What is the chance of the Hermes crew in the Martian dying from cancer?

[SomeGuy123]

Numerous news articles I have seen in several sources by credible scientists declare that everyone in The Martian would have died from radiation sickness.  Here's an example of one.  Quote, "Everyone would die of cancer due to excessive radiation."  The writer, Rhett Allain, "is an Associate Professor of Physics at Southeastern Louisiana University."

Let's check these numbers.  

Curiosity Probe rode a low energy trajectory to Mars.  NASA reports 1.8 milli Sievert per day.  This has already been adjusted for human equivalent dose if exposed to this radiation, whole body, inside an unshielded spacecraft.

According to the timeline, it was July 7 2035 - December 21 2037.  This is 898 days per Wolfram Alpha.  898 * 1.8 = 1616 milliSievert.  According to wikipedia, 1000 millisievert (1 Sv) is about a 5.5% lifetime chance of dying from fatal cancer.  

So 1.616 Sv * 5.5% = 8.9% chance of cancer.

This doesn't sound like "everyone would die from cancer" to me.  It sounds more like "out of the 5 people on the crew, statistically there's less than a 50% chance that one of them might get cancer and die from this mission eventually if not successfully treated".

As for Watney, since he spent most of his time on Mars, where the distance from the Sun and the bulk of the planet protects him from more than half the dose, his chance of cancer would have been somewhere under 5%.  Those sores we see in the film must have been from not showering or malnutrition.   

Shielding would have helped, but the spaceship as displayed in the movie clearly has minimal, if any, shielding.

 

[*Aqua*]

But don't forget he eats potatos from Marsian soil. What kind of radiation is in there and how strong is it?

Afaik eating and inhalating radiated stuff is far more dangerous than just holding it in the hand.

[Steel]

1 hour ago, SomeGuy123 said:

So 1.616 Sv * 5.5% = 8.9% chance of cancer.

I'm just going to stop you right there. This is just in no way how these things work. The percentages for this kind of thing don't scale with anything even close to a linear relationship when you look at prolonged doses, so this sort of maths doesn't hold up, despite what the Wikipedia article says.

The reality is that sustained radiation for prolonged periods of time are likely to be much more damaging than this estimate (also the model this 5.5% per Sv is taken from is disputed by a fair number in the scientific community)

Edited January 10, 2016 by Steel

[RainDreamer]

We still have no idea what kind of progress in material science NASA has made in the movie. Perhaps they made some breakthrough and got much better radiation shield, reducing the radiation that the crew is exposed to significantly.

Watney is probably still going to die from cancer/other health problems though, since he is not on hermes, but eating stuff from martian soil (all that perchlorate can't be healthy, even if survivable) and living in a hab designed for 30 days.

Edited January 10, 2016 by RainDreamer

[Kryten]

1 hour ago, *Aqua* said:

But don't forget he eats potatos from Marsian soil. What kind of radiation is in there and how strong is it?

Afaik eating and inhalating radiated stuff is far more dangerous than just holding it in the hand.

Induced radioactivity is mostly from neutrons, which aren't a significant component of solar or cosmic radiation. There's no reason to expect martian soil to be much more radioactive than earth soil.

Edited January 10, 2016 by Kryten

[Spaceception]

Didn't NASA create radiation shielding strong enough to block radio waves (In the book)? If so, then no, they wouldn't have died from radiation, and the people who made the articles are probably thinking about the radiation shielding we have today

[SargeRho]

blocking radio waves is easy, and they aren't ionizing, thus not causing cancer. X-Rays, Gamma Rays and Cosmic Rays are a different issue entirely, and very hard to shield.

[Hcube]

2 hours ago, SomeGuy123 said:

.  According to wikipedia, 1000 millisievert (1 Sv) is about a 5.5% lifetime chance of dying from fatal cancer.  

So 1.616 Sv * 5.5% = 8.9% chance of cancer.

It does not work that waaay !

 

There is no linear relationship between the dose and the probability of developing cancer ! The wikipedia article about radioprotection sucks.

The risk depends on the dose "flow" (i have no idea how to translate that in english, but you see what i mean  )

It basically comes down to this : for small doses (up to 100mSv in a short period of time or even very high doses distributed over years) the effects are stochastic wich means it is not possible to know if you will get sick in 10 years, 40 years or if it will have any effect at all.

