Krastanov's answer is good, but it's worth adding that 'cyclers' are a similar but practical idea: https://en.m.wikipedia.org/wiki/Mars_cycler https://en.m.wiki

Krastanov's answer is good, but it's worth adding that 'cyclers' are a similar but practical idea: https://en.m.wikipedia.org/wiki/Mars_cycler https://en.m.wikipedia.org/wiki/Mars_cycler