Galactic Cosmic Rays (GCR) - Showstopper or What?

[Warren Platts]

This topic keeps popping up all over the place, even in unexpected places, so in the interest of conciseness, if it's OK with everyone else, I propose that the discussion be encysted here.

My take is that if the increase in the risk of cancer is no greater than smoking and if people sign informed consent waivers, and in the case of NASA astronauts, they are promised the best medical care for life, I don't see what the big deal is.

However, a few other people seem to think it is a HUGE deal, so have at it!

[DLR]

Radiation levels on the surface of Mars are similar to those found in LEO, according to MSL data. In addition to that, Habitats - in which astronauts would be spending 80%-90% of their time - would most likely be buried under metres of regolith.

So no show stopper.

[guckyfan]

Radiation levels on the surface of Mars are similar to those found in LEO, according to MSL data. In addition to that, Habitats - in which astronauts would be spending 80%-90% of their time - would most likely be buried under metres of regolith.

So no show stopper.

I am waiting for release of more precise Curiosity data on radiation. That will clarify a lot of things. Preliminary data show radiation levels similar to LEO, as you stated. Radiation levels during transfer seem app. double that according to Curiosity. Given that a Bigelow Habitat has better shielding than present ISS modules there should be no problem. Precautions would be required for possíble radiation bursts from the sun. A lot can be achieved by pointing the propulsion module towards the sun and maybe some directed shielding in the same direction.

So certainly not a showstopper.

Also recent research in Chernobyl gives strong indication that the body is very well able to cope with low radiation levels. There seems to be a big difference between getting some dose through an X-Ray or CRT and receiving the same dose over weeks.
Actually lab animals exposed to Chernoby radiation for some period could deal a lot better with high radiation applied to them than another group that was not exposed to radiation before.

[SpacexULA]

I don't believe it's a show stopper, from the data I have seen written about from our unmanned probes.

But I would love to see a unmanned mission including rats outside of the Moon/Earth system to gather real medical data.

Send an Orion on a flyby of Mars or Venus with a payload of rats.  They can live 3-4 years, and can breed at 6 weeks meaning we could have many generations of exposure by the time the capsule returned.

[muomega0]

GCR mitigation mass is completely ignored in the architecture studies to date (no mass included).  Passive systems weight ~ 100 tons.

The transit time to mars and back, beyond L2 (BL2), is one of key drivers, in addition to the time on the surface of Mars, since Earth's magnetic field does not protect the crew unlike in an ISS LEO orbit.

Active systems have not been funded and implemented, yet they trade better in terms of mass and overall intensity reduction.
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What is GCR?
GCR comes from outside the solar system.

GCR is composed of the nuclei of atoms that have their surrounding electrons stripped away and our traveling at the speed of light!

GCR particles were probably accelerated within the last few million years by *magnetic fields* of supernova remnants (but not the explosion itself).   

GCR permeates interplanetary space and is extremely damaging to materials and biology because they possess significantly high ionizing power.

In general, the earth is protected by the atmosphere and the magnetic field, whereas the moon can only block about half the particles, like the earth, due its mass.

the sun can deflect GCR and decrease the average intensity of GCR in proportion to its magnetic field.

Note the common theme:  the sun and earth magnetic fields can and  deflect GCR.
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To no surprise, one see comments already that restate the misconception:

"Given that a Bigelow Habitat has better shielding than present ISS modules there should be no problem" 

"I don't believe it's a show stopper"

IOW:  reject any evidence contradicting their beliefs or substantiation of pet programs.

Perhaps they could read a bit more on the subject:

To be fair, Some 2000s studies showed that magnets were alone would result in huge masses, but so would passive systems for the equivalent amount of shielding.   What is causing this large difference in mass estimates?

A comparison of active versus passive shielding for GCR by Spillantini 2010  and the numbers are an order of magnitude lower than passive absorbers.

One must abandon the concept of 'absorbing' the radiation by shielding for space travel:  Passive absorbers have a cutoff energy and allow higher energy particles (GCR) to pass through to the inside

Development of active systems for GCR was hindered by initial choice of passive shields and the incorrect evaluation that immense magnetic fields and volumes were required

Build it. Test it.  Improve it.  'It' being the active system and compare the predictions to the test data.  Start at the L2 Gateway--cheaper than going to the lunar surface.   Adjust the BL2 architecture accordingly.  They great news is that 'it' is going to be way better than an absorber, with substantial room for improvement, with guaranteed spinoffs back to earth.

[guckyfan]

So the ISS is now a higly radioactive death trap due to all the accumulated secondary radiation?

