child’s play

“Mars -- different in almost all respects from Earth -- is nonetheless the closest thing to a sister planet, at least one close-by. But close is a relative term. Our elliptical orbits are such that we come as close as 34 million miles to each other and as far as 250 million. A rocket leaving Earth for Mars has a choice of many possible paths, but the most economical in terms of fuel is called a Hohmann transfer and takes between six and nine months one way. Our two orbits are such, however, that a crew arriving at Mars from a Hohmann would have to wait a year or more for a favorable return alignment. Therefore, a round trip would take more than two years. Compared with Apollo’s eight days, that is huge, and creates a host of new issues. All in all, Apollo was child’s play compared to a Mars landing.” Michael Collins; Excerpted from the Preface to the 2019 edition of “Carrying the Fire: An Astronaut’s Journeys”; Natural History (New York); Jul/Aug 2019.