The European Space Agency's Venus Express (VEX) unmanned probe is being put through a series of maneuvers in hopes that its remaining fuel can push it into a higher orbit. If successful, the orbit change will give the spacecraft a bit more life before it plunges into the Venusian atmosphere it was sent to investigate.
This is not the first time that VEX has gone through a life extension procedure. In July, mission control directed the orbiter to carry out a dramatic aerobraking maneuver, which sent the spacecraft skipping through the outer edge of the atmosphere to slow it down and send it into a more stable, more circular orbit.
This maneuver proved successful, though it did change the orbit from a 24-hour period to 22 hours. According to the space agency, this caused a number of operational problems as activities had to be rescheduled. This was especially the case in regard to the heavily booked deep space tracking and communications networks.
Now VEX’s orbit is decaying at the rate of 3 to 5 km (1.8 to 3.1 mi) per day as it pericenter, the lowest point of its orbit, grazes the atmosphere. To stave off the inevitable, ESA has ordered nine firings of the spacecraft's engine that began on November 23 and and will be completed on December 1.
The biggest question mark hanging over the future of VEX is how much fuel the orbiter has left. The space agency estimates that the orbiter has 3 kg (6.6 lb) of fuel and 5 kg (11 lb) of oxidizer in its tanks. Since only 1.4 kg (3 lb) of fuel and 2 kg (4.4 lb) of oxidizer are needed for the orbit change, that seems plenty, but because VEX is weightless, there's no guarantee that the liquids aren't floating in bubbles away from the engine intakes. If so, then the engine will not be able to fire.
Launched in 2006, Venus Express was designed to study the upper reaches of the Venusian atmosphere's structure, dynamics, composition and chemistry. VEX has already had its mission extended by double its best case scenario schedule. Originally, it was meant to orbit Venus for two years with a two-year extension. However, the mission has now clocked in at eight years.
According to ESA, the spacecraft is healthy and if the orbital maneuver is a success, it will continue operations until sometime next year when orbital decay will eventually send VEX to burn up in the super dense Venusian atmosphere.
As to the "if" – the final verdict on whether the engine firings have succeeded won't be until the next communication period after Monday's final firing.
"Venus Express is, after Rosetta and Mars Express, the most recently launched of ESA’s interplanetary jewels," says Paolo Ferri, Head of Mission Operations. "It was supposed to be a short mission, but the robustness of the spacecraft and the skills of our operations and flight dynamics teams have made it a much longer lasting, incredibly successful mission."
“Its mission at Venus has been not only a major scientific achievement, but also very important for our teams to gain experience in operating a probe so close to the Sun," Ferri continues. "This will be extremely useful also for the preparation of the upcoming BepiColombo mission to Mercury."