Mars Declared Unsafe For Humans: No one can survive for longer than four years | Hacker News Reader

Mars Declared Unsafe For Humans: No one can survive for longer than four years

physics-astronomy.com

33 pointsbirriel31 comments

“ We considered a spherical water phantom in a spherical spacecraft shell, and analyzed how the radiation dose absorbed in the phantom depends on the aluminum spacecraft shielding thickness (surface density values of 0, 5, 10, 20, 30, 40, 50, and 60 g•cm^2)”

To help you make sense of those gcm2 values, a 1 cm cube of aluminum has a density of 2.7g and presents (roughly) 1 cm^2 surface area when part of a sphere, so it’s “0cm thick, 2cm thick, 4cm thick, 8cm thick, 12cm thick,…” etc.

The first and most important point is that this should be titled “Spaceships flying to Mars declared unsafe for humans”, as the study concerns itself solely with radiation received in travelling to Mars. It has nothing to do with Mars itself and in fact their result is probably broadly true of any spaceflight above low earth orbit.

Other potential titles might be “Aluminum declared insufficient for radiation shielding”* or “1 Sievert limit declared impractical for interplanetary spaceflight”.

*: Although they do claim that more complicated multilayer systems using other materials as well would only get at most 20% more protection; it seems the fundamental issue is what we think of as “radiation shielding” is more like “radiation heatsink”, and as you absorb more and more radiation from space, that energy will have to go somewhere - in the form of secondary radiation released by the shielding itself.

Strange how the paper chose aluminum GCR shielding, not something more sensible like water and/or polyethylene (often in the form of supply mass you already carry).

It's long been known that aluminum shows a local minimum around 30 g/cm^2. Water and PE don't have this problem.

See Figure 13 https://www.sciencedirect.com/science/article/abs/pii/S22145...

Oh, if it’s true that aluminum alone has this local minimum issue, then the paper is even weaker than I initially thought. I took them at their word when they said other shielding may have better coefficients but still suffers from the same general limitation, but your paper makes it sound like that’s a false (but commonly accepted) assumption.

"spherical water phantom"

What a great album title.

From the actual paper: “The shortest Earth–to–Mars flight times will be in 2030 and 2050, corresponding to periods of solar max. Current work shows that for the previous solar cycle, the smallest effective dose would have been accumulated for a flight starting in 2000, during solar max. For an optimal average shielding of 30g/cm², the effective dose would be 0.5 Sv after a 1.9-years flight and astronaut's career dose limit of 1 Sv would be accumulated after a 3.8-years flight.”

This is talking about the flight time to and from mars, not the time actually spent on mars.

Even ignoring that it's 4 years of flight time, “No one can survive longer than 4 years” is utterly ridiculous: an astronaut who exceeds his career dose limit does not suddenly drop dead of cancer.

Where did they pull the 1.9 years of flight? The SpaceX plans to go to Mars talk about 80 to 150 days, with 115 days average [1].

[1] https://en.wikipedia.org/wiki/SpaceX_Mars_program#Colonizati...

They're talking more in terms of “if we wanted to maximize the time spent in transit”:

“[…] Several studies considered radiation doses during 500- and 1000-days flights, according to NASA plans (Drake et al., 2009). However, there is still no clear answer about optimal flight conditions that would enable the longest mission duration. In this study, we present the net radiation doses from SEP and GCR radiation as an accumulated dose during a spaceflight, dependent on flight duration and launch date for the time period between 1998 and 2006. […] Our simulations show that for solar cycle 23 and aluminum shielding, the mission duration–assuming a 1 Sv mission limit–should not exceed approximately 4 years.”

-- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/202...

Reference Drake et al, 2009: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/202...

I don't get it. Why would they do that, and then "declare Mars unsafe for humans"? It's like saying "you can't finish a Marathon if you start by shooting yourself in the foot". Well, duh?

That's my point: the headline is utterly misleading as to the content of the paper it's talking about. The paper is talking about travel time, but the blogspam and its title is making an statement about mars itself.

Even worse, weightlessness has a negative impact on brain fluids:

> There’s really not enough that we know about the human body and space for us to safely send someone to Mars and back on a three-year round trip

Study shows astronaut brains at risk from space travel - https://news.ycombinator.com/item?id=36258004 - 9 days ago (0 comments)

Thought there was research that they'd have to have some kind of artificial gravity as in the 2001 family of movies? If not brain fluids than bone mass.

Also, what's the weight in food that's required to keep somebody alive for 4 years? Will water be more of a problem than food? As per the Martian, they can pre-position food and supplies for the stay and the return, but it seems energy-expensive to chase down a capsule on the voyage to Mars to drop off supplies. Hell of a DoorDash, eh?

