Free_Astronomy_-_SeptemberOctober_2019

47

ASTRONAUTICS

T

he human ex-

ploration of

Mars (illustration

below) is partly

braked by the im-

possibility of ade-

quately defend-

ing astronauts

from space radia-

tion. Recent data

from the ExoMars

Trace Gas Orbiter

(side illustration)

showed that dur-

ing a six-month

journey to the

red planet an as-

tronaut could be

exposed to at

least 60 % of the

total radiation

dose limit recom-

mended for their

entire career.

[NASA, ESA/D.

Ducros]

The intravehicular dose is totally unpre-

dictable because the interaction between

heavy ions and the spacecraft hull causes

the fragmentation of the former into a cas-

cade of lighter secondary

particles, whose nature

and energy depend on

those of the original ion

and the targeted mate-

rial. This process, called

“spallation,” actually in-

creases the destructive

potential of the incoming

flow and, depending on

the dynamics of the phe-

nomenon and the materi-

als involved, it may turn

out that a thicker shield

proves more deleterious

than a lighter one, lead-

ing to the creation of a

larger subset of particles.

Not knowing the GCR

makeup that interacts

with a given spacecraft,

most effective shielding materials can only

partially reduce the so-called “intravehicu-

lar dose,” the flow of particles that invades

the cockpit and its inhabitants.

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