The venerable HF dipole has found a new home and purpose in space. The Mars advanced radar for subsurface and ionospheric sounding (MARSIS) on Mars Express uses a simple 40-meter dipole as the antenna for its subsurface sounding radar.

The dual-channel low-frequency sounder operates between 1.3 and 5.5 MHz for subsurface sounding and between 100 kHz and 5.5 MHz for ionospheric sounding. It’s the first high-frequency sounding radar operating from orbital altitudes since the Apollo 17 lunar sounder in 1972. It’s been operating successfully since August 2005.

The sounder has obtained returns from several kilometers below the Mars surface.