> Could someone with better knowledge of astronomy/aerospace explain (with less hyperbole) which part is the "impossible" part here?
Hyperbole is the operative term. When first proposed it would have been impossible with then-current hardware, but since such missions take time to germinate, sometimes people use the term "impossible" to add a sense of drama and daring, but with the expectation that the goal will become possible in time.
Also, according to Arthur C. Clarke, "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."
Hyperbole is the operative term. When first proposed it would have been impossible with then-current hardware, but since such missions take time to germinate, sometimes people use the term "impossible" to add a sense of drama and daring, but with the expectation that the goal will become possible in time.
Also, according to Arthur C. Clarke, "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."