This view of a portion of the descent stage of NASA's Mars Science Laboratory shows two of the stage's three spherical fuel tanks flanking the bridle device assembly. The photograph was taken in early October 2008 from the center of the descent stage looking outward. The top of the descent stage is toward the top of the image.
The bridle device assembly is about two-thirds of a meter, or 2 feet, from top to bottom, and has two main parts. The cylinder on the top is the descent brake. The conical-shaped mechanism below that is the bridle assembly, including a spool of nylon and Vectran cords that will be attached to the rover.
When pyrotechnic bolts fire to sever the rigid connection between the rover and the descent stage, gravity will pull the tethered rover away from the descent stage. The bridle or tether, attached to three points on the rover, will unspool from the bridle assembly, beginning from the larger-diameter portion. The rotation rate of the assembly, hence the descent rate of the rover, will be governed by the descent brake. Inside the housing of that brake are gear boxes and banks of mechanical resistors engineered to prevent the bridle from spooling out too quickly or too slowly. The length of the bridle will allow the rover to be lowered about 7.5 meters (25 feet) while still tethered to the descent stage.
The Starsys division of SpaceDev Inc., Poway, Calif., provided the descent brake. NASA's Jet Propulsion Laboratory, Pasadena, Calif., built the bridle assembly. Vectran is a product of Kuraray Co. Ltd., Tokyo. JPL, a division of the California Institute of Technology, manages the Mars Science Laboratory Project for the NASA Science Mission Directorate, Washington.