ESA’s New Space Mission: Reaching Venus

Last time, we told you about the European Space Agency’s (ESA) plans for 2024-25. This time, we’ll look even further ahead. Over the next ten years, Europe has very important plans in store for Venus. In fact, the second planet from the Sun is shaping up to be a substantial focus for both American and European astronomy in the coming years. Between 2029 and 2031, three missions to Venus will be launched: DAVINCI (estimated to launch in 2029) and VERITAS (planned for no earlier than 2031), which will be carried out by NASA, and EnVision, for which ESA is responsible.

Today, we’ll take a closer look at EnVision, one of ESA’s most ambitious programs of this decade. The EnVision mission will serve two functions: first, it will be a demonstration of the capabilities of the new Ariane 6 rocket; second, it will provide the most complete picture yet of Venus and its past. This is important since the processes that destroyed this once-watery world could also play out on Earth.

NASA’s Contribution: the VenSAR module

EnVision is part of ESA’s wider “Cosmic Vision” program, which is a master plan for the agency’s ambitions to study the planets of the Solar System. EnVision itself will operate in a polar orbit around Venus for 15 months and will focus on four main areas of interest, some of which will intentionally overlap with the areas surveyed by NASA’s Magellan spacecraft, which orbited Venus from 1990 to 1994.

The intention to study Venus using an automated scanning satellite was officially announced in 2021. It was at that time that the main probe to be used on the EnVision mission, consisting of a compact scientific laboratory equipped with advanced radar mapping systems, was chosen. 

The EnVision space laboratory will be equipped with four science modules, each of which has a specific function. Discussions between ESA and NASA on EnVision’s scientific equipment resulted in a division of responsibilities, with NASA participating in the development of the VenSAR module, a synthetic aperture radar designed by a team of scientists led by Scott Hensley at the Jet Propulsion Laboratory (JPL) in California. 

The VenSAR module will be able to perform several different functions, but its primary focus will be on topographical surface mapping. VenSAR’s radar will operate in the S-band, with an operating frequency close to 3.2 GHz. The resolution of the terrain image that VenSAR will be able to make will reach about 10 meters per pixel, which is quite detailed for orbital radar imaging.

Surface polarimetry is one of the more interesting mapping methods offered by VenSAR. It involves measuring the change in polarization of electromagnetic waves reflected from the surface. Polarimetry is a kind of topological surface scanning using radar in conditions close to the atmosphere, where signals with a wavelength of approximately 9.4 cm have the greatest penetration.

With VenSAR, the probe will be able to perform regional mapping of Venus with the ability to focus on specific areas of interest through orbital maneuvering. The module will also provide  radiometric and scatterometric data, which measure the interferometry of a reflected laser beam. 

A SAR can also use stereo rendering techniques, which can provide artificial depth enhancement that creates the illusion of a three-dimensional image. This methodology is possible due to the constant movement of the spacecraft in orbit around Venus, meaning that the position of the scanner changes between when the signal is emitted and when it is received. This interval between measurements (the parallax between radar images) can be visualized as “depth” within an image using data processing tools. Stereo visualization methods are also used in the processing of ordinary satellite photos. 

The equipment included in the American VenSAR module will provide EnVision with a direct way to carry out 3D mapping of areas of interest on Venus nearly in real-time (not taking into account the time delay between data transmission and when it is received on Earth). 

The SAR module will also include altimetry capabilities (measurement of the altitude of the probe above the surface) to assist in orbital control. The radar also features a special temperature channel that can track gradual temperature changes on the surface of Venus as the probe traverses waypoints.

Venus SRS: an opportunity to look beneath Venusian soil

The EnVision probe will also carry out other experiments using instruments designed by the ESA and other leading astronomers and aerospace engineers at several major European research centers. Each of the three modules will have a separate function, including atmospheric measurement of the content and migration of sulfur dioxide, the study of geological structures, and the analysis of Venus’s gravitational field. 

The Venus Subsurface Radar Sounder (SRS), a low-frequency subsurface radar device, will be responsible for geological research. The SRS is a dipole radar antenna that receives a signal in the 9-30 MHz range. The module was developed and implemented by researchers at the University of Trento, Italy, under the supervision of Lorenzo Bruzzone. 

Unlike the SAR radar, which operates using relatively short waves of up to 10 cm, the SRS operates in the megahertz range, with the length of emitted electromagnetic waves  between 10 to 100 meters. This will allow the SRS science instrument to peer beneath the Venusian surface in search of hidden craters and other topographic features that may be hiding beneath a thick layer of rock. 

The 9 MHz operating frequency provides greater penetration capability, allowing EnVision to peer nearly 600 meters deep into the Venusian soil (depending on the scanned rock type). However, a signal like this will significantly degrade the spatial resolution of the image, which will be approximately 16 meters per pixel. On the other hand, a shorter wavelength in the 30 MHz range will decrease the depth limit to approximately 350 meters, but will significantly increase the quality of the acquired images, up to 5 meters per pixel. 

