[orionblamblam]

This is not a "design change." The four segment RSRMs are available *now.* by doing a preliminary test launch with an existing motor, we can test out some of the other systems... controls and such, and prove out other aspects of the design.

[GonzoGOP]

Sounds a lot like when they used the completely reliable, but underpowered Redstone launches for the first two Mercury launches until they could get all the bugs out of the Atlas missile. They could test the capsule, launch and recovery procedures, but had to wait for the big missile to do the real work in orbit. Same here. They can test the CEV with the smaller, but currently available booster, and then fly the missions with more science cargo when the more powerful booster becomes available.