The New Horizons Radio Science Experiment (REX)

Abstract

The New Horizons (NH) Radio Science Experiment, REX, is designed to determine the atmospheric state at the surface of Pluto and in the lowest few scale heights. Expected absolute accuracies in n, p, and T at the surface are 4 · 10 19 m −3 , 0.1 Pa, and 3 K, respectively, obtained by radio occultation of a 4.2 cm-λ signal transmitted from Earth at 10-30 kW and received at the NH spacecraft. The threshold for ionospheric observations is roughly 2 · 10 9 e − m −3 . Radio occultation experiments are planned for both Pluto and Charon, but the level of accuracy for the neutral gas is expected to be useful at Pluto only. REX will also measure the nightside 4.2 cm-λ thermal emission from Pluto and Charon during the time NH is occulted. At Pluto, the thermal scan provides about five half-beams across the disk; at Charon, only disk integrated values can be obtained. A combination of two-way tracking and occultation signals will determine the Pluto system mass to about 0.01 percent, and improve the Pluto-Charon mass ratio. REX flight equipment augments the NH radio transceiver used for spacecraft communications and tracking. Implementation of REX required realization of a new CIC-SCIC signal processing algorithm; the REX hardware implementation requires 1.6 W, and has mass of 160 g in 520 cm 3 . Commissioning tests conducted after NH launch demonstrate that the REX system is operating as expected.

Color, composition, and thermal environment of Kuiper Belt object (486958) Arrokoth

“…The Multi-spectral Visible Imaging Camera (MVIC) provides panchromatic and color imaging in four color filters, "BLUE" (400-550 nm), "RED" (540-700 nm), "NIR" (780-975 nm), and "CH4" (860-910 nm) (15). The highest spatial resolution MVIC color observation of Arrokoth designated as CA05, was obtained on 2019 January 1 at 5:14 UTC (coordinated universal time), from a range of 17,200 km, at an image scale of 340 meters per pixel, and phase angle 15.5°. This provides more spatial detail than the 860 meters per pixel CA02 MVIC color scan (1).…”

“…6B. The radiometric signal was converted to radio brightness temperature using procedures developed earlier in the mission, accounting for the solid angle subtended by Arrokoth within the antenna beam (15,17,36,37). Accounting for the 414.4 km 2 cross section of Arrokoth and noise from instrument and background, we obtain a mean brightness temperature T B , averaged across the night-side visible face of Arrokoth, of T B = 29 ± 5 K, which is within the range of brightness temperatures estimated from an earlier analysis (1).…”

Prerequisites for explosive cryovolcanism on dwarf planet-class Kuiper belt objects

“…Such measurements include atmospheric thermal profiles (to constrain heating from extreme ultraviolet radiation) and structure (in particular, the exobase altitude from which escape may take place), as well as ejection velocity in potential plumes. New Horizons is well equipped to perform such measurements: ultraviolet spectra and atmospheric maps will be acquired by the Alice instrument ; atmospheric temperature and structure profiles will be inferred from radio occultations using REX (Tyler et al, 2008);and SWAP (McComas et al, 2008) and PEPSSI (McNutt et al, 2008) will be used to perform solar wind measurements and energetic particle spectrometry to determine in situ escape rates (Stern and Spencer, 2003).…”

Introduction to ‘Pluto, Charon, and the Kuiper Belt Objects’: Pluto on the Eve of the New Horizons Encounter

“…Simulations of the encounter by the Radio Science Experiment (REX) indicate the potential accuracies of the combined and individual mass determinations of Pluto and Charon are on the order of 0.1% (Paetzold et al, 2013;Tyler et al, 2008), a substantial improvement in precision (especially for Charon). Simulations of the encounter by the Radio Science Experiment (REX) indicate the potential accuracies of the combined and individual mass determinations of Pluto and Charon are on the order of 0.1% (Paetzold et al, 2013;Tyler et al, 2008), a substantial improvement in precision (especially for Charon).…”