LIVE: Dennis Tito's Inspiration Mars Foundation Announcement and Reaction Thread

[guckyfan]

@Hibernaut

You seem to have a wrong idea about how much radiation there is. It is really very, very low. Some of it reaches the ISS. If such concerns were true the ISS would have long turned into some radioactive hell and would have been abandoned.

[Hibernaut]

Hydrogen gas production IS a problem that has to be mitigated in nuclear reactors!

[Hibernaut]

Once you go beyond the protection of the earth's magnetosphere ionizing radiation/particles are a well investigated problem, and stands at much, much higher levels than what you'll find in low earth orbit. Where not talking just about background galactic cosmic radiation but SPEs as well.

[Dalhousie]

Once you go beyond the protection of the earth's magnetosphere ionizing radiation/particles are a well investigated problem, and stands at much, much higher levels than what you'll find in low earth orbit. Where not talking just about background galactic cosmic radiation but SPEs as well.

And the amounts are known and the means to keep them to acceptable levels well understood.  The RAD instrument on the Curiosity mission encountered 0.466 Sv of all radiation types over the 253 day mission.  Inspiration Mars would experience about 0.923 Sv over it's 501 day mission with similar shielding. 

[guckyfan]

And the amounts are known and the means to keep them to acceptable levels well understood.  The RAD instrument on the Curiosity mission encountered 0.466 Sv of all radiation types over the 253 day mission.  Inspiration Mars would experience about 0.923 Sv over it's 501 day mission with similar shielding.

The RAD instrument on Curiosity is not shielded. It was intended to measure radiation as is. Any shielding would reduce radiation exposure. But shielding would mainly be for solar radiation.

[Dalhousie]

And the amounts are known and the means to keep them to acceptable levels well understood.  The RAD instrument on the Curiosity mission encountered 0.466 Sv of all radiation types over the 253 day mission.  Inspiration Mars would experience about 0.923 Sv over it's 501 day mission with similar shielding.

The RAD instrument on Curiosity is not shielded. It was intended to measure radiation as is. Any shielding would reduce radiation exposure. But shielding would mainly be for solar radiation.

On the journey to Mars Curiosity t was inside the aeroshell, which provided 10 g/cm2 of shielding in most directions.  In some directions there was up to 80 g/cm2, presumably that pointing to the cruise stage.  This is roughly equivalent to a lightly shielded crewed spacecraft.This is covered in the 2013 paper by Zeitlin et al. in Science http://www.sciencemag.org/content/340/6136/1080 

[Hibernaut]

Several thoughts for the case against:

- those (quoted) values don't consider the possibility of solar flares and spiked in the solar wind which even considering solar cycle minimum is recognized to be unpredictable, potentially increasing the quoted doses by one to two orders of magnitude;

- irradiation of water yields hydrogen and oxygen gas which escapes the liquid. This build-up does not cease until a steady-state pressure is created, which depends on the intensity of the radiation and the temperature of the liquid; increasing temperature decreases solubility. Moreover, both hydrogen and oxygen are highly insoluble in water; hydrogen is an extremely insoluble gas in water. Furthermore, if there are any impurities in the water the evolution of gas continues well after irradiation ceases; &,

- An interesting thought, a question really, and I could be mistaken:
if incident (particle) radiation dose is proportional to the cube of the particle velocity (read that somewhere?) does that mean there might exist a sizable difference in what is experienced at the front- compared to back-end of a very fast traveling spacecraft. If indeed that might be the case, would it mean, quite ironically, that a quick transit, generally favored to minimize the radiation time-dose exposure, might actually yield a worse radiation exposure outcome... Could be reaching here!


Ref:
Allen, A. O. (1952). Mechanism of decomposition of water by ionizing radiations. Discuss. Faraday Soc., 12: 79-87.

[Robotbeat]

At first thought Inspiration Mars' `water-walls´ idea of a passive radiation shield sounds good, but at second thought it's also clear that it can't protect against high-energy galactic cosmic radiation. In fact, it makes it worse because of the secondary and tertiary radiation any material shield creates....

