Author Topic: Radiation  (Read 616885 times)

Offline smartcooky

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Re: Radiation
« Reply #210 on: March 25, 2018, 03:14:57 PM »
My point is that mission dose for a lunar transits should as a minimum be at least .47 mgy/day.

So its .47 mgy/day now is it? Earlier, you said it was 470mgy/day, and before that, .45Mgy/day

You can't even be consistent with your units of measure

You do realise that .47Mgy is a billion times greater than .47mgy ?
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline Drewid

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Re: Radiation
« Reply #211 on: March 25, 2018, 03:16:05 PM »
470 mgy/day isn't too far off 0.45 Mgy/day,

Just saying.

Is this one of those situations where capitalization can totally change the meaning of an abbreviation? Like megabit (Mb) and megabyte (MB)? I hate that. Surely it can lead to some deadly mistakes when dealing with something like radiation?

I am wondering if there a bit of case-insensitivity going on in someone typing stuff up at some point in the past.

Offline timfinch

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Re: Radiation
« Reply #212 on: March 25, 2018, 03:22:19 PM »
Cosmic Rays

Cosmic ray fluxes, consisting of completely ionized atomic nuclei originating outside the solar system and accelerated to very high energies, provided average dose rates of 1.0 millirads per hour in cislunar space** and 0.6 millirads per hour on the lunar surface. These values are expected to double at the low point in the 11-year cycle of solar-flare activity (solar minimum) because of decreased solar magnetic shielding of the central planets. The effect of high-energy cosmic rays on humans is unknown but is considered by most authorities not to be of serious concern for exposures of less than a few years. Experimental evidence of the effects of these radiations is dependent on the development of highly advanced particle accelerators or the advent of long-term manned missions outside the Earth's geomagnetic influence.

Source:  https://history.nasa.gov/SP-368/s2ch3.htm

Offline JayUtah

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Re: Radiation
« Reply #213 on: March 25, 2018, 03:31:30 PM »
Sometimes people take risks knowing they could very easily die. You did it every time you boarded a nuclear submarine.

Or a conventional submarine.  Or any warship.  Or any seagoing vessel.  It's a gradation of accepted risk.  You can't directly compare ordinary nuclear Navy operations -- where there is a much greater impetus to keep the crew safe and alive -- to exploratory missions at the far edge of capability.  The Apollo crews accepted a greater risk to do a great thing.  Expecting the mission design to guarantee safety, or even achieve a high level of safety and reliability commensurate to ordinary activities, is just unwarranted.  It's a straw man.  Heck, we live in a time today when people are chomping at the bit to sign up for a one-way suicide mission to Mars.
"Facts are stubborn things." --John Adams

Offline JayUtah

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Re: Radiation
« Reply #214 on: March 25, 2018, 03:33:22 PM »
...provided average dose rates of 1.0 millirads per hour in cislunar space** and 0.6 millirads per hour on the lunar surface.

Put on your borrowed astrophysics hat and explain to us why these two numbers should differ.
"Facts are stubborn things." --John Adams

Offline timfinch

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Re: Radiation
« Reply #215 on: March 25, 2018, 03:56:19 PM »
It seems the moon is shielded in part by the earth and to some extent by the other planets and the sun from GCR's.  As the alignment of the planets change and as solar activity wanes and ebbs so does the background radiation on the moon.

Offline JayUtah

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Re: Radiation
« Reply #216 on: March 25, 2018, 04:01:57 PM »
It seems the moon is shielded in part by the earth and to some extent by the other planets and the sun from GCR's.

Nope.  Try again.
"Facts are stubborn things." --John Adams

Offline raven

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Re: Radiation
« Reply #217 on: March 25, 2018, 04:13:19 PM »
It seems the moon is shielded in part by the earth and to some extent by the other planets and the sun from GCR's.

Nope.  Try again.
Because about half the sky is blocked by the moon itself, compared to floating through cislunar space?