Workers exposed to radiation legally are limited to 0.1Gy in give years, and even 0.5Gy on the skin/fingers ! The 1.6Gy estimation you calculated is not so much.

Only for high doses, determinist effects take place.

Obviously the man you quoted is a physician and not an expert in radioprotection because it's simply impossible to get cancer in six months by taking 1mSv a day. You either get fried by taking 5Gy and die before any kind of tumor takes place, or get a (relatively) small dose and the random effects wich often appear years after the exposition

 

Also the cosmic radiation is (AFAIK) is made for a big % of charged particles radiation, and a (relatively) thin layer of a heavy metal is often enough to shield yourself from those. So i'm thinking there could actually be some "good" radioprotection in the Hermes that we simply don't see   so 1.6mSv per day is veeery probably a big overestimation.

 

[KerbMav]

We can only guess at the risk for a crew making the same voyage with todays technology. In Weir's future NASA has access to radiation shielding materials that are effective enough to allow them to be worked into the rather thin hab canvas. Being able to do that, shielding a rover, EVA-suit or spaceship is rather easy.

[J.Random]

The whole dose calculation is wrong: you forget that Rich Purnell would take them down to the orbit of Venus. Still, I wouldn't say that the crew was guaranteed to get cancer or die from rad poisoning even then.

Edited January 11, 2016 by J.Random

[Workable Goblin]

It's not correct to extrapolate from Curiosity, because Curiosity essentially lacked radiation shielding, which would (in reality) be a major driver of vehicle design. In fact, one of the main advantages of electric propulsion systems such as those said to have been used by the Hermes is the fact that they allow relatively easy reuse (compared to chemical rockets) and high dry mass fractions, making it much more practical to build interplanetary transit vehicles with large amounts of radiation shielding. If we assume that the Hermes was in fact built as a "mothership" using electric rockets to enable massive radiation shielding and rotational gravity and such technologies, then many otherwise curious design choices suddenly make sense. For instance, the use of an opposition-class mission profile allowing only thirty or so days on Mars is sensible if being on Mars means low gravity and high radiation exposure compared to being in space.

In any case, present NASA guidelines are to limit cumulative exposure to about a 2% elevated cancer risk over one's lifetime, which works out, IIRC, to about 250-300 mSv of exposure. Hermes was probably designed to reduce exposure to limits lower than that (for buffer space and to allow astronauts who had flown before to fly without breaching lifetime limits), but in the book and movie their mission was extended for the rescue. So overall radiation exposure was probably in that range or a bit higher, perhaps up to 500 mSv or so as a complete guess. They certainly would not be keeling over from radiation sickness during the mission.

Edited January 11, 2016 by Workable Goblin

[Hcube]

250-300mSv sounds very low to me on a lifetime... Radiation-exposed workers are allowed to take 100mSv every five years : let's imagine a 40 years career, those would be 0.8Gy ! And they don't get a significant cancer rate augmentation...

I guess NASA is playing it safe ^^

[peadar1987]

1 hour ago, Hcube said:

250-300mSv sounds very low to me on a lifetime... Radiation-exposed workers are allowed to take 100mSv every five years : let's imagine a 40 years career, those would be 0.8Gy ! And they don't get a significant cancer rate augmentation...

I guess NASA is playing it safe ^^

You almost never hit that limit though. In 12 months working on-site in a nuclear plant, I got a dose of less than 100uSv. And I was doing some of the "dirtier" everyday work. We had a company-imposed limit of 10mSv a year (If there was a particularly dirty "20mSv job" to be done, like a boiler entry, people would arrange it so it fell over the administrative year change, so you could get two years worth of dose in a matter of days, but not break any annual limits!). 50mSv is a legal limit in the US, I think, and 100 and 500 are recommended by the IAEA for people saving critical equipment and lives, respectively, although I am working from memory here, and the actual doses could be different. I was never on a team that would ever be carrying out rescue work, so the numbers weren't really relevant to me.

[SomeGuy123]

5 hours ago, J.Random said:

The whole dose calculation is wrong: you forget that Rich Purnell would take them down to the orbit of Venus. 

I don't know how to account for that.  All I could do was try to make a rough estimate using the given numbers, which seem to say it was survivable.

