Though to be sure, in the sort of classic "saying something can't be done" style, I was inspired to comment:
To be sure, motives can be fixed more than one way. My muse loves nothing more than to take a plot or something deemed irreparable and make them work.
Now it is (or at least it should be) apparent that if the hero has even half of the brain with which the author has so carefully endowed him, he is not going to land his spaceship and, without examination or precaution, gallop heedlessly away from it, specifically to be captured by ferocious natives. Yet how often that precise episode has occurred, for exactly that reason!
Give him a problem with the spaceship so that the risk of natives is less than the certainty of injury or death if he stays.
Or have him carrying crucial stuff that MUST NOT be found on the ship for one reason or another.
An attempt at time-critical rescue might work, but does have the stigma of needing to succeed despite the capture — otherwise more haste less speed — come to think of it, getting vital supplies to the captives of these natives, you might want to be captured, knowing they would drag you to their king who holds the captives.
Similarly, if anyone connected with the take-off of a rocket-ship—especially an experimental model—had any fraction of a brain, there would be just about as much chance of a beautiful female stowing away aboard it as there would be in the case of a 500-mile racer at Indianapolis.
Put a crisis — an enormous crisis — on top of the launch. This gives the hero an excuse to have not been scrupulous in his checking, and the heroine (if you give her enough brains) a reason to get onboard.
Hmm. The mad scientist’s assistant is trying to get the ship off before it gets seized by the Bad Guys. The mad scientist’s daughter — who actually knows more about how it works, the assistant was brought in for mechanical skills to build, not design, it — takes refuge in a location he did not know could conceal her and then berates him for not realizing he would only crash it, she knows how the controls work better than he does.
because it reminded me of the great axiom:
There is no such thing as a stupid act. There is only an act for which inadequate motivation has been provided.
Some acts need more motives than others.