can't
enclose a man completely, and even if you do, there still is the air he
breathes and food he eats. Radiation in space contaminates everything
the body needs. And part of the radioactivity finds its way to the
reproductive system."

* * * * *

Marlowe didn't need to glance at the charts; the curve _was_ beginning
to flatten. Mathematically, it was determinable when it wouldn't rise at
all. According to analysis, Man someday might be able to endure the
radiation encountered in space as long as three years, if exposure times
were spaced at intervals.

But that was in the future.

"There's a lot you could do," he told Demarest. "Shield the atomics."

"Working on it," commented Demarest. "But every ounce we add cuts down
on the payload. The best way is to get the ship from one place to
another faster. It's time in space that hurts. Less exposure time, more
trips before the crew has to retire. It adds up to the same thing."

_On Mars, Amantha fondled the picture. "Pretty. But it ain't real." She
laid it aside._

_Ethan squinted at it. "I could make you think it was. Get it enlarged,
solidified. Have them make it soft, big as a baby. You could hold it in
your lap."_

_"Outgrew playthings years ago." Amantha adjusted the chair switch, but
the rocking motion was no comfort._

_Ethan turned the picture over, face down. "Nope. Hate to back you up,
'Mantha, but it ain't the same. There's nothing like a baby, wettin' and
squallin' and smilin', stubborn when it oughtn't to be and sweet and
gentle when you don't expect it. Robo-dolls don't fool anybody who's
ever held the real thing."_

In the interval, Earth had drawn ahead. The gap between the two planets
was widening.

"That's another fallacy," objected the training director. "The body can
stand just so much acceleration. We're near the limit. What good are
faster ships?"

"That's your problem," said Demarest. "Get me tougher crewmen. Young,
afraid of nothing, able to take it."

It always ended here--younger, tougher, the finest the race
produced--and still not good enough. And after years of training, they
had twenty-five months to function as spacemen. It was a precious thing,
flight time, and each trip was as short as science could make it.
Conjunction was the magic moment for those who went between the planets.

It was the heredity block that kept Man squeezed, confined to Earth,
Mars and Venus, preventing him from ranging