Contact lost with ESA's Venus Express orbiter
Sen—While most attention to planetary probe action over the past decade has been directed towards Mars, another visiting robot has been quietly studying our inner neighbour Venus.
Europe’s Venus Express was launched in November 2005 and got to the second planet from the Sun in April 2006, on what was originally a two-year mission. Since then it has sent data streaming back from its polar orbit.
But the probe’s days are numbered, and last month the flight control team at the European Space Operations Centre (ESOC) at Darmstadt, Germany, reported loss of contact with it.
According to ESA’s Venus Express blog, it is possible that the remaining fuel on board the spacecraft was exhausted during recent manoeuvres and that the spacecraft is no longer in a stable attitude (the spacecraft’s high-gain antenna must be kept pointed toward Earth to ensure reliable radio contact).
Due to the gravitational pull of Venus and the Sun, Venus Express’s closest point of approach, the pericentre, is constantly descending closer to Venus. This “decay” of altitude would eventually damage the spacecraft (due to drag) if it was not raised away from the atmosphere.
Between 23 and 30 November, the operations team at ESOC attempted manoeuvres to raise the pericentre of Venus Express’s orbit again.
Repeated attempts to re-establish contact have been made since then, and there has been some limited success since 3 December. Some telemetry packets were successfully downlinked. These confirm that the spacecraft is oriented with its solar arrays pointing toward the Sun, and is rotating slowly.
The peak Idunn Mons is thought to be an active volcano. This picture of it combines imagery from NASA's Magellan probe (in brown) with colours indicating heat measured by Venus Express. Image credit: ESA/NASA/JPL
Dr Colin Wilson, a Senior Research Fellow at the University of Oxford, is Science Operations Co-ordinator for the Venus Express mission. He told Sen: “Venus Express has done really well—originally designed for a mission of only 500 days, it’s kept going for eight and a half years at Venus.”
“Note it’s not dead yet! When we couldn’t get a signal from the spacecraft we thought we might never hear from it again, but the team at the Mission Operations Centre in Darmstadt have, heroically tried lots of different techniques to communicate with the spacecraft and eventually (on 3 Dec) managed to get signals back from the spacecraft.
“They now are managing to get telecommands up to the spacecraft and data back, but intermittently, so it will take a few more days before they get enough information back about the spacecraft to diagnose exactly what’s going on.
“The spacecraft has kept its solar panels facing the Sun and has plenty of power. Also, it’s high enough above Venus that it will be several weeks before we have to worry about it burning up in the atmosphere.”
The operations team is currently attempting to downlink the sequence of events stored in protected memory on board. The root cause of the anomaly remains to be established.
Dr Wilson told Sen there had been many highlights in the Venus Express mission. He said: “It’s provided a wealth of new insights on Venus. Possibly its most intriguing legacy is the hints it’s provided about active volcanism.
“Venus is covered in volcanoes—we know that from the Magellan radar mapping orbiter of 1989-1994—but no one knew if they were active or not. Venus Express has provided three tantalising hints.
“First, it found that some volcanoes were surrounded in unusually black terrain, interpreted as as-yet-unweathered volcanic flows. Second, it found enormous (tenfold!) changes in atmospheric sulphur dioxide, which might be linked to volcanic eruptions.
“Thirdly, imaging of infrared emission for the surface appears to show spots which appear to get very hot and then cool off again, which look a lot like hot lava flows—but note it’s difficult to reach firm conclusions because we’re looking through a cloud deck which is 20 km thick! The search for active volcanism will be a priority for future mission proposals.”