How much force?

A couple of posts ago we calculated that the constant acceleration mission would have an acceleration of about 0.04 m s^-2.  If our vessel is wholly payload then this means that we need a force of only about 0.04 x 10⁶ newtons to push the spacecraft.  This is a total of 2.4x10⁵ newtons.  This is comparable to the force exerted by a reasonably large elevator.  It's about 0.1% of the force of a Saturn V rocket The long duration of the flight means that the average force required is quite modest.  Of course if we have a large fuel supply to carry along, the force needed goes up with it. We may also choose a mission profile with much higher accelerations during early and late phases of the mission to minimize the velocity needed.