MMS has two double-probe instruments, an Axial Double Probe (ADP) and a Spin-plane Double Probe (SDP). The Axial Double Probe (ADP) consists of two 10-meter antennas deployed axially near the spacecraft spin axis. The ADP provides full three-dimensional electric field measurements over a range from DC to 100 kHz with an accuracy of 1.0 mV/m. The double-probe instruments were developed by the Swedish Institute of Space Physics, the Swedish Royal Institute of Technology, the University of Colorado, Boulder, and the University of New Hampshire. The ADP is part of the FIELDS suite, which is led by Co-I R. B. Torbert (University of New Hampshire).