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Robotbeat | on: The Shape of a Mars Mission
On the contrary, we can easily get people there alive. What exactly do you think is beyond our capacity to send crew to Mars while still being alive? Crew regularly do year long expeditions on ISS (edited for clarity), with total radiation dose similar to Mars transit (and show no measurable effects of that radiation).

Again, I’m addressing the point “getting them there alive”. Unquestionably, we know how to get crew to Mars alive, and even for the full mission duration, radiation isn’t even in the top 10 of the hazards that could actually kill them during the mission. (It’s a long term hazard, comparable to lung cancer if you’re a cigarette smoker.)

Retric | parent | next
The world record duration still sits at 438-days after 35 years. We limit people below that due to medical issues, suggesting no we don’t know how to safely do multi year space flight.

It’s possible people spending significant time on the surface of mars would recover, but that’s more speculation than proven.

somenameforme | root | parent
The person who went 438 days was Valeri Polyakov, and he experienced exactly 0 ill effects from such, going so far as to intentionally briefly walk immediately after landing precisely in order to demonstrate that working on Mars after any transit would be possible.

Going beyond that is not really meaningful since that's far longer than any normal transit to or from Mars, which is the immediate target.

[1] - https://en.wikipedia.org/wiki/Valeri_Polyakov

Retric | root | parent
A young formally fit person being capable of making a few steps doesn’t demonstrate “0 ill effects.” He was vastly weaker upon his return as shown by making a few steps being considered a significant achievement rather than an actual sign of fitness like lifting a heavy weight and moving it around.

Living on mars at 38% earths gravity is believed to make things worse over time, so no you can’t just consider transit times independently. On arrival they would likely be fine inside a habitat. But trying to walk around in an Apollo 11 era 180 lb pressure suit in 38% gravity would be nearly as strenuous as walking around on earth and we’d like them to be able to work not just take a few steps and sit down. It’s possible to reduce that weight, but needing to carry oxygen tanks means there’s quickly a tradeoff between lighter weight and less time outside.

Now, for an extremely brief touch Mars and come back while burning a huge amount of fuel to make a shorter trip sure they’ll survive. But start talking a 3 year mission and things don’t look good.

somenameforme | root | parent
Polyakov was 52 years old when he did his 438 day stay, and astronauts always take a couple of days to readjust to gravity. The overall effects of well over a year in space seem pretty comparable to a few months in space. It's just not a big deal. Those Boeing astronauts (both around their 60s) have been stuck on the ISS for going on 9 months now, and NASA's basically like ¯\(ツ)/¯.

Back on Mars they'll be able to quickly regain their motor skills coordination, as well as strength/bone density. So it will be effectively equivalent to Earth in this regard - actually it will be even better than Earth because the reduced gravity will probably send the overall adjustment time down from a couple of days to a couple of hours, especially with a normal duration transit.

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idlewords | parent
No one has ever done a "years long" expedition to ISS, and the radiation flux in transit to Mars, in particular GCR dose, is much higher than experienced on the space station.
Robotbeat | root | parent
I’m well aware, just mistyped. The total equivalent radiation dose on a fast transit to Mars is less than some ISS expeditions.

Note that the magnetic field only deflects lower energy galactic cosmic rays which have a lower gyro radius than the real whoppers. The magnetic field is less important to overall radiation shielding than the earth’s atmosphere.

idlewords | root | parent
Total GCR dose is 3-5x in transit to Mars compared to what you get on ISS; on the Martian surface it's from 1.5-2x the ISS dose. (see https://www.swsc-journal.org/articles/swsc/pdf/2020/01/swsc2...).

On a long-stay Mars mission, that adds up to 12-18 times the accumulated GCR exposure compared to a six-month ISS increment.

Robotbeat | root | parent
Ah, you’re being tricky. You’re ignoring the substantial trapped radiation dose on ISS (it is, after all, the total dose that causes the defects). That, combined with GCR, gives an equivalent dose the same at Curiosity altitude as on ISS.

In fact, look at Table 2. It shows that at ISS, the dose from the SAA is about the same as the GCR dose, so by ignoring trapped radiation, you’re manipulating the result by a factor of 2.