Because of the huge expense and perceived need for gargantuan launch vehicles that don’t yet exist, the conventional wisdom in the space community is that a human mission to Mars is many years off, perhaps not to be achieved until 2030 or so. But space adventurer Dennis Tito is about to announce a plan to do one privately about five years from now.

What’s the catch? Well, first of all, there are no plans to land on the planet itself, which is one of the hardest parts of a Mars mission, due to its thin atmosphere, demanding a lot of propellant that must be hauled all the way there. In fact, there are no plans to even go into orbit around the planet, which itself would also be costly in propellant, both to enter and depart. The mission is much simpler — a two-person flyby on a so-called “free return” trajectory, allowing it to get back to earth without the need for an engine burn at Mars. The total trip time will be about a year and a half. It would be the ultimate human adventure to date.

Is it possible? Yes, in theory, if SpaceX delivers on their promise of the Falcon Heavy, the proposed launch vehicle for the mission. For a non-stop sprint to the Red Planet and back, one or two of them probably have adequate performance. The proposed spacecraft seems to be the existing SpaceX Dragon, which has only been used for cargo missions to the International Space Station so far, but is planned for crew delivery within three years. While those are low-earth-orbit (LEO) missions, SpaceX claims that the heat shield is capable of coming all the way back from earth-escape velocities (over twice the energy of a LEO entry), such as would be the case for a moon or Mars mission. The life support system will be provided by Paragon, which is the contractor for ISS crew delivery missions as well. Given that a Dragon is priced at about sixty million, and a Falcon Heavy flight at $120M, one can imagine a total mission cost of less than half a billion dollars, perhaps quite a bit less, putting it in the reach of many wealthy individuals.

The question is, will it be possible in practice? That’s more problematic.

The Dragon is roomy enough for a few-day trip to the ISS, but it might become pretty cramped after a couple weeks for two people, let alone the 500 days it will take for the trip to Mars and back. The trip will be spartan. One of the biggest dangers of the trip might be psychological — humans, like rats, can become aggressive, and even murderous when confined in too-close quarters for too long. And packing enough food and water for that many months won’t leave a lot of volume for stretching out, or basic privacy.

And even if they manage to survive the trip without killing each other, radiation in deep space will be a major issue. Most NASA plans for Mars missions assume the use of large amounts of water for shielding, but there isn’t enough volume or mass to have that in the Dragon. Other health problems will arise from the long period spent in weightlessness, which deconditions the cardiovascular system and reduces bone density, and even affects eyesight. But for this mission, that won’t be a problem until the return to earth, since there are no plans to descend into the gravity well of Mars or operate on the alien world.

Some of these problems  — the lack of habitable volume the radiation issues, for example — could be alleviated with a larger vehicle, such as a Bigelow BA 330 module. Coupling the Dragon with such a facility would make the trip relatively luxurious, but also much more costly in terms of required mass delivered to orbit, demanding multiple Falcon Heavy flights, rather than a single one. Between the extra launches and the cost of the Bigelow module, it would take the mission costs from less than half a billion to closer to a full billion. On the other hand, it would allow more people to go in more comfort, so perhaps the money could be raised with additional ticket sales.

One thing is certain — this is not a mission that NASA, in its institutional risk aversion (encouraged by Congress) could or would attempt, particularly since it would have the appearance of a stunt, with no scientific benefit. If it occurs, such boldness will be left to the private sector. And that’s perhaps not such a bad thing. In any event, we’ll find out when they make their formal announcement early next month, a week from Sunday.