That's not true except in certain circumstances. Lighter elements  absorb more dosage than they create through secondary radiation, so a water wall works while a wall of aluminum or especially lead would make things worse.

But regardless, you're more concerned about the effects of a solar storm since those would be acutely felt.

[meekGee]

Several thoughts for the case against:

- irradiation of water yields hydrogen and oxygen gas which escapes the liquid. This build-up does not cease until a steady-state pressure is created, which depends on the intensity of the radiation and the temperature of the liquid; increasing temperature decreases solubility. Moreover, both hydrogen and oxygen are highly insoluble in water; hydrogen is an extremely insoluble gas in water. Furthermore, if there are any impurities in the water the evolution of gas continues well after irradiation ceases; &,

Before you go any further, did you compare the amount of H and O that is produced by the expected radiation with the amount of dissociated H and O that occurs in any water sample, simply by way of equilibrium?

Did you quantify it at all?

You realize that even if all of the energy carried by the radiation was converted into separating water into H and O, then the total energy available for the hypothetical combustion would be equal to the total energy carried by the radiation, right?   So you can see how warm a lead brick gets in space because it is absorbing that radiation anyway.

In short, I wouldn't worry about that aspect of it too much. (oh, and you can also vent it through a membrane, just to be extra extra extra sure.  Or suck it into Palladium.)

WRT to secondary radiation, the lighter the shield material, the better.  (Lighter as in lower atomic mass nuclei)

[Russel]

My understanding is that the majority of radiation from the sun comes in the form of protons so you need low atomic number shielding (stuff with lots of hydrogen in it). But the cosmic background is often heavier particles and for that you initially need something that's denser, then backed by something lighter to capture the secondaries. So metal/polymer skin backed by a layer of water would be good (assuming wrapping the whole thing in lead is out of the question).

[Lampyridae]

Radiation absorption is a tricky thing. The aluminium radiation shielding on ISS causes a net reduction in dosage but it's not as much as hoped (probably due to the secondary radiation effects mentioned above). Outside the magnetosphere it would make the radiation environment worse. The various cosmic ray ions and their different energies make a whole zoo of sparticles but the biggest problem is neutrons.

The current research indicates that plastics, LH2 and nanofibre hydrogen storage offer the best protection in roughly that order.

Electrostatic and magnetic shielding require quite a bit of work but there may be workable concepts for these.

[Lampyridae]

Several thoughts for the case against:

- irradiation of water yields hydrogen and oxygen gas which escapes the liquid. This build-up does not cease until a steady-state pressure is created, which depends on the intensity of the radiation and the temperature of the liquid; increasing temperature decreases solubility. Moreover, both hydrogen and oxygen are highly insoluble in water; hydrogen is an extremely insoluble gas in water. Furthermore, if there are any impurities in the water the evolution of gas continues well after irradiation ceases; &,

Before you go any further, did you compare the amount of H and O that is produced by the expected radiation with the amount of dissociated H and O that occurs in any water sample, simply by way of equilibrium?

Did you quantify it at all?

You realize that even if all of the energy carried by the radiation was converted into separating water into H and O, then the total energy available for the hypothetical combustion would be equal to the total energy carried by the radiation, right?   So you can see how warm a lead brick gets in space because it is absorbing that radiation anyway.

In short, I wouldn't worry about that aspect of it too much. (oh, and you can also vent it through a membrane, just to be extra extra extra sure.  Or suck it into Palladium.)

WRT to secondary radiation, the lighter the shield material, the better.  (Lighter as in lower atomic mass nuclei)

Hibernaut, you're comparing hydrogen production from fluxes found at the centre of a nuclear reactor or from high-level radioactive waste (enough to kill instantly) to that encountered in a SPE. If the problem was as serious as you suggest, Europa would have an oxygen atmosphere. Numbers are the difference between science/engineering and arm-waving.

