Pros
Working on actual flight missions and pre-phase A studies from day one — not coffee runs or toy problems. The technical depth of your colleagues is extraordinary and you absorb a huge amount just from proximity. Access to JPL's internal tools, simulation frameworks and mission heritage is something you can't get anywhere else. Pasadena is a great place to live, and the lab culture is collaborative and intellectually stimulating. Supervisors generally treat you as a real contributor rather than a student.
Cons
Onboarding and badging can be slow and bureaucratic — expect delays getting computer access and lab clearances in the first weeks. The sheer size of the lab means it can take time to understand where your work fits in the broader mission context. Housing in Pasadena on an intern stipend is tight given California costs. Some teams are more structured than others so the experience varies a lot depending on your supervisor and group.