InSight Diary: Mars mission ready to rumble

The InSight mission will investigate the interior structure and composition of Mars

Prof Tom Pike from Imperial College London is part of the science team on the US-led InSight mission to Mars. His group has supplied seismometers that will enable the Nasa lander to detect "Marsquakes", which should reveal the internal structure of the Red Planet. Over the course of the coming months, Prof Pike will be updating us on InSight's progress.

"Help… we absolutely need your feedback as soon as possible."

It's not the email you want to get just a few days before your sensors are due to launch to Mars.

Our sensors are microseismometers, part of a Marsquake detection instrument currently sitting upside down on top of a rocket in California.

The last stage, the nose cone, had been winched up to the top of the launch tower a few days before, bolted on securely and the electrical connections completed.

InSight is now encapsulated and sitting on the top of its launch rocket

Over the last few weeks we've been seeing the stack slowly growing up the tower at Space Launch Complex 3 of Vandenberg Air Force base, about 100 miles up the coast from Los Angeles.

The nose cone contains our lander, folded up in its thermal protection that allows it to slow down at the other end of our journey, six months and some 90 million miles later.

We're due to launch on Saturday, and the mists that have been swirling around the launch tower should be clear at 4am.

It's an early start but we'll be heading over to be there and see the launch.

Our mission, InSight, should be worth the wait.

I've been working on getting a microseismometer on Mars for more than 20 years, but I'm a latecomer compared with some of my colleagues.

InSight is led by Bruce Banerdt from the Jet Propulsion Laboratory.

Bruce first encouraged me to work on developing seismic sensors back in the nineties when I was working at JPL, and now we hope to finally see them on their way.

The three microseismometer sensors designed and fabricated at Imperial College London. Each sensor is 25mm square

The microseismometers are only one part of the Marsquake detection instrument, and Philippe Lognonné has been working nearly as long as Bruce on developing in France a Mars equivalent of the best seismometers we use on Earth.

Just between the three of us, there's nearly 100 years of collective effort. It's good we all started young!

So that email was more than worrying. We'd already tested all aspects of our instrument thoroughly, and so far everything was working very well.

The only part of the instrument that we could still check out on top of the rocket were two of our three microseismometers. These two sensors still worked even if the instrument itself was upside down, while our third sensor and the French seismometer would have to wait at least another six months to operate again once we reached Mars gravity.

But what we were seeing from this last test before launch was unexpected, and this was the very worst time to enjoy a surprise.

The two sensors were not responding to a calibration signal that we used to check they were operating properly. Instead, they were both seeing a much stronger signal.

As we analysed these signals, I remembered seeing something like this before. Our sensors are put together with their electronics and tested in Oxford, and on Sundays we often saw a distinctive signature in the basement of the physics department.

Dreaming spires: Testing in Oxford had noticed something similar

Oxford is famous for its spires and on Sundays the bell towers of the colleges and churches vibrate as the bells are rung.

Unlike the peals of the bells these vibrations are far too low a frequency to be heard, but our microseismometers are sensitive enough to pick them up from hundreds of metres away.

This time we were seeing the vibrations not of bell towers but the rocket itself as it shook our two sensors.

If I displayed the signal they were hearing like a line of music, I could see a steady tone, again too low a frequency to be heard, but deafening to the sensors that were designed to detect the faintest of Marsquakes.

Our sensors simply couldn't hear the calibration signal we were sending to them above the notes the rocket was singing. But the rocket sometimes more gently hummed, and then the distinct chirp of our calibration signal was clearly detected.

On Saturday our sensors will be turned off as we launch.

If the rocket was already too loud for them during the wait on the launch pad, they would certainly not appreciate the roar of the thrusters.

The next time we turned on the sensors, they would be in the profound silence of the journey to Mars.

We hope the sensors will then be able to hear our calibration signal as we check they have survived the launch.

Maybe then they would be able to hear themselves think, or rather we'd see just how quiet the sensors themselves could be.

The silence of deep space would be a much better test for our microseismometers than the song of the rocket that would take them there.

Artwork: The launch from California is scheduled for Saturday