Isn the 70+ mT CLV performance a little excessive for ISS Crew Launch flights?
No. It is always better to have spare performance capacity than to have too little — which is one of the critical concerns with the Ares-I. Both Jupiter launchers have more than sufficient performance to lift the 22mT Orion CEV. But, having the ability to also bring up a further 40-50mT of additional payload gives NASA the option to launch a cargo module to space the same way that Shuttle can with every crew. This is an ability the US will lose after Shuttle retires in 2010 because the Ares-I is unable to lift any additional payload at all. This extra performance is primarily intended for use by the Lunar missions, where the Crew Launch will lift the Altair Lunar Surface Access Module (LSAM) as well as the Orion spacecraft. A two-launch strategy using this technique is capable of sending almost 80 metric tons of payload towards the moon on every manned mission. For ISS flights, the Crew Launch can bring up large quantities of spares, supplies and scientific equipment, all for no extra
