The mystery over what happened to the Beagle 2 spacecraft may have been solved, five years after contact with it was lost as it entered the Martian atmosphere on Christmas Day 2003. An Australian team of hypersonics engineers say a flawed calculation probably resulted in Beagle 2 tumbling out of control as it descended.

Until now, the loss of the probe has been attributed to the general failings of a poorly funded mission: despite an exhaustive enquiry by the European Space Agency, no single cause for the loss of the £50 million spacecraft has been identified.

Beagle 2
© ESAWhy did Beagle 2 disappear?
Beagle 2 was designed to self-stabilise during its descent through the Martian atmosphere. This was to be achieved through careful design of the spacecraft's aerodynamics and centre of gravity, and by spinning the craft as it was released from the European Space Agency's Mars Express orbiter. This generated a gyroscopic force for correcting wobbles as it descended.

The ideal spin rate was difficult to determine because the forces on a spacecraft change sharply as it plunges from the thin upper atmosphere to the denser gas closer to the surface. The Beagle 2 team simulated the forces in both these regimes but could not afford to simulate the way the forces change during the transition between the two. Instead, they estimated the forces using a mathematical process called a bridging function, and settled on a rate of 14 revolutions per minute.

After Beagle 2's disappearance, hypersonics experts Michael Macrossan and Madhat Abdel-Jawad at the University of Queensland in Brisbane, Australia, simulated the transition and published the results in this month's Journal of Spacecraft and Rockets (DOI: 10.2514/1.37034).

They reckon it is now clear that Beagle 2 was spinning too fast. The spin rate would have corrected any problems in the thin upper atmosphere but as the atmosphere thickened, it would have worked against the self-stabilising aerodynamic forces the craft was generating. As a result, the spacecraft probably tumbled out of control and burned up just seconds after dropping into the atmosphere. "The spin rate was just too high," says Abdel-Jawad. "It counteracted the stabilisation you'd expect."

Arthur Smith, chief engineer at Fluid Gravity Engineering in St Andrews, UK, which carried out the original stability work and supplied its data to the Australian team, says recent studies have also shown that atmospheric bridging functions can be inaccurate.

"It's an interesting analysis and we are going to run their figures through our own model to see if they are right," says Colin Pillinger, the planetary scientist at the UK's Open University, Milton Keynes, who led the Beagle 2 team. They expect to know if the Australian team's analysis is correct in the new year.