Next time you are asked to deliver what seems like the impossible, give a thought to the technology and engineering team that landed the Mars Curiosity Rover.
In August 2012, the Curiosity landed on Mars, having only 7 minutes to go from the top of the planet’s atmosphere to ground surface, at a speed of 13,000 miles an hour to zero. If the timing, speed, aerodynamics, density or anything had of deviated from the plan, it would have been game over and all efforts would had gone to blitz.
Speaking at the recent YOW! conference in Sydney, Anita Sengupta, engineer at NASA’s Jet Propulsion Laboratory (JPL), spoke about one of the most challenging technology and engineering projects to have worked on.
When it comes to projects as ambitious as landing on Mars, there’s little room for error. It takes an immense amount of careful calculating, planning, designing, testing and deploying, only to then get one chance to either make it or break it. A ‘quickly release to market and see how it goes’ strategy does not translate to these types of NASA missions that cost billions of dollars.
“The environment between Earth and Mars is so different – different atmospheric density, different atmosphere composition, and different speed relative to the speed of sound,” Sengupta said of the challenges in designing equipment that will work with another planet’s physics.
“The problem with Mars is that the atmosphere is very thin; you only have 1 per cent of what it is on the surface of Earth. So landing on Mars is very, very difficult because of this.”
The other challenge was that NASA scientists wanted the Curiosity to land in a tight location in the Gale Crater. It’s this location that is believed to be rich in information on Mars’ history as being an ancient riverbed.
Fun fact: The Gale Crater is named after an Australian (Sydney based) astronomer called Walter Frederick Gale, who closely observed Mars back in the late 19th century.
“You can think about it as a bullseye on Mars,” Sengupta said of the tight space the Curiosity vehicle had to land in, while plummeting towards it at thousands of miles per hour.
“We are going from a distance of 300 million kilometres away and we are landing in an area of 20 km by 7 km. That's very, very difficult to do from a precision perspective.
“In Gale Crater, we wanted to land in a landing ellipse to ensure we wouldn't collide with the mountain in the middle or collide with the crater walls.”
The on-board computer had to handle all that to control the equipment and properly land the vehicle, which took an incredible amount of software, Sengupta said.
“One of the critical technologies is the ability to fly the vehicle. So the vehicle is a lifting body, and by rotating the location of the lift vector, you can actually [generate a] lift and change your course direction as you go down. All of that is flown autonomously by the on-board flight software,” she said.
Computer simulations were also key to making the landing project successful. As Earth is very different to Mars, it would be impossible to fully simulate the right environment on Earth to test if the vehicle and the attached parachute to help it land when closer to the ground would work.
Monte Carlo simulations ran on supercomputers, which take into account the density, speed, aerodynamics and other parameters. The simulations were also validated against subscale experiments in a supersonic wind tunnel to see if the findings matched.
“We ran the simulations to be able to understand what's going on with the interaction with the supersonic flow field and the interaction with the parachute.
“It was confirmed that the physics that we were seeing in the simulation was actually happening in the supersonic wind tunnel of about 3 per cent of the scale of the full size.”
High speed cameras (about 2000 frames per second) and post digital image processing technology were used to capture the events happening at extremely fast speeds in the wind tunnel, which helped with designing the parachute to ensure it could withstand Mars atmosphere.
Although the team was almost spot on in landing in the exact ideal spot in the Gale Crater, the vehicle is not yet equipped to automatically re-adjust the speed or whatever it needs to in real time if there's a slight miscalculation or something isn't fully taken into account when doing the simulations.
However, Sengupta said margins are used when doing calculations on things that are not well-known in Mars such as aerodynamic heating, and these margins are also factored into the simulations.
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