Time And (Sex In) Space

Time
In an unfinished novel, "The Dark Tower," CS Lewis argues that physical time travel is impossible and then presents mental transference between timelines.

In two stories and one novel, Robert Heinlein presents three classic statements of the circular causality paradox.

In many stories and novels, Poul Anderson addresses every aspect of time travel.

(Sex In) Space
In Heinlein's " - All You Zombies -," the time traveler changes sex and is both his own parents. While female, she joins the:

"'Women's Emergency National Corps, Hospitality & Entertainment Section...'"
-Robert Heinlein, " - All You Zombies - " IN Heinlein, The Unpleasant Profession Of Jonathan Hoag (London, 1980), pp. 126-137 AT p. 128 -

- known in other periods as:

"'Auxiliary Nursing Group, Extraterrestrial LegionS'..."
-ibid. -

and:

"Women's Hospitality Order Refortifying & Encouraging Spacemen..."
-ibid.

Heinlein makes the same points as Lewis in "Ministering Angels":

it is recognized that men sent into space for extended periods will need a release of tension;
"'But most volunteers were old hookers...'" (ibid.)

By the time of Anderson's Young Flandry Trilogy, space travel is no longer difficult or dangerous so that more acceptable young women can be sent to extrasolar Naval bases.