Can astronauts be in space for long periods

[wolram]

https://www.sciencedaily.com/releases/2016/10/161010052832.htm

Date:
October 10, 2016
Source:
University of California, Irvine
Summary:
Will astronauts traveling to Mars remember much of it? That's the question concerning scientists probing a phenomenon called "space brain." Scientists have found that exposure to highly energetic charged particles -- much like those found in the galactic cosmic rays that will bombard astronauts during extended spaceflights -- causes significant long-term brain damage in test rodents, resulting in cognitive impairments and dementia.

 

[mfb]

People working for extended periods on the International Space Station, however, do not face the same level of bombardment with galactic cosmic rays because they are still within the Earth's protective magnetosphere.

Yes, about a factor 3 lower at the same level of shielding. Which makes the 437 day record in LEO equivalent to ~140 days in interplanetary space, a typical time of a trip to Mars. It gets better if the spacecraft has better shielding than the MIR.

 

[fresh_42]

I think (my two cents), there are basically four difficulties to overcome for long periods in space: oxygen, nutrition, shielding and gravity. Every single one will kill you sooner or later if it fails. The better these can be solved, the longer people can survive in space.

 

[mfb]

Oxygen and food consumption are well-known from the ISS. Oxygen is not the critical point: You have the remove CO2, and every reasonable way to do this releases sufficient oxygen, so you can keep this in a closed cycle. Currently we do not close the carbon and hydrogen cycle, which means we need a supply of food and water (easier to store than liquid hydrogen). Closing the hydrogen cycle is the next step, and closing the carbon cycle (which means food production) would be the final step.

 

[fresh_42]

Oxygen is not the critical point: You have the remove CO2, and every reasonable way to do this releases sufficient oxygen, so you can keep this in a closed cycle.

Does this hold for all processes which include $O_2$, e.g. metabolism? I would assume that there always will be some inevitable losses, which might get important, e.g. for generation ships. Also interesting is, how these recovery processes influence the energy balance. The usage of sun sails is restricted to nearby stars which poses the question how long nuclear batteries will last.

 

[mfb]

Does this hold for all processes which include $O_2$, e.g. metabolism?

What other processes do you see?
Neglecting nitrogen and elements with smaller contributions, human food is mainly a collection of C, H, and O with C+4H > 2O and C>4H, we add oxygen from the air until both sides are equal, and emit CO2 and H2O.

The ISS scrubs the CO2 out of the air, adds hydrogen and produces CH4 and H2O. The CH4 is vented to space. As our food has C>4H, electrolysis of the produced water (from humans and the Sabatier reaction) is not sufficient to keep the reaction running, additional hydrogen from a water storage tank is needed. You constantly add oxygen to the system - both from the water tanks and from the food. A small amount of oxygen (and other elements) is lost via human products that cannot be broken down at the ISS. Some oxygen has to be discarded because we cannot use it. Sending pure hydrogen to the ISS would save mass, but storing hydrogen is challenging.

Proposed next steps would be 2CH4 -> C2H2 + 3 H2, which reduces the loss of hydrogen by 3/4, and ultimatively CH4 -> C+2H2, which reduces hydrogen loss to 0. If we can do this, sending food up would be sufficient.

All those processes need electric power, of course, but a spacecraft without electric power is lost anyway.

 

[Fervent Freyja]

All those processes need electric power, of course, but a spacecraft without electric power is lost anyway.

Useful aboard the ISS? http://phys.org/news/2016-10-nano-spike-catalysts-carbon-dioxide-ethanol.html

 

[mfb]

Just 25% more hydrogen-efficient than the conversion to methane, but if it is cheap and easy: maybe?

 

[DiracPool]

From: https://www.sciencedaily.com/releases/2016/10/161010052832.htm

"For the study, rodents were subjected to charged particle irradiation (fully ionized oxygen and titanium) at the NASA Space Radiation Laboratory at New York's Brookhaven National Laboratory and then sent to Limoli's UCI lab.

Six months after exposure, the researchers still found significant levels of brain inflammation and damage to neurons. Imaging revealed that the brain's neural network was impaired through the reduction of dendrites and spines on these neurons, which disrupts the transmission of signals among brain cells. These deficiencies were parallel to poor performance on behavioral tasks designed to test learning and memory."

This is likely a bunch of hype. Rodent studies are notoriously poor predictors of human cognitive capacities and mental disease models. A healthy 40 year old human traveling to Mars for a 1000 day mission with current-technology radiation safety protocols will not likely suffer a major or even minor memory deficit upon return.

 

[Ryan_m_b]

Oxygen and food consumption are well-known from the ISS. Oxygen is not the critical point: You have the remove CO2, and every reasonable way to do this releases sufficient oxygen, so you can keep this in a closed cycle. Currently we do not close the carbon and hydrogen cycle, which means we need a supply of food and water (easier to store than liquid hydrogen). Closing the hydrogen cycle is the next step, and closing the carbon cycle (which means food production) would be the final step.

Does this hold for all processes which include $O_2$, e.g. metabolism? I would assume that there always will be some inevitable losses, which might get important, e.g. for generation ships...

Bolded for emphasis. Keeping astronauts safe, healthy and supplied for periods of months to single-digit years is a world apart from an extremely long lasting closed-economy of a generation ship. For missions to Mars or other such places you "just" need to keep the vehicles functional and self-sustaining for the duration of the mission. For a generation ship you've got to bring along your own industrial economy and biosphere to keep the whole thing functioning for centuries-millenia. The complexity scales non-linearly because if you need to build spare parts you need factories which means you need skilled workers which means you need educational facilities, healthcare (therefore doctors, medical equipment manufacturers), administrators, a bureaucracy etc etc.

IMO the "ship" part of generation ship is inherently misleading. Without magic wand technology it's not a ship but rather a city-state nation, with all the industrial, social and political requirements such a state would require.