Perhaps even more challenging is finding the money to go there, and in the case of the sample-return, to come back.
So what else is there to innovate for this new mission and its successor? Curiosity has simple, shallow-surface sample-gathering machinery, but robotic deep-drilling and especially core-extraction technologies are still in their infancy. Drilling a few inches of rock into powder and transporting a few grams of that up into a collection drum is one thing; extracting a core sample is much more challenging. Remember, whether mudstone or harder targets, these are rocks the rovers will be sampling. This will require incremental, but careful, innovations that can be designed, tested, tested again and deployed to work in a harsh and remote environment.
Likewise the on-board analytical instrumentation will be a challenge. The Viking landers shrank a rudimentary life-science laboratory down to the size of a dishwasher. Fast-forward to Curiosity and you have machines that can test samples to a molecular level, even revealing atmospheric analysis and the isotopic numbers of gasses given off by the baking of rock samples. To search for true biosignatures in rock and soil samples will require even more finesse and technological acumen. [NASA Space Tech, Science & Exploration Goals in 2015 in Pictures (Gallery )]
The 2020 rover will rely heavily on Curiosity's successful platform in terms of overall design and function. The differences will be mostly in the above-mentioned areas — instrumentation and sampling improvements. But a subsequent landing mission — to return with Martian soil samples — would require a new overall design and another major overhaul of the landing system. Pathfinder and the MER rovers used airbags to bounce to a landing, scrubbing off energy as they did so. Curiosity used (and the 2020 rover will use) guided entry and the sky-crane system, the amazing rocket pack and rappelling device that worked so well in 2012. This change was dictated by the mass of the lander and a continuing desire for improved precision in the landings. A sample-return mission, which would by design be intended to seek out the cache of samples left by the 2020 rover, will likely be heavier still, and a new landing system will be required. That system may be derivative of Curiosity's, but this is currently under study. Much of the engineering team from Curiosity was moved to the 2020 mission, and some were sent off to study new and alternative landing technologies. This might entail a collapsible landing stage, which is crushed during touchdown, absorbing much of the energy. Or it might utilize something involving larger rockets in different a configuration. Or it could be a not-yet-conceived system as outrageous as the sky crane seemed when the world first laid eyes upon it back in the early 2000s.
New and innovative guidance techniques are also under development, based on experience from Curiosity. That spacecraft was guided to its narrow landing corridor by inertial guidance coupled with ranging radar. Put simply, it knew its exact location relative to Mars when it encountered the atmosphere, and then calculated the navigational adjustments to reach the assigned spot at Gale Crater. Velocity and atmospheric measurements from the outer hull refined this glide path. It was a remarkable bit of computation.
The Mars 2020 mission will reduce the size of the landing zone — or "landing ellipse," in the parlance — down to about 4 miles by 7 miles, smaller than even Curiosity's by half. Two promising technologies are being studied. The first, called range trigger, releases the parachute only after measuring the distance to the surface and factoring in other variables such as wind speed and air density (previous landers did this by measuring velocity). The second, terrain relative navigation, combines measurements of the bearing of known landmarks with other onboard measurements to further refine landing accuracy. These and other technologies will help to guide the 2020 rover to its prime landing site, and subsequent sample-return missions, if any, to the sample cache the 2020 rover prepares.