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Mission profile

The proposed mission will launch in late December 2024 on  Soyuz-Fregat for conventional delivery to Venus. Following orbit insertion and periapse walk-down in May 2025, orbit circularisation will be achieved by aerobraking over a period of several months, with the main mission phase starting towards the end of 2025. From a nominally 258 km altitude circular orbit, the imaging radar will operate in three different modes across four orbits, repeated sequentially. Each four-orbit sequence will consist of one stereo pair stripmap; two interferometric pass-to-pass stripmaps; and a targeted acquisition of high resolution multipolar images. After seven Venus days (cycles), this strategy permits 20 m resolution stereo coverage of the entire planet, repeated interferometric pairs for change detection across one third of the globe and high resolution (<5 m) imaging of approximately 10% of the surface. Core mission instruments will also provide continuous subsurface sounder profiles (see Figure 1 below), and global infrared emissivity mapping from nightside observations and spectroscopic data to identify key volcanic gases. At the end of the nominal mission, and following any extended mission, EnVision will burn up in the Venus atmosphere.

Figure 1 :   Imaging and data return strategy. Left: from its nominal 88˚, 258 km orbit EnVision first acquires a 60˚, 6200 km StereoSAR stripmap pair (blue swaths, A), then two repeat-pass InSAR stripmaps (green swaths, B and C), followed by targeted HiRes Multipolar images (red box, D). Each orbit is offset 10 km by the rotation of Venus, so that StereoSAR pairs overlap after 12 orbits (M). VEM swaths and VIVO data are acquired during darkside operations; SRS profiles are continuous. Orbit crossovers provide geodetic control and gravity data. Right: the full mapping sequence is progressively reduced as data rate declines with increasing Earth-Venus distance. To ensure continuous repeatable InSAR coverage, data are stored through superior conjunction and returned thereafter.

Payload Configuration

The core payload (Figure 2) is supported by a 3 m X/Ka-band high gain antenna and a conventional bipropellant thruster. The 24 phase centre, dual polar, VenSAR is arranged in two rows on a 5.47 m by 0.64 m plank aligned along the orbit track. Operating at 3.2 GHz (9.4 cm) significantly reduces atmospheric losses compared with the 5.4 GHz (5.6 cm) C-band radar used in Sentinel-1. Parallel to this is the 10 m SRS dipole antenna, which shares a common radar processor and storage. VEM and VIVO are located at the rear of the spacecraft for uninterrupted visibility. Additional instruments may be carried for in situ study of the outer atmosphere.

Figure 2: Schematic illustration of EnVision's core instruments. HGA = high gain antenna; Li-ion = battery unit; RCE = radar central electronics; Flash = solid state storage; PCDU = power control and distribution unit. Not shown are the 370 litre fuel tank, reaction wheels and thrusters, sun sensor, stellar compass, 3-axis accelerometers, ultra stable clock and solar panels.

Potential Payload Consortium:

It is proposed that ESA fund the launcher, spacecraft, and ground segment; funding for the scientific payloads, including the radar systems, is being solicited from member states. VenSAR has been designed with support from Airbus Defence & Space (Space Systems) and is a customised derivative of their NovaSAR-S radar payload. VEM is being developed by a consortium between DLR, Germany, and CNES, France.

International Collaboration:

The baseline mission is proposed as an ESA-only mission, with science payloads funded by ESA member states as outlined above; no funding from external partners is expected. Nevertheless there are several opportunities for international collaboration: internationally contributed payloads would be considered in response to the AO for additional payload; and as recommended by the International Venus Exploration Working Group, we will consider carrying a proximity communications link to enable EnVision to perform data relay functions for other in situ elements. We note that this mission is complementary to that of several other missions in development worldwide, such as Russia’s Venera-D mission or the American Surface and Geophysics Explorer (SAGE) New Frontiers mission; our proposal will list possibilities for international collaborations which could reduce the cost to ESA.