I find it very odd for NASA to take so long on the decision for what rocket to use when they know that designing a totally new rocket is out of the question due to huge initial cost and such little available cash within there new modified budget to get the job done.
Take a lesson out of the Russian play book build from what is available with small modifications as you move towards your final goal.
Atlas V uses lox/kerosene see link for engines http://www.astronautix.com/props/loxosene.htm
with second stage Lox/LH2 same as delta 4 rocket
all the engines that burn this fuel type http://www.astronautix.com/props/loxlh2.htm
which includes the shuttles engines SSME I think. Each table list
Engine Thrust(vac)
kgf Thrust(vac)
kN Isp
sec Isp (sea level)
sec Designed for Status
But the one table index that I would also need would be an engine weight specification and support hardware index of complexity to control engine as well as it's total weight. To make the best selection of what to use over the shelf as it were.

Yes Harold, we cannot afford to build a whole new rocket delivery system. The best soulution I would think, is to modify the shuttles external tank and boosters to accomplish our Mars mission. This has the advantage of using existing tech while keeping a large segment of the shuttle industry employed. Another thought, wouldnt it be possible to include more fuel in the shuttles cargo bay? I was thinking of a self contained fuel supply connected to the engines at the rear of the bay. The cargo bay could then still open and release your Mars lander. Any thoughts?

Well if cargo bay has extra fuel then do not release external tank bring it to orbit and start a fuel transfer process from the smaller tank in the cargo bay to the larger external tank. Begin the process of rocket contruction in space for the much larger Mars rocket as conpared to what is requires for a Moon mission.

Also this is another reason to know more specifics for the engines other than there thurst capabilities, you also needed to know there max thurst duration time to prvent damaging of engine during normal operations.

It also would be possible to use the first stage of the Atlas Lox/ kerosene stapped around the external tank as an extreme heavy lift placing the payload at the top of the external tank with a new structural casing around it for more support.

But we still need a new capsule or mini plane for the crew in either case. Which I feel must be either the recycling of the x-38 series plane or a brand new capsule, from who ever can supply them no contracts to design or build put that responsibility on the supplier not NASA. Have NASA just be a consumer instead ordering what they need off the shelf from who ever can supply it.

The only practical way to explore the solar system in and make the passages in reasonable amounts of time would be the use of nuclear rockets. Of course the anti-nuke crowd will go all bug-eyed and raise holy hell, but screw 'em. Trips between the planets that take months will always be a barrier. We need to reduce that time to a few weeks at most for purposes of exploration and colonization, and the the only way to do that is with an appreciable steady thrust which currently only nukes could provide. We need to get past our nuclear phobia and use the best and most efficient technology at hand if we are going to become a truly spacefaring race. Until something better comes along, that is nuclear rockets. The preliminary research has already been done. It's doable. We need to just do it.

All Nuclear engines that were being developed were of the ion style propulsion only the reactor was used to heat the propellents here is a link for engine an thrust http://www.astronautix.com/props/nucarlh2.htm

Though ion drive gives you steady and long duration run times there is a draw back in that it is slow to reach velocity and equal much more effort is needed to slow down.
Floating gas stations is a better solution at this time.

One could say that before any space mission should take place, we should invent machines first that can take us fast and easy far beyond our own solar sytem.
That way we could start with traveling to a planet that looks excactly like earth and that might be hospitable to mankind.

One could say that we are taking the long way home because of our impatience and urge to travel into space right now.
Why invest in terraforming techniches while we could use the money to invent those far traveling machines?

Therefore I think all of this stuff is quite interesting.
But still, I am very happy that we are investigating space with our "lame" spacecrafts right now so we don't have to wait for 200 or more years. I preffer the "and and method" of traveling into space right now while research is being done for better spacecrafts that indeed can conquer the universe. So: more power (=$) to both diciplines!

Well I personally belive that neccessity IS the mother of invention. Faster modes of travel were developed because early travelers were inconvienced. Perhaps the best reason for going to Mars is that it will spin off tons of new technology.

Remember, if my decentdants had waited till the automible was invented to 'Go West' then the USA would be a spanish or french speaking country.

Zach, you are right. That is a better reason to start missions than just impatience.
You know a lot about this stuff. I appreciate your comments.

I would like to think that frustration is the mother of invention though, i.s.o. neccessity.