[Hibernaut]

Ok, here's some numbers of some unpredictable SPE events. One instant killer SPE event narrowly missed the Apollo 16 and 17 crews. Source NASA.

[meekGee]

Ok, here's some numbers of some unpredictable SPE events. One instant killer SPE event narrowly missed the Apollo 16 and 17 crews. Source NASA.

Can you convert "Killer" to SI?

The chart indicates REMs.  REMs are biologically-weighted units of energy per kg of sample.  Therefore, while this chart has numbers, it's not very helpful.

However, again, a burst that is medically dangerous barely carries any tangible energy with it.  It is fatal since it messes with your DNA, not because it roasts you. 

Therefore, any effect it might have on separating water into its constituents is negligible.

[Hibernaut]

Thanks for your input, but the point is the radiation need only be strongly ionizing, not atom splitting, which cause radioactivity things. The ioinzation of water, whether in a drinking-cup or in one's cells will hydrolyse by radiolysis. The yield of reacting ion, atoms and moleculular species produced: hydroxyde, hydronium, proton, hydrogen peroxide, and oxygen will depend on the ionizing energy., the ionizing ration `out there´ is of sufficient  energy to trigger hydrogen evolution. If conditions are conducive and the H2/O2 mix it is technically possible to have an exploion, less you introduce anoth countermeasure.

A note on the shields, any passive shields, of water or whatever:
The US National Research Council Committee on the Evaluation of Radiation Shielding for Space Exploration (2008), i.e., beyond LOE stated:

”Materials used as shielding [i.e., including hydrogen, liquid water, Al, PET] serve no purpose except to provide their atomic and nuclear constituents as targets to interact with the incident radiation projectiles, and so either remove them from the radiation stream to which individuals are exposed or change the particles’ characteristics–energy, charge, and mass – in ways that reduce their damaging effects.”

[Sesquipedalian]

The inspirationmars.org website is now offline, and has been so for over a week.  I suppose that finally puts a fork in it.

A real shame.  I was really excited when this was first announced and thought it had a real chance of getting somewhere.

[Robotbeat]

My understanding is that the majority of radiation from the sun comes in the form of protons so you need low atomic number shielding (stuff with lots of hydrogen in it). But the cosmic background is often heavier particles and for that you initially need something that's denser, then backed by something lighter to capture the secondaries. So metal/polymer skin backed by a layer of water would be good (assuming wrapping the whole thing in lead is out of the question).

Actually, it's even more important to use low atomic mass shielding for cosmic rays than it is for solar radiation. Lead is pretty much the worst thing you could use for cosmic ray shielding, making things actually worse (by secondaries, as you mention). Layering things in a certain order helps, but mostly only if you HAVE to use metal. You're always better off using, say, just polyethylene rather than a mix of polyethylene and aluminum (of the same total mass), for instance, though if you HAVE to use some aluminum, there is a certain order which is superior (and I believe that is polyethylene THEN aluminum, not the other way around).

[Hotblack Desiato]

- irradiation of water yields hydrogen and oxygen gas which escapes the liquid. This build-up does not cease until a steady-state pressure is created, which depends on the intensity of the radiation and the temperature of the liquid; increasing temperature decreases solubility. Moreover, both hydrogen and oxygen are highly insoluble in water; hydrogen is an extremely insoluble gas in water. Furthermore, if there are any impurities in the water the evolution of gas continues well after irradiation ceases; &,

At least this point can be easily solved.

Hydrogen and oxygen recombine to water in the presence of a platinum-sponge or another catalytically activated platinum surface. If the spaceship is propelled with a SEP, the minimal thrust should be sufficient to collect the gas and push it to the platium, where it can recombine. As this process runs constantly, it shouldn't generate much heat, and it can be easily cooled. If there is no SEP present, the ship could rotate (even one round per hour should be sufficient to drive the gas inwards). Prolonged stays in orbit should be no problem either (due to the rotation).

[Robotbeat]

The radiation rate isn't even close enough for oxygen/hydrogen production to be any kind of concern.