Wernher von Braun, father of the American space programme (not to mention something, ahem, else) had a feasible scheme for getting a human colony on Mars. Apparently there were redundancies built into his plan to cover problems he knew nothing of.
And finally, like all space visionaries before Mariner 4 in 1965, Von Braun did not know that the Martian atmosphere was only one tenth the density estimated, and that there was not multi-cellular life on the surface, as astronomers were sure they had observed from earth. His graceful long-winged landing boats could not have made a horizontal landing on the surface. But even this was not insurmountable. Von Braun's glider would have had been subsonic at the 47 km altitude of his assumed atmosphere, corresponding to the actual surface pressure of Mars. An alternate landing scenario could have been to jettison the wings just over the surface, deploy a drag chute, and bring the fuselage/ascent stage down to a vertical rocket-powered landing on the surface. Von Braun's design had the margins and flexibility to handle even this worse-case contingency.