was moving at 7 km/s so it would only flash over any one spot on the ground for a second. Had wanted it to stay in place they would have had to put it 36,000 km above the earth, i.e. in geostationary orbit. According to Scottish physicist, Scott Manley, if China were to put it that high, a much bigger mirror would be needed; Russia’s had a diameter of 65 metres.
With little news released about the Chengdu artificial moon of late, the project may have missed its initial self-imposed deadline. The plan for the satellite was for it to be launched at some point in 2020 but an exact date was never given. It was also said that if it was successful, then China would launch three more by 2022.
Where there are plenty of ups and downs to the project, Chengdu’s authorities, the moon’s designers and the media at large seemed to have missed perhaps the singularly most important point. What if it’s cloudy?
none of this changes the fact that an open, modular structure is less likely to experience decompression events due to debris collision than a totally pressurized structure. This is common sense - an open, modular structure has lower collision cross section. The sole increase in cost will be an elevator mechanism. But that's still cheaper than a totally pressurized section.
With assembly in orbit, many components that are not immediately life critical can be placed in a non-pressurized section and connected to the main section with vacuum tight feedthroughs, saving space.
Anything you can do to a totally pressurized structure, you can do to a modular structure for less money.
That's actually part of a design I was imagining. It doesn't detract from still needing extra shielding for the habitation modules.
interesting part to note about collisions: the bigger the spacecraft, the more efficient it is against collisions, not less.
this is an interesting thought experiment:
The ISS has pressurized sections equal to roughly a 109 length x 4.2 m diameter cylinder going by total length and diameter of the Destiny module. The volume would then be 1510 m3 (bigger than reality of 910 m3, since not all modules are that size). It has 109x4.2 = 458 m2 collision cross section. For a maximal comparison, we take t. The volume of Nauka is 180 m3.
For a hypothetical km scale Chinese spacecraft, let's say that for it to qualify as km scale, it has to have at least 501 m length. Let's have it be assembled using modules launched by the Using equivalent form factor (3 meters lower than maximum rocket diameter) we have a 6.5 m diameter x 24 m length module with volume 800 m3 each or almost as big as the entire ISS volume.
Let's assume 25 launches: 10 pressurized modules, 15 for nonpressurized components (solar panels, backup power, radiators, instruments, maybe a laser CIWS... for debris only, of course). 10 modules would be 8000 m3 volume and can be used for living space, space farming, etc. End to end, the pressurized modules would be 240 m in length.
Let's estimate power consumption. in direct sun with panel sizes 35x12 m. There are 8 panels for a total area of 2400 m2. Power generation is 0.07 kW / m2, power density is 0.16 kW/m3. Let's assume that due to efficiency increases in the next 20 years, the power generation increases to 0.1 kW / m2, power density required is 0.1 kW/m3. Then the requirements will be 800 kW for 10 modules, which requires 8000 m2 of solar panels. Let's say that we want some power headspace. 10000 m2 of solar panels required. Deploy that as 10x panels in 20x50 m form factors.
Stacked end to end, that'd be 500 m for panels + 240 m for modules. Thus fulfilling the km scale requirements. This seems doable once LM-9 is out.
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Not really. All you said is that smaller volume offers smaller cross-sectional area for collision. By that same argument, don't build manned spacecraft or just don't build a spacecraft at all — zero chance of decompression! Nothing in that argument says modular architecture is superior to a monolithic one.
Given identical internal volume as requirement, modules have to be clustered together to minimize the exposed area to open space, and the end result is just similar to a monolithic structure. There is no advantage there. Splitting them up is actually disadvantageous because of increased surface area without any added internal volume.