Poll

Are GCR's going to be a showstopper for long duration BEO missions?

Yes
11 (6.2%)
No
127 (71.3%)
It depends
40 (22.5%)

Total Members Voted: 178


Author Topic: Galactic Cosmic Rays (GCR) - Showstopper or What?  (Read 126206 times)

Offline Dalhousie

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #300 on: 11/16/2015 10:21 pm »

Also calculating with sieverts is not really valid IMO.

You have any evidence to support this opinion?
Apologies in advance for any lack of civility - it's unintended

Offline Dalhousie

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #301 on: 11/16/2015 10:25 pm »
The RAD instrument on MSL measured  cosmic ray doses of  1.84 +/- 0.33 mSv/day behind moderate (~8 g/cm2) shielding.  So for a 200 day transit that's 368 mS, for a 400 day round trip (no landing) 736 mS.
Apologies in advance for any lack of civility - it's unintended

Offline Robotbeat

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #302 on: 11/17/2015 02:58 am »
The RAD instrument on MSL measured  cosmic ray doses of  1.84 +/- 0.33 mSv/day behind moderate (~8 g/cm2) shielding.  So for a 200 day transit that's 368 mS, for a 400 day round trip (no landing) 736 mS.
Remember that was aluminum shielding. For GCRs, aluminum sometimes does more harm than good. (Although in this case, I'm pretty sure that the aluminum shielding did slightly reduce the dose in transit vs free-space).
« Last Edit: 11/17/2015 02:59 am by Robotbeat »
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline guckyfan

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #303 on: 11/17/2015 03:47 am »

Also calculating with sieverts is not really valid IMO.

You have any evidence to support this opinion?

Sievert is a value given as a biologic equivalent radiation effect. It is invented to make the effects of different types of radiation comparable. So the response of the biologic system, in this case called a human, is in the mix. Presently we don't even know how exactly the human body responses to GCR, so any Sievert value is based on assumptions. Actually the response of the body for any kind of long term low level radiation is not well understood. What we have is the effect of Hiroshima and Nagasaki radiation. This is what our assumptions are based on, and that is not a long term low level environment.

Everything is based on the linear no threshold assumption which is itself very much in doubt given new research in Chernobyl.

Offline Dalhousie

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #304 on: 11/17/2015 04:03 am »

Also calculating with sieverts is not really valid IMO.

You have any evidence to support this opinion?

Sievert is a value given as a biologic equivalent radiation effect. It is invented to make the effects of different types of radiation comparable. So the response of the biologic system, in this case called a human, is in the mix. Presently we don't even know how exactly the human body responses to GCR, so any Sievert value is based on assumptions. Actually the response of the body for any kind of long term low level radiation is not well understood. What we have is the effect of Hiroshima and Nagasaki radiation. This is what our assumptions are based on, and that is not a long term low level environment.

Everything is based on the linear no threshold assumption which is itself very much in doubt given new research in Chernobyl.

We do have cosmic ray data on Earth and it is been the subject of many studies.

Low level radiation studies are not just based on atomic bomb survivors, we have more than a century of radiation worker data medical and industrial  X-rays to call on.

You are right about the non-linearity of low doses, but they do provide a conservative margin.
Apologies in advance for any lack of civility - it's unintended

Offline guckyfan

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #305 on: 11/17/2015 07:26 pm »
We do have cosmic ray data on Earth and it is been the subject of many studies.

How would that be done with constant background radiation? Have they done studies with flight crews and inhabitants of the High Andes?

Low level radiation studies are not just based on atomic bomb survivors, we have more than a century of radiation worker data medical and industrial  X-rays to call on.

Which are all data on short time overdoses. Radiation doses in normal operations would always be very low. Have relatively high doses in a few areas in the world shown increased radiation risk, like in the uranium mining area in Germany or that Town in Iran?

You are right about the non-linearity of low doses, but they do provide a conservative margin.

If arbitrary margin like this leads to the conclusion that Mars flights are too dangerous and people on the surface of Mars need extreme shielding which severely limits design possibilities then it is not a good thing. I really want studies performed on Mars but agree until they are done, caution is a good thing. I really don't want studies that still contain large error possibilities like substituting constant low radiation with radiation pulses.

Offline Dalhousie

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Re: Galactic Cosmic Rays (GCR) - Showstopper or What?
« Reply #306 on: 11/17/2015 09:28 pm »
We do have cosmic ray data on Earth and it is been the subject of many studies.

How would that be done with constant background radiation? Have they done studies with flight crews and inhabitants of the High Andes?

Low level radiation studies are not just based on atomic bomb survivors, we have more than a century of radiation worker data medical and industrial  X-rays to call on.

Which are all data on short time overdoses. Radiation doses in normal operations would always be very low. Have relatively high doses in a few areas in the world shown increased radiation risk, like in the uranium mining area in Germany or that Town in Iran?

Ramsar in Iran shows no effects.  Not sure what Germany mine you mean, but areas of locally very high background radiation in France from natural uranium occurrence do show negative effects for plant living on top of it.  Because the radiation levels are variable, it is hard to extrapolate these spots highs to the whole environment.  Which is why there is reluctance to include the results from these areas in the models.

You are right about the non-linearity of low doses, but they do provide a conservative margin.

If arbitrary margin like this leads to the conclusion that Mars flights are too dangerous and people on the surface of Mars need extreme shielding which severely limits design possibilities then it is not a good thing. I really want studies performed on Mars but agree until they are done, caution is a good thing. I really don't want studies that still contain large error possibilities like substituting constant low radiation with radiation pulses.
[/quote]

The models are not arbitrary.  What is arbitrary is deciding the limits for space missions, 1 Sv, or a 3% lifelife increase in cancer mortality.  Why not 0.5 Sv, or 1.5, why not 2%, or 4%?

One reason why the US accepts a lower level than the rest of the spacefaring world is that people there are worried about the uncertainty in the risk. 
Apologies in advance for any lack of civility - it's unintended

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