Man will never reach Mars!
At lealst, that's the conclusion drawn from some news articles based
on this researlch: https://www.ucl.ac.uk/news/2024/jun/would-astronauts-kidneys-survive-roundtrip-mars
Microgravity for extended periods of time does have its bad effects on
the human body. And the same is true of the radiation levels in space.
Up to a point, putting heavier shielding on spacecraft only makes
matters worse, because of secondary radiation from cosmic rays.
But only up to a point; otherwise, how do you explain the fact that on
Earth, there is less radiation than in outer space, not more
radiation?
The immediate response to raising that point is often to point out
that it would take very big rockets indeed to launch capsules into
space with, say, cement walls that were a foot thick.
However, we have the successful Apollo moon missions as evidence that
humans can survive _short_ journeys into space while enduring
microgravity and radiation.
And so it seems clear that sending astronauts to Mars is possible. Use
material from the Moon, or from asteroids, to build space habitats in
which a rotating structure that supplies effective gravity is
contained within a shell of thick solid rock that provides the kind of shielding that is needed.
Of course Mars missions haven't been planned this way. It had been
hoped that microgravity and radiation could be endured, so we could do
a manned Mars mission on the cheap. Doing it the way I propose would
be much more costly, and so it won't happen as soon if that's the only
way it can happen.
Fine.
But "it's not going to be easy" is _not_ the same as "it can never be
done". Those are two very different things. One way or another,
someday we will get to Mars; either by building giant space habitats
that replicate Earlth-like conditions - or by developing improved
propulstion systems which remove the need to stick to the most
economical (but slow) Hohmann orbit to move between planets. Radiation
and microgravity wouldn't be showstoppers either if we used spaceships
that flew directly to Mars, near opposition, in a matter of a few days
instead of in a year and a half or so.

John Savard

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