Shields up! Shields up! ASTRONAUTS flying to MARS will arrive BRAIN DAMAGED, boffins claim A NASA-funded study into the effects of long-term space travel has a troubling conclusion: astronauts going to Mars could arrive with brain damage. The research, conducted by the University of California Irvine and published in the Science Advances journal, involved bombarding mice with ionised oxygen and titanium nuclei for …
Having very quickly eyeballed the paper, which is freely accessible, I don't think that's actually what they did.
They exposed mice to a dose of ionising radiation (they say a low dose - as I understand it, intended to be equivalent to space-flight), then six weeks later, found this impaired performance.
From the paper:
//The persistent reduction in the ability of irradiated animals to react to novelty after such low-dose exposures suggests that space-relevant fluences of HZE particles can elicit long-term cognitive decrements in learning and memory.//
Well... the issue is that they gave them the dose all at once, and a quick check around the numbers makes me think it's a lot higher than anyone would expect to be exposed to in space.
Skylab 4 was an 84 day mission. The astronauts were exposed to about 17 rems cumulative over that time, or 0.17 Grays. That's for 84 days, or a rate of 0.0000082 Gy/minute (Assuming I can indeed count and am not ballsing up the conversion between rems and Grays, and I'd appreciate if someone checked the maths). This test exposed the mice to between 0.5 and 1 Gy per minute for a short but sustained period. If the skylab astronauts had suffered that sort of radiation absorption for the entire mission then they would have take on board 120,000 Grays of radiation. They'd be dead. In fact they'd probably have cooked right through.
This experiment suffers the same issue that a lot of mouse experiments suffer - they expose the mice to an unrealistically high dose of whatever is being tested and assume a linear relationship between dose and effect, and assume that a single large dose is equivalent to a chronic low dose. They don't examine whether there's an effect from low-level cumulative radiation exposure. They just blast them in the brain with what would be a fatal dose of radiation if it was sustained for more than a minute, and then act surprised when they turn out brain damaged.
Thing is, even assuming there is a cumulative effect from radiation, you have to account for the body's ability to absorb and adapt to radiation over a sustained period. If you expose someone to a cumulatively high dose of radiation over a period of a few years they will likely not suffer any effects from it, beyond an increased risk of particular cancers. Expose them to the same high dose of radiation over a second and their organs will melt and dribble out of their behind.
tl;dr the experiment assumes a linear relationship between dose and effect. The experiment posited an unrealistic environment and did not test what would happen in reality.
Sources:
http://srag-nt.jsc.nasa.gov/spaceradiation/faq/faq.cfm
http://en.wikipedia.org/wiki/Gray_%28unit%29
(and an assumption that the 1:1 rad/rem relationship holds in the particular situation described)
Skylab 4 was an 84 day mission. The astronauts were exposed to about 17 rems cumulative over that time, or 0.17 Grays
I could be wrong here, but wasn't skylab in low earth orbit so was protected from the majority of the nasties by the earths magnetic field? I guess the closest equivalent is the moon missions but of course they only lasted 4 days so it would be difficult to extrapolate to a 2 -3 year mission.
Of course the best way to reduce exposure would be to get them there and back faster....
The Apollo 14 astronauts were apparently exposed to 1400mrem over 4 days, which seems to be even less than skylab. There's a lot to account for there though. They were on the moon for a good portion of the mission and likely shielded from a fair amount of radiation by its sheer bulk.
All of which leads me to the only sane conclusion: in order to get to mars safely, we need to use the moon as a spaceship.
The Apollo astronauts may have gotten some shielding from deep-space radiation by having the Moon under their feet, but since all the missions happened during daylight periods, they were exposed to particle streams from the Sun, with essentially zero protection against x-rays and gamma-rays afforded by their space suits and the tinfoil-like structure of the Lunar Excursion Module (LEM). The most energetic cosmic rays emanate from cataclysmic events and distant objects quite unlike the Sun, though, so, except during times of solar flares, their exposure would have been fairly benign.
The Earth's magnetic field deflects most of the external radiation from the Sun and cosmos, but it also traps a part of it in the Van Allen radiation belts. The magnetic field is tilted and offset from the geographic poles, so there is one region (the South Atlantic Anomaly) where the belts are lower than elsewhere. That's where astronauts in low orbit pick up most of their radiation dose.
