2.1 Introduction and Flight Plan

Introduction

In this chapter I will demonstrate a lunar flight in Orbiter, a space flight simulator created by Martin Schweiger. The flight scenario is as follows: fly a cargo spaceship called the Shuttle-A from a lunar base to an orbiting space station called the ESS. The ESS is in a circular orbit at an altitude of about 500 km above the surface of the Moon. The ship will carry a payload of 120 metric tonnes. 

The roadmap listed in Part 1 covers all the knowledge needed to plan the flight. This will be a demo flight, not a tutorial; I will assume the reader is already familiar with the material laid out on the road map. The point of this chapter is to illustrate how Orbiter can be used as a tool for practicing orbital mechanics. 

Flight Plan

Before launch it's necessary to plan out a sequence of maneuvers that will be flown, and get an estimate for how much fuel should be taken. One of the fun parts of orbital mechanics is that it is like a strategy game; the choice of maneuvers, and which sequence to order them into, will have big effects on how much fuel is required, how much payload can be carried, and how much time will be used. For this demo flight, I just created a simple sequence of steps without doing any tradeoff studies or optimizations. 

The sequence is:

• Step 1) Launch into orbit. Point the nose to heading 090°, pitch the nose up to 10° over the horizon, and fire the engines for 2-3 minutes. After main engine cutoff, coast until apoapsis. 

• Step 2) Circularize the orbit. At apoapsis, fire in the prograde direction to raise the periapsis to match the apoapsis. 

• Step 3) Adjust the orbital plane to match the orbital plane of the target space station

• Step 4) Correction burn (optional): re-circularize the orbit, only if necessary.

• Step 5) Establish a temporary phasing orbit: temporarily adjust the shape and period of the orbit to synchronize with the space station's position. This will put the spaceship within a few kilometers of the space station. Once synchronized, "undo" the burn to re-establish the circular orbit.

• Step 6) Dock with space station

With some back-of-the-envelope planning I decided that half-tanks would be enough fuel to complete this mission. I then calculated the burn estimates for each step in the sequence. The summarized mass breakdown and the fuel budget for the flight are shown below. For now I am just showing the trip summary, but in the sections that follow I will provide more details about each step, and show how each burn is computed. 

It's helpful to visualize these numbers to get a feel for their relative weights, so below we have added plots. 

Fuel budget: