The Venus Express Mission Venus Express Mission Donald McCoy, Thorsten Siwitza & Roy Gouka Venus Express Project, ESA Directorate of Scientific Programmes, ESTEC, Noordwijk, The Netherlands enus evokes the ever-attractive image of a goddess from antiquity, and yet Vour sister planet, although attractive, is far from hospitable. The reasons for such a great difference between Earth and Venus have still to be understood and so, considering that they are very close in terms of astronomical distances, a mystery is invoked. Whether Earth is a unique planet, for which life was destined, or whether both planets were created under similar circumstances and subsequently evolved in different manners, is fundamental to the understanding of our place in the Solar System and, indeed, perhaps the Universe. Introduction Building on what we know from the Russian and American spacecraft that visited Venus in the seventies and eighties, Venus Express will continue the quest to understand the fundamental mysteries of the planet, but now using the latest state- of-the-art scientific instrumentation. Similar to Mars Express, the technical precursor of the Venus Express mission, the information produced around Venus will allow scientists to compare our nearest neighbour with our home planet. The link to Mars Express goes beyond the science, since the satellite is essentially derived from the same design. esa bulletin 124 - november 2005 11 Science Venus Express is a mission that was and the payload in more detail. This lives, they are not so great when compared proposed to ESA in response to a Call for introductory article is intended to provide to the distances to the giant planets Ideas to re-use the Mars Express platform, the reader with an overall impression of the orbiting our star. Why then is there such a issued in March 2001. The Venus Express mission and how it was created in a great difference between the environments proposal competed with nine others and resource-critical environment with a short of our planets? Mars is cold with a very was selected as one of three candidates for development time and limited budget. thin atmosphere composed primarily of a preliminary three-month study by carbon dioxide, while Venus is very hot industry to establish the feasibility of re- Science with a massive atmosphere also consisting using the Mars Express spacecraft bus. Venus, Mars and Earth, which represent primarily of carbon dioxide. Earth, on the That study, performed in the period July- three out of the four inner or rocky planets other hand, balances the composition of its October 2001 by ESA, Astrium and a team of our Solar System, have much in atmosphere with a small amount of carbon of scientific institutes, demonstrated that an common: a solid surface of comparable dioxide mixed in with a large amount of orbiter mission to Venus could indeed be composition, an atmosphere, a weather oxygen in an atmosphere dominated by carried out by adapting the Mars Express system and a location in space where the nitrogen. satellite. At the completion of the study, solar energy flux is moderate. However, Through a regular and extended period ESA’s Solar System Working Group and the differences between the planets of global observations, the Venus Express Space Science Advisory Committee themselves are striking, particularly in the instruments will provide scientists with a recommended to the Science Programme case of Venus, which is very similar to broad range of spectral data in the infrared Committee (SPC) in November 2001 that Earth in terms of size and gravity, and and ultraviolet spectral bands. the Venus proposal be chosen for further there are radical differences in the Furthermore, in-situ measurements of investigation. As a result, the SPC environments of the planets. Surface atomic particles at the boundary between recommended that a Pre-Phase-B study be pressures on Venus are 90 times greater the Venusian atmosphere and space will implemented to prepare the Venus Express than those on Earth and surface provide insight into the interaction with the mission for an implementation decision in temperatures reach 470°C (about ten times solar wind. Magnetometer measurements 2002. Finally, on 4 November 2002 the higher than the hottest temperatures on will support the measurements of plasma Venus Express project was fully accepted Earth), although the Sun's energy falling around the planet. by the SPC for implementation, with a on Venus is only double that of the Earth's. The multi-disciplinary science package modification to exclude the VENSIS radar Clearly, the ‘greenhouse effect’ is at work onboard Venus will enable scientists to experiment due to lack of financial support. on Venus! The evolution and behaviour of correlate many physical phenomena An enabling factor for embarking on the the Venusian atmosphere must be of keen affecting the planet and will provide cross- Venus mission was the availability of interest to us, if