Tau Zero: The Successive Crises

Perceiving the cosmos from a vaster perspective than before, the crew of the uncontrollably accelerating Bussard ramjet spaceship Leonora Christine in Poul Anderson's Tau Zero (London, 1973) coin a new terminology. Knowing already that "...a cluster or family of galaxies like our local group..." belongs to a larger association, they decided to call such  larger associations "...clans..." rather than "Superfamilies -," now that they are about to fly between them. (p. 129)

 A later passage:

" '...we can pick the clan, family, cluster, and individual galaxy we want to make our destination...'" (p. 184)

- confusingly implies that a "family" is not a cluster but a grouping intermediate between a "clan" and a cluster.

The successive crises that the crew members encounter and address are:

(i) the interstellar and even intergalactic mediums are too dense to allow repair of the decelerators so it is necessary to plunge through the galactic center, a passage taking over a hundred millennia, in order to accelerate into inter-cluster space;

(ii) but the inter-cluster medium is still too dense so it becomes necessary to plunge through several galaxies, then through what had become their target cluster, in order to accelerate into inter-clan space where the decelerators can be repaired hundreds of millions of years later;

(iii) but now the ship is moving so fast that its target clan is unable to brake its velocity so it continues to accelerate through and between clans, which are separated from each other by hundred million light-year stretches of dark and empty space, hoping to find a large clan, a group of clans or a rapidly moving clan that can brake the ship's velocity;

(iv) however, the universe ages, dims and contracts so that the ship must now orbit around the newly forming monobloc in the outer layer of its hydrogen envelope that is not too hot, radiant or dense, in order to survive into the next cosmic cycle. At last, this works.