Offline timfinch

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Re: Radiation
« Reply #218 on: March 25, 2018, 04:16:14 PM »
It seems the moon is shielded in part by the earth and to some extent by the other planets and the sun from GCR's.

Nope.  Try again.

Impress me as I am convinced that is the correct answer.

Offline JayUtah

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Re: Radiation
« Reply #219 on: March 25, 2018, 04:19:40 PM »
Because about half the sky is blocked by the moon itself, compared to floating through cislunar space?

Correct.  GCR is isotropic, meaning it flies equally in all directions.  Floating in free space, you're bombarded by GCR from all directions.  Standing on the lunar surface, the bulk of the Moon itself blocks GCR from about half the sphere surrounding you -- the part of that sphere that's underneath you.  In a generalized exposure model, this is called the "configuration factor."  It's essentially a function of intensity over the domain of the surrounding sphere.  It works for many different kinds of radiation, and also can be parameterized for anisotropic sources.
"Facts are stubborn things." --John Adams

Offline smartcooky

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Re: Radiation
« Reply #220 on: March 25, 2018, 04:20:15 PM »
Cosmic Rays

Cosmic ray fluxes, consisting of completely ionized atomic nuclei originating outside the solar system and accelerated to very high energies, provided average dose rates of 1.0 millirads per hour in cislunar space** and 0.6 millirads per hour on the lunar surface. These values are expected to double at the low point in the 11-year cycle of solar-flare activity (solar minimum) because of decreased solar magnetic shielding of the central planets. The effect of high-energy cosmic rays on humans is unknown but is considered by most authorities not to be of serious concern for exposures of less than a few years. Experimental evidence of the effects of these radiations is dependent on the development of highly advanced particle accelerators or the advent of long-term manned missions outside the Earth's geomagnetic influence.

Source:  https://history.nasa.gov/SP-368/s2ch3.htm

This is not the whole story.

Again, you show that you don't understand the physics, and in particular you don't understand why a particular measured dose to an UNPROTECTED body differs from that which might be suffered by a shielded body


The cosmic ray spectrum clearly shows that the number of cosmic rays (the cosmic ray flux) detected drops off dramatically as we go to higher energies. The spectrum exhibits a ‘knee’ and an ‘ankle’, both of which deviate from the standard exponential decline (blue line).

The range of energies encompassed by cosmic rays is truly enormous, starting at about 107 eV and reaching 1020 eV for the most energetic cosmic ray ever detected. By plotting this range of energies against the number of cosmic rays detected at each energy we generate a cosmic ray spectrum which clearly shows that the number of cosmic rays drop off dramatically as we go to higher energies.

Roughly speaking, for every 10% increase in energy beyond 109 eV, the number of cosmic rays per unit area falls by a factor of 1,000. However, if we look at the spectrum more closely we can see a knee at ~ 1015 eV and an ankle at ~ 1018 eV.


http://astronomy.swin.edu.au/cosmos/C/Cosmic+Ray+Energies

Let me try to put this is layman's terms for you., since you seem to not understand

Imagine that you have to go into an area (in order to perform some task) where there are 10,000 people shooting with shotguns from some distance; not close enough to blow a hole in you, but far enough away so that you will be constantly showered with pellets. However, in among those shooters are a some people armed with .22 cal rifles each firing one round per minute, a couple with a 7.62 mm rifle who will shoot once every 10 minutes, and finally a shooter armed with a 20mm cannon, who will be firing once per hour.. None of these shooters are actually aiming at you, but they are shooting in the general direction of where you are going to be.

What these shooters will be firing at you represents a spectrum of missiles.... at the less dangerous end of the spectrum are the shotgun pellets, huge numbers and frequency, and at the more dangerous end, the 20mm cannon;  far more dangerous but far less frequent.

If you go in unprotected, the shotgun pellets will do you serious damage
If you wear minimal protection, say, heavy leather coveralls, they will protect you from the shotgun pellets but not from anything else
If you wear a lightweight bullet proof vest, it will protect you from the pellets and the 22 cal.
If you go for full Kevlar body armour, that will protect you from everything except the 20mm cannon.
If you wear a suit made of one inch armour plate, it will protect you from the 20mm cannon.

