Don’t you hate it when you think you’re underground, but you're actually several kilometers in the air?

Sure, probably not a regular occurrence for most of us – but that’s probably what happened to ESA’s Schiaparelli ExoMars lander last month, according to a statement from the agency after studying available data.

Schiaparelli was supposed to pass through the atmosphere of Mars, deploying its parachute and jettisoning its heat shield, before using thrusters to touch down on the surface on October 19.

Everything seemed to be looking good. The lander deployed its parachute correctly 12 kilometers (7.5 miles) above the surface at a speed of 1,730 kilometers per hour (1,075 miles per hour), and released its heatshield at 7.8 kilometers (4.9 miles).

But then things went wrong. An instrument that was measuring the rotation of the lander, the Inertial Measurement Unit (IMU), hit a maximum reading and recorded a rotation 1 second longer than expected.

This glitch was enough to cause the navigation systems to go haywire. Due to the “erroneous information”, in ESA’s words, the lander suddenly thought it was below ground level – when it was actually still 3.7 kilometers (2.3 miles) above the ground.

The result was that it immediately released its parachute and backshell (the casing on top of the lander), fired its thrusters, and turned on its ground instruments – thinking it had landed. Instead, it went into freefall, ultimately crashing into the surface at more than 300 km/h (186 mph), where it was instantly destroyed.

^{This image shows the remains of Schiaparelli on the surface of Mars. NASA/JPL-Caltech/University of Arizona}

"This is still a very preliminary conclusion of our technical investigations," said David Parker, ESA's Director of Human Spaceflight and Robotic Exploration, in the statement. "The full picture will be provided in early 2017 by the future report of an external independent inquiry board."

Despite the failure, ESA seemed pretty positive about the experience, which will give it vital data for the upcoming attempted landing of its ExoMars rover in 2021. Of course, a successful landing probably would have been a bit more useful, but hopefully enough has been learned that this mission – which will search for past and present life on Mars – can proceed without a hitch.

And there was some good news too, as the Trace Gas Orbiter (TGO) – the orbiting spacecraft that carried Schiaparelli to Mars – is starting its first science observations of the Red Planet, with full science operations scheduled to begin in March 2018.

Still, it’s a somber farewell for Schiaparelli. But this isn’t the first time an incorrect measurement has resulted in the failure of a Mars spacecraft; NASA’s Mars Climate Orbiter infamously disintegrated in the Martian atmosphere in 1999 due to a mix up with metric and imperial units.

It's worth making sure, then, that if you do plan to land on Mars, get your maths right – or you might find yourself up in the air when you think you're underground.

^{This is how the landing should have gone, but things went wrong at an altitude of 3.7 kilometers. ESA/ATG medialab}