Sounds like a slight oversight with the mission site location being in orbital cruise distance, don't think you're missing anything you just got unlucky.
Had something similar with a 'Weapons Fire' USS spawn just within orbital cruise distance Friday evening with a low ranked wanted Python inside, killed it easy enough but as soon as it popped the wreckage and all the components started free-falling toward the surface, couldn't catch up and scoop them up because of the silly enforced judder and orientation over-ride behaviour that magically kicks in when you point at a surface no matter the distance away you are, so even hundreds of KM above the surface as soon as I looked toward the surface to scoop the materials my ship orientation would spaz out.
I'd suggest throwing up a bug report just so someone can remind the chaps who design the framework for missions that gravity exists, and gravity in conjunction with enforced ship spazzing when facing the ground leads to mission sites being created that are for all intents and purposes impossible to complete.
