Keep the first combine it with the fourth and let the private sector handle 2 & 3 if there is any real justification for them. CATS is needed for opening space for business and colonization, but not exploration. CATS should be pursued in tandem with exploration. NASA's budget is sufficient to due both. I believe than half NASA's current budget is needed based on the SLI and NASA Mars reference mission budgets. The tough part is determining which of the many other interesting projects NASA is pursuing to delay.

NASA has already about worn out the public's patience with snail pace exploration. We can ignite public support with a real scientific expedition to Mars capable of developing technology needed to live on Mars as well as investigating the scientific questions it poses while cocurrrently pursuing the technology needed to get people there and elsewhere cheaply.

The potential opportunity costs of your go slow approach are:

1) NASA looses public support through lack of projects with broad public appeal.

2) Economic problems or other new priorities such as the war on terrorism render NASA a low priority.

3) Resources become scarce before your time table establishes a permanent presence in space and space travel seems even more of a luxury than it does now.

4) Etc, There are many other potential scenarios wherebye we have only a limited window of opportunity to blaze the trail into space.

Regards,
Mark