[Hcube]

35 minutes ago, peadar1987 said:

You almost never hit that limit though. In 12 months working on-site in a nuclear plant, I got a dose of less than 100uSv. And I was doing some of the "dirtier" everyday work. We had a company-imposed limit of 10mSv a year (If there was a particularly dirty "20mSv job" to be done, like a boiler entry, people would arrange it so it fell over the administrative year change, so you could get two years worth of dose in a matter of days, but not break any annual limits!). 50mSv is a legal limit in the US, I think, and 100 and 500 are recommended by the IAEA for people saving critical equipment and lives, respectively, although I am working from memory here, and the actual doses could be different. I was never on a team that would ever be carrying out rescue work, so the numbers weren't really relevant to me.

Yeah the values i know are in the EU, there might be some variation ! The values also vary depending on what is exposed (whole body/fingers and skin)

Well 100uSv is pretty close to nothing, lucky you

[Workable Goblin]

4 hours ago, Hcube said:

250-300mSv sounds very low to me on a lifetime... Radiation-exposed workers are allowed to take 100mSv every five years : let's imagine a 40 years career, those would be 0.8Gy ! And they don't get a significant cancer rate augmentation...

I guess NASA is playing it safe ^^

Not really. The NRC lifetime exposure limit is 5 times the yearly exposure limit (per § 20.1206(e)(2)), which in turn is 50 milliSieverts (per § 20.1201(a)), so lifetime exposure limits for radiation workers in the United States are very close to NASA's astronaut lifetime exposure limits. Funny, that.

[Sciencek]

Why assume that the Hermes is restricted to the same low-energy trajectories as unmanned rovers?
It's clearly described as being an ion-drive craft, and it's delta-v reserves are probably absolutely insane.

[Superfluous J]

Edit: Welcome to the forums!

1 hour ago, Sciencek said:

Why assume that the Hermes is restricted to the same low-energy trajectories as unmanned rovers?
It's clearly described as being an ion-drive craft, and it's delta-v reserves are probably absolutely insane.

The book described in quite a bit of detail the path Hermes went on. Enough that - if I had the mind to - I'm pretty sure I could plot the course. The movie skipped a lot of that but did (IIRC) state how long they were in space. At the very least, it told how many days Watney was on Duna and we know Hermes was in space that entire time.

So to tl;dr it, time spent and places traveled by the Hermes are not assumptions. They're derivations.

Edited July 29, 2016 by 5thHorseman

[nightingale]

42 minutes ago, 5thHorseman said:

At the very least, it told how many days Watney was on Duna

You know you play too much KSP when...

[Sciencek]

3 hours ago, 5thHorseman said:

Edit: Welcome to the forums!

The book described in quite a bit of detail the path Hermes went on. Enough that - if I had the mind to - I'm pretty sure I could plot the course. The movie skipped a lot of that but did (IIRC) state how long they were in space. At the very least, it told how many days Watney was on Duna and we know Hermes was in space that entire time.

So to tl;dr it, time spent and places traveled by the Hermes are not assumptions. They're derivations.

Thanks for the welcome!

So we know how long the crew are in space; do we know off hand what the solar weather activity is for the period(s) that the rovers spent in transit? Was it average? Above? Below?

<EDIT>

Oh, is that the on-surface per-day dose?

</EDIT>

On a similar matter, why assume that when designing the Hermes, they would skimp on shielding? They DO have a nuclear reactor to be concerned about shielding from, and electric engines allow for very high payload fractions for any given delta-v budget.

Also, IIRC, Weir's pre-movie imagining of the Hermes was essentially a cone (for ease of aerobreaking) which could split in half (for ease of bolo-spinning gravity). I can't help but think that this leaves precious few places to mount such an inconveniently bulky/long thing as an unshielded nuclear reactor, and few (but more!) options for a more compact, but heavier, shielded one.

Edited July 29, 2016 by Sciencek
Realized a meaning in post responding to

[Superfluous J]

3 hours ago, nightingale said:

You know you play too much KSP when...

ROFL wow I don't think I've ever done that before.

[radonek]

Also, en-route radiation is not even close to stable. You get a lot of radiation from solar wind during solar maxim, but plasma also to some degree shield solar system from interstellar radiation. So, during solar minimum you get more of that. To make it more fun, alpha radiation in solar wind call for different shielding then gamma rays from the great outside. And solar events can mix up all of that in a bad way. AFAIK Weir got around this by having NASA invent some magical shielding plastic, but I guess it is still safe to assume that Hermes had storm cellar on board and crew spend there quite some time during perihelion.