In Stranger in a Strange Land, Robert Heinlein claims that travelers to

Question

Mars spent 258 days on the journey out, the same for return, \plus 455 days waiting at Mars
while the planets crawled back into positions for the return orbit." Show that travelers would
have to wait about 455 days, if both Earth-Mars journeys were by Hohmann transfer orbits.

Answer 1

The time required for a Hohmann transfer orbit from Earth to Mars is approximately 687 days. This is calculated by taking the average orbital period of Earth (365.25 days) and Mars (686.98 days) and dividing by two (365.25 + 686.98 / 2 = 526.12). This is then multiplied by the ratio of the semi-major axes of the two orbits (1.5233) to get the total time of 687 days. Therefore, the travelers would have to wait 455 days, as stated in the book.