National Aeronautics and Space Act, Sec 102 (d) declaration of purpose

Here is how I would lay out purpose for NASA:
1) Expand human knowledge through basic research in space
2) Utilize space resources for the efficient usage and protection of resources on earth
3) Expand knowledge of space resources and develop plans for the (ultimately profitiable) exploitation of space resources
4) Protect earth from a catastrophic collision from asteroid or comet
5) Provide resources and knowledge for US defense when needed (space defense should be primarily handled through the Air(aerospace) Force)
6) Foster private utilization of space
a) through knowledge and resource sharing of solutions to common problems and issues
b) and through prizes, contracts, and incentives to aid in the above other goals
7) Utilize all of the above for the ultimate goal of creating self sustaining/synergistic off world colonies

The NASA business model should be one of figuring out ways to bootstrap utiilization of space with a relatively small outlay. In other words, most of these things won't happen until space pays for itself. In this vein, I think NASA's been largely on the wrong track throughout the space shuttle and ISS era. We'll spend 150B on ISS and have returned virtually nothing in new knowledge. Space shuttle launches probably cost 1B each when you add up all the associated costs. When I do the math I see a 15B NASA budget of which only about a billion a year actually returns much in the form of space probes. NASA is bloated and in my opinion beyond redemption in terms of wrong headed political guidance and influence peddled guidance from the big aerospace companies.

My theory is that a small base funding should be provided supplemented by funds derived from interested and benefited parties. Below I've tried to match some funding sources with my list of goals/purposes.

Sources of funding and justification of funding:
1) a) basic research sources, competing with NSF,etc
b) education (tool for inspiring young to advance science) --one of the few non-local federal funded education intiatives that would make sense
2) a) climate change monitoring, development of models --carbon taxes fund this
b) monitoring of resouce/land use,polution, weather forecasting--taxes on polluters, resource utilizers fund this
3) Small piece of taxes on all resource oriented companies (mining, drilling, etc) used for long term prospecting and utilization of space resources
4) Homeland security funds
5) defense, some funding can come from the air force to utilize common resources for peaceful and defensive purposes (e.g. gps technology, weather forcasting)
6) Initially subsidized, but ultimately derived from taxes on profitable space companies.
Some funds from entities utilizing space resources (e.g tax on all gps based technology to pay for gps)
7) Part of NASA's fixed funding--steady and long term--but focused on shortest path for colonization
a) funding for plans
b) development of enabling technologies
Finally, NASA's should be able to license and sell media products of space developments to supplement its budget.
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Some Justifications for the lay person--
1) NASA can be of great benefit for the efficient utilization of earth bound resources and acquisition of knowledge to protect our planet. With better knowledge to create accurate predictive models, we will make more efficient decisions governing such things as climate change policies. That will potentially save orders of magnitude times the current NASA budget in itself. As a side note, exploration of other planets weather systems will be invaluable in creating earth models--modeling is so much more effective when you have more than one data point.

2) If you can think in terms of grandchildren rather than yourself, then you can get behind the resource exploration that is tantemount to automated lewis and clark expeditions. The potential value of the limitless resouces of space to supplement our earth bound ones is worth some long term vision and funding.

3) While the odds are low, the level of catastrophe makes it clear that we must survey our solar system for collision threats and if necessary build systems to avoid them.

4) The obvious everday uses of space such as gps, weather forecasting, resource monitoring, etc deserve a budget, 5) You need a governing regulatory body for all space and satellite companies
There are more but by now the average person has nodded off.
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I've posted enough that most are already aware that I believe the shortest path to all the most ambitious off world goals is through an initial phase of robotic exploration and reconaisance, a second phase of robotic exploitation of off world resouces and building of infrastructure, and only in the 3rd phase manned space colonization. In that vein I find NASA funding of the manned space program to date to have been a horrible waste of resources. It should exist at a much lower level of funding, while robotic probes get the lion's share of funding.