we believe that the same correlation of these phenomena to help instruments from previous missions such effect is beginning on Earth. The ESA them understand why Venus is so radically as Mars Express and Rosetta, both of mission will therefore study Venus in different from its neighbours. which were projects already managed by greater detail than ever before, using it as a the Scientific Projects Department. The ‘living laboratory’ to gain better insight The Mission spacecraft design modifications were kept into the life cycles of planets like our own The Venus Express spacecraft was to an absolute minimum to satisfy the and perhaps help us predict the future for launched by a Soyuz-Fregat launcher from Venus Express mission requirements. As a the Earth's environment. the Baikonur Cosmodrome in Kazakhstan consequence, the Venus Express spacecraft Although the distances to our planetary on 9 November at 04:33 CET. The maintains large similarities to Mars neighbours, Mars and Venus, are huge launcher put the combined spacecraft and Express. The system concept, such as the relative to those experienced in our daily Fregat upper stage onto a trajectory that structural design, propulsion subsystem, avionics units and operational concept, have been maintained while some Venus Express mission characteristics, such as the proximity to the Sun, the constellation of planets, and the distance to Earth, have led to unavoidable design changes, primarily in the areas of thermal control, communications and electrical power. The following articles in this Bulletin describe the spacecraft, the ground system Venus Express’s journey to Venus 12 esa bulletin 124 - november 2005 www.esa.int Venus Express Mission the Venus Mission Operations Centre at listed in the accompanying panel, together ESA’s European Space Operations Centre with the nominal planning dates for each (ESOC) in Darmstadt, Germany. event. Venus Express will spend approximately 150 days on its interplanetary journey, The Ground Segment during which time any necessary trajectory The concept for controlling Venus Express corrections will be made using the is based on the use of a single control spacecraft's thrusters. At least one centre in conjunction with ESA’s new correction, planned to take place about Cebreros 35 m station near Madrid sixty days after launch, will be required. (Spain). The New Norcia 35 m station near On arrival at Venus, a significant Perth (W. Australia) will be used to support deceleration manoeuvre will be made the Venus Orbit Insertion phase and for using the spacecraft’s own engine. The data acquisition in support of the Radio 53 minute burn will reduce the spacecraft's Science investigations. The baseline arrival speed by about 1.3 km/sec, operations philosophy is to acquire sufficient for it to be inserted initially into scientific data primarily during the 95 a highly elliptical polar orbit around the minute pericentre planetary passes, store it planet, with a pericentre altitude of about onboard, and downlink it during a single 250 km and a period of about ten Earth pass each day. By digging into the atmosphere, Venus Express will provide clues days. Smaller engine burns will then be All phases of the mission will be about the whole planet used to lower the apocentre and reach the controlled from the Venus Express Mission operational orbit. Operations Centre (VMOC) located at allowed the Fregat to circularise the orbit The nominal arrival of the spacecraft at ESOC. The Launch and Early Orbit Phase into a temporary parking orbit about Venus is planned for 11 April 2006. After (LEOP) will use the Main Control Room 190 km above the Earth. After about one some time for trimming the orbit (MCR) at ESOC and will be supported for revolution around the planet, the upper parameters to achieve the required 24 hour tracking, telemetry and commanding by stage was reignited to put the composite on polar orbit, the commissioning of the the ESA ground stations in Kourou an interplanetary trajectory towards Venus. spacecraft and the scientific payload will (French Guiana) and New Norcia. Separation of the spacecraft from the upper start. Full nominal operations will then The VMOC is the primary interface with stage was commanded by the Fregat commence for a period of 2 Venusian days, the spacecraft through the ground 90 minutes after launch and this action corresponding to 486 Earth days. A station(s) and will be responsible for initiated the deployment sequence onboard mission extension beyond this time is a monitoring and control of the complete the spacecraft. Once the solar arrays had possibility since the onboard consumables mission. The principal mode of operations been deployed and the propulsion system have been sized to cope with that. is that all routine payload operations must primed, the spacecraft was controlled by The major events of the mission are be pre-planned and executed according to an agreed Science Activity Plan (SAP).