These things aren't impossible.
They're just very, very difficult.
The 10 years to fusion, and the 10 year to a space elevator folks are just deluding themselves about the difficulty.
It may be difficult, everything amazing is. Until you look up in the sky and see Flight 95, United Airlines non stop to Atlanta, blasting by overhead. It will be challenging, and what the heck is so wrong with being part, however small, in helping accomplish something which at it's greatest, most civilization altering iteration may not be finished in a lifetime? I can't think of a more noble, life affirming pursuit, to work tirelessly on something which when completed will benefit not just you, but the entire planet. Count me freakin in.