[sdsds]

Many US astronauts will die of cancer. Guess what? Many US non-astronauts will die of cancer too! The tricky part is going to be determining which astronaut cancer deaths were caused by radiation exposures during spaceflight. Some facts:

Number of deaths for leading causes of death
(Data are for the U.S. and are final 2009 data)

Heart disease: 599,413
Cancer: 567,628
Chronic lower respiratory diseases: 137,353
Stroke (cerebrovascular diseases): 128,842
Accidents (unintentional injuries): 118,021
[...]

http://www.cdc.gov/nchs/fastats/lcod.htm

If the goal were to minimize the number of astronauts who die from cancer, one approach would be to select astronauts who are at high risk of dying from heart disease.

[randomly]

This is a very complex problem with a lot of unknowns. However human tolerance of low level radiation seems to be a lot better than originally assumed from the Linear No Threshold model that was concocted back in the 40's. Given the lack of data on long term low level radiation effects that was the most simplistic and conservative model and allowed them to extrapolate from the high dose radiation data they did have (Hiroshima and Nagasaki victims). It's just assumes that all intensities of radiation are bad, that total dose directly correlates to damage and it's totally cumulative.

However it assumes no cellular and DNA repair mechanisms and apoptosis. Even from a conceptual point it's lacking, and the data seems to back this up.

One fascinating incident in Taiwan where a cobalt-60 source got recycled into structural steel and people were living in the resulting apartment and office buildings for decades before it was discovered.

It was heavily investigated and even adjusting for other factors the incidents of cancer in people with long term exposure was 3 times LESS than the general population, birth defects on children was also several times lower. So clearly our current grasp of effects of long term low level exposure are not complete.

This incident is of course gamma radiation and not GCR and you can't necessarily equate the two. But certainly biology is more resistant than the Linear No Threshold model predicts. We need a lot more data, but GCR doesn't seem to be the show stopper it once seemed. Here's hoping it pans out.

[Warren Platts]

People keep talking about how we need a hundred tonnes of protection, but with an abundant chemical architecture with big MTV's, you're going to need hundreds of tonnes of LH2/LO2 anyways.

We all know that LH2 provides pretty good protection, but does anybody know about LO2?

I've posted this picture before, but I think short-term, this is pretty much the way to go. Of course it will require some massive Lunar ISRU!

[KelvinZero]

---
To no surprise, one see comments already that restate the misconception:

"Given that a Bigelow Habitat has better shielding than present ISS modules there should be no problem" 

"I don't believe it's a show stopper"

IOW:  reject any evidence contradicting their beliefs or substantiation of pet programs.

I don't believe it's a show stopper.

What I mean is, it seems that the risks are acceptable for the sorts of missions currently being considered, especially if we send older astronauts.

The points you bring up don't seem relevant within the context of the term 'show stopper' as I define it. (I define a show stopper as something that stops an intended action until the issue is resolved) I think you might be using the term differently from the rest of us. For example I would readily agree we should keep researching things like mini magnetosphere shielding, I would readily agree that GCR would appear to be a show stopper for families living and working in space.

It might help if you made a more specific claim, eg "This evidence suggests the danger to an astronaut on a mars mission is a doubling of the risk of cancer in the following decade and I define this as a show stopper", or 'this evidence suggests we really cannot quantify the risk, and the above situation is entirely possible, and I define this as a show stopper.'

[spectre9]

I think it's a pointless argument.

If it's about cancer so what?

People get it just by living.

Somebody isn't going to get instant cancer and die on a 3 year space mission. People don't die from instant cancer when exposed to radiation disasters such as Fukushima.

I think it's scaremongering and means nothing.

Zubrin flips it off with his "lowers risk of cancer for cigarette smokers" line and I agree with him.

[QuantumG]

What's the impact on the mission of long duration exposure to the increased GCR dose in interplanetary space?

I once asked Dr Jim Logan that and got two answers: there's no risk to the mission, and there might be serious neurological risks to the mission.

That's about the usual response I get from doctors though, even when I ask them less difficult questions.

[guckyfan]

A link to a post by joek in advanced concepts. It is a report on Fukushima but there are very interesting infos on radiation in general in a pdf document by the Los Alamos National Laboratory.

The ost:
http://forum.nasaspaceflight.com/index.php?topic=30470.msg985012#msg985012

The document:
http://www.hsdl.org/?view&did=721676

See pages starting at p. 33

There is substantial evidence that exposure to low radiation levels will actually decrease the cancer risk. In that sense radiation in LEO or Mars transfer is certainly low radiation.

[HappyMartian]

The Space show  Nov/23/2012  Guest: Dr. Marcelo Vazquez. Topic: Galactic cosmic radiation & human spaceflight in deep space.
At: http://thespaceshow.com/

[muomega0]

People keep talking about how we need a hundred tonnes of protection, but with an abundant chemical architecture with big MTV's, you're going to need hundreds of tonnes of LH2/LO2 anyways.

We all know that LH2 provides pretty good protection, but does anybody know about LO2?

I've posted this picture before, but I think short-term, this is pretty much the way to go. Of course it will require some massive Lunar ISRU!

