Mars? Pah!
The "public" is all excited about going to Mars. It makes great sound bites for politicians when they campaign in tech heavy regions. Engineers and physiologists shake their heads and moan.
With the relatively recents success of MER, Phoenix, and Curiosity, the tally is up to a 50%ish success rate of getting to Mars. Many of the failures have made their "mark" on the surface of the Red Planet. That's pretty dismal. There will be plenty of people that will sign up to go, but a 50/50 chance of crashing at the end of the first leg isn't good enough odds to spend the billions of dollars it will require.
On the hardware side, there is a lot of work to be done on just recycling human waste. For a vehicle to have a mass that can be sent, there will need to be a very high reuse rate of water. I don't think there is anybody on the planet that could go 6 months without bathing while confined in a small space that wouldn't drive their own nose into revolt.
It won't be just one rocket taking the crew and all of their stuff. There will need to be many launches to deliver the tools and supplies before the crew is sent. All of the gear will need systems to check that it has arrived in good condition. If anything is damaged or destroyed, replacements will need to be sent the next time the planets line up again for a Hohmann transfer orbit. Around 2 years, and then that delivery has to be verified. A F9H launcher to push enough mass all the way to Mars is only the first step. The mass that it's pushing also needs engineering.
Secondly and most importantly will be the health of the crew. To have a mission that is any use, the crew need to arrive healthy and sane. They may have to spring into action to resolve a critical issue right away. Radiation during the journey from solar flares could have some serious implications. There have never been any studies on how the human body reacts to fractional G. We know about how our bodies react on Earth (1G) and also in freefall (0G), but nothing in between. The visits to the moon were not long enough to get any data. Will the crew be fit enough to survive a return trip and adjust to living in Earth's gravitational field again or will their health be so deteriorated as to make coming home fruitless?
"Initial results from a study of Chris Hadfield and other astronauts who spent months aboard the International Space Station have turned up changes like those seen in someone developing Type 2 diabetes on Earth." -www.theglobeandmail.com
We won't even get into issues of sex and pregnancy beyond that trials with mice and rats in 0G were not pretty.
Being physically healthy has to be balanced with good mental health. Being locked up in a cramped high stress environment with other people pushes some people over the edge. The Russians have had a couple of issues during their programs on space stations. There are reports of some problems encountered with US astronauts as well. Gomez and Morticia might be at each others throats locked in a walk-in closet for months on end.
If you aren't an avid reader of science fiction, you are missing out on some great thought experiments into just the issues that will need to be addressed to make a trip to Mars successful. Read the first book in the Mars trilogy by Kim Stanley Robinson, Red Mars. The second 2 volumes and the tail end of the fist one delve almost exclusively into societal and political issues. If you have seen videos and read books by Robert Zubrin, you can see his thinking in the storyline. There are some Mars lectures by Robert Zubrin on YouTube. Time for The Stars by Robert Heinlein and Variable Star by Robert Heinlein and Spider Robinson describe some aspects of living on a starship.
Many of my friends work for NASA, JPL, AFRL (Air Force Research Labs), ULA, SpaceX and other aerospace firms and when we get together we invariably talk about space stuff. Except for one dreamer, the rest of us see returning to the moon and establishing a base there as a needed step in any long term goal of sending people to Mars. While there are challenges in building a lunar base that won't exist on Mars, there are many technologies that can be tested in a real off-Earth environment. The most important item to test is the human body. Some long term data on how the human body reacts in a reduced gravity environment will be of major importance. The benefit of a lunar base might be more valuable than any other endeavor to date. He3 might be a minor factor. A facility that can work on genetic engineering or nasty viruses like ebola would be as safe as one could get. Just don't connect it with anything else. If the worst happens the facility could be opened up to vacuum and raw sunlight or sealed, never to be accessed again. The nearness of luna means that emergency supplies could be sent quickly and evacuating a crew can be accomplished anytime it's needed. Two things that aren't possible with Mars.
I would like to see Jackass Flats reactivated and work restarted on nuclear thermal rocket engines. We could use chemical rockets to get into Earth orbit and a NTR for the trip to Mars. If there were issues, using a propellent depot to top up the chemical (liquid stage) of the rocket for the initial push before starting up a NTR at a further point away from Earth could be a possibility. The objective would be a system that could get a crew to Mars in the least amount of time. We would have to find the best way to collect Hydrogen on Mars to refuel the main propulsion stack (left in orbit) for the trip back.