Using both types of signal, EnVision SRS will be capable of two main types of surveys: high-sensitivity SRS for obtaining data on the most interesting areas of Venus (~20% of the surface), and lower-quality SRS for the remaining ~80% of the planet. The SRS will focus mainly on the study of impact craters (including possible deposits of valuable minerals), lava flows (which can provide information about the planet’s internal structure), and other types of geological formations that will be of interest to scientists. 

Atmospheric research: 3 VenSpec detectors

The Venus Spectroscopy Suite (VenSpec) is a scientific module used to study Venus’s rocks and atmosphere and consists of three devices: VenSpec-M, VenSpec-H, and VenSpec-U, each of which is being developed at a different European institution. 

• VenSpec-M is an instrument designed to determine the chemical composition of Venusian rock. This versatile geological observatory will allow ESA to thoroughly study rock types and, most importantly, investigate elemental residues. This could provide insights into the planet’s geological history. The VenSpec-M experiment was developed by scientists from the Berlin Institute of Planetary Research at the German Aerospace Center (DLR), under the leadership of Jörn Helbert.

• VenSpec-H is an ultraviolet spectrometer and infrared mapper designed for studying the Venusian atmosphere. The primary task of VenSpec-H will be to investigate the planet’s troposphere and study volcanism through an unusual prism: the presence of volcanic gasses in the planet’s atmosphere. Specifically, the concentration of sulfur dioxide (SO2) and its ratio with residual H2O still present in Venus’s atmosphere could provide insights into the mechanisms of volcanic cloud formation and dispersion. This project is being led by Dr. Ann Carine Vandaele from the Royal Belgian Institute for Space Aeronomy (BIRA-IASB).

• VenSpec-U (also known as VeSUV) is a spectrometric instrument designed for monitoring the excess of volcanic sulfur gasses (SO, SO2) in the Venusian atmosphere. Over nearly 40 years of research, it has been established that the presence of SO2 in the planet’s atmosphere exhibits periodic intervals, with initial high emissions followed by a gradual decline over subsequent decades.

This kind of CO2 circulation in the planet’s atmosphere could either indicate intense volcanic activity or represent slow atmospheric circulation on the planet itself. The Venusian atmosphere, in fact, could resemble an ocean, with decade-long surges and colossal sulfuric cloud dispersals. Additionally, VenSpec-U is capable of measuring ultraviolet contrasts through spectral analysis of scattered sunlight reaching the receiving sensor, meaning that this technology will be exclusively used on the planet’s daytime side.

Such a comprehensive approach will ensure the acquisition of more complete spectral data, providing essential diversity in initial variables for building models on Earth. This instrument was developed by scientists from LATMOS (Laboratoire atmosphères, milieux, observations spatiales), the main aerospace research hub of Versailles University in France. The project is led by Emmanuel Marc.

RSE surface gravity scanner

The final module is EnVision’s Radio Science Experiment (RSE), developed by two scientists from the University of Nantes in France: Caroline Dumoulin and Pascal Rosenblatt. The RSE Gravity Measurement Laboratory will be able to detect ultra-sensitive fluctuations in the gravitational field, which the probe continuously updates as it travels through Venus’s orbit, especially as it flies past the planet’s poles. 

During its mission, EnVision aims to accumulate sufficient data to construct comprehensive gravity maps of the northern and southern hemispheres of the planet. From this perspective, the EnVision mission represents a significant opportunity, since measuring Venus’s surface gravity from Earth is quite challenging due to its proximity to the Sun. This distorts the planet’s gravitational field, a result of the Sun’s huge mass. EnVision will orbit close to the planet’s surface, and the spacecraft’s low orbital eccentricity will enable highly sensitive measurements of the gravitational field.

With a gravitational field map on one hand and topographic data of the planet obtained from VenSAR on the other, it should be possible to construct a detailed model of Venus’s core, allowing scientists to delve into the processes that govern the “life” (if it can be called that) of the planet.

Despite its inevitable end, EnVision will be capable of “seeing” Venus at depths never before accessible to humans. Employing a full battery of powerful modern electromagnetic scanning technologies will provide scientists with a vast array of data, particularly regarding the evolution of this once humid, now arid and dehydrated, world.

The launch of EnVision is scheduled for 2031, pending any schedule changes. The spacecraft will launch on an Ariane 6 rocket (variant 62), which by then will have been tested and proven during commercial launches and other scientific missions.

It should be noted that previous versions of the Ariane rocket series were unable to carry out missions like EnVision. The spacecraft alone will weigh 2607 kg. Adding another 255 kg of payload with scientific-experimental equipment, it is clear why Europe plans similar journeys only in the next decade: the rocket needs thorough testing first. However, the development of new rockets will provide Europe’s space sector with a unique opportunity to explore the inner circle of the Solar System.

The EnVision mission will be only the first of three journeys to Venus planned over the next decade, a joint effort between NASA and ESA. Together, these three voyages will provide scientists with terabytes of observational data that will form the basis for further research and publication on Venus’s evolution in the past and observations of its current cycles.