Curiosity, also known as the Mars Science Laboratory, will touch down on Mars at 6:31 (BST or La Palma local time). I hope it won’t crash into Mars hard enough to create a new impact crater.
Mars is currently on the opposite side of the sun to Earth, and radio signals from Mars take 14 minutes to reach Earth. That’s far too long for the engineers at NASA to control the descent. When they get confirmation that Curiosity has hit the thin Martian atmosphere, Curiosity itself will have been on the surface for 7 minutes – alive or dead and smoking. They’ve programmed the whole thing, and they just have to hope that everything works perfectly: 6 different stages, half a million lines of computer code, and 76 explosive devices (to separate things like the heat shield).
This is NASA, arguably the best engineers on the planet, and it still looks crazy.
So why did they design such a complicated system, with so many chances for things to go wrong?
The main problem is that Mars has just enough atmosphere to burn things falling through it, and not enough to slow them down much. So he computers will:
- jettison the cruise stage (the engines which controlled its flight from the Earth)
- hit the Martian atmosphere at 20,800 km/h,
- stop spinning,
- jettison weights,
- turn so that the heat shield faces down,
- heat to 1,600 º and slow to 1,600 km/h,
- deploy a parachute (which works less well in the thin Martin air) to provide 9 G of deceleration to slow to 320 km/h
- jettison the heat shield
- jettison more weights
- activate the radar (which won’t work if the heat-shield’s still there)
- jettison the back shield (the bit holding the parachute)
- turn on the rockets of the descent stage
- fly sideways, away from the parachute so it doesn’t get tangled
- at 20 m above the surface, dangle the rover on a rope down form the descent stage (because if the rockets get close enough to kick up dust from the ground, the dust might clog up something on the rover)
- touch the rover down gently, close to Gale Crater.
- cut the rope
- fly the descent stage off to the side.
I repeat, this all has to work perfectly, first time, without human intervention.
No wonder the engineers are calling it the” seven minutes of terror.” To paraphrase, they know exactly why they made all those decisions, but they look at the simulation and think, “Meep!”
On the other hand, if it all works, Curiosity can get on with finding out if there ever was life on Mars.
I really hope Curiosity makes it. I really want to know.
You can watch it live on http://www.nasa.gov/multimedia/nasatv/index.html
More details at : http://www.spaceflight101.com/msl-landing-special.html