Yep, artificial gravity. "Space health" could be its own industry. Varda for pharma recently [1], and even space manufacturing in the future.

[1] Varda: The Space Drug Factory - https://news.ycombinator.com/item?id=36293504 - 6 days ago (0 comments)

Centrifugal force seems like a good solution for simulating gravity, but maybe I'm underestimating the difficulty of getting a spacecraft spinning sufficiently.

This is what I thought as well. There might be issues with angular momentum and inertia, and problems with windows (gravity would be perpendicular to the axis of rotation) but they could finesse this by having the living/exercise/sleeping quarters artificially lit and the control environment with those velcro sox padding about on carpet.

The actual paper, which isn't linked from the article as far as I could tell: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/202...

Should be (2021).

Better source: https://newsroom.ucla.edu/releases/safe-for-humans-fly-to-ma...

At the time of publishing, headlines were "Mars safe for humans for missions up to four years"

That's still an utterly misleading headline, as it's talking about the transit time, not the time spent on mars itself.

Apparently it is about 22t of food per astronaut on a one-way trip to Mars.

See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8747021/ for a review article.

Summary: there are many risks, from menu fatigue, energy consumption vs expenditure (e.g. exercising), adverse effects of space travel from microgravity, long-term radiation exposure, metabolic stress, and so on.

Water is probably the major concern.

Thinking about hiking/camping, with dehydrated food 3 calories per gram is fairly standard.

22 tons at 3 calories per gram is about 7.3 million calories.

That's 3000 days at 2500cal/d.

But when you're hiking you can just source water along the way. You can't do that on a Mars journey. Can you do it on Mars?

edit: in response to the recycling comment - of course! doh! then it should be easier, no?

Water isn’t actually consumed, but rather cycles through the biosphere. The ISS recycles its water, and so would a Mars expedition.

Water can be recycled easily. Like it's done on ISS.

> 22t of food per astronaut on a one-way trip to Mars

That's not what your link says. It actually says:

"It is estimated that a 3-year Mars mission with a crew of six would have a total energy expenditure of 12 megajoules per person per day, regardless of water requirements, and would carry 22 tons of water-containing food on the spacecraft"

A friend showed me this once while we were taking about how radiation sort of makes mars colonization unviable

How to terraform Venus quickly:

https://youtu.be/G-WO-z-QuWI

Tardigrade: https://en.wikipedia.org/wiki/Tardigrade

"Scientists Put Tardigrade DNA Into Human Stem Cells. They May Create Super Soldiers." (2023) https://www.popularmechanics.com/science/animals/a43509580/t...

- https://news.ycombinator.com/item?id=35447885

Tardigrade: https://en.wikipedia.org/wiki/Tardigrade#Physiology :

> Tardigrades are thought to be able to survive even complete global mass extinction events caused by astrophysical events, such as gamma-ray bursts, or large meteorite impacts.[9][10] Some of them can withstand extremely cold temperatures down to 0.01 K (−460 °F; −273 °C) (close to absolute zero), while others can withstand extremely hot temperatures up to 420 K (300 °F; 150 °C)[36][37] for several minutes, pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space.[38] Tardigrades that live in harsh conditions undergo an annual process of cyclomorphosis, allowing for survival in subzero temperatures. [39]

What selected for tardigrades' radiation shielding features?

Perhaps humanoid robots (that children can push over) could better withstand high-radiation environments.

What are some of the other advanced solar and cosmic radiation shielding approaches? IIRC spinning Superconducting materials have better shielding, but may not be as shielded as drilling into an asteroid already on a trajectory similar to the desired transit.

Barring that, I think it's going to need to be matter teleportation (which we don't want to imagine un-friendly aliens having either).

Site has "legitimate interest" turned on by default, which is an auto navigate back.

I'll no longer putting up with bad practice spyware sites.

I asked ChatGPT to write about landing Mars. It believes Elon Musk himself will be piloting. This should make everybody onboard feel better.

Does this consider the fact that humans will always be either in facilities or space suits that have protection against such radiation?

> The modeling determined that having a spacecraft’s shell built out of a relatively thick material could help protect astronauts from radiation, but that if the shielding is too thick, it could actually increase the amount of secondary radiation to which they are exposed.

There is also no space suit that provides full protection against radiation in space.

> if the shielding is too thick, it could actually increase the amount of secondary radiation

That's because the paper assumes aluminum shielding, not something more sensible like water/polyethylene.

It's long been known that aluminum GCR shielding has a local minimum around 30 g/cm^2. Water and polyethylene don't have this problem.

https://www.sciencedirect.com/science/article/abs/pii/S22145...

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