Later in the mission, NASA may change the orbit so the Lunar Prospector spends half of its time behind the moon, out of sunlight. The test system contains three solar-panel simulators that engineers can program to simulate all power waveforms that are possible in space. The valves are operated by nominal 28-V pulses. You can also get arcing, which can cause EMI that can upset the spacecraft's systems. The ADC monitors current by measuring voltage across shunt resistors and temperature from thermistors.
Pressure transducers produce a voltage proportional to pressure.
Logging the data from the measurement sensors and simulating the position sensors' outputs requires precise timing. For example, the triggers on the two AWGs must be synchronized so the simulated sensor outputs will appear as they will in space. In addition, the simulation of shadows as the booms pass over the solar strings requires time synchronization. The PC's clock may not keep accurate absolute time, but that's not important. With the two computers in sync, engineers can time correlate all measurements to command and telemetry signals.