I'm sure the technology for it will come sooner or later, the crafts for those missions must probably be built in space so it is a huge project.
Here's the thing. Right now, all the materials necessary to build something in space will have to be brought from Earth at about $1K per pound. Imagine if a Falcon large were built in space. It wouldn't speed up travel to Mars by an hour.
Imo, most likely will be more sophisticated robots sent to Mars in order to collect materials that could be used for human habitation. Robots won't care about being in space for a few years, won't worry about radiation, or about coming back. Even sending a preformed habitable space is viable with current technology. The big problem is trying to land something large on a planet with little atmosphere. Sure, you can try to get there a lot faster, but then you have to slow down very fast. The physics make it difficult. And, ya better not miss at that speed because there won't be any coming back or turn arounds --like we see in Star Wars.
Everybody thinks going fast is the problem. Actually, given time, that's easy. A colleague of mine worked on space sail projects for NASA. For interstellar exploration, a sail with even a small ion drive will achieve enormous speeds. Putting the brakes on that puppy is a whole 'nother subject. Newtonian laws will still apply
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"A man is rich when he has time and freewill. How he chooses to invest both will determine the return on his investment."