Nature of radiation on interplanetary space exploration

[wally_moot]

I've heard tell that a mission to the Galilean satellites is difficult for many reasons, but radiation is one of them. Is it safe to say that above all, the worst radiation is when you are landing and have landed on the surface of the Galilean satellites, because you are in Jupiter's Van Allen belts? Or, is the nature of cosmic rays so degradative that it is the greatest risk?

I'll cut to the chase. I thinkI have an idea that will help protect a lander, if we are ever crazy enough to send people to Europa. However, assuming it takes hours if not days to deorbit a lander into a plausible entry path the lander will be in Jupiter's deadly Van Allen belt for a long time before any system that is meant to protect it from Van Allen radiation is put in place.

I've heard of a double wall system where the astronauts go into an extra layer of radiation protection, however they can't continue to remain in a double walled claustrophobic pod forever. That's where my system might come in, but unfortunately it is once they've landed. Does it still count by then? Do they need an all inclusive system for the duration of the flight to and back? Or is the primary concern radiation once they've landed IN the Van Allen belts on Europa?

 

[Bobbywhy]

Here are four articles, with many references within them, for you to research and attempt to evaluate the potential value of your proposed radiation shield for space traveling astronauts:

Space Radiation Hazards and the Vision for Space Exploration:
Report of a Workshop (2006)
http://www.nap.edu/catalog.php?record_id=11760

"The health threat from cosmic rays is the danger posed by galactic cosmic rays and Solar energetic particles to astronauts on interplanetary missions.[1] Galactic cosmic rays (GCRs) consist of high energy protons (85%), helium (14%) and other high energy nuclei HZE ions.[1] Solar energetic particles consist primarily of protons accelerated by the Sun to high energies via proximity to Solar flares and coronal mass ejections. They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft .[2][3]"
http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays

Cosmic rays may prevent long-haul space travel
15:01 01 August 2005
http://www.newscientist.com/article...event-longhaul-space-travel.html#.UjVrQ77D_DcRadiation Environment During Space Flight and on Other Planets
Anne Adamczyk, PhD
http://hps.org/publicinformation/ate/faqs/spaceradiation.html

 

[qraal]

I've heard tell that a mission to the Galilean satellites is difficult for many reasons, but radiation is one of them. Is it safe to say that above all, the worst radiation is when you are landing and have landed on the surface of the Galilean satellites, because you are in Jupiter's Van Allen belts? Or, is the nature of cosmic rays so degradative that it is the greatest risk?

The Van Allen Belts are the chief concern when near Jupiter - though they're not really generated in the same way as Earth's. The deadly particle flux around Jupiter comes from solar wind particles that have been accelerated by Jupiter's magnetic field to high energies (several MeV), while the Earth's deadly radiation is mostly from high-energy particles kicked off the atmosphere via cosmic rays, then trapped in a magnetic mirror.

I'll cut to the chase. I think I have an idea that will help protect a lander, if we are ever crazy enough to send people to Europa. However, assuming it takes hours if not days to deorbit a lander into a plausible entry path the lander will be in Jupiter's deadly Van Allen belt for a long time before any system that is meant to protect it from Van Allen radiation is put in place.

Minutes to deorbit from Europa orbit - its gravity is less than the Moon's - but getting to Europa orbit may take days.

I've heard of a double wall system where the astronauts go into an extra layer of radiation protection, however they can't continue to remain in a double walled claustrophobic pod forever. That's where my system might come in, but unfortunately it is once they've landed. Does it still count by then? Do they need an all inclusive system for the duration of the flight to and back? Or is the primary concern radiation once they've landed IN the Van Allen belts on Europa?

Cosmic rays are the main problem of ANY extended spaceflight which has crews spending more than a year or two in interplanetary space. Storm-shelters - what you describe - are effective against solar-flares and coronal mass ejections, but are irrelevant against the 1 GeV to 10 GeV cosmic-ray flux that is of the most concern.

Unfortunately we have NO good solid biological data on the long-term effects of cosmic-ray primaries (the energetic particles themselves) and only rough data on the effects of the secondaries (bits of particles when primaries crash into the shielding, like pions & muons. Extrapolating from the lower energy radiation we encounter on Earth is fraught with uncertainty - we can either exaggerate the threat or understate it.

The good news is, that if we have shielding against cosmic-rays, then Jupiter's radiation belts are an irrelevance. Their peak energy is much lower.

 

[wally_moot]

Unfortunately we have NO good solid biological data on the long-term effects of cosmic-ray primaries (the energetic particles themselves) and only rough data on the effects of the secondaries (bits of particles when primaries crash into the shielding, like pions & muons. Extrapolating from the lower energy radiation we encounter on Earth is fraught with uncertainty - we can either exaggerate the threat or understate it.