You may choose the full protection, but that is going to compromise your ability to carry out whatever task you need to carry out.

The Apollo missions (and indeed all space missions) are designed and built such that shielding is incorporated into design. This protects the spacecraft (and its occupants) from the vast majority of the radiation (the shotgun pellets, and possibly, the .22 cal). The exposure to the higher end particles (the 7.62 and the 20mm cannon) is the risk they take, but even then, there are procedures put in place to use the existing shielding to help with protection, such as, in the case of a CME, orienting the spacecraft to put the maximum amount of its mass between the crew and the Sun. (not sure of the was a plan on Apollo, I'll leave other more knowledgeable people to answer that)       

 

If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline JayUtah

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Re: Radiation
« Reply #221 on: March 25, 2018, 04:23:15 PM »
Impress me as I am convinced that is the correct answer.

Then you've convinced yourself of a wrong thing.  Someone else already got the right answer.  This is a pattern with you.  You convince yourself of a certain thing, and not even wild horses can change your mind.  They can't even persuade you to look elsewhere, beyond the thing you've already decided.  You claim you're open to having your mind changed, but we can observe in this debate that your claim isn't true.

Now given that the bulk of the Moon, when you're standing on its surface, shields you from a little less than half of GCR you would receive while not in the proximity of a large absorptive body, what would be the expected GCR exposure of a spacecraft orbiting 90 nautical miles above the lunar surface?  Can you estimate the configuration factor for that?
« Last Edit: March 25, 2018, 04:25:24 PM by JayUtah »
"Facts are stubborn things." --John Adams

Offline timfinch

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Re: Radiation
« Reply #222 on: March 25, 2018, 04:24:09 PM »
Measurements taken by NASA's Lunar Reconnaissance Orbiter show that the number of high energy particles streaming in from space did not tail off closer to the moon's surface, as would be expected with the body of the moon blocking half the sky.

Rather, the cosmic rays created a secondary — and potentially more dangerous -- shower by blasting particles in the lunar soil which then become radioactive.

"The moon is a source of radiation," said Boston University researcher Harlan Spence, the lead scientist for LRO's cosmic ray telescope. "This was a bit unexpected."

While the moon blocks galactic cosmic rays to some extent, the hazards posed by the secondary radiation showers counter the shielding effects, Spence said at a press conference at the American Geophysical Union meeting in San Francisco this week.

Overall, future lunar travelers face a radiation dose 30 percent to 40 percent higher than originally expected, Spence said.

Source:  http://www.nbcnews.com/id/34470642/ns/technology_and_science-space/t/moon-poses-radiation-risk-future-travelers/#.WrgEpOjwaUk


Offline timfinch

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Re: Radiation
« Reply #223 on: March 25, 2018, 04:28:39 PM »
That didn't hurt did it?  I did not intend that it should...

Offline JayUtah

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Re: Radiation
« Reply #224 on: March 25, 2018, 04:29:47 PM »
Measurements taken by NASA's Lunar Reconnaissance Orbiter show that the number of high energy particles streaming in from space did not tail off closer to the moon's surface, as would be expected with the body of the moon blocking half the sky.

"High energy particles" is not the same as GCR.

Quote
Rather, the cosmic rays created a secondary — and potentially more dangerous -- shower by blasting particles in the lunar soil which then become radioactive.

Secondary radiation is not universally "more dangerous."  It is inevitably of lower energy than the primary radiation, although possibly of higher flux.  Lower energy means it's more susceptible to conventional forms of attenuation than GCR.

Quote
While the moon blocks galactic cosmic rays to some extent, the hazards posed by the secondary radiation showers counter the shielding effects...

But that doesn't tell the whole story.  Converting GCR to a different species of radiation rather mucks up an argument based solely on GCR exposure.
"Facts are stubborn things." --John Adams