Radiation

[bknight]

If any of the group has a personal contact in NASA, It would be beneficial to have access to the MSL/RAD values, especially during time from launch to 238000 miles.

The report he reference an AVERAGE number and I don't know if there may be a difference as distance from the Earth/Moon vicinity--distance because I don't know if it traveled close to the Moon.

[smartcooky]

Back in 1986/87, on the Giotto Spacecraft that rendezvoused with Comet Halley, the designers used a shield to protect the spacecraft (during its approach) from particles of matter being shed by the comet as its ices sublimated. IIRC, it was essentially a double layered shield, the idea being that the outer layer would stop most of the smaller particles, slightly larger particles that might penetrate outer layer would either vaporise, or lose most of their energy, and would then not penetrate the inner shield.

I wonder if a similar arrangement would help (or hinder) in the the case of GCR? Would multi-level thinner shielding be any more or less effective than a thicker shield? Could it help with mitigation of secondary radiation, or would it potentially make it worse?

It wouldn't help.  You're thinking of laminated armor that uses alternate layers of dense and sparse material.  It's actually how the micrometeoroid shield on the Apollo LM was designed, and to a lesser extent the space suits.  It works for ballistic particles where "particle" here means dust, not some exotic thing ending in -on.  The theory behind laminated armor is that the collisions with the hard outer layers fragment (in a mechanical, not subatomic, way) both the injectile and the armor.  The soft inner layers (if they aren't just empty space) attenuate the velocity, but what they really do is provide distance for the collision products to fan out and vent their energy on the next hard layer across a broader surface area.  You don't really need that allowance to shield against ions.  So you fall back to the general rule that density is king:  you want collision products from GCR to encounter another atom within the shielding as soon as possible.  I recall the ANR reference for the LM had a good drawing of how the micrometeoroid shield worked.

Ok, thanks Jay. I will keep in mind this phrase from your answer

"density is king:  you want collision products from GCR to encounter another atom within the shielding as soon as possible."

I guess all I can do is to quote Thomas Huxley

"The great tragedy of science - the slaying of a beautiful hypothesis by an ugly fact"

[Allan F]

Sorry I'm late to the party. I'm working my way though this, and is currently on p.27. Eye-watering stuff from you-know-who.

I have a question: As I understand it, secondary radiation from particle impacts on the spacecraft (or any other matter) is usually photons (bremsstrahlung), but there can be created other particles also.

As I understand it, the energy of those photons are organized in discrete bands, depending on which orbitals the affected electron is excited from and falls back to. This energy is different for different materials. Heavier nuclei have more options for excited states - because they have more electrons and use more orbitals.

Is there a table which shows the energy of these x-rays organized by material/atomic number?

Would be very interesting to compare those energies to the energy of x-rays used in commercial/medical applications. Commercial x-ray machines produce photons with an energy insufficient to penetrate most metals - like iron/steel. If they did penetrate, they would be unable to detect metal objects in the body.

If a bremsstrahlung event involving aluminium had only 10% of the energy of medical x-rays, it would be totally unable to penetrate steel. Carbon, Oxygen and Hydrogen are even lighter, and should provide even less energetic x-rays.

Am I totally lost here or is there som validity to my idea?

[Bryanpoprobson]

The CM hull had a dosimeter in it didn't it? Were the results from those ever published?

I used the data from Apollo 12 some years back in an argument with your old friend Adrian, but I can’t remember on which forum it was on, or where I linked the data.

[MBDK]

Sorry I'm late to the party. I'm working my way though this, and is currently on p.27. Eye-watering stuff from you-know-who.

I have a question: As I understand it, secondary radiation from particle impacts on the spacecraft (or any other matter) is usually photons (bremsstrahlung), but there can be created other particles also.

As I understand it, the energy of those photons are organized in discrete bands, depending on which orbitals the affected electron is excited from and falls back to. This energy is different for different materials. Heavier nuclei have more options for excited states - because they have more electrons and use more orbitals.

Is there a table which shows the energy of these x-rays organized by material/atomic number?

Would be very interesting to compare those energies to the energy of x-rays used in commercial/medical applications. Commercial x-ray machines produce photons with an energy insufficient to penetrate most metals - like iron/steel. If they did penetrate, they would be unable to detect metal objects in the body.

If a bremsstrahlung event involving aluminium had only 10% of the energy of medical x-rays, it would be totally unable to penetrate steel. Carbon, Oxygen and Hydrogen are even lighter, and should provide even less energetic x-rays.

