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Many basic materials, like water, make great shields if necessary. For Mars one plan is simply to organize the ship such that the water reserves can act as an r

Many basic materials, like water, make great shields if necessary. For Mars one plan is simply to organize the ship such that the water reserves can act as an radiation shield when necessary. You don't need anything particularly massive or overly fancy.

MeImCounting 2y ago
The problem is that paradoxically, thicker shields can cause higher doses of radiation due to secondary radiation production. Theres a balance there to minimizing primary and secondary dosage but you cant really get it below a certain threshold without some form of active shielding. Theres a lot of promising ideas for active shielding but they all require alot of power. All this to say that someone on a trip to mars will indeed get a high dose and this is something that needs to be given thought. Its not an intractable problem but it is also not even close to being solved or trivial. Folks on Mars is still quite a ways away. Not impossible or pointless by any means but it will require significant advancements in many domains before we can really do it safely.
- timschmidt 2y ago
  https://en.wikipedia.org/wiki/Radiotrophic_fungus https://en.wikipedia.org/wiki/Radiotrophic_fungus have also been discussed as an option.
- somenameforme 2y ago
  The secondary radiation you're talking about is called bremsstrahlung (braking) radiation [1]. This is precisely why water is, to my knowledge, the current leading idea. It works not only as an excellent primary shield but also helps to minimize secondary radiation, and you also naturally have literally tons of it. As an aside, this is why the original Moon missions used simple aluminum. One of the typical angles people who don't think we landed on the Moon used is that to safely get through the Van Allen Belts we would have needed massive lead shielding on the craft, when in reality it was shielded by a pretty thin layer of aluminum, precisely to minimize secondary radiation. If you put that thick lead shielding on the craft that people intuitively think you'd need, it very well could have killed the astronauts. [1] - https://en.wikipedia.org/wiki/Bremsstrahlung https://en.wikipedia.org/wiki/Bremsstrahlung
  - MeImCounting 2y ago
    Polyethylene is similarly a good shield because its got high hydrogen content so is pretty good at moderating neutrons. I image a polyethylene structure containing a layer of water is probably something like what we'll end up settling on. Its also quite strong and would make decent structural components.
me_me_me 2y ago
1m3 of water weights a metric ton, do the astronauts stay in a broom closet for duration of the flight? You still need (literally) tons of water. And every ton you take increases fuel cost. Currently you need what 10-20 trips to fuel for moon. How many trips would you need to fuel trip to mars? You would need a fucking conveyor belt of starship to prep the mission. Who is going to pay for it? And why? Just because the materials for shielding/tools are simple it doesnt make the solution simple.
- somenameforme 2y ago
  You hit on two really different topics at the same time. So let's hit on the fuel topic first. People tend to draw intuitive parallels of rocket fuel with gas. A short trip doesn't need much, while a long trip needs a lot. But it turns out that's not really how it works in space. In space the way you travel is you point at something, accelerate a bunch, and then coast there. So the typical measurement for something analogous to fuel is called delta-v, or the total required change in velocity. The delta-v required to get to the Moon is around 19km/s. The total delta-v required to get to Mars is around 21km/s. Wiki has a nice table for the delta-v required to get to different locations here. [1] Not only are they very close, but you might also notice that you spend about half your delta-v budget just getting off of Earth's surface! That's why in-orbit refueling is so useful. On the water topic, here's [2] a very readable little writeup on the mass inputs required for longterm space missions. Water makes up the overwhelming majority of your requirements. Starship, in its current form, can carry 150 tons. And that will be substantially increased once the tech is stabilized. A sizable chunk of that storage, for Mars missions, will be water. Also, the big threat is not the persistent ambient radiation, but infrequent extremely high energy bursts from solar weather. [1] - https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_between_Earth,_Moon_and_Mars https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_betwee... [2] - https://ntrs.nasa.gov/api/citations/20190027563/downloads/20190027563.pdf https://ntrs.nasa.gov/api/citations/20190027563/downloads/20...
  - imtringued 2y ago
    Why does this matter? The delta V requirements are so steep Starship can't return from the martian surface. It is a completely different game to go to Mars than to the moon unless you are planning on building a mars gateway in orbit and never landing anywhere.

