They say that it’s not the fall that kills you, it’s the sudden stop at the bottom – it is one life’s constants: fall a great distance at high speed and, unless you can slow down before you hit the ground, you will be at least partially disassembled into your component parts.
This is a fate that engineers and scientists at Nasa will be hoping to avoid when, in a week’s time, they attempt to land the largest and most complicated robotic rover yet built safely on the surface of Mars.
The Mars Science Laboratory, or Curiosity, is almost at the end of its eight month journey to the Red Planet and, at 6.31am (BST) on August 6th, it will begin its perilous decent to the Martian surface.
When it does enter the Martian atmosphere, it will have just seven minutes to slow from 13,800 miles per hour (that’s about seven times faster than a bullet shoots from a rifle) to almost zero – and it has to do it all by itself.
Slowing a craft that weighs the same as an old school Mini Cooper by such an extent would be quite easy on Earth – our atmosphere is a relatively thick gaseous soup that, when struck at 13,000mph, is only slightly more yielding than a brick wall – but the Martian atmosphere is only about one per cent as dense as Earth’s. It is just too thin to slow such a hefty vehicle.
But, rather annoyingly, it is just thick enough to create enough friction to incinerate Curiosity if it were to plunge in unprotected. So, in order to put the brakes on, the craft will have to use a combination a heat shield and a parachute.
But that parachute will only work for a while – there just aren’t enough molecules in the atmosphere to push against it – so, while still traveling at 200mph, it must cut itself loose and fire up its thrusters.
Finally, when it is just 20 metres from the surface, the rover will be lowered on a tether to make a (hopefully) gentle landing in a crater at the foot of the Martian mountain, Aeolis Mons.
To further complicate matters, the craft will be totally blind for all but the last two minutes of its decent – when it jettisons its heat shield and can finally use its radar.
That is why mission engineers have called the descent ‘seven minutes of terror’.
Infographic: Seven minutes of terror – how Curiosity will make it's daring descent. Click for a crash course in not crashing.
To add to tension at Nasa’s mission control, because of the 14 minute radio delay caused by Mars’ distance from Earth, engineers will have to endure a nail-biting seven minute wait before they find out if Curiosity is safe, or if there is a new man-made crater decorating the rusty Martian surface.
Assuming it survives its attempt to make the most ambitious (and precise) landing yet attempted on the Red Planet, Curiosity will head off to explore Mars’ climate and geology and search for evidence of life (past or present).