3. Dynamics and Control

3.1 Transit Orbits Kassandra De Voto Abstract The interplanetary trajectory we choose affects a number of mission parameters, including launch requirements, arrival velocity and thus thermal protection requirements, and flight time, which is limited by human endurance. All of these need to be optimized in order to reduce overall cost and risk. However, optimizing one parameter tends to adversely affect others, so a “best” trajectory is a compromise between various requirements. This section presents our trajectories and explains the compromises we made and the reasoning behind them.

3.2 Tether System Anne DeLion Abstract Creating an artificial gravity spacecraft is a novel approach to counteract the adverse effects of weightlessness on humans. Our mission calls for the use of a spinning tethered system and in this section, we discuss tether structure, deployment, artificial gravity spin-up, and retrieval method. We have two tethered systems. The Hab is tethered to the spent NTR during the outbound trip, and the ERV is tethered to the spent MLV for the return trip. Each tether is a HoytetherTM made from the material Spectra 2000, and each is strong and lightweight. To deploy each tether, we spin the docked vehicle configuration, undock the vehicles, and let of the principle of conservation of angular momentum unreel the tether. We choose this method because the spin of the system always keeps the tether in tension. Incremental burn times spin up the tethered system to create artificial gravity to keep total burn time low. As the tethered system approaches a planet, we release the manned module from the tether to impart a non-propulsive ΔV, therefore saving fuel. All of these factors work to ensure the health and strength of the astronauts during the long time spent in weightlessness.

3.3 Inertia Properties and Tethered Correctional Maneuvers Debbie Klein Abstract Both the voyage to Mars and the return trip to Earth involve a system consisting of two modules connected at opposite ends of a tether. The nuclear thermal reactor (NTR) serves as the counterweight to the Habitation module (HAB) for the trip to Mars. For the return trip to Earth, the spent stage of the Mars Launch Vehicle (MLV) acts as the counterweight to the Earth return vehicle (ERV). We determine the inertia properties of the system by modeling the spacecraft as a set of simple shapes. An algorithm numerically integrates the equations of motion for the system. A coupled thrusting scheme allows the velocity vector to change, which applies to both in-plane and out-of-plane maneuvers. The coupled thrusting method proves more cost efficient and more convenient than the single thrusting scheme.

3.4 Attitude Dynamics Chris Heidelberger Abstract In this section, we describe the attitude dynamics and orientation information of the vehicles during the interplanetary transfers. The discussion contains conclusions on stability, initial conditions, and methods to control the communications pointing, solar array pointing, and thermal heating issues. The conclusions include the nominal motion for each vehicle during their transfer and the initial orientation of that motion.