Skylab was in a low inclination orbit, and the belts are aligned mostly east-west. The ISS is in a higher inclination orbit to accommodate launches from the various international partners. So it crosses the South Atlantic Anomaly more perpendicular, and thus spends less time in it. The ISS also has more equipment around the walls of the modules compared to Skylab, which provides some amount of shielding. So the exposure rate is considerably lower (about 2/3 lower, but I would have to check).
"Someone hasn't read their Larry Niven..."
I plead guilty m'lud, and throw myself on the mercy of the court.
"The logical conclusion, therefore, being that the first colonists on Mars would have to be Clangers - right…?"
No. Mars has no blue string. They'd never survive.
As I said I did just scan the paper - and I didn't do any checking on the numbers - but I think they do address that. They're concerned about cosmic rays - which cause a sudden, large amount of damage along their path through secondary ionisation. So although the _average_ dose throughout the trip might be low, it'll have occasional high spikes. It's these spikes that they're trying to model.
// Our data clearly demonstrate that low-dose HZE particle exposure leads to persistent impairments in behavioral performance ...//
They do mention that the exposure isn't exactly like a cosmic ray strike:
// Although we cannot simulate exactly the complex and prolonged charged particle irradiation pattern encountered in space, ...//
So they're at the very least thinking about how the exposure works.
In practice, animal experiments are not cheap and easy, so they tend to be planned out carefully. I suspect that it would be difficult to get ethical approval for a half-arsed random exposure experiment, even if the law on that in America is less stringent than the UK.
Some background in Radiobiology is needed here with regards to dose-rate and high LET Radiation.
Dose-rate does not matter at low doses because its a binary encounter either a biomolecule gets hit or it does not get hit by a particle. Its only when the dose is high that the dose-rate has an effect because biomolecules or even cells will get hit more than once. Even then the reduction at the same dose (say 1 Gy of X-rays) is about a factor of two less as shown in hundreds of experiments. Not that large as you go from high to low dose-rate.
But this experiment is with cosmic ray heavy ions which are high LET (linear energy transfer) radiation and there is no dose-rate effect that will occur at these low doses (0.05 or 0.3 Gy). The FACT that little or no dose-rate effect occurs for high LET at low to even high doses (up to more than 1 Gy) also has been shown in many hundreds of radiobiology experiments.
Also the region of the brain effected is the Pre-frontal cortex neurons. These are differentiated cells and no new ones in adults. Dose-rate effects are even less for differentiated cells and tissue compared to rapidly dividing tissues.
Understand if readers are not aware of the literature. Zurbin and the Mars society comment like their experts but their not. I have seen in last two years Zubrin say the cancer risk for a Mars mission is low based on the BEIR II report from the 1960's. Too deceptive or lazy to read BEIR VII report from 2007 which estimates a four times higher cancer risk for the same physical dose and all of this is for low LET not high LET, which is very uncertain risk because no human data. There are issues in going from mice to humans but nothing to do with the dose-rate or doses used in the experiments.
But the point is that they exposed the mice to one dose of radiation in a short time, instead of exposing the mice to the same total amount of radiation over the time a Mars mission would take, so that the brain could repair itself between receiving a little radiation and then receiving some more.
For most parts of the body, this is a very valid objection. But most of the brain doesn't undergo constant cell division the way the tissues of the rest of the body do. So it isn't renewed constantly.
No doubt the mice were much more likely to develop cancer than astronauts would have been, making the study entirely invalid for measuring that risk.
>All of which leads me to the only sane conclusion: in order to get to mars safely, we need to use the moon as a spaceship.
There is also the Mars Cycler concept promoted by Buzz Aldrin:
http://en.wikipedia.org/wiki/Mars_cycler
As I understand it, you get a bloody great rock into a cyclic path back an forth between Earth and Mars, and then human craft hop on at one end and hop off at the other. The mass of your rock isn't an issue, so more shielding can be used.
As regards going faster, do you remember those tests of an Electromagnetic Drive the Reg reported on? Last year thrust was observed without the expulsion of any propellant. Last month, it was tested in a vacuum and thrust was still observed.
http://www.nasaspaceflight.com/2015/04/evaluating-nasas-futuristic-em-drive/
Please note, despite the linkied article jumping enthusiastically to potential spaceflight applications, this isn't yet a prototype engine; engineers still may have overlooked some alternate cause of the observed 'thrsust', or physicists have some retrhinking to do.
No. Water ones.
The only way to provide reasonable shielding is if the astronauts are shielded by the propellant. 1m of water goes a very long way towards shielding both nuclear propulsion and cosmic rays. 1m tank + shield around a sphere with 10m radius is ~ 400 tons. If some of this water is used as a propellant to get to Mars orbit and back you are also looking at a journey time under 30 days.
The problem is getting all that water onto the spaceship in the first place. If you are launching from Earth - not a way in hell. It is not feasible. If it has been brought into Earth orbit from the Asteroid belt., than it is a completely different ball game.
IMHO, we are planning things in the wrong order. We have to get (via automated capture ships) to the asteroid belt first and only then we can go to other places in the solar system.
> The problem is getting all that water onto the spaceship in the first place. If you are launching from Earth - not a way in hell. It is not feasible. If it has been brought into Earth orbit from the Asteroid belt., than it is a completely different ball game.
The inner Solar System is filled with asteroids in random orbits. 12,500 have been found in the "near Earth" category alone, and there should be similar numbers between Earth and Mars. Some, the Chondrites, contain up to 20% water and hydrocarbons. The answer is then to send a tug to move some of that asteroid rock into a repeating Mars transfer orbit, and stuff it into a cylindrical shell of storage lockers. When you launch your crew mission, you meet up with this shell, and slide the habitat module inside, then travel protected by the shielding layer.
Since the asteroids are in random orbits and there are lots of them, you will always find ones that are already close to the orbit you want, and therefore don't have to move them very far. For a bonus, you can process some of the rock for supplies. Your tug can maintain the shielding's transfer orbit, since such orbits are not naturally stable. You can then use it on later missions.
> We have to get (via automated capture ships) to the asteroid belt first and only then we can go to other places in the solar system.
It's fairly standard S.F. dogma that once you can capture an asteroid, a metalic 'un could be hollowed out to create a shielded space habitat / Mars spacecraft.
Water, shielding and propellant.
Hmmm. I guess the lower remaining mass on the way back might allow them to scurry back before they use up all their shielding?
Or is this where the feces comes into the equation?
Imagine 400 tonnes of feces reentering the atmosphere. Yuck.
Can lift 20 tons to GTO in a single trip, so only 20 trips if that's where the final assembly was done. I'm presuming as much assembly as possible would be done in LEO to make it easier for astronauts to get to/from to do the work. Then the ship can boost into GTO, load the water, and go forth.
The ISS is more than 400 tons. Should I call the astronauts on board to tell them their home is not feasible?
ISS is only in LEO. This chart might come in handy.
Please keep in mind I was replying to a post which suggested that the majority of the 400 tons of water was for shielding and only a small amount of that would be needed as propellant: see my emphasis below. (p.s. I haven't checked the feasibility of Voland's right hand's proposal so I admit I am making one assumption there by accepting the hand's suggestion). This is important because it means much less than 400 tons would be needed to be lifted from Earth to LEO to be used as propellant.
The only way to provide reasonable shielding is if the astronauts are shielded by the propellant. 1m of water goes a very long way towards shielding both nuclear propulsion and cosmic rays. 1m tank + shield around a sphere with 10m radius is ~ 400 tons. If some of this water is used as a propellant to get to Mars orbit and back you are also looking at a journey time under 30 days.
It is a lovely chart, yes I've seen it before, and thanks for reminding me of it. What the chart shows is that the Δv needed to get from LEO to Mars (9.51) is pretty much the same as the Δv needed to get from Earth to LEO (9.4). So, it's do-able. Especially if Voland's right hand is correct and the propellant needed to go from LEO to Mars and back is only a small part of the 400 tons of water.
Actually sort of, yes. Shielding from cosmic rays is done in layers. A layer of material like gold foil intercepts the particle, turning it into a shower of secondary particles - distributing the energy. After some distance second and third layers slow them even more. Foamed plastic might be effective also. Shipping the water on the outside of the ship might be a solution as well.
The use of 'ray' for these physical particles moving at relativistic speeds is a historical artifact. They are fast moving matter (or in rare cases, antimatter), not radio energy.
Whatever people claim about this mission, the primary reason to send people to mars is to tick off that particular feat.
The guinea-pigs chosen to 'fly' the mission won't have to actually do much other than try not to fall out too badly with their colleagues while cooped up for months in a confined space. If their brains are a little fried, it shouldn't stop us landing them on Mars.
It would be a huge human achievement, but it would not be a precursor to a human colony on Mars, any more than the Apollo missions paved the way for human moon colonies.
Having achieved this feat, the political appetite for spending vast sums sending more people to die on Mars will fade quickly away. And I hope it does, because the clever way to explore is remotely, and it would be a huge shame if funding for that glorious effort was starved to make way for sending more human guinea-pigs to die on Mars or on the way to it.
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