Am I totally lost here or is there som validity to my idea?

The bremsstrahlung phenomenon occurs over a continuous distribution path as the electron is slowed as illustrated here for molybdenum (closer interaction to the nucleus results in higher x-ray energy):
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Each element will have its unique distribution spectrum.

It is the ejection of K-shell electrons that give rise to characteristic x-rays for which there is this graph (Moseley Plot):
http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/moseley.html

Here is a good description of how x-ray machines work (not all that much different, just more controllable regarding overall energy of produced x-rays):
http://www.austincc.edu/rudygarz/xRayMachine/xRayMachine.pdf

So, basically the bremsstrahlung radiation is dependent on two major factors -
1.  The energy of the ionizing photon/particle and its distance from the nucleus (wide range of x-ray energies).
2.  The composition of the affected material (characteristic x-rays).

I hope this helps somewhat.

Note:  Edited because I screwed up.

[Allan F]

As expected. The subject is much more complicated than I initially thought. Will take some time to read and digest.

[Count Zero]

"Why waste time learning, when ignorance is instantaneous?"  -- Hobbes

[Allan F]

"Why work hard to succeed, when you can fail with no effort at all?" - Me.

[Obviousman]

"Anything above a pass is wasted effort"

"If you're not cheating, you're not trying"

Navy sayings

[Abaddon]

Dammit. In behind the flounce. Second time this guy has done that to me.

[molesworth]

Dammit. In behind the flounce. Second time this guy has done that to me.

Ditto 

I did want to ask him whether he though all spaceflight beyond LEO was faked, or if there's some secret cabal of spacecraft engineers who hold the secret truth about the radiation levels in space.

We've had spacecraft operating all the way from Mercury out to beyond Pluto, and currently have quite a number actively operating well outside the VAB region.  If the data used in designing these craft was drastically incorrect, there would be many more failures.  And despite the usual HB's focus on NASA, there are multiple countries launching missions, not to mention things like the Lunar X-Prize where independent groups were encouraged to get their own landers to the Moon.

It's just not possible that the radiation data we use for spacecraft design, or for manned mission planning, is wrong...

[JayUtah]

Some GPS satellites are in the Van Allen belts and spend their entire operational lifetimes there.

Tim's claim is a twist on the "searing radiation hell" argument.  He seems to have arbitrarily considered one set of measurements to be an incontrovertible baseline against which all other measurements can be compared.  He then seems to have compared a set of Apollo measurements against it and concluded it could not be high enough to represent an interplanetary mission based solely on comparison to the arbitrary baseline.  He hasn't considered any reasonable sources of error.  It's not a matter, in his mind, of "standard" models of radiation being misleading or falsified.  In fact, he relies on the notion that all the data he's looking at are real.  The matter is, frankly, in his mind where he keeps a very simplified, very rudimentary model of the space radiation environment, and any departure from those expectations immediately raises the claim of hoax.

[inconceivable]

The one thing that gets me about the radiation question is about the space suits.  They offered layers of protection for the body.  But the most critical part of a human is the brain and the helmet provided the least protection to the astronaut.  Lab tests on mice have concluded that mice lost cognitive skills with an equivalent of 10 day exposure to charged particles 16O, Ti48.  Is this why the astronauts stay in LEO?  LEO offers protection from alpha radiation, high speed protons, electrons, and high energy helium atoms.  How much protection can the glass in the helmet provide other than UV protection?  If Apollo missions helmets offered this much protection, shouldn't they make spacecrafts out of glass for deep space missions? er30.3

[JayUtah]

Lab tests on mice have concluded that mice lost cognitive skills with an equivalent of 10 day exposure to charged particles 16O, Ti48.

And the spectrum of these in space is ... ?

[Allan F]

The one thing that gets me about the radiation question is about the space suits.  They offered layers of protection for the body.  But the most critical part of a human is the brain and the helmet provided the least protection to the astronaut.  Lab tests on mice have concluded that mice lost cognitive skills with an equivalent of 10 day exposure to charged particles 16O, Ti48.  Is this why the astronauts stay in LEO?  LEO offers protection from alpha radiation, high speed protons, electrons, and high energy helium atoms.  How much protection can the glass in the helmet provide other than UV protection?  If Apollo missions helmets offered this much protection, shouldn't they make spacecrafts out of glass for deep space missions? er30.3

Glass?