December 11, 2014 – After eight years in orbit, the European Space Agency’s Venus Express may be nearing its end. On November 28, 2014, the European Space Operations Center (ESOC) at Darmstadt, Germany reported loss of contact with the spacecraft. Repeated attempts to re-establish contact using ESA and NASA deep-space tracking stations have been made since then, with limited success, but the root cause of the anomaly remains unknown.
Some telemetry packets have been successfully downlinked. These confirm that the spacecraft is oriented with its solar arrays pointing toward the Sun, and is rotating slowly. The operations team is currently attempting to downlink the table of critical events that is stored in protected memory on board, which may give details of the sequence of events which has occurred.
The demise of Venus Express is not altogether surprising. The spacecraft, for which University of Colorado professor Larry Esposito is a mission scientist, was originally designed to orbit in Venus’ challenging conditions for a mere two years. The spacecraft has far exceeded its life expectancy and provided a wealth of information about Venus. Most notably, data has provided tantalizing hints that the planet may be volcanically active.
Venus Express was launched on a Soyuz-Fregat from the Russian Baikonur Cosmodrome in Kazakhstan on November 9, 2005 and arrived at Venus in April 2006. During its primary mission, it orbited Venus in an elliptical 24-hour loop that took it from a distance of 66,000 km over the south pole to an altitude of around 250 km above the surface of the north pole, close to the top of the planet’s atmosphere. With a suite of seven instruments, the spacecraft provided a comprehensive study of the ionosphere, atmosphere and surface of Venus.
In May, with the spacecraft’s propellant running low, the Venus Express team began an aerobrake campaign, dipping the craft progressively lower into the atmosphere on its closest approaches. The experiment directly explored previously uncharted regions of the atmosphere and also provided information on how a spacecraft responds when encountering the tenuous upper reaches of an atmosphere at high speed.
During the aerobraking phase, some limited science measurements were made with the spacecraft’s magnetic field, solar wind and atom analyzing instruments. Temperature and pressure sensors also recorded the conditions the spacecraft was experiencing. The controlled plunge helped scientists gain new insight into how a spacecraft and its components respond to such a hostile environment. This information will be invaluable for future missions.
Following a month of aerobraking, the spacecraft underwent periapsis-raising maneuvers and resumed observation. With so little fuel remaining on board, it’s possible that Venus Express has now exhausted its supply and that the spacecraft is no longer in a stable attitude. Fuel is necessary to counteract the gravitational effects of Venus – without fuel, the spacecraft will plunge into the planet’s hostile atmosphere.
For now, the team will continue trying to establish contact with the spacecraft and to determine the cause of the anomaly. It’s likely, however, that Venus Express will soon make its final descent, closing an exciting chapter in Venusian history.