Hello. I just wanted to throw in my two credits on this topic.
Mis-clicking with the mouse is an age old traditional ever since the useful little long-tailed devils entered our computer lives.
I vote for a cancellation button to provide the ability to Cancel a Mining Mission!
Like Bullwyf, I also simply mis-clicked on a mission and now must spend almost 400 fuel (round trip) and 20+ travelling minutes to complete something that was a simple mistake.
I honestly cannot come up with a reason why players should be "punished" for this very common occurrence. Suggesting that we make our choices more carefully doesn't really help. Most of us drive cars carefully but accidents still happen.