REX (New Horizons)


REX or Radio Science Experiment is an experiment on the New Horizons space probe to determine various aspects of the atmosphere of Pluto during the 2015 flyby. It is an experiment designed with several goals including to determine the pressure and temperature of Plutonian atmosphere, to measurements of a possible ionosphere of Pluto and/or Charon, to record thermal emission temperatures, and to take more accurate chord lengths of Charon and Pluto.
To accomplish the objectives, as the spacecraft passes by Pluto, it is targeted on a path that takes it behind the dwarf planet in relation to where Earth is, and at that time radio signals from the flyby spacecraft pass through atmosphere of body, and from this various aspects can be determined. REX also is designed to take measurements of the atmospheric conditions at Pluto's moon Charon as part of the mission. REX utilizes an ultrastable oscillator, various electronics, and radio hardware aboard the New Horizons spacecraft. REX utilizes the X-band radio uplink on the spacecraft.
REX hardware weights 160 g and consumes 1.6 watts of spacecraft electrical power. It also makes use of other NH hardware, overall key hardware components for REX include:
To take the measurements, REX communicates with the Deep Space Network back on Earth. REX can also directly measure the thermal radiation of Pluto at 4.2 cm wavelength.
Observation goals:
REX is also planned for use in the New Horizon's post Pluto extended mission, including the 486958 Arrokoth flyby. The belt was discovered starting in 1992, and can be studied more closely by the New Horizons mission which is passing through it starting in the late 2010s.
During the post Pluto cruise, REX is usually turned on monthly to measure the electron density of the solar wind between Earth and the spacecraft.
The timing of the Arrokoth flyby was adjusted in part to aid the use of the REX experiment, in particular time it so more radar dishes on Earth could be used for this experiment.

Data from REX

Using REX radio occultation data the diameter of Pluto was found to be in a 2017 paper.