<P> In the Crocco grand tour, a crewed spacecraft would get a flyby of Mars and Venus for under a year in space . Some flyby mission architectures can also be extended to include a style of Mars landing with a flyby excursion lander spacecraft . Proposed by R. Titus in 1966, it involved extending a flyby mission with a short stay lander . Basically, a short stay lander - ascent vehicle would separate from a "parent" Earth - Mars transfer prior to its flyby of Mars . The Ascent - Descent lander would arrive sooner and either go into orbit around Mars or land, and depending on the design offer perhaps 10--30 days before it needed to launch itself back to the main transfer vehicle . (see also Mars flyby). </P> <P> Aerobraking at Mars was estimated in the 1980s to cut the mass of a Mars mission lifted off the Earth by half . As a result, Mars missions have designed interplanetary spacecraft and landers capable of aero - braking . </P> <P> When an expedition reaches the orbit of Mars, it may drop into orbit around Mars by either of two main options: using rockets to slow down, or aerocapture . The same is true for missions to the surface . The state of the atmosphere, the altitude, and the properties of the landing site must come into consideration for a surface landing . It may be necessary to avoid a scientifically interesting site in the interest of safe touchdown . </P> <P> Aerocapture at Mars for human missions was studied in the 20th century . In a review of 93 Mars studies 24 used aerocapture for Mars or Earth return . One of the considerations for using aerocapture on crewed missions is a maximum G - limit to experience, for which it was noted 5 - g's (5 times Earth gravity) was a common limit to be planned for . </P>

When is the first planned mission to mars