Aren't the nature of almost all particle interactions known? I know it's a zoo of particles that are nothing like the normal hadrons, but since we know most of the particles in cosmic radiaiton, couldn't we reverse engineer it depending on the type of shielding?

The good news is, that if we have shielding against cosmic-rays, then Jupiter's radiation belts are an irrelevance. Their peak energy is much lower.

Actually, this is not good news for me, because it sort of makes any additional shielding system while on the surface of the moon kind of superfluous. Oh well, it simplifies the system.

Thank you, by the way. :]

 

[qraal]

I said: Unfortunately we have NO good solid biological data on the long-term effects of cosmic-ray primaries (the energetic particles themselves) and only rough data on the effects of the secondaries (bits of particles when primaries crash into the shielding, like pions & muons. Extrapolating from the lower energy radiation we encounter on Earth is fraught with uncertainty - we can either exaggerate the threat or understate it.

Aren't the nature of almost all particle interactions known? I know it's a zoo of particles that are nothing like the normal hadrons, but since we know most of the particles in cosmic radiaiton, couldn't we reverse engineer it depending on the type of shielding?

It's not the particle interactions, but the biological outcomes of such high energy particles passing through living tissue. We try to extrapolate from our experiences with lower energy radiation, but that's not really sufficient to the task. Hard data is needed. The exposure is episodic, so the biological response may alter the end outcomes. Astronauts have stayed on the various space stations for more than a year, without any apparent ill effects from the high-energy cosmics they're exposed to. Due to their proximity to the Earth, they're shielded from about 50% of the sky, so the exposure is somewhat lower, but they still encounter the high-energy stuff.

I said: The good news is, that if we have shielding against cosmic-rays, then Jupiter's radiation belts are an irrelevance. Their peak energy is much lower.

Actually, this is not good news for me, because it sort of makes any additional shielding system while on the surface of the moon kind of superfluous. Oh well, it simplifies the system.

Thank you, by the way. :]

You're welcome. Contrary to the more hysterical popular press, there are designs which can reduce the cosmic ray exposure, though their utility due to the uncertainty of effects is unknown.

 

[Chronos]

Going to the moon is no big deal. It's only a few days trip and we could orient the craft to blunt the harmful effects of something like a solar flare. A trip to Mars could be ugly. Its an 18 month trip each way and yields a significant dose of interplanetary space radiation. Radiation shielding adds dead weight to the vehicle which poses serious build problems, where each kilogram carries a shocking expense in fuel. This is one of the reasons robotic probes are so attractive.

 

[bahamagreen]

One way trip to Mars, for example, is estimated at about 80% lifetime allowable exposure, so it's a problem.
Cosmic rays are very penetrating; the kind of shielding needed is measured in meters of thickness...(lead or similar stuff).

There is a possibility that the human genome project's amazing advancement may be the solution. The fundamental problem is energetic particles passing through the tissue and disrupting DNA molecules, causing a cascade of biological failures.
The solution may be an exotic future treatment (nanobots, etc.) that basically repairs DNA and other critical molecules as soon as they get busted up. Something like that... damn the torpedoes and just fix what breaks on the fly at the bio-molecular level.

It's going to have to be something like that in order to do extended travel beyond low Earth orbit (where there is some protection) and in order to avoid the problems with shielding.

 

[Astronuc]

Cosmic and solar radiation (high energy protons, electrons, deuterons, alpha particles, etc) are highly ionizing. The radiation will have deleterious impact on solid-state electronics and biological entities.

The optimal shielding will be a combination of high Z and low Z materials. High Z materials (with their high electron density) are effective at mitigating gamma radiation and beta particles, while low Z materials (with light nuclei) are effective at scattering the protons and other radiations. Some metal hydrides make good shielding with a combination of high Z + H.

One also has to be careful of spallation reactions in which the incident radiation will knock out protons, neutrons or alpha particles from nuclei, or in the case of some light Z nuclei, the nuclei will fission/split into two lighter nuclei.

The total mass of the system must be considered, since that mass must be transported.

One approach has been to surround critical systems and personnel with the propellant (e.g., LH2, NH3, diborane) and propellant storage tanks. However, one must realize that propellant decreases over time. More mass requires higher specific power to realize the same mission goals, and higher specific power must be offset against system/material degradation.

http://home.web.cern.ch/about/physics/cosmic-rays-particles-outer-space

See also - Shielding Strategies for Human Space Exploration (NASA Conference Publication 3360), Dec. 1997
(link subject to disruption) - http://www.engineering.dartmouth.edu/~d76205x/research/Shielding/docs/NASA-97-cp3360.pdf

Nuclear and Space Radiation Effects on Materials (NASA SP-8053)
http://www.dept.aoe.vt.edu/~cdhall/courses/aoe4065/NASADesignSPs/sp8053.pdf