Author Topic: NASA & Georgetown University study on Cosmic Ray dangers to space travelers  (Read 5873 times)

Offline Dalhousie

  • Senior Member
  • *****
  • Posts: 2210
  • Liked: 330
  • Likes Given: 404
There is a whole cottage industry involving this form of study.  They feature giving massive doses (many times what astronauts would experience) in a very short period of time (minutes as opposed to years).  They typically use the wrong units (Grays rather than Sieverts).  They generally unrealistic Mars mission radiation doses.  The results are always of the "we exposed mice to massive radiation doses over short periods of time surprise!  They don't do very well.   

I struggle to see how this work can get funded, pass ethical or peer review.  It's relevance and usefulness appears zero.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline envy887

  • Senior Member
  • *****
  • Posts: 5180
  • Liked: 3073
  • Likes Given: 1547
The full paper is here: http://www.pnas.org/content/pnas/early/2018/09/26/1807522115.full.pdf

they hit mice with 10 Sv of heavy ions... This compares unfavorably with the estimated 1 Sv total dose (mostly from protons, not heavy ions) for a 860 day Mars mission...

Looking at their reasoning and method:

Quote
While protons are the major component of space radiation, energetic heavy ions such as 56Fe, 28Si, and 12C contribute significantly toward the dose equivalent, and ∼30% of astronauts’ cells are predicted to be hit by heavy ions during a round trip to Mars...

Since the estimated radiation dose for a 1,000-d Mars mission is about 0.42 Gy (21), with an estimate of an 860-d Mars mission dose equivalent of ∼1.01 Sv (22) so doses of 0.5 Gy or less are more relevant, we have used 0.5 Gy to study IEC migration, which is important for intestinal homeostasis.

Wild-type mice... were irradiated (dose: 0.5 Gy) using a simulated space radiation source at the NASA Space Radiation Laboratory (NSRL), Brookhaven National Laboratory for iron (56Fe; energy: 1,000 MeV per nucleon; LET: 148 keV/μm) irradiation, and a 137Cs source was used for γ-ray (LET: 0.8 keV/μm) whole-body irradiation of mice.

How did you calculate 10x overdose?

0.5 Gy of 56Fe is 10 Sv, already more than 10x the estimated biological effective dose of ~1 Sv for a 860-day Mars mission.

Factor in shielding, dose rate, dose mix, etc. and this has no basis in reality for an actual Mars mission.

Offline Dalhousie

  • Senior Member
  • *****
  • Posts: 2210
  • Liked: 330
  • Likes Given: 404
The full paper is here: http://www.pnas.org/content/pnas/early/2018/09/26/1807522115.full.pdf

they hit mice with 10 Sv of heavy ions... This compares unfavorably with the estimated 1 Sv total dose (mostly from protons, not heavy ions) for a 860 day Mars mission...

Looking at their reasoning and method:

Quote
While protons are the major component of space radiation, energetic heavy ions such as 56Fe, 28Si, and 12C contribute significantly toward the dose equivalent, and ∼30% of astronauts’ cells are predicted to be hit by heavy ions during a round trip to Mars...

Since the estimated radiation dose for a 1,000-d Mars mission is about 0.42 Gy (21), with an estimate of an 860-d Mars mission dose equivalent of ∼1.01 Sv (22) so doses of 0.5 Gy or less are more relevant, we have used 0.5 Gy to study IEC migration, which is important for intestinal homeostasis.

Wild-type mice... were irradiated (dose: 0.5 Gy) using a simulated space radiation source at the NASA Space Radiation Laboratory (NSRL), Brookhaven National Laboratory for iron (56Fe; energy: 1,000 MeV per nucleon; LET: 148 keV/μm) irradiation, and a 137Cs source was used for γ-ray (LET: 0.8 keV/μm) whole-body irradiation of mice.

How did you calculate 10x overdose?

0.5 Gy of 56Fe is 10 Sv, already more than 10x the estimated biological effective dose of ~1 Sv for a 860-day Mars mission.

Factor in shielding, dose rate, dose mix, etc. and this has no basis in reality for an actual Mars mission.

Even that 1 Sv dose is based on  wrong assumptions.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Online Slarty1080

  • Full Member
  • ****
  • Posts: 711
  • UK
  • Liked: 320
  • Likes Given: 133
Has anyone ever actualy tried to simulate the likely radiation environment of an actual Mars mission?
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline guckyfan

  • Senior Member
  • *****
  • Posts: 6871
  • Germany
  • Liked: 1861
  • Likes Given: 1910
Has anyone ever actualy tried to simulate the likely radiation environment of an actual Mars mission?

Why would they? Not scary enough.

