We've flown a radiation-blocking vest to the Moon and back, and it worked
arstechnica.com62 points by rbanffy 4 days ago
62 points by rbanffy 4 days ago
It's kind of buried in the article, but it's worth noting that this vest is meant only to guard against solar storms, not cosmic rays; those remain a significant problem.
> The vest, though, does nearly nothing against galactic cosmic rays (GCR), which are the other major radiation source astronauts face. Unlike solar storm radiation, GCR arrive continuously at much higher energies, which makes them harder to shield against. “Using the vest against these rays would not be reasonable,” Houri says. “You’d have to wear it at all times.”
See for instance this article on how the cosmic ray problem would affect a Mars mission: https://mceglowski.substack.com/p/radiation-tradeoffs-for-ma...
The same protection against solar storms (which does nothing against cosmic rays) WILL also protect against exposure to the Van Allen belts.
Remember the van allen belt radiation is what spawned a lot of fake moon landing theories that suggested transit thru the van allen belts was not survivable with the limited/no protection that our astronauts had at the time.
I remember reading, long ago, an assertion that most shielding ideas were counterproductive for astronauts.
It was stated that most shielding would turn high energy photons into much more harmful showers of particles, worse than the original photon going directly through tissue. Was this an untested myth?
HDPE has been around since the beginning of the space race, so it seems like someone ought to have considered this before? Has the understanding of particle interactions improved a lot since then, such that HDPE shielding would not have been considered before?
It's not a new idea, here's an article from 20 years ago:
https://www.sciencedirect.com/science/article/abs/pii/S01685...
I can't find a good source but it seems that the radiation shielding properties of polyethylene were discovered some time after WWII. But I think this was an inevitable discovery, not some sort of accident. HDPE has a lot of hydrogen atoms which are perfect for blocking high energy particles without creating secondary radiation. A block of solid hydrogen would be ideal but that's not practical. Water works well but it's heavy and needs a container which adds more weight.
Dense metals and concrete do a fine job but are heavy relative to amount you need to stop the same amount of radiation as HDPE. Plus you get the secondary radiation effects from metals that can harm humans or sensitive electronics. It's like being behind armor that's hit with a round. The armor may stop the round from getting through but very hot fragments of the backside of the armor (spalling) can fly off and injure someone. Now you need additional protection from the spalling too.
Here's a photo from 2017 of a NASA facility using white HDPE sheets to attenuate high energy particles:
https://www.flickr.com/photos/brookhavenlab/33642244296/in/a...
Long video but informative: https://www.youtube.com/watch?v=DJcbevbBzsc (~26 min)
This targeted shielding is a classic aerospace mass tradeoff much like armoring a fighter pilot instead of the entire plane.
This seems sort of interesting as a sort of emergency backup, but it seems like the real solution for any sort of long distance/long duration in space is just making mass to orbit dramatically cheaper and shielding the spacecraft.
A spacecraft with a 4m diameter spherical living space and 4m of water shielding around it will weigh about 1,000 tons. The propellant tanks needed to move it around the solar system will be similarly titanic.
How many orders of magnitude were you figuring for your "dramatically cheaper"?
That's 5 Starship block 4 launches, seems fine? Propellant, presumably for long duration voyages we're not relying entirely on chemical combustion. If we're using cyclers, once they're up to speed, you need barely any fuel for corrections, just to taxi to/from the cycler.
Could use empty plastic water tanks in the walls and have a satellite in orbit that already has the water onboard and they just transfer the water back to the satellite before returning to earth. Water blocks radiation very well it’s the reason we use pools of it to store fuel rods when they are not in reactors.
this is a common concept in space-craft thought experiments because of the dual-use nature; can shield yourself with a big water balloon essentially at the tip of the space craft to catch all those pesky extra energetic particles that are bombarding you against your fantastically high velocity, while also providing water to grow things in, or whatever.
then neutron activation becomes even more nuanced because it affects not only your craft/infrastructure/armor but your semi-perishable goods.
Thought it might be useful for the untapped market for air crews on passenger airlines but the company said it does not block cosmic gamma rays.
The NASA Space Radiation Laboratory uses HDPE panels to attenuate neutrons, protons, and heavy ions. The lab sits at the tail end of a particle accelerator which is used to test radiation effects on various materials including electronics and mice. When I saw the plastic panels, I asked one of the NSRL physicists about it as we had just finished setting out some tungsten blocks to isolate the beam only a certain area on our experiment. Why plastic? Why not a dense metal? He explained that HDPE is dense with hydrogen that does really well against slowing down particles and that most importantly, HDPE is made from low atomic numbers that do not emit secondary radiation effects. This prevents radiation from hitting sensitive electronics outside the beam and also making nearby objects radioactive. When the beam hits an object with high atomic numbers (metals, especially dense ones), it can create very strong x-rays that can knock neutrons out of nearby stable metal nuclei and create unstable isotopes, effectively creating a bunch of unintended radiation sources. This isn't a big deal for the experiment, that goes away at the end of the day but not good for permanent equipment.
You can see the HDPE sheets in this photo, they can be lowered or raised to adjust attenuation:
“It still gets people surprised,” Milstein says. “Everybody asks, what about the head? But we’re actually able to reduce the effective dose by 60 percent without protecting the head, the arms, or even the legs.”
Whilst I understand the maths here, I can see why someone would be nervous!
You need to protect anything with relatively fast dividing cells best because this is where the cancer risk is highest. The brain with its slow dividing cells and fast killing tumors is the last thing to protect.
It's ok, everything except your brain will be protected from radiation!
Your brain is quite robust against cancer and when it gets it, if is often a relatively fast death.
The use of “we” in this headline is really jarring.
I agree actually. I understand the use of "we" to mean an achievement of humanity (like: we've been to the moon) but I find that often "we" is a substitute for "someone not me" - as in "we should make healthcare free" coming from someone who doesn't perceive a role in actually doing any of it.
In this case it's kinda just confusing. The headline should be "Israeli startup + NASA ..."
Why wouldn't it?
The difficulty is making it protective but light enough to not significantly hinder the spacecraft or person wearing it, all of which is covered in the article.
Poor design, flawed assumptions, manufacturing defects, inability to bear the gravitational and rocket launch forces, inability of the jacket to last the duration of the radiation exposure - these are some reasons that come to my mind on why a radiation-blocking vest wouldn't have worked for the journey to the moon and back (i.e. your question "Why wouldn't it?".)