By Mike Deliman
This afternoon I watched the press conferences for Mars Science Laboratory “Curiosity” that were hosted by NASA/JPL from Pasadena, Ca. These conferences were broadcast over NASA-TV, both on the cable/satellite channels and over the web. If you haven’t seen the Seven Minutes Video I encourage you to watch it.
Various scientists, directors and managers of the project discussed various aspects of the mission, including discussing how the craft does what it’s designed to. The biggest message I carry away from today’s two conferences is “Complexity”. This is by far the most complex robotic probe ever launched to space, perhaps the most complex robotic probe mission ever.
If you watch the video, you will notice that during the landing, the probe plummets through the atmosphere like a well-guided rock. This is literally what it is doing – falling like a rock that knows how to keep itself upright. It manages to do this by using guidance rockets, a heat shield with a “just right” shape, and weights that help keep one side tilted slightly towards the ground. While it’s in this configuration, the guidance rockets make minute adjustments as needed, keeping the probe on course. This precision guided entry is a large part of how Curiosity is able to make the landing ellipse small. This whole phase is a series of fantastic engineering achievements. It is tied in history to the Apollo reentry methods, where we brought astronauts back to Earth, safely.
At just the right time, the probe will deploy its parachute. Parachutes are something you can see almost every day. There are folks who jump out of airplanes for the fun of it, and assemble as groups, doing acrobatic maneuvers on their way down. There are military personnel who do various dangerous styles of parachute jumping. It seems like this isn’t such a big deal, right? All of those humans carry back-up chutes, just in case something goes wrong. Sometimes even those fail. MSL does not have a backup. That one parachute is all it’s got. And it’s deployed when the robot is plummeting at about a thousand miles an hour in an atmosphere much thinner than the Earths!
Then we get to the part where the heat shield pops-off, the radar and images kick in, and the robot starts looking for the right place to land. When it’s getting close, it will deploy the sky crane and cut the parachute cords.
Why do a sky crane? We could have done an airbag system like the previous rovers, or a “hard landing” like we did with Viking and Phoenix, right? Well… no. The impact would be so hard with airbags that there isn’t cloth anywhere in the world that could withstand the landing, it would shred on impact. That would be catastrophic for the rover. The hard-landing style Viking and Phoenix used are also inappropriate for this lander. The problem is two-fold – these landings are difficult enough for robots that don’t move after landing – they have to fire up and shut-off retro rockets at just the right times. Even harder, to deploy a roving robot, the lander would have to land on perfectly flat terrain to avoid falling over, and stick that landing better than an Olympic gymnast. This lander weighs about a metric ton. It would have to have incredible legs!
One of the engineers coined the phrase “we’re landing a small compact car with a trunk loaded with scientific instruments on Mars!” We can’t afford to get it there and not be able to let it rove. The retros would have to be very strong to slow it down enough to prevent damage, and this presents a problem itself: pressure. With the rockets down low, the terrain and thinness of the atmosphere could make back-pressure unpredictable, increasing the likelihood that the lander could flip over.
So we have the sky crane left as the only really viable solution for providing a gentle landing, with enough precision that the rover will be able to choose where it lands.
All of these events are controlled autonomously by the computers, operating system, and applications on-board. There will be no human interaction possible. By the time we get receive the signal indicating it has entered the atmosphere, MSL will have already been on the surface of Mars for about 7 minutes. The computer does all of this work without human intervention! What a marvelously complex robot!
It’s going to take a while for the rover to check itself out – perform all the health checks necessary before it can start “doing” much on the surface. This will take perhaps up to a month. During that time, though, we will use the satellites we’ve placed around Mars to relay back the data and pictures it’s collected on the way down to the surface. It may take another month before it starts running chemistry experiments. That’s about 60 days before we see it sample Mars itself. Thinking about it though, that’s less than 10% into the mission, we will have over 600 more days to crawl about – an entire Martian year.
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