Launch order, launch separation, and loiter in the constellation 1½-launch solution

The NASA Constellation Program (CxP) is developing a two-element Earth-to-orbit launch system to enable human exploration of the Moon. The first element, Ares I, is a human-rated system that consists of a first stage based on the Space Shuttle Program\´s solid rocket booster (SRB) and an upper stage that consists of a four-crew Orion capsule, a service module, and a launch escape system. The second element, Ares V, is a Saturn V-plus category launch system that consists of the core stage with a cluster of six RS-68B engines and augmented with two 5.5-segment SRBs, a Saturn-derived J-2X engine powering an Earth departure stage (EDS), and the lunar-lander vehicle payload, Altair. Initial plans called for the Ares V to be launched first, followed the next day by the Ares I. After the EDS performs the final portion of ascent and subsequent orbit circularization, the Orion spacecraft then performs a rendezvous and docks with the EDS and its Altair payload. Following checkout, the integrated stack loiters in low Earth orbit (LEO) until the appropriate trans-lunar injection (TLI) window opportunity opens, at which time the EDS propels the integrated Orion-Altair to the Moon. Successful completion of this "1frac12-launch" solution carries risks related to both the orbital lifetime of the assets and the probability of achieving the launch of the second vehicle within the orbital lifetime of the first. These risks, which are significant in terms of overall system design choices and probability of mission success, dictated a thorough re- evaluation of the launch strategy, including the order of vehicle launch and the planned time period between launches. The goal of the effort described in this paper was to select a launch strategy that would result in the greatest possible expected system performance, while accounting for launch risks and the cost of increased orbital lifetime. A discrete event simulation (DES) model of the launch strategies was created to determine the proba- bility of a second launch not occurring in a timely fashion (i.e., before the assets waiting in LEO expire). This data was then used, along with vehicle capability data, cost data, and design changes that increased loiter, to evaluate the impact of changes in strategy. The specific changes in strategy that were considered include decreasing the planned time between launches from 24 hours to 90 minutes, changing the launch order, and varying the LEO loiter capacity of the EDS and Orion systems. An overview of the launch strategy evaluation process is presented, along with results of specific cases that were analyzed. A high-level comparison of options is then presented, along with the conclusion derived from the analysis.