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Imagine a world very similar to Earth (and about the same distance from its star as we are to our star (it's the planet from my other question). But in another solar system (let's say in Alpha Centauri). How big would a space station in low orbit need to be to support three humans for about five years compared to the ISS?

  • It needs sleeping rooms, a kitchen, at least three storage rooms, a small farm to grow easy crops (lettuce, carrots, etc), and an electricity room.

  • It needs to hold fuel and lift fuel (after liftoff, it would primarily use solar power).

  • It needs to hold a lander capable of bringing two people to the surface of the planet and back to the station.

  • It needs to be able to hold water (or a way to get water (it can get water from the planet on its third year)).

  • This can be in the future. Preferably as close to our present-day as possible.

  • I'm willing to take some creative liberties.

  • Partial answers are ok, as long as they add something to the information.

If you have any questions, please ask.

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    $\begingroup$ Does the space station receive regular supply deliveries like the ISS? Or does it need to be entirely self-sustaining? $\endgroup$ – F1Krazy Oct 23 '20 at 16:53
  • $\begingroup$ preferably self-sustaining. But it can get water from the planet. $\endgroup$ – Anderson Oct 23 '20 at 16:56
  • $\begingroup$ "lander capable of bringing two people to the surface of the planet" - but not back? $\endgroup$ – Alexander Oct 23 '20 at 17:14
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    $\begingroup$ This very much depends on the tech level. "And back" means that tech level is substantially above our present day. Which, in turn, means that space requirements can be quite different. $\endgroup$ – Alexander Oct 23 '20 at 17:26
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    $\begingroup$ Please note that we strongly encourage users to wait at least 24 hours before accepting an answer, as doing so may discourage other, better answers from appearing. $\endgroup$ – Frostfyre Oct 23 '20 at 19:23
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Living Compartment:

For this you can look at underground bunker floor plans to get an idea of what space limited people need. A floor plan similar to this 10x30ft (600 sqft) bunker could easily accommodate a 2-3 person crew's living space needs.

Life Support Needs:

In general, any mission as short as 5 years is better off using stored food than trying to grow it. Growing food takes a LOT of power per person, uses up a lot of space, and needs a lot of specialized equipment that might malfunction before your mission is over. The average person needs about 2 kg of food per day, and food weighs an average of about 1g/cm^3; so, for a 2 person, 5 year mission you need 7300kg of stored food which has a volume of about 260 cubic feet. The average person consumes about an equal volume of other consumables to food (toilet paper, soap, cloths, etc) So you could actually cram your entire consumable needs into a storage space about 8x11x6ft; though, for organization reasons, assume you need walkspace to get to everything. So what you really need is a storage room that is about 200-300 sqft with a ceiling about 6-7ft high. For comparison to farming, you would need about 2000sqft per person to grow your own food during the mission even using stacked aeroponics; so, for a mission this short, just bring the non perishables.

Air and water recyclers are not that big for a two person crew. They'd fit into the flooring or walls of your habitat rather than needing a whole module. You'd probably need a few hundred gallons of water to cycle through and some extra air storage to compensate for any loss of atmosphere over time; so, assume maybe an extra 300-600cuft of space for some large tanks.

Power Needs

Since you are not growing food or running extensive scientific experiments (like ISS), your solar needs would not be anything extraordinary. However, you will need to know how far you are from Alpha Centauri you are. Assuming you are aiming for dead center of the goldilocks zone, you can assume similar energy density to getting solar in orbit of Earth. That said, Earth's atmosphere absorbs about 50% of light before it hits the ground and we can not maintain peak daylight for more than 5hrs per day; so, satellites can get a lot more power out of solar than we can on the ground. Infact, a 600cm^2 solar panel in space can produce enough power for a standard American Household. Obviously, in space you need a lot more power to run your recyclers and climate controls, but in total, you'd only need a few square meters worth of solar panels to run everything.

Lander & Lift Fuel:

The specs on this will have a LOT to do with the planet in question. Earth like worlds need HUGE rockets to get off of. The average Earth rocket needs 83-96% of its mass to be fuel; so, even small space stations need huge rockets. But a smaller world like the moon could use something like the Apollo Lander which is more craft than fuel. See The Tyranny of the Rocket Equation to get a better grasp on how to figure this out for your situation.

Conclusion:

All-in-all, I'd assume your station only needs a pressurized volume of about 6000ft^3. This is ~5 times smaller than the international space station; so, you could for simplicity just ignore everything I said and scale ISS down 5 fold.

Your lander may need some hand wavy fuel source if you are orbiting an Earth sized planet, Otherwise it will need to be bigger than your whole station to get to the ground and back.

Humans also don't do well in Zero-G for as long as 5 years; so, you'll need some manner of artificial gravity. Centripetal force is often used in Hard Sci-fi to simulate gravity, but this station is much too small for that to be practical without doing some very interesting engineering. In general, any spinning vessel that is too small will have significantly more simulated gravity at your feet than head which would is quite disorenting just in the short term. In the long term who knows what kind of health issues it could cause; so, again you may want to consider hand waving in some "gravity plating" or else your station will need to be very heavily engineered around solving the gravity issue.

