A potentially more serious issue for using Ares V for planetary missions concerns the need for a dedicated upper stage to provide high excess escape velocities for spacecraft (known as C3). Several of the mission concepts evaluated in this report, including Solar Probe 2, Interstellar Probe, Solar Polar Imager, Neptune Orbiter with Probes, and Titan Explorer, would require some kind of upper stage. The current most likely upper stage, the Atlas V Centaur III Dual Engine Configuration, is relatively tall and thin compared with the Ares V. When placed under the current baseline launch shroud, it would leave relatively little room for a spacecraft (Figure 5.15). An extended shroud would provide more room, but it is unclear if this would be sufficient for many of these mission concepts. The Titan IV Centaur was shorter and wider than the current Centaur but has long been out of production. Neither upper stage takes advantage of the increased diameter of the Ares V payload shroud. Planetary missions could better use an upper stage that is shorter and takes advantage of the full width of the Ares V; however, development of such a stage could be expensive.
In order for Ares V to be attractive for future science missions, vehicle designers will have to consider the requirements of potential science missions.