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Retric | on: The Shape of a Mars Mission
> To the average layman

That’s a meaningless yardstick here. People at NASA definitely thought hitting that target was achievable before the speech.

> Landing on Mars

Landing isn’t the issue. Get people there alive and having enough deltaV to get back is.

somenameforme | parent | next
No, NASA also didn't think it was possible at the time. There's an informative little paper here. [1] It only gets more informative from the first sentence, "Mathematical risk analysis was used in Apollo, but it gave unacceptably pessimistic results and was discontinued." By the time of the launch to the Moon NASA's internal estimates were looking at around a 50% chance of success based on Gene Krantz's (mission controller) "Failure is Not an Option" book.

It was a mission they dedicated themselves to, and humans have this way of making things happen when we actually set our minds to tasks. A reality that's often been lost in modern times as we have mostly moved away from pursuing, let alone achieving, great things in the real world. One of the many reasons to get humans on Mars.

[1] - https://ntrs.nasa.gov/api/citations/20190002249/downloads/20...

Retric | root | parent
You’re confusing specific low odds of success for “didn't think it was possible.”

The Apollo missions got unbelievably lucky in that none catastrophically failed despite multiple close calls. However, if you’re willing to try multiple times the odds any mission being successful is much better than every mission being successful.

IE: Six missions landed on the moon. If they each had independent 50% odds then six heads is a long way from impossible ~1.6%, but at least 1 head is quite likely ~98.4%. I doubt we would have tried for a 6th mission after 5 failures in a row, but the point is definitions of success matter a great deal here.

Similarly failures improve odds of success in the future because you learn from mistakes and success means the system is functional eliminating some risks.

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Robotbeat | parent
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 | root | 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

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idlewords | root | 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.