We define a new class of “rapid round trip” interplanetary missions for which the principal characteristic is a total mission duration that is 1 or more years shorter than the traditional round trip using Hohmann transfers. Round trip missions using Hohmann transfers to near-Earth asteroids or other nearby interplanetary objects may require many years. (For example, 8 years for a round trip to a Near-Earth Asteroid at 1.1 AU.) Consequently, rapid round trips are the only practical means for human space travel to these objects.
The Hohmann round trip mission to Mars typically requires about 2.7 years. Rapid round trips to Mars can be as short as 5 months in total mission duration, but these trips require delta V’s 5 times or more greater than for Hohmann round trips. This paper explores rapid round trip missions that are intermediate in terms of both total mission duration and total delta V required. These are significantly faster and take a greater delta V than Hohmann round trips, but are not as fast and use less delta V than the very rapid missions. For example, an intermediate round trip mission to Mars can have a total duration of 14 to 15 months, stay on the surface of Mars of 2 to 3 months, and a total applied delta V of around 14 km/sec if direct entry is used.
Wertz, J.R. International Astronautics Federation Congress, Vancouver, Canada. October 4–8, 2004.