Rather than an actual point or smooth, aerodynamic surface, the very top of the Ares I-X rocket is capped by an instrument called the “five-hole probe.” As its name suggests, this instrument has five holes on its conical point, which take in air during flight. The probe is actually a set of sensors that collects aerodynamic data, including total air pressure, static air pressure, angle of attack, and other measures that verify how well the vehicle is being controlled—one of the primary objectives of the test.
Because of the importance of this sensor, the five-hole probe is kept under a protective cover, which will be removed by someone standing on top of the launch gantry and pulling it off with a lanyard. The cover will be removed about 45 to 50 minutes before launch time. Once the cover is off, the five-hole probe will be ready to slice through the air and make its contribution to the flight test…pointy end up, of course.