6 ms·

Is more shielding not the obvious answer? A thin sheet of lead around the sensitive parts should do the trick. (Note: I'm not a physicist and have no idea what

Is more shielding not the obvious answer? A thin sheet of lead around the sensitive parts should do the trick. (Note: I'm not a physicist and have no idea what I'm talking about in this domain)

klodolph 2y ago
1. You’d need more than a thin sheet of lead. The radiation in space can be very energetic. It can easily penetrate several cm of shielding and if it is absorbed, you get secondary radiation. 2. Even a thin sheet of lead may be too heavy.
JumpCrisscross 2y ago
> Is more shielding not the obvious answer? A thin sheet of lead around the sensitive parts should do the trick Lead "is effective at stopping gamma rays and x-rays" [1]. Jupiter's radiation comes from "trapped particles [that] are about ten times more energetic than the ones from the equivalent radiation belts of Earth" and "several orders of magnitude more abundant" [2]. When those encounter lead they cause bremsstrahlung radiation [3], a sort of subatomic shrapnel that can be more dangerous than the original radiation. Lead is also heavy, which means not only increasing the mass of the spacecraft, but its balance and thus propulsion profile. That might mean upgrading and moving thrusters and propellant tanks--in effect, a complete redesign. (It's a good question that doesn't deserve to be downvoted.) [1] https://en.wikipedia.org/wiki/Lead_shielding https://en.wikipedia.org/wiki/Lead_shielding [2] https://www.spenvis.oma.be/help/background/planetary/traprad_jup.html#TRPP https://www.spenvis.oma.be/help/background/planetary/traprad... [3] https://en.wikipedia.org/wiki/Bremsstrahlung https://en.wikipedia.org/wiki/Bremsstrahlung
- basementcat 2y ago
  Europa Clipper electronics are contained in a 9.2 mm thick aluminum-zinc vault. https://europa.nasa.gov/resources/342/electronics-vault/ https://europa.nasa.gov/resources/342/electronics-vault/
  - JumpCrisscross 2y ago
    > Europa Clipper electronics are contained in a 9.2 mm thick aluminum-zinc vault Were it designed today we'd probably dope it with titanium [1][2]. [1] https://www.tandfonline.com/doi/full/10.1080/10420150.2023.2249180 https://www.tandfonline.com/doi/full/10.1080/10420150.2023.2... [2] https://www.sciencedirect.com/science/article/abs/pii/S0149197020302201 https://www.sciencedirect.com/science/article/abs/pii/S01491...
  - indoordin0saur 2y ago
    Could they find some margin to make it a bit thicker? I know this would increase the weight but if my image of how big this electronics vault must be I'd imagine they could find something less critical to shave off to offset it.
    - JumpCrisscross 2y ago
      > I'd imagine they could find something less critical to shave off to offset it You’re still changing the spacecraft’s balance. Imagine moving one of an airliner’s engines a foot to the left. It can be done. But it’s a big change. Now consider that “modern jet airliners have…useful load fractions, on the order of 45–55%,” while orbital rockets’ payload fractions are “between 1% and 5%” [1]. Deep space craft are another order of magnitude more sensitive. Adding a little shielding here and there is the aeronautical equivalent of hanging a bag of bar bells off the tips of one of the wings. [1] https://en.m.wikipedia.org/wiki/Payload_fraction https://en.m.wikipedia.org/wiki/Payload_fraction Note: useful load != payload fraction, but within orders of magnitudes they’re comparable
    - basementcat 2y ago
      Unless the launch is postponed 2 years, I think any redesign of the vault at this point is unlikely. Clipper was originally designed to be launched on an SLS rocket and that was swapped out for a less powerful Falcon Heavy* so there isn’t going to be much room for extra mass. Additional mass may require more planetary "slingshots" and add more years before Jupiter arrival. Hopefully SpaceX is able to resolve its Falcon second stage problems before Clipper is scheduled to launch. * There were some discussions about adding a Thiokol Star 37 or Star 48 apogee kick motor to the Falcon Heavy stack for Clipper but for various reasons this didn’t happen. https://en.m.wikipedia.org/wiki/Star_(rocket_stage) https://en.m.wikipedia.org/wiki/Star_(rocket_stage)
nick238 2y ago
