"Back of envelope calculations" for thurst, specific impulse, etc. I am working on a project that is really out of my realm of experience, so if you could give me some basics, that would be much appreciated. How do you determine the amount of thrust, power, etc. needed to travel a distance of 630 million kilometers in space? What if the payload is 2000 kg and I want the journey to take 1 year? Don't worry about trajectories and orbital mechanics....I just want a simple calculation. The thrust calculations I am familiar with are those in which the thrust is the force necessary to overcome drag, but I'm assuming there's a more general form? How do I get the specific impulse? Power? Suppose I'm launching from high earth orbit as well. I guess I need escape velocity for HEO? I really have no experience with propulsion, but I just need some ballpark figures to base a design on.