The energetically cheapest way to get to Mars is the Hohmann Transfer Orbit.

You wait for the planets to get to the right places in their orbits relative to one another, then you boost. When you get there, you fire your rockets again to slow down, and yet again to land. You do a little exploring or whatever, wait until the planets line up again, take off from the bottom of the gravity well and repeat the process for the trip home, including decelerating once again when you get to earth.

The Hohmann requires several years after the initial launch, most of the time with the crew just waiting, coasting in free fall, or waiting on the surface for the planets realign. The ship will have to carry everything it needs to complete its mission, as well as keep its crew alive for the entire time–with material it has to carry with it from the start. So you not only have to accelerate the payload, but all the consumables you will need: reaction mass, food, water and air, toothpaste, tampons and toilet paper.

These problems will eventually be solved, but its not likely we will have the solutions any time soon. The trip CAN be done faster than the requirements of the Hohmann transfer, and we can expect advances in rocket technology will allow us to save some time. But we’re still talking about a round trip of many months, and unless we postulate some exotic form of propulsion such as nuclear or ion drives, there is nothing we’re likely to come up with soon that will have us ready to launch within the next few decades.

The major problem is consumables. Water and air can be recycled, but food is something else. Each crew member will consume a minimum amount of about a kilo/day of mass just to keep him alive, much more if the recycling system is not perfectly efficient. We may be able to grow much of our own food, while recycling our wastes hydroponically–in theory. But remember, no one yet has managed to do that right here on earth. In space it will have to be done in limited conditions and with great constraints, not to mention zero gravity. And the system will have to be guaranteed to work perfectly or everybody dies. No vegetable garden on Earth can promise to do that. I doubt if you could design, test and build one in a few years that could that could also fit in a spacecraft and be operated by engineers with a crash course in hydroponics.

There’s always the possibility that resources could be found on the Martian surface–H20, CH4, CO2, but you’d need a small chemical refinery (and a power plant to run it) to convert them to a usable form for the trip back. I doubt you could harvest the resources available in the JPL parking lot any easier.

Of course, you could save a lot of mass if the crew signed on for a one-way trip; a group of pioneers committed to colonize the planet in the name of Mankind, living off the land after they got there (The Mars Manifest Destiny Mission). But I doubt anyone willing to sign on under those conditions could pass the basic NASA psychiatric entrance exam. I wouldn’t want to entrust my multi-billion dollar mission to them.

Sending men to Mars is not inherently impossible, and if we make some lucky propulsion system breakthroughs, we could probably start designing the ships today. But until that happens, space cadets, NFW.