The rad vault on Clipper is an aluminum-zinc alloy, not lead. There are different kinds of radiation to worry about (alpha, beta, gamma, neutron, protons, heavy ions), and I think certain shielding approaches good for one aren't always good for the others. Different sources of radiation interact with electrons or nuclei (1:1 with number of atoms) or nucleons (individual protons/neutrons, 1:1 with the mass). For instance, neutrons bounce off nuclei in nuclear reactors, and the lighter they are, the more energy the bounce can siphon off from the neutron. So having more, lighter (low-Z) nuclei (hydrogen in water and carbon in graphite are commonly used) provides better slowing of the neutrons vs. heavier (high-Z) elements, like lead. Smashing ions (alpha, protons, heavy ions) into materials can also cause a https://en.wikipedia.org/wiki/Particle_shower https://en.wikipedia.org/wiki/Particle_shower
perihelions 2y ago
Yes, and if they had larger mass budgets they could over-engineer things like shield thickness to have wider safety margins, and mitigate unexpected problems like this one. One can speculate future space probes generally will become more more reliable, as the the cost of mass-to-orbit goes down, and engineering constraints become looser. (I wonder if Starship is useful for this type of problem: if you could adapt the orbital-refueling method to serve as radiation shielding, and put an electronics vault in the middle of the propellant tank? Could you adapt Starship into a spacecraft bus in this way?)
- mandevil 2y ago
  Water tanks are the most likely source of radiation shielding: propellant tanks get used up and go empty, while for any lengthy mission, water is either going to be recycled back into the tanks or you will have to take blue water tanks and over time turn them into grey water tanks, either way you will have those tanks much more filled than the propellant.
- indoordin0saur 2y ago
  These spacecraft always have tons of instruments for measurings along loads of different axes. For example, a magnetometer specifically designed for testing a hypothesis about Europa's magnetosphere. Looking at the wikipedia page it seems like there are about a dozen of these. Perhaps worst case scenario they could determine which one was least critical relative to its weight and eliminate it to increase the mass budget.
Tuna-Fish 2y ago
In space, a thin sheet of lead is not radiation shielding but a radiation amplifier. The problem being that high-energy cosmic rays are unlikely to interact with the lightly built spacecraft, going right through it. But if you add a thin layer of a good radiation shielding material, then there is substantially increased chance that they will interact with that material, and produce a very large spray of secondary particles. And those secondary particles will also be going fast enough that when they hit more shielding material, they will also result in more particles. Then some of those secondary particles will be neutrons, which will easily penetrate the thin shielding (lead half thickness for 4MeV neutrons is 68mm), and irradiate the surroundings. This has been very clearly demonstrated on the ISS, any metal tool has substantially higher radiation levels around it.
- gosub100 2y ago
  Thank you for this post. I was wondering if a thin lead sheet would be beneficial for the cockpit ceiling and maybe aisles of jetliners to protect the crew from the prolonged exposure to increased radiation. Do you think this is a bad idea for the same reasons as the spacecraft? (Of course there are other materials besides lead, that was what first came to mind because I incorrectly thought it was a panacea for all radiation types).
  - chasil 2y ago
    I had read elsewhere that water is a useful shield. A quick search found this document, that mentions the danger of secondary particles. https://www.nasa.gov/wp-content/uploads/2009/07/284275main_radiation_hs_mod3.pdf?emrc=f9d9bd https://www.nasa.gov/wp-content/uploads/2009/07/284275main_r...
  - perihelions 2y ago
    Air pressure at airliner altitudes is still about 20-30% of the sea level value. That means 20-30% of the atmosphere is above that—a column of mass equal to 2-3 meters of liquid water. A thin lead sheet would be a rounding error next to that. This is an oversimplification that's rather wrong, but: a decrease in altitude of just 300 meters, at airliner levels, puts an additional atmospheric mass equal to ~1 cm of lead (Pb) above your head.

