The Constellation program architecture - particularly the Ares I/Orion crew launch system and the Ares V heavy lifter parts of it - is often portrayed by NASA and the media as though it was the result of years of extensive analysis at NASA. In fact, much of it came out of a 60 day study ordered by Mike Griffin in the summer of 2005. The Exploration Systems Architecture Study (ESAS) cast aside many of the plans developed during Sean O’ Keefe's time at NASA such as launching the Crew Launch Vehicle (CEV) on an existing EELV rocket. The ESAS plan that emerged more closely resembled one put together by a small team led by Griffin and sponsored by the Planetary Society before he became administrator (see Extending Human Presence into the Solar System (pdf)).

Though the primary chapters of the ESAS plan are available on line, the data and assumptions used in the analyzes and simulations are in appendices that have not been released. There have long been rumors that there were biases in the study that favored the Ares I vehicle over the EELVs but without the appendices there was no way for outsiders to investigate this.

Recently, NASASpaceflight.com obtained 11 of the 12 ESAS appendices, though they have unfortunately kept the documents behind the subscription membership wall. Jon Goff has been examining the appendices and says that they do in fact show quite a few inaccurate assumptions and numbers that favor Ares I over the EELVS: Reason to Get an NSF L2 Subscription #2921: ESAS Appendices - Selenian Boondocks - May.1.09. As Jon indicates, we can hope that NASA finally releases these documents

publicly, because these discrepencies need to be explained. Hopefully if NASA ever does a study like this again in the future, they’ll be more open along the way, and thus expose themselves to less negative feedback when their data finally does see the light of day.