Is this the simplest sequence of events and machinery they could come up with the achieve the landing? There are a lot of motors, sensors, and propulsion engines that could fail.
Why is the heat shield jettisoned 7km above the surface exposing the rover to the atmosphere while its travelling at over 500kph? Does anyone have any insight into the design decisions in this landing sequence?
is a paper written by the engineers who designed the system, explaining these decisions. I suspect that the reason is that - in Mars's thin atmosphere - 500kph isn't as much pressure as it would be on Earth. (The constraint appears to be that the heat shield needs to fall away.)
I found the way MSL detects landing to be clever. Instead of a switch or sensor, it records the throttle setting required to descend at a constant speed. When that setting drops (for a sufficient time), the rover must have touched down.
“We call it the Supersonic Transition Problem,” said Manning. “Unique to Mars, there is a velocity-altitude gap below Mach 5. The gap is between the delivery capability of large entry systems at Mars and the capability of super-and sub-sonic decelerator technologies to get below the speed of sound.”
The article is in the context of landing humans on Mars, but the principles are the same.
Thanks for sharing the link, it's a really interesting read.
I'm curious - wouldn't a large, variable geometry lifting body do the trick? Land like a shuttle would, but with a bigger wing, and deploy more wing and lift devices as you get lower.
The wingspan required for something like a manned spacecraft would put the Spruce Goose to shame. You need something huge to be able to slow you to a reasonable speed.
You can bet that there's no better simple solution. This problem has been analyzed extensively by groups with lots of resources (intellectual and monetary).
Besides the other commenter who mentioned the size of the lift surface, think of the mass requirements, the variable atmosphere density mentioned in the linked article, the need for an autonomous lander (because of light time), and the small amount of time you have to land.
Thanks for that. From wikipedia, surface atmospheric pressure is less than 1% of that on Earth so you're probably right. A wind pressure from 500 kph wind at the surface of Mars would be roughly equivalent to wind pressure from a 50kph (Force 7) wind on Earth. It will be less still higher up in the atmosphere. (Assuming I didn't just get the physics embarrassingly wrong, please correct me if I did)
http://www.youtube.com/watch?v=BudlaGh1A0o