Accessible Latitudes for Planetary Entry Probe Missions to Saturn, Uranus or Neptune

In-situ probe measurements of planetary atmospheres add an immense value to remote sensing observations from orbiting spacecraft or telescopes, as highlighted and justified in numerous publications [1,2,3]. Certain key measurements such as the determination of noble gas abundances and isotope ratios can only be made in situ by atmospheric entry probes, but represent essential knowledge for investigating the formation history of the solar system as well as the formation and evolutionary processes of planetary atmospheres. Following the above rationale, a planetary entry mission to one of the outer planets (Saturn, Uranus and Neptune) has been identified as a mission of high priority by international space agencies. In particular, an entry probe mission proposal to Neptune has been selected as a flagship mission study in the next NASA decadal survey.

Within the scientific frame of atmospheric planetary sciences, a two- to three-year research study called IPED (Impact of the Probe Entry Zone on the Trajectory and Probe Design) investigates the impact of the interplanetary and approach trajectories on the feasible range of atmospheric entry sites as well as the probe design, considering Saturn, Uranus and Neptune as target bodies. The objective is to provide a decision matrix for entry site selection by comparing several mission scenarios for different science cases.

In this presentation, the focus is on approach circumstances of the planetary entry probe upon arrival at a normalized, spherical planet. Science objectives are organised in four (planetocentric) latitude ranges: (1) low latitudes < 15°, (2) mid latitudes between 15° and 45°, (3) high latitudes between 45° and 75° and (4) polar latitudes of > 75°. The latitude ranges are considered as potential entry zones for the implementation. The implementation strategy will be explained and discussed. Astrodynamically accessible latitudes are presented as a function of the approach velocity  vector v_∞ (both declination of the approach asymptote and magnitude). A roadmap is shown that explains the next implementation step to include the physical characteristics of the destination planet such as the planet’s size, rotation period, shape, ring geometries and obliquity.

The presented research was supported by an appointment to the NASA Postdoctoral Program (NPP) at the Jet Propulsion Laboratory (JPL), California Institute of Technology, administered by Universities Space Research Association (USRA) under contract with National Aeronautics and Space Association (NASA). © 2020 All rights reserved.

[1] Mousis, O. et al., Scientific Rationale for Saturn’s in situ exploration, Planetary and Space Science 104 (2014) 29-47.

[2] Mousis, O. et al., Scientific Rationale for Uranus and Neptune in situ explorations, Planetary and Space Science 155 (2018) 12-40.

[3] Hofstadter, M. et al., Uranus and Neptune missions: A study in advance of the next planetary science decadal survey, Planetary and Space Science 177 (2019) 104680.