How bad are the radiation belts?

[Laie]

Asking for roleplaying purposes.

I'm about to send a mission to mars. Low-TWR transfer stage poses the old problem of long burns and lack of precision. Would periapsis-kicking even be an option IRL? The crew is about to spend 2x nine months in transit, and another twenty on Mars. Considering this, will a few passes through the vanAllen belt even matter?

[Bill Phil]

Not if you have loads of shielding, but that's a lot of mass.

[wumpus]

You need about ~4000m/s from LEO to get to Mars, and your escape velocity is ~3000m/s. I'm guessing this means about 4 kicks around ~1k/ms apiece.  I'm pretty sure the Mangallayan probe used more, but that last one has to be big.

We know that the ~3000m/s flight used in the Apollo missions barely went through the radiation belts at all, so at most two trips.  I suspect that the flight and surface of Mars are sufficiently exposed that you don't want any more radiation exposure than strictly necessary, but I'm sure you can handwave it away if you want.  I'm not even sure that ~1km/s will even get to the belts (I've tried to figure this out as such tricks could make manned mars vastly more feasible).

[Kryten]

The van Allen belts aren't that bad for a few passes, particularly if you miss the denser patches like the SAA. Most of the overall exposure for Apollo was cosmic radiation after passage through the belts.

[PB666]

The radiation is much less of a problem than the complete lack of air in the belts.    Short exposure to much higher doses are not too much of a problem, chronic exposure to highe doses is a problem, because cells have to replicate through damage DNA whereas short exposures tolerate repair. This is for ionizing radiation, for atomic radioactivity thats a diiferent story. The radiation belts take out some of the higher energy cosmic radiation alot of it still reaches the earths atmosphere. If you are traveling from Earth to mars you major concerns are going to be the interstellar cosmic radiation and the occassional solar magnetic storm, which can be avoided when passing through the radiation belts by timing the departures. 

[magnemoe]

4 hours ago, wumpus said:

You need about ~4000m/s from LEO to get to Mars, and your escape velocity is ~3000m/s. I'm guessing this means about 4 kicks around ~1k/ms apiece.  I'm pretty sure the Mangallayan probe used more, but that last one has to be big.

We know that the ~3000m/s flight used in the Apollo missions barely went through the radiation belts at all, so at most two trips.  I suspect that the flight and surface of Mars are sufficiently exposed that you don't want any more radiation exposure than strictly necessary, but I'm sure you can handwave it away if you want.  I'm not even sure that ~1km/s will even get to the belts (I've tried to figure this out as such tricks could make manned mars vastly more feasible).

Belt if less an issue on a trip to the full moon as its behind earth relative to the sun, the belt give some protection against solar storm on a full moon. 
And the radiation is an issue with very low TWR, most don't want to use ion engines getting from LEO to GEO, moon or outward even if this would cut the transfer stage cost a lot, the Indian mars probe was some of the few who did an slow escape burn. 

[DDE]

How low is your TWR and do you have a nuke onboard? If the whole transjection takes a week or so you could lock your crew up in the "storm cellar".

[lajoswinkler]

As for the Apollo crews, they've received doses similar to abdominal x-rays. Except, I think, Apollo 14. They've received more.

There's a great webpage dedicated to these things. http://www.braeunig.us/apollo/VABraddose.htm

[Laie]

2 hours ago, lajoswinkler said:

There's a great webpage dedicated to these things. http://www.braeunig.us/apollo/VABraddose.htm

Of course @OhioBob has something on that matter!

Alright, looks as if Apollo11 went out on a higher inclination than strictly necessary or useful for a lunar transfer. Now I also recall that me mission plan called for TLIs on either the Atlantic or Pacific Node, which amounts to about equatorial, giving you a high inclination while you pass by (not through) the belts. One might almost think this was by design...

For my mission, I don't think I have much choice regarding the outgoing trajectory. This would require me to get into much more advanced planning tools, dV budgets would need to be recast, the whole vessel re-designed from scratch. Not gonna happen. What I can do is a pretty large first kick, up to a one-day orbit (75Mm AP). By first guesstimates, this can still mean the astronauts will have to spend several hours in the thick of it. So (handwave) storm shelter it is.

While the van Allen belts are well documented, I still haven't found a resource about radiation doses in "deep space".

[ShotgunNinja]

The outer belt is composed mostly of mid-to-low energy lightweight ions, and shielding is effective. Its thickness is not uniform and is very small near the poles. All manned missions that had the need to cross the outer belt did so at the less thick areas. It is also possible to launch from the poles and completely avoid the outer belt, but that is not really practical.

The inner belt can be avoided. You especially want to avoid putting living matter through the inner belt in all cases, as it is composed mostly of very high energy ions and shielding in not that effective.

Absorption levels vary with space and time, but 500 rad/day for the inner belt and 100 rad/day for the outer are good estimates.

[lajoswinkler]

49 minutes ago, ShotgunNinja said:

The outer belt is composed mostly of mid-to-low energy lightweight ions, and shielding is effective. Its thickness is not uniform and is very small near the poles. All manned missions that had the need to cross the outer belt did so at the less thick areas. It is also possible to launch from the poles and completely avoid the outer belt, but that is not really practical.

The inner belt can be avoided. You especially want to avoid putting living matter through the inner belt in all cases, as it is composed mostly of very high energy ions and shielding in not that effective.

Absorption levels vary with space and time, but 500 rad/day for the inner belt and 100 rad/day for the outer are good estimates.

Have you considered using Sv/h instead? It's much more relatable. Rads are obsolete units.

1 hour ago, Laie said:

Of course @OhioBob has something on that matter!

Is that his page?

Edited September 5, 2016 by lajoswinkler

[OhioBob]

2 hours ago, lajoswinkler said:

http://www.braeunig.us/apollo/VABraddose.htm

Is that his page?

Yes it is.

The biggest concern passing through the VAB are the high-energy protons in the inner belt.  By the time you're 1 Earth-radii out, you'll be past the danger zone.  Beyond that there is just electrons, but those don't carry enough energy to penetrate the hull.  The electrons will produce secondary x-rays (bremsstrahlung), but any dose from those will be small because the x-rays are low energy.