Even if you're as rich as Dennis Tito, if you're going to suddenly announce the formation of a private foundation to send humans to Mars and back as of 2018, you'd better have some data to back things up. In a technical feasibiliy announcement made public on its website, the Inspiration Mars Foundation has provided some intriguing details on its plan to send two people on a 500-day trip around Mars in a modified SpaceX dragon capsule.
Who gets to go?
500 days is a long time, and there's literally no room for personal disputes in the spaceship. The mission would be looking for a middle-aged married couple with non-type A personalities who've already had kids, and (ideally) have shown that they can get along for 500+ days at a stretch. A couple is also important because these people are gonna get really, really bored, and you'd better believe that some freakyness will be goin' on. Although, we should point out that space sex is probably kinda gross, because — Well, we won't get into detail, but use your imagination when it comes to sweating and zero gravity and being 30 million miles from the nearest shower.
Will it be safe?
The reason that the couple should already have had kids is that they may not be able to by the time they get back. Even traveling during the solar minimum, they're going to be exposed to a lot of radiation. Storing water at the back of the spacecraft (between the humans and the sun) will help mitigate that, but still, it's going to be risky, and a major solar event could potentially be fatal.
Furthermore, there's a small but not insignificant risk of micrometeorite strikes, a single one of which could potentially be a mission-ending event. There won't be room for space suits or an airlock, so if anything breaks, it has to be accessible and fixable from inside the ship.
The thing to understand here is that this mission is going to be 500 days. No less. As soon as the spacecraft makes its burn for Mars, the only way it's coming back is by heading all the way out and all the way back again. There's no auxiliary engine, and even if there was, there won't be enough fuel to turn around and come back to Earth. If there's some sort of serious problem on day two, well, they're just going to have to figure out a way to deal with it for the next 498 days.
Everyone is very well aware of the risks, here: they're prepared for something to go wrong, even catastrophically so, but that's just part of the deal with our first try at a mission like this.
How will they stay alive?
The Environmental Control and Life Support System (ECLSS) will be designed to keep two 70kg men alive for 500 days. This is funny, because they're definitely sending a heterosexual couple, but I digress. There won't be anything designed to keep people comfortable; it'll be "survival needs only." No showers. No privacy. No sleeping quarters. Total personal volume of just seven cubic meters. There will be exercise equipment because it's necessary for health. Food will be entirely dehydrated (all 1,384kg of it), and will likely be really, really boring. Water will probably be recycled, but it'll still be the biggest consumable by mass.
What will the Mars flyby be like?
The reward for all of this misery will be about 10 hours spent within 100,000 km of Mars, including a closest approach over the night side of the planet at 100 km of altitude, about four times closer to the surface of Mars than the ISS orbits above the surface of the Earth. At nearly 8 km/s, the spacecraft will be traveling about 10 times faster than the ISS does.
How will they land back on Earth?
The landing will be Apollo-style, with a capsule and heat shield using the atmosphere to slow down followed by parachutes and an ocean landing. The problem is, this will be the fastest atmospheric reentry ever attempted by a significant amount, with an initial aerocapture speed of 14 km/s. Apollo, by contrast, topped out at 11 km/s. This also means that the people in the spacecraft will set the record for the fastest moving humans ever, which is pretty cool, although our guess is that the whole first humans to Mars thing will probably overshadow that just a bit.
How much will it cost?
Estimates suggest that the overall mission will run somewhere from $1 billion to $2 billion. Sending Curiosity to Mars cost $2.5 billion.
Is a 2018 launch really possible?
Whether or not it's possible, launching in 2018 is essential, for two reasons: that's when an optimal free-return trajectory to Mars is available, and that's also a solar minimum, meaning that solar radiation will be less of a factor and the likelihood of a solar flare is small. This mission will either launch in 2018, or it won't launch at all: significant delays will probably result in cancelation, and the next orbital window won't open until the 2030s.
Making the deadline seems to be possible, barely, if everything goes right with both Inspiration Mars' spacecraft development and SpaceX's Falcon heavy launch schedule. And that's a big "if:" space is hard, things often don't work like they're supposed to right out of the gate, and it pays to be cautious, which is why the first humans to travel around the Moon were on the eighth Apollo mission.
We don't mean to suggest that Inspiration Mars is being hasty or reckless, by any means. It's just important to understand that this mission is willing to accept a level of risk that, historically, we haven't been entirely comfortable with when it comes to space travel. There is a very real chance that something will go seriously wrong, and there's very, very little safety margin and zero chance of a rescue. The astronauts who end up on this mission will have accepted that risk, and we have to as well: if something does go wrong, it needs to be understood that it is the price that we pay for expanding our horizons as a species, and we can't let it dissuade us from our drive for exploration.