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #25 on: 11/28/2018 10:41 pm »
The results from experimenting on mice with heavy ion galactic cosmic rays (GCR) aren't promising, their GI tracts took a heavy toll.  Note, this is not electromagnetic radiation, but atomic nuclei traveling very fast:

https://www.space.com/42018-deep-space-travel-damage-astronauts-gut.html

See also: 

https://www.extremetech.com/extreme/278004-deep-space-exploration-could-permanently-damage-human-gi-tracts
https://phys.org/news/2018-10-animal-deep-space-significantly-gi.html
http://blogs.discovermagazine.com/d-brief/2018/10/01/deep-space-could-seriously-damage-astronaut-gi-tracts-a-new-study-finds/#.W_8k3zCIZaQ
https://www.sciencedaily.com/releases/2018/10/181002102727.htm

The fact is that before we send people to Mars on a ship that can't direct-abort, someone should do a near-earth mission to establish with certainty the actual health impacts of human travel outside of the earth's magnetosphere for 6+ months.
« Last Edit: 11/28/2018 10:42 pm by DaveJes1979 »

Online ncb1397

  • Full Member
  • ****
  • Posts: 1299
  • Liked: 561
  • Likes Given: 6

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #27 on: 11/28/2018 10:58 pm »
It is hard to read in to such a small sample size as the Apollo astronauts, and their deep space exposure was only on the order of a few days.  That simply isn't enough time.  It could simply be that some of them ate more carbs than others!

I've also heard that the Apollo missions were timed for both low solar activity and for periods where earth's magnetosphere provided some protection, although I can't find a source to confirm this.
« Last Edit: 11/28/2018 11:12 pm by DaveJes1979 »

Online ncb1397

  • Full Member
  • ****
  • Posts: 1299
  • Liked: 561
  • Likes Given: 6
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #28 on: 11/28/2018 11:17 pm »
Hard to read in to such a small sample size, and their deep space exposure was only on the order of a few days.  That simply isn't enough time.  It could simply be that some of them ate more carbs than others!

If you have a bigger sample of people exposed to a deep space environment, let me know.

Put together this list of those who traveled to "deep space" and have since died with cause noted if under 80.

John Young - 87
Gene Cernan - 82
Neil Armstrong - 82
Pete Conrad - 69 (motorcycle accident...presumably not Apollo related unless related to brain degeneration)
Richard Gordon - 88
Alan Bean - 86
Jack Swigert - 51 (cancer)
Alan Shepard - 74 (leukemia)
Stuart Roosa - 61 (pancreatitis
Edgar Mitchell - 85
James Irwin - 61 (heart attack)
Ronald Evans -56(heart attack)

average life expectancy -  73.5 years
average male life expectancy in U.S. - 76.5 years

Apparently, a trip measured in days/weeks isn't a huge problem in terms of living a roughly normal length life afterwards.

edit:and just for fun, those that have made a trip into deep space twice:
John Young - 87
Gene Cernan - 82
average: 84.5
« Last Edit: 11/28/2018 11:28 pm by ncb1397 »

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3851
  • Sunnyvale, CA
  • Liked: 2559
  • Likes Given: 3263
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #29 on: 11/28/2018 11:28 pm »
This is an old story, and it was already discussed in these forums when the story first came out.

The bottom line conclusion was that the study isn't very convincing.  It's just too different from reality to be able to draw any conclusions about effects from space travel and/or Mars life from this study.

Meanwhile, numerous other studies have provided evidence that there is some small amount of increased risk of death from the dosage Mars travelers would get, but not a huge amount.  The other risks of space travel -- the space ship blowing up, the airlock leaking, etc -- are likely far higher than the risks from radiation.

The exception is is there's a coronal mass ejection from the sun that happens to be directed right at the space travelers.  That can be fatal.  For that, a storm shelter is needed to avoid serious radiation injury.

Offline eric z

  • Full Member
  • ***
  • Posts: 303
  • Liked: 211
  • Likes Given: 556
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #30 on: 11/28/2018 11:28 pm »
 There is an obvious answer to this problem: Get there a helluva lot faster!

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3851
  • Sunnyvale, CA
  • Liked: 2559
  • Likes Given: 3263
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #31 on: 11/28/2018 11:31 pm »
It's important to note that on Earth we are not immune to Galactic Cosmic Rays.  Some portion of them hit the surface of the Earth.  Air crews on airliners have significantly higher dosage of such GCR strikes than the general population.  So we have a lot of good data to go on about how much GCRs affect human health.

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #32 on: 11/28/2018 11:42 pm »
This is an old story, and it was already discussed in these forums when the story first came out.

It is not old, it is from October.

Quote
Meanwhile, numerous other studies have provided evidence that there is some small amount of increased risk of death from the dosage Mars travelers would get, but not a huge amount.  The other risks of space travel -- the space ship blowing up, the airlock leaking, etc -- are likely far higher than the risks from radiation.

Most of these focus on electromagnetic radiation or protons, but not the heavy ions that exist in our solar system independent of solar activity.

Airliners and astronauts in LEO are well within earth's magnetosphere, so their GCR doses are quite small.

It would be unethical to send people to Mars until a near-earth research mission is conducted on humans- or at least some primates.  It might be difficult to find volunteers to be the guinea pigs.

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #33 on: 11/29/2018 12:15 am »
There is an obvious answer to this problem: Get there a helluva lot faster!

