Astronauts' rhymes with:
astronauts, astronauts, astronauts, astronauts, argonaut's, argonauts, astronauts, cosmonauts, cosmonauts', argonaut's, argonauts, astronauts, cosmonauts, cosmonauts'
Astronauts' sounds like:
accouterments, accoutrements, astronaut's, astronautic, astronautics, astronauts