It was a year ago, on August 5, 2012, that Curiosity – a rover the size of an SUV – survived what its designers nicknamed “7 minutes of terror”, including a new landing technique known as the Skycrane maneuver. Prior to the landing, the world was introduced to the video which portrayed the complexity of the landing problem. Fundamentally, Curiosity was so much larger than previous rovers that it could not land using the same techniques, which often involved inflated thick-skinned balloons bouncing several times before coming to rest. Curiosity was just too large. A new series of engineering tricks had to be invented, and each trick had to work in succession until the rover was landed on the surface of the planet.
In some locations, NASA hosted gatherings for people who wanted to see the landing live. These sites had direct feeds from JPL. I attended the outdoor event at NASA Ames with 6,000 other people. The accompanying photos were shot of the big screen (about 20 feet tall) of the JPL video feed.
NASA Ames had a vested interest in the landing because the heat shield tiles were developed there. Once on the surface, the CheMin (Chemistry and Mineralogy) experiment from NASA Ames would analyze samples of the Martian soil. Assuming, of course, that all the parts of the automated complex landing process would actually work. While lots of testing was done on Earth, there are some conditions of a Martian landing that simply cannot be duplicated extensively.
The atmosphere on Mars is 1/100th the density of the atmosphere on Earth. Nevertheless, entry into the Martian atmosphere at interplanetary speeds (an equivalent of escape velocity, but in reverse) piles on combined heat and deceleration G forces for several minutes. On Earth, you can heat a sample of material for an extended period. You can generate G forces separately for the same period. But you can’t necessarily do both together. You hope that there is not a failure mode that only exists when the two work together.
The newest innovation in the landing was the Skycrane. After the heat shield was jettisoned, the Skycrane cradling the rover would deploy, and rocket off to the side. If it were to go straight down, chances are that the parachute and aeroshell that it had just separated from would continue down and impact the vehicle. Thus, the first order of business was a collision avoidance maneuver.
As it neared the surface, the rover was winched down, unwinding several meters of cable to provide a distance between the Skycrane and the rover. The objective was to minimize the blast of the rocket engines on soil and loose rocks of the Martian surface, thus minimizing potential damage to the rover. Once touchdown was detected, the rover had to disconnect the cables holding it to the Skycrane, leaving it to rocket away into the distance. All of the cables had to release, all at the same time. If one cable did not release, the unbalance would send the Skycrane gyrating into the ground, not far from the rover, probably destroying it in the process.
Understandably, for the designers of the EDL system (EDL = entry, descent, and landing), the time period from atmospheric entry to touchdown and release was sheer terror. After that, the designers of the instruments get to worry if their handiwork survived the trip.
If you don’t remember the seven minutes of terror, and what it represented, here is a video reminder.
As this writing, a year after landing, Curiosity has fired over 75,000 laser shots at the soil to facility spectrographic analysis. It is taken over 70,000 images, and has sent nearly 200 gigabytes of data back to Earth. The rover is on its way to Mount Sharp, a mountain that shows several geological layers, including ones that indicate a once wet environment.
Curiosity has been so successful, that a new rover of similar design will be launched in about 7-8 years. Meanwhile, a series of smaller spacecraft will be sent to Mars to study the planet.