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  • $\begingroup$ Thank you so much. The part about the food was very informative. Would a retractable space elevator from the station to the planet work? $\endgroup$ – Anderson Oct 23 '20 at 18:03
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    $\begingroup$ @Anderson Your station would then be 99.999999% space elevator and 0.000001% station. Space elevators are MASSIVE super structures which kinda invalidates any reason for being concerned about how small your station can be. Humans are probably closer to nuclear propelled rockets than we are to space elevators if you want to solve the there and back problem $\endgroup$ – Nosajimiki Oct 23 '20 at 19:34
  • $\begingroup$ Ok. Thanks, I might have to take some creative liberties. $\endgroup$ – Anderson Oct 23 '20 at 19:35
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    $\begingroup$ It's also worth noting that "retractable" is not a term one can use to describe a space elevator. $\endgroup$ – jdunlop Oct 28 '20 at 0:05
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About the same size as the current ISS (915 cubic meters)

Lets start with food
It takes 6-8 weeks to grow lettuce in hydroponics. One head of lettuce gives 120 calories, which in useful energy units is 500kj. You need ~6600kj to keep your bodies critical systems running if you sleep/watch TV all day, ~9000kj a day for a mostly idle human moving around a bit and doing some light work, and 14,000 for an astronaut doing lots of complex tasks and exercising. Lets assume they're idle. You'll need to eat 18 lettuce heads a day. cycling through 1000 lettuces growing can feed 1 person full time, to feed 3 people nothing but lettuce you'll need 3000 lettuces growing in hydroponics.

I don't know exactly how tightly you can pack them in, heat and light sharing complicate this problem, but assuming 30cm x 30cm x 60cm of space is required for the plant and it's proportion of shared light, water, nutrient, and all support systems, that's 162 cubic metres for your farm.

Bunks for 3 and 3 storage rooms
The current ISS has room for 6. So turn 3 crew bunks into storage rooms. If you need really big storage modules use one of the extra lab modules.

Kitchen and electricity room
I don't know what you do in an electricity room, but it would have a counterpart on the ISS. There are basic food prep facilities on the ISS, basically a microwave and hot water source. However you can steal some space from a lab module for a nicer kitchen if needed.

Manoeuvring
The Zvezda service module has an engine for manoeuvring

Lander
Assuming there's no fuel depot on the ground, getting them back to the space station is going to be a nightmare without future-teching this. You'd basically have to keep a space shuttle (and external fuel tank, and 2 solid fuel boosters). Docked in orbit. The space consumed by the rocket on the station is the size of the docking door, so I'm going to exclude it. Handwave your fuel source and then dock it to the tiny door I've included.

Water
ISS is capable of perfect recycling of water. So you'd have a tank like they do (perhaps water in the walls to protect from radiation and act as an emergency water source).

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  • $\begingroup$ Thank you! What is the easiest fuel for landers found in nature? I am doing some research, and I'm wondering if you know anything about this? $\endgroup$ – Anderson Oct 23 '20 at 18:18
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    $\begingroup$ @Anderson Depends on if your planet has fossil fuels or just natural chemicals, and how much gravity you are trying to overcome. If your planet is Earth like, then probably Kerosene. NASA uses it in cases where cheap is more important than efficient. $\endgroup$ – Nosajimiki Oct 23 '20 at 19:20
  • $\begingroup$ Thank you a lot. There are no animals so natural chemicals. $\endgroup$ – Anderson Oct 23 '20 at 19:22
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    $\begingroup$ @Anderson in this case Methane is probably the most useful inorganic hydrocarbon. Methane and Water can be processed into into Kerosene, but it is a harder process to my understanding. But as your tech level increases, non-rocket fuels may be your go to. $\endgroup$ – Nosajimiki Oct 24 '20 at 23:55
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I mean it just depends on what you are looking for. Or what the Station is suppose to do, besides keeping everyone alive.

Food

To make it simple, there is no point in investing into any kind of on Board food Production. The Avg American eats 900kg of Food each Year. So even with a very unhealty diet and a bit of extra on top of that, you would not even reach 3 Tons of Food. In terms of Space, thats like maybe one big Module worth of Space at worst. And again, 3000kg is more than you would need.

Water

Water too will be brought from the Planet and just Recycled. I would guess another Module worth of Space. Maybe a bit more or a shielded Backup or something.

Rooms

If you want to go all rich people, you give each person one Module worth of Space. It can be smaller though. In the end, that just depends on the Missions budget.

So all in all, we are at 5-6 Modules. The size of those also depends on the budget but something like 12 Meters long and a Radius of 4 Meters or so is probably more than enough.

Energy is another Module and then another one for the Lander. So plus 2. This sets us at 8-9 Modules. I would assume that Ventilation and Air recycling are in the same Module as the Water supply.

This leads us to conclude that such a Station would be rather small. Maybe 100 Meters long. Of course, this Station dosnt do anything funny. It just keeps people alive for 5 Years.

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    $\begingroup$ 900kg * 3 people * 5 years > 3000kg $\endgroup$ – Ash Oct 23 '20 at 18:12
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    $\begingroup$ Uff. Yeah forgot the 5 Years. Damn. Still though, 15 Tons is not to bad :D $\endgroup$ – Erik Hall Oct 23 '20 at 18:13
  • $\begingroup$ Thank you so much. The mission is to eventually populate the planet, so the mission is going to take longer than five years; I just said that to put a baseline. And none of the plants on the planet are poisonous since there are no animals, so they can get food and water from there.s $\endgroup$ – Anderson Oct 23 '20 at 18:28

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