Propellant shielding does not address GCR

In the image you provided in the post, the propellant does *not* completely surround the crew, which means very limited shielding in many directions from the particles with energies below the absorber cutoff energy.  Particles above the absorber cutoff energy and all those in the gaps pass through.  Uh-oh!

If the DSH is surrounded with 20 g/cm2 of passive shielding (~20 mT), it will protect a male for less than 300 days in deep space from GCR, based on current requirements and certainty levels.  Orion has 2-4 g/cm2.

"Radiation physics has shown that shielding should be successful for SPE.  Physics has shown how poorly shielding approaches against GCR work based on detailed understanding of nuclear reactions and secondary radiation that occur from the passage of protons and HZE nuclei in all materials including tissue"(Durante, Cucinotta)

All of the architecture studies to date completely ignore the physics of GCR shielding.

Attached is the crew habitat from the baseline Mars DRM 5, which does not surround the crew with rocks, propellant, nor an active shield.  the nuclear option of Mars DRM 5 uses drop tanks--not even considering GCR protection with propellant, which is in a ~6:1 ratio of LOX:LH2.  LOX is not the solution.

The great news is that Active systems are trading way better in terms of weight than mass absorbers and deflect all the energy levels of importance


The mass trade combines both active and passive absorbers by varying the cutoff energy versus the dose level and rates  Here is one table of dose rates

---
As pointed out, 'this is a very complex problem with a lot of unknowns.'

Yet rather than build test improve active systems to extend crew duration and gather important data at L2.... well...... 

You see, the fallback position is 6 day lunar sorties or crew living like moles...it will always be a fallback option....anyone up for the challenge?  What do the CDTs think?

If your heading to the moon, do not restate one of the flaws in the VSE.

---
Abundant Chemical

The problem with abundant chemical is the mass fraction:  one cannot use propellant for shielding and eat (burn) it, plus it does not block all the higher energy particles

----
To no surprise, comments continue to restate the misconception:

"Given that a Bigelow Habitat has better shielding than present ISS modules there should be no problem"   --- ISS is in the Earth's protective magnetic field, which blocks most GCR

"I don't believe it's a show stopper"  -  data?

"I think it's a pointless argument.  If it's about cancer so what?  Would you place your leg in a SEM to get a bone density scan?  How long and often?

"There is substantial evidence that exposure to low radiation levels will actually decrease the cancer risk. In that sense radiation in LEO or Mars transfer is certainly low radiation."  And the high energy particles that are not stopped by the mass aborbers?

IOW:  reject any evidence contradicting their beliefs or substantiation of pet programs.

----

“The more that you read, the more things you will know. The more that you learn, the more places you'll go.”

The physics of GCR radiation protection is interesting and can be addressed with active systems  and not by mass absorbers alone.  Deployment of these systems increases the flight rate, and begins a long term scientific study.  Once deployed, it can be incrementally improved to extend time in space beyond L2, a very worth goal.

One must abandon the concept of 'absorbing' the radiation by shielding for space travel:  Passive absorbers have a cutoff energy and allow higher energy particles (GCR) to pass through to the inside

Development of active systems for GCR was hindered by initial choice of passive shields and the incorrect evaluation that immense magnetic fields and volumes were required
---
While active depots have no showstoppers and could save big $ versus HLV,
unfortunately, depots and GCR mitigation hardware is not part of the plan nor budget with sequestration.

[Warren Platts]

@ muomega:

GCR's are never going to be eliminated entirely. They are something that we must learn to live with and manage. Now the ULA AChem-MTV does not provide complete encapsulation, but the idea would be to burn roughly half the propellant for the departure burn, reserving roughly half for the injection burn. As you can see from the diagram, the rotation would cause the LH2 to pool at the bottom of the LH2 tank that happens to be in the center of the vehicle. Thus the average thickness of the LH2 layer is going to be something like roughly 5 meters. That's where you want to put the crew quarters where they will be spending most of their time. Thus, I'm guessing that such an arrangement could reduce GCR exposure by 75% compared to the DRM 5 vehicle you depected because of (a) the sheilding provided by the LH2 and (b) the shortened transit time enabled by a refuelable, 10 km/sec dv, abundant chemical MTV.

[The Off Topic Sheriff]

No Off Topic Posts.

Offender logged.

[HappyMartian]

Designing Spacecraft and Mission Operations Plans to Meet Flight Crew Radiation Dose Requirements: Why is this an “Epic Challenge” for Long-Term Manned Interplanetary Flight (Hint – It’s About the Money)  By Steve Koontz   NASA/MIT Workshop    06/26/12
At: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120012405_2012011633.pdf

[douglas100]

Voted no. Agree with Warren's point that interplanetary travelers are going to have live with this background. Apart from the various vehicle shielding designs that are possible, it may be possible to mitigate any damage medically, once the level of danger is better understood.

[Khadgars]

All the more reason to have an EML-2 gateway to better understand it.  I agree that risk will always be apart of any long duration deep space mission.