Is more shielding not the obvious answer? A thin sheet of lead around the sensitive parts should do the trick. (Note: I'm not a physicist and have no idea what I'm talking about in this domain)

klodolph 2y ago

1. You’d need more than a thin sheet of lead. The radiation in space can be very energetic. It can easily penetrate several cm of shielding and if it is absorbed, you get secondary radiation. 2. Even a thin sheet of lead may be too heavy.

JumpCrisscross 2y ago

> Is more shielding not the obvious answer? A thin sheet of lead around the sensitive parts should do the trick Lead "is effective at stopping gamma rays and x-rays" [1]. Jupiter's radiation comes from "trapped particles [that] are about ten times more energetic than the ones from the equivalent radiation belts of Earth" and "several orders of magnitude more abundant" [2]. When those encounter lead they cause bremsstrahlung radiation [3], a sort of subatomic shrapnel that can be more dangerous than the original radiation. Lead is also heavy, which means not only increasing the mass of the spacecraft, but its balance and thus propulsion profile. That might mean upgrading and moving thrusters and propellant tanks--in effect, a complete redesign. (It's a good question that doesn't deserve to be downvoted.) [1] https://en.wikipedia.org/wiki/Lead_shielding https://en.wikipedia.org/wiki/Lead_shielding [2] https://www.spenvis.oma.be/help/background/planetary/traprad_jup.html#TRPP https://www.spenvis.oma.be/help/background/planetary/traprad... [3] https://en.wikipedia.org/wiki/Bremsstrahlung https://en.wikipedia.org/wiki/Bremsstrahlung

basementcat 2y ago
Europa Clipper electronics are contained in a 9.2 mm thick aluminum-zinc vault. https://europa.nasa.gov/resources/342/electronics-vault/ https://europa.nasa.gov/resources/342/electronics-vault/
- JumpCrisscross 2y ago
  > Europa Clipper electronics are contained in a 9.2 mm thick aluminum-zinc vault Were it designed today we'd probably dope it with titanium [1][2]. [1] https://www.tandfonline.com/doi/full/10.1080/10420150.2023.2249180 https://www.tandfonline.com/doi/full/10.1080/10420150.2023.2... [2] https://www.sciencedirect.com/science/article/abs/pii/S0149197020302201 https://www.sciencedirect.com/science/article/abs/pii/S01491...
- indoordin0saur 2y ago
  Could they find some margin to make it a bit thicker? I know this would increase the weight but if my image of how big this electronics vault must be I'd imagine they could find something less critical to shave off to offset it.
  - JumpCrisscross 2y ago
    > I'd imagine they could find something less critical to shave off to offset it You’re still changing the spacecraft’s balance. Imagine moving one of an airliner’s engines a foot to the left. It can be done. But it’s a big change. Now consider that “modern jet airliners have…useful load fractions, on the order of 45–55%,” while orbital rockets’ payload fractions are “between 1% and 5%” [1]. Deep space craft are another order of magnitude more sensitive. Adding a little shielding here and there is the aeronautical equivalent of hanging a bag of bar bells off the tips of one of the wings. [1] https://en.m.wikipedia.org/wiki/Payload_fraction https://en.m.wikipedia.org/wiki/Payload_fraction Note: useful load != payload fraction, but within orders of magnitudes they’re comparable
  - basementcat 2y ago
    Unless the launch is postponed 2 years, I think any redesign of the vault at this point is unlikely. Clipper was originally designed to be launched on an SLS rocket and that was swapped out for a less powerful Falcon Heavy* so there isn’t going to be much room for extra mass. Additional mass may require more planetary "slingshots" and add more years before Jupiter arrival. Hopefully SpaceX is able to resolve its Falcon second stage problems before Clipper is scheduled to launch. * There were some discussions about adding a Thiokol Star 37 or Star 48 apogee kick motor to the Falcon Heavy stack for Clipper but for various reasons this didn’t happen. https://en.m.wikipedia.org/wiki/Star_(rocket_stage) https://en.m.wikipedia.org/wiki/Star_(rocket_stage)

