To protect the rover's motors from the blistering heat of the lunar day, they are mounted inside the rover's body. (This isn't necessary in Mars' chilly atmosphere; motors are placed out in the individual wheel hubs.) However, the motors' gear trains eventually must emerge from the rover body to connect with the chain drives on each side, and these pathways will allow heat to seep into the rover. The rover's design includes composite straps around each motor to drain the heat away to the radiator. In the photo below, the dark orange tape on the large silver gear train is a heater, mimicking the external heat that will flow into the rover toward the motor, shown at the extreme right encased in the thermal strap. Thermocouples at various points measure temperatures during the test. In the photo below, the motor is on the right but barely visible because it is enveloped by the thermal strap with the four bolts clamping it tightly around the motor. The motor is about the size and shape of a D cell battery. At the left is part of the gear train, which includes planetary and harmonic drives.