Planning observations of EnVision regions of interest

EnVision is ESA’s fifth Medium-class mission in the Cosmic Vision programme. It has been adopted in January 2024 and is set to launch in 2031, in partnership with NASA.

EnVision's scientific goal is to study Venus from its core to its atmosphere, focusing on the planet's history, activities, and climate [EPSC-DPS2025-850]. The mission seeks to understand Venus' geological evolution, current geodynamic state, and interactions with its atmosphere. Additionally, EnVision will search for signs of past liquid water on Venus' surface.

A crucial part of fulfilling these objectives will be to observe high value targets from diverse types of terrains and across the entire surface to help piece together its history, look for activity and to understand surface atmosphere interactions. To that end, the EnVision science team has been working on a list of regions of interest to be observed with the VenSAR instrument, EnVision’s Synthetic Aperture Radar payload provided by NASA to obtain repeat imaging, stereo imaging, and polarimetry data at medium and/or high resolution. A further focus of the group has been to determine which other observations need to be done in synergy, including VenSAR altimetry and radiometry observations, observations by the subsurface radar SRS, and surface and atmosphere observations by the VenSpec suite.

The data generation is relatively high for a planetary mission, varying between 70 and 350 Gbit/Day and the data downlink rates vary by a factor of 10 during a synodic period. The data rate and observation plan also need to be well distributed across the 5 instruments and the radio science experiment. Full SAR coverage cannot be achieved within the 6 Venus cycles, and coverage distribution will be dependent on the arrival date. The observing plan and hence location of observations must be adapted to the allowed data rates; observations with higher data rates such as polarimetry or high-resolution observations, can only be planned at certain times. More operational limitations such as thermal constraints (e.g. MZ face remaining cold or cool down periods to be observed in certain conditions) further complicates the planning.

The challenge of balancing the data generation, storage and downlink, means that not all potential targets can be observed, and selection and prioritization is required. The SAR imaging observations have requirements on viewing angle and overlap for stereo observations and change detection measurements (requiring 3 repeat observations), thus further limiting the opportunities to observe targets. This has been a particular focus of the EnVision Science Working Team (SWT), the instrument science teams as well as the ESA science planning team, who aim to demonstrate that the coverage in area and target type meet the mission’s objective.  In this presentation, we want to break down the different operational challenges we are facing and the tools and methods we are developing to address them.