Seven minutes of terror

Next week the most recent Mars mission – Mars Science Laboratory, or Curiosity – is scheduled to set down on the surface of the red planet. The mission has four goals: Determine whether Mars could have ever supported life, study the climate of Mars, study the geology of Mars, and plan for a human mission to Mars.

The Curiosity rover, being roughly the size of a Mini Cooper, is much larger than any of the previous mars rovers. As a result, the approach of using airbags to cushion the final landing stage, used in previous rover missions, isn’t an option.

Entering the Martian atmosphere at a brisk 3.5 miles/second. (credit: NASA/JPL-Caltech)

The craft will use a heat shield to protect itself during initial atmospheric entry. This ‘aerobraking’ manoeuvre will slow Curiosity from a speed of about 12,600 mph to roughly 1000 mph (Mach 2).

A “gentle” 200 mph parachute descent. The heat shield has been ejected by this stage. (credit: NASA/JPL-Caltech)

At this point, 6 miles above the Martian surface, a parachute will be deployed. However, Mars’s atmosphere is too thin for this to be enough to ensure a gentle landing, and will only slow the craft to about 200 mph.

Burn, thrusters, like your lives depend upon it. (credit: NASA/JPL-Caltech)

Next, the parachute will be detached, and rocket thrusters (similar to the Viking landers’) will be used to slow the rest of the descent, with the descent stage and rover coming to a hover at an altitude of 25 feet.

Easy does it… (credit: NASA/JPL-Caltech)

Now comes the new bit: so that the thrusters don’t kick up dust which might clog up the rover, Curiosity will be lowered by cables to the surface. Once on the surface, the cables will be cut, and the descent stage (with the thrusters) will fly off to crash away from the landing site.

Touchdown! (credit: NASA/JPL-Caltech)

The entire landing sequence will take about seven minutes, but Earth will be fourteen light minutes away. So when Curiosity transmits its first signals after landing, we will still be receiving messages it transmitted seven minutes before entering the atmosphere. As such the craft has been programmed to determine for itself when to initiate each stage, identify its landing site, and set itself down on the surface. All we can do is hope for good Martian weather.

Good luck, Curiosity.

The first signals from Curiosity on the Martian surface are expected to arrive at 06:31 BST on 6th August (for people in the US, that’s 22:31 PDT or 01:31 EDT). You will be able to watch the live feed from NASA here.


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