Sadly, not practical with chemical rockets.  As Robert Zubrin points out, you really don't want to go any faster than a 6 month transit to Mars anyway, or you lose your free return trajectory.

Also, your worries have not ended when you get to Mars, because Mars has no magnetosphere along with a very thin atmosphere.
« Last Edit: 11/29/2018 12:16 am by DaveJes1979 »

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3851
  • Sunnyvale, CA
  • Liked: 2559
  • Likes Given: 3263
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #34 on: 11/29/2018 12:32 am »
This is an old story, and it was already discussed in these forums when the story first came out.

It is not old, it is from October.

Yeah, the press release was October 1.  Seven weeks ago.  Which is old, in the context I used the term -- old enough that it was discussed here and the discussion ended weeks ago.

Quote
Meanwhile, numerous other studies have provided evidence that there is some small amount of increased risk of death from the dosage Mars travelers would get, but not a huge amount.  The other risks of space travel -- the space ship blowing up, the airlock leaking, etc -- are likely far higher than the risks from radiation.

Most of these focus on electromagnetic radiation or protons, but not the heavy ions that exist in our solar system independent of solar activity.

No, I'm talking specifically about GCRs.  There have been studies of their effects, and those are the studies I'm talking about.

Airliners and astronauts in LEO are well within earth's magnetosphere, so their GCR doses are quite small.

It doesn't matter if they're small.  They're an order of magnitude greater at the altitude airliners use than at the surface of the Earth, which is enough to be able to detect the health effects, if there are any.

It would be unethical to send people to Mars until a near-earth research mission is conducted on humans- or at least some primates.  It might be difficult to find volunteers to be the guinea pigs.

No, not unethical if they volunteer.  And plenty of people are willing to volunteer.

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3851
  • Sunnyvale, CA
  • Liked: 2559
  • Likes Given: 3263
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #35 on: 11/29/2018 12:35 am »
Here's the original thread on this study:

https://forum.nasaspaceflight.com/index.php?topic=46477.0

Note that the discussion started October 1, the day the press release came out.

Mods: can we merge this thread with the original one?

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #36 on: 11/29/2018 12:43 am »
Quote
No, I'm talking specifically about GCRs.  There have been studies of their effects, and those are the studies I'm talking about.

Unless those studies also irradiated mammals with iron nuclei and examined effects on the GI tract it is hard to imagine how they would overturn these results.  This research was done because it, in fact, has not been done before.

Quote
It doesn't matter if they're small.  They're an order of magnitude greater at the altitude airliners use than at the surface of the Earth, which is enough to be able to detect the health effects, if there are any.

This is simply false.  You can't simply extrapolate across environments that are orders of magnitude difference in dosage.

Quote
No, not unethical if they volunteer.  And plenty of people are willing to volunteer.

I'm not willing to go as far as to say that the voluntarism of the customer is ethically exculpatory for the carrier.  The carrier is responsible to do some due diligence research.

Offline envy887

  • Senior Member
  • *****
  • Posts: 5180
  • Liked: 3073
  • Likes Given: 1547
Re: Galactic Cosmic Rays - A Deep Space Travel Show-Stopper?
« Reply #37 on: 11/29/2018 12:50 am »
As Robert Zubrin points out, you really don't want to go any faster than a 6 month transit to Mars anyway, or you lose your free return trajectory.

There aren't many situations where a free return from Mars is useful. If you aren't able to either land or perform a propulsive Earth injection at Mars, you also won't be able to land or propulsively capture when you get back to Earth.

In most cases, if you have an emergency post-TMI, the fastest way to get help will be to go to Mars, not take an extra 8-month trip to swing back to Earth.

Offline DaveJes1979

  • Full Member
  • **
  • Posts: 254
  • Wrightwood, CA
  • Liked: 52
  • Likes Given: 3
It wouldn't be all that hard to send a Starliner or Dragon with a small habitat/mission module to a Lagrange point outside of earth's magnetosphere for 6 months or so with a handful of astronauts. If anyone's health declines too rapidly, they can come home anytime.

Forget the ethics, it makes business sense to retire this risk before spending billions developing and building a Mars spacecraft.

Offline freddo411

  • Full Member
  • *
  • Posts: 143
  • Liked: 142
  • Likes Given: 416
Are moderate levels of radiation problematic?  Maybe not so much.

Here's one example from Wikipedia:
https://en.wikipedia.org/wiki/Radiation_hormesis#Effects_of_no_radiation

Quote
Very high natural background gamma radiation cancer rates at Kerala, India
Kerala's monazite sand (containing a third of the world's economically recoverable reserves of radioactive thorium) emits about 8 micro Sieverts per hour of gamma radiation, 80 times the dose rate equivalent in London, but a decade long study of 69,985 residents published in Health Physics in 2009: "showed no excess cancer risk from exposure to terrestrial gamma radiation. The excess relative risk of cancer excluding leukemia was estimated to be -0.13 Gy_1 (95% CI: -0.58, 0.46)", indicating no statistically significant positive or negative relationship between background radiation levels and cancer risk in this sample.[45]


Tags: