Mars Space Vehicle 

The spacecraft has trusses 18.3 meters in length that spin at a rate of 6 rpm to produce an artificial gravity of .4 g's.  This is done to counter the debilitating effects of zero gravity, which include the decalcification of bones, the weakening of muscles, the deterioration of the cardiovascular system, and several other complications.  In long flights the heart can shrink by as much as 10 percent, which can pose a serious health risk when re-exposed to gravity, and bones can lose enough calcium that they become brittle and are at risk of breaking when subjected to the high g forces of reentry.  Diet and intensive exercise can counter these effects, but not entirely.  

Artificial gravity, however, has its drawbacks.  The risk of a mechanical malfunction increases because the structure of the craft is considerably more complex.  There are also medical concerns, such as dizziness and sickness produced by the Coriolis force, an effect caused by a rotating object.  Due to these complications, it is undecided whether artificial gravity should be used on the first manned mission to Mars.

At the front of the ship is an aeroshield, which protects the ship as it aerobrakes through the Martian atmosphere.  In the aerobraking technique, the ship plunges into the Martian atmosphere to lose speed through air friction.  The entry must be exact, for if it is too steep the craft will burn up and if it is too shallow the craft will bounce off the atmosphere.  The deceleration lasts about six minutes and produces 2.4 g's.

The trans-Mars injection (TMI) stage of the craft contains 450,000 kilograms of propellant.  The propellant is liquid hydrogen and liquid oxygen.  The combustion of these two fuels produces a thrust that propels the craft to a speed of 26,000 kilometers per hour.  The propulsion stage performs three burns, Mars orbit injection (MOI), trans-Earth injection (TEI), and Earth orbit injection (EOI).