With its impeccable landing on Thursday, NASA's Perseverance became the fifth rover to reach Mars—so when can we finally expect the long-held goal of a crewed expedition to materialize?

NASA's current Artemis program is billed as a "Moon to Mars" mission, and acting administrator Steve Jurczyk has reiterated his aspiration of "the mid-to-end of the 2030s" for American boots on the Red Planet.

But while the trip is technologically almost within grasp, experts say it's probably still decades out because of funding uncertainties.

Wernher von Braun, the architect of the Apollo program, started work on a Mars mission right after the Moon landing in 1969, but the plan, like many after it, never got off the drawing board.

What makes it so hard? For a start, the sheer distance.

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