Thread by @DrPhiltill

Lots of discussion today on space radiation including errors like this one. This has confused water with regolith. Using too thin a layer of *regolith* creates secondaries, increasing the dose. But using water, or PTFE (lots of hydrogen), even very thin, always reduces the dose/1

https://twitter.com/pinboard/status/1768688352717365501

2/ The thing about using regolith for shielding is that you use it when you are on the surface of a planet, and there’s so much available and you do t carry it on a spaceship so you have no reason to use a thin amount. It entirely solves the problem!

And…

3/ …if you want shielding on your spaceship you aren’t going to use regolith. You’ll use water, food, rocket propellant — mass you need to carry anyhow — and low-density material designed for shielding with lots of hydrogen. And you can travel *faster* to reduce the dose, too.

4/ Contrary to what OP said, I know tons of NASA engineers and scientists who think we are going to Mars and do not think there is a show-stopping problem with radiation. In fact, I don’t know *a single informed person* who thinks it’s a show stopper.

5/ Part of the reason that NASA does not consider it a show stopper is because the dose limit is an arbitrary line that has huge margins around what we consider acceptable. When I worked on radiation shielding (briefly, many years ago), the limit was set by Congress such that…

6/…the death rate of astronauts would not be higher than steel workers. When we did the math, this meant the lifetime radiation dose had to be low enough that excess rates of leukemia over their lifetime had to be very small. Some astronauts will die of leukemia anyways, and…

7/…you will never know if an astronaut who dies of leukemia later in life would have died of it anyways or if they got it because years earlier they did a Mars mission. But statistically we will see a tiny blip of additional leukemia cases among astronauts so we will know that

8/… *some* of those cases were the result of doing Mars missions. And Congress said that this statistical blip will not exceed the number of lifelong job-related deaths among steel workers. *That* is where the radiation limit came from. It’s not as though…

9/ …astronauts would be dropping dead during the mission or shortly after the mission with blistering skin or anything.🤦‍♂️ It’s just a tiny statistical effect.

So when we say there’s a challenge with radiation, we mean that it’s hard to make this small statistical blip…

10/ …soooo tiny tiny tiny that it’s safer to be an astronaut than a steel worker.

But even so, I never knew *anybody* in NASA who thought we couldn’t achieve it. When NASA engineers talk about how challenging it is, that’s because they want more funding for their projects…

11/…because they believe their projects *can* solve it. Some want to develop nuclear propulsion to go faster to Mars to reduce the dose (so the blip will be super tiny), so they argue how it is soooo important to fund their project. Others argue for shielding research. Etc.

12/ Apparently, people outside nasa have been listening to this and misunderstood the severity. They thought it meant, wow, we can’t do Mars missions because astronaut’s faces will melt off and it’s sooo bad that we cannot solve it without a miracle. This is totally wrong. /end