Future of Planetary Atmospheric, Surface, and Interior Science Using Radio and Laser Links

Abstract

Scientific studies using spacecraft radio links, which are shared with communications and navigation functions, have been carried out on almost every solar system exploration mission in the past five decades. They have led to numerous scientific discoveries as well as technological advances. These radio science experiments have investigated the interior structure of every planet in the solar system and several of their satellites, the Moon, and several comets and asteroids and sounded the atmospheres of every planet in the solar system except Mercury, and the atmospheres of Pluto and several large satellites, the Io Plasma Torus, Saturn's and Uranus' rings, and the solar corona. Future experiments at Mercury, the Jovian system, asteroid Psyche, and other targets are currently in various planning and development phases. Over the next 30 years, significant advances in radio and laser link science technologies, including one order of magnitude improvement achievable in range rate and range accuracy and advanced calibration techniques, could enable many additional scientific breakthroughs. Future exploration concepts focus on applications of small spacecraft and entry probes and can include constellations for studies of atmospheric dynamics, interior structures, and surface properties. Selected science-enabling technologies specific to small spacecraft instrumentation on future missions are under study. Examples include field tests of radio scattering to determine surface properties, constellations for high-resolution spatial and temporal atmospheric sounding, small science-quality software-defined transponders, miniature ultrastable oscillators, and advanced radiometric calibrations at the Deep Space Network.Plain Language Summary Radio links are used to communicate with spacecraft by sending them commands from ground controllers and receiving back science data. The same links are used to examine important properties of planetary atmospheres, surfaces, and interior structure by carefully studying small changes in the radio signal's frequency and other parameters caused by geophysical phenomena when the spacecraft are close to the planets. Improving the radio system on the spacecraft and ground stations can lead to additional scientific discoveries. There is a trend to use small spacecraft to explore the solar system in future, and research teams are preparing instrumentation systems that are compatible with such possible missions. Key Points:• Spacecraft telecommunications links are powerful tools to study planetary atmospheres, interiors, and surfaces as proven over five decades • Instrumentation design and calibration techniques have significantly improved, and concepts are developed for additional breakthroughs • There is a trend to miniaturize spacecraft and components and fly them in groups, sometimes in formation flying

Science Goals and Mission Concept for a Landed Investigation of Mercury

“…This lander concept study has the capability for both X-band (8-12 GHz) and Ka-band (26-42 GHz) measurements, with the latter providing data with less noise and less susceptible to interference from solar plasma (e.g., Bertotti et al 1993;Asmar et al 2005Asmar et al , 2019Iess et al 2012). The use of Ka-band data with proper calibration for effects from, for example, Earthʼs atmosphere and solar plasma will allow the determination of the line-of-sight velocity with a precision close to 0.01 mm s −1 at a 60 s integration time (e.g., Iess et al 2012Iess et al , 2018Asmar et al 2019). For comparison, InSight currently uses an X-band system (Folkner et al 2018), which in general has a precision close to 0.1 mm s −1 at a 60 s integration time.…”

A Technique for the Analysis of Radio Occultation Data to Retrieve Atmospheric Properties and Associated Uncertainties

“…The occultation point is then determined uniquely for one‐way data. However, this data type relies on the stability of the onboard ultra‐stable oscillator (USO) that is a key instrument of radio occultation investigation (Asmar et al., 2019; Shapira et al., 2016). The MRO USO is characterized by a poor frequency stability with respect to the frequency standards used by the Deep Space Network ground stations, and to other USOs (e.g., Mars Global Surveyor; Tyler et al., 2001).…”

Collaborative Actions to Enable Richer and More Complex Planetary Science Mission Data

“…The ability to precisely measure key properties of spacecraft radio signals-frequencies, phases, amplitudes, polarizations-has provided and will continue to provide unique leverage to extract information about planetary ionospheres, atmospheres, rings, surfaces, shapes, internal structure, and rotational dynamics. Radio Science or Gravity Science investigations have been a standard feature since the first interplanetary missions and are a portion of both current missions, e.g., Juno and BepiColombo (Asmar et al 2017), and planned or likely for many future missions (e.g., Asmar et al 2019Asmar et al , 2020.…”