REX (New Horizons)

[1] Experiment was designed with several goals including determination of pressure and temperature of Plutonian atmosphere, measurements of a possible ionosphere of Pluto and Charon, recording thermal emission temperatures, and taking more accurate chord lengths of Charon and Pluto.

[2] Observation goals:[4] REX is also being used in the New Horizon's post Pluto extended mission, including the 486958 Arrokoth flyby.

[5] The Kuiper belt is a ring of orbiting bodies between approximately 30 to 55 AU (Earth-Sun distances), home to Pluto and short-period comets it is estimated to consist of hundreds of thousand if not millions of small icy objects.

[7] During the post Pluto cruise, REX is normally turned on monthly to measure the electron density of the solar wind between Earth and the spacecraft.

[9][10] The timing of the Arrokoth flyby was adjusted in part to aid the use of the REX experiment, so that more radar dishes on Earth could be used.

Diagram of the trajectory of New Horizons , which enables the REX experiment to utilize the occultation of Pluto between the spacecraft and Earth to determine atmospheric data
Part of the radio network on Earth, a 70 m antenna at Goldstone , California . REX picks up the signal from Earth during the flyby to record some types of data about the Plutonian system.