Venus probes
Would be interesting to research designs for probes that could last much longer on the Venusian surface.
Active cooling would be an interesting problem, probably requiring several stages of refrigeration technology before arriving at something where the radiator outside would actually be hotter than the environment.
Creating technology that would be passively resistant to the heat would have its own challenges, but probably be more effective. The probe should be as simple as possible, with maybe most of its "brains" in an orbiter.