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Sunday, August 5, 2012

Fingers crossed

It's going to happen soon.
Not sure if I will have popcorns with me as it will be early in the morning here in Eruope and popcorns are not my favorite breakfast.
They call it "the seven minutes of terror" and in those seven minutes the most daring, complex space probe landing will happen.
Curiosity will hit Mars, hopefully it will slow down as planned before, this is supposed to happen at around 5AM GMT on Monday August 6th 2012, few hours from now.

I know you may think : "we did that before, nothing new".
Nope, we did not, not this way.

This landing procedure is something so complex that nobody ever tried it before.
Landing an autonomous probe packed with sensors and communication devices on another planet is never an easy task.
This one is much bigger and heavier than the ones that landed before, it has the size and weight of a small car, making things ever harder.

Normally the technique used to slow down the probes before the touch down and protect them from the impact relies on parachutes and airbags.
In this case, due to the mass of the probe, Nasa realized the parachute would have not been enough to slow down  Curitosity.
They had to create a sequence of interventions to slow it down, each step will decelerate the probe in a specific speed range and will uses a different system.

Video from NASA

The first part will use a traditional approach :
The probe will enter Mars atmosphere with a precise angle, a speed of about 13.000 Miles per hour and a shield will protect it from the enormous heat generated by the friction against the atmosphere.

This phase will allow the first deceleration (most of the speed reduction is obtained this way), down to a speed at which, controlling the trajectory and orientation with small rockets, a big parachute can be deployed.
At this point the front shield is separated from the probe.
Getting closer to the surface, with a speed of about 175Mph the parachute will be detached together with the back shell and the probe, now leveled with the surface, will start a free fall descent, controlled by small rockets.
This free fall is then decelerated with rockets, much like the LEM landing in the Apollo mission, however the gravity constant on Mars is about 3.7 m/s2 which, while it is considerably lower than the Eaths's one (9.8m/s2), is roughly double of the Moon's one.
Nasa did not want all that mass attached to the probe at the moment of the touch down, so they opted for a novelty : the sky crane.
Few meters (about 30 according to the simulation) above the surface, the actual rover will detach from the device that contains the rocket engines, which will act as a crane and hopefully will gently place Curiosity on the surface, detaching itself right after the touchdown and flying away to avoid potential collisions with the rover.

While each single step has many risks and possible reasons to fail, the most critical one is probably after the back shell is detached.
Due to the time it takes to communication to travel between Mars and Earth and then back, the whole process needs to be completely autonomous and no intervention will be possible from the control center.

You can preview the whole process in a nice computer simulation here :
It also provides a "live" option which, while still clearly being a simulation, shows the current situation with (hopefully) the current position of the probe.

In the picture you can see the how it should look now, at the time I am writing.

I am glad that human kind can still "push the limit", dare to face complexity and learn from it.
Success in this project is not granted, there are obviously good reasons to be optimistic, but the number of variables involved suggests that anything could go wrong, anytime.
Any way this is going to end, it's a great project.
There will be a live webcast and a lot of fingers crossed.

[update after landing .: it worked!! everything was smooth and as planned, communication was solid during the process and some images were immediately sent right after the touchdown ]

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