As several people have pointed out, the shuttle has been used for aerodynamic testing for a long time, and the first shuttle was outfitted with special instrumentation for that purpose. And a lot was learned about the boundary layer, but a precise experiment was never performed on that subject.
If we are to design future hypersonic aircraft and spacecraft, we need to understand this phenomenon in a very specific way. Precisely controlled data collection is required. That is what is going to happen on the next shuttle flight.
Here is a picture of the apparatus as it was being installed on Discovery in the Orbiter Processing Facility:
The older tiles have grayed with repeated flights, new tiles are shiny black, and the green painted aluminum skin is where tiles are yet to be installed. The wires hanging down are for the instrumentation. The black tile in the center of the picture has a quarter inch ridge down the middle of it, oriented crosswise to the airflow; that is our controlled trip mechanism.
If this experiment is successful, there are two more iterations with larger steps on the test tile.
Funny how it seems so simple, but it takes so much planning!
If we are successful, a better understanding of the transition will lead to a prediction capability. This will make it possible to design the engines and aircraft for the next leap forward in aircraft!