MeImCounting 2y ago

The problem is that paradoxically, thicker shields can cause higher doses of radiation due to secondary radiation production. Theres a balance there to minimizing primary and secondary dosage but you cant really get it below a certain threshold without some form of active shielding. Theres a lot of promising ideas for active shielding but they all require alot of power. All this to say that someone on a trip to mars will indeed get a high dose and this is something that needs to be given thought. Its not an intractable problem but it is also not even close to being solved or trivial. Folks on Mars is still quite a ways away. Not impossible or pointless by any means but it will require significant advancements in many domains before we can really do it safely.

timschmidt 2y ago
https://en.wikipedia.org/wiki/Radiotrophic_fungus https://en.wikipedia.org/wiki/Radiotrophic_fungus have also been discussed as an option.
somenameforme 2y ago
The secondary radiation you're talking about is called bremsstrahlung (braking) radiation [1]. This is precisely why water is, to my knowledge, the current leading idea. It works not only as an excellent primary shield but also helps to minimize secondary radiation, and you also naturally have literally tons of it. As an aside, this is why the original Moon missions used simple aluminum. One of the typical angles people who don't think we landed on the Moon used is that to safely get through the Van Allen Belts we would have needed massive lead shielding on the craft, when in reality it was shielded by a pretty thin layer of aluminum, precisely to minimize secondary radiation. If you put that thick lead shielding on the craft that people intuitively think you'd need, it very well could have killed the astronauts. [1] - https://en.wikipedia.org/wiki/Bremsstrahlung https://en.wikipedia.org/wiki/Bremsstrahlung
- MeImCounting 2y ago
  Polyethylene is similarly a good shield because its got high hydrogen content so is pretty good at moderating neutrons. I image a polyethylene structure containing a layer of water is probably something like what we'll end up settling on. Its also quite strong and would make decent structural components.

me_me_me 2y ago

1m3 of water weights a metric ton, do the astronauts stay in a broom closet for duration of the flight? You still need (literally) tons of water. And every ton you take increases fuel cost. Currently you need what 10-20 trips to fuel for moon. How many trips would you need to fuel trip to mars? You would need a fucking conveyor belt of starship to prep the mission. Who is going to pay for it? And why? Just because the materials for shielding/tools are simple it doesnt make the solution simple.

somenameforme 2y ago
You hit on two really different topics at the same time. So let's hit on the fuel topic first. People tend to draw intuitive parallels of rocket fuel with gas. A short trip doesn't need much, while a long trip needs a lot. But it turns out that's not really how it works in space. In space the way you travel is you point at something, accelerate a bunch, and then coast there. So the typical measurement for something analogous to fuel is called delta-v, or the total required change in velocity. The delta-v required to get to the Moon is around 19km/s. The total delta-v required to get to Mars is around 21km/s. Wiki has a nice table for the delta-v required to get to different locations here. [1] Not only are they very close, but you might also notice that you spend about half your delta-v budget just getting off of Earth's surface! That's why in-orbit refueling is so useful. On the water topic, here's [2] a very readable little writeup on the mass inputs required for longterm space missions. Water makes up the overwhelming majority of your requirements. Starship, in its current form, can carry 150 tons. And that will be substantially increased once the tech is stabilized. A sizable chunk of that storage, for Mars missions, will be water. Also, the big threat is not the persistent ambient radiation, but infrequent extremely high energy bursts from solar weather. [1] - https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_between_Earth,_Moon_and_Mars https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_betwee... [2] - https://ntrs.nasa.gov/api/citations/20190027563/downloads/20190027563.pdf https://ntrs.nasa.gov/api/citations/20190027563/downloads/20...
- imtringued 2y ago
  Why does this matter? The delta V requirements are so steep Starship can't return from the martian surface. It is a completely different game to go to Mars than to the moon unless you are planning on building a mars gateway in orbit and never landing anywhere.