Space.com is carrying this article detailing a new mission proposal to solve the "Pioneer anomaly". Turns out the Pioneer space probes, which are the most distant human-created objects in history, aren't moving away from the sun as fast as they should be. The discrepancy is very small, but over this distance it is quite real. At first it was thought the probes were causing the anomaly, but every possible explanation along those lines has been explored and discounted.
In other words, it would appear there's nothing wrong with the probes, it's the universe that's messed up. Or, rather, our theories about how gravity works in our universe seem to be slightly but significantly off, and the Pioneer probes are simply providing experimental proof, albeit unintentionally.
The proposed space probe would use state-of-the-art instruments in an attempt to measure the anomaly. The hope is it will provide data to help us refine our knowledge of gravity, perhaps profoundly.