nick238 2y ago

The rad vault on Clipper is an aluminum-zinc alloy, not lead. There are different kinds of radiation to worry about (alpha, beta, gamma, neutron, protons, heavy ions), and I think certain shielding approaches good for one aren't always good for the others. Different sources of radiation interact with electrons or nuclei (1:1 with number of atoms) or nucleons (individual protons/neutrons, 1:1 with the mass). For instance, neutrons bounce off nuclei in nuclear reactors, and the lighter they are, the more energy the bounce can siphon off from the neutron. So having more, lighter (low-Z) nuclei (hydrogen in water and carbon in graphite are commonly used) provides better slowing of the neutrons vs. heavier (high-Z) elements, like lead. Smashing ions (alpha, protons, heavy ions) into materials can also cause a https://en.wikipedia.org/wiki/Particle_shower https://en.wikipedia.org/wiki/Particle_shower

perihelions 2y ago

Yes, and if they had larger mass budgets they could over-engineer things like shield thickness to have wider safety margins, and mitigate unexpected problems like this one. One can speculate future space probes generally will become more more reliable, as the the cost of mass-to-orbit goes down, and engineering constraints become looser. (I wonder if Starship is useful for this type of problem: if you could adapt the orbital-refueling method to serve as radiation shielding, and put an electronics vault in the middle of the propellant tank? Could you adapt Starship into a spacecraft bus in this way?)

mandevil 2y ago
Water tanks are the most likely source of radiation shielding: propellant tanks get used up and go empty, while for any lengthy mission, water is either going to be recycled back into the tanks or you will have to take blue water tanks and over time turn them into grey water tanks, either way you will have those tanks much more filled than the propellant.
indoordin0saur 2y ago
These spacecraft always have tons of instruments for measurings along loads of different axes. For example, a magnetometer specifically designed for testing a hypothesis about Europa's magnetosphere. Looking at the wikipedia page it seems like there are about a dozen of these. Perhaps worst case scenario they could determine which one was least critical relative to its weight and eliminate it to increase the mass budget.

Tuna-Fish 2y ago

In space, a thin sheet of lead is not radiation shielding but a radiation amplifier. The problem being that high-energy cosmic rays are unlikely to interact with the lightly built spacecraft, going right through it. But if you add a thin layer of a good radiation shielding material, then there is substantially increased chance that they will interact with that material, and produce a very large spray of secondary particles. And those secondary particles will also be going fast enough that when they hit more shielding material, they will also result in more particles. Then some of those secondary particles will be neutrons, which will easily penetrate the thin shielding (lead half thickness for 4MeV neutrons is 68mm), and irradiate the surroundings. This has been very clearly demonstrated on the ISS, any metal tool has substantially higher radiation levels around it.

gosub100 2y ago
Thank you for this post. I was wondering if a thin lead sheet would be beneficial for the cockpit ceiling and maybe aisles of jetliners to protect the crew from the prolonged exposure to increased radiation. Do you think this is a bad idea for the same reasons as the spacecraft? (Of course there are other materials besides lead, that was what first came to mind because I incorrectly thought it was a panacea for all radiation types).
- chasil 2y ago
  I had read elsewhere that water is a useful shield. A quick search found this document, that mentions the danger of secondary particles. https://www.nasa.gov/wp-content/uploads/2009/07/284275main_radiation_hs_mod3.pdf?emrc=f9d9bd https://www.nasa.gov/wp-content/uploads/2009/07/284275main_r...
- perihelions 2y ago
  Air pressure at airliner altitudes is still about 20-30% of the sea level value. That means 20-30% of the atmosphere is above that—a column of mass equal to 2-3 meters of liquid water. A thin lead sheet would be a rounding error next to that. This is an oversimplification that's rather wrong, but: a decrease in altitude of just 300 meters, at airliner levels, puts an additional atmospheric mass equal to ~1 cm of lead (Pb) above your head.