Grasshopper and the Falcon 9R Dev were the two rockets of spaceX which landed back successfully. Those were limited altitude test flight, this one were the expended first stage of a revenue flight. This rocket went higher, and faster before separation and performing a boost back burn. Might seem as just a quantitative difference, but the different aerodynamical regimes (vacum, hypersonic, supersonic, transonic) provides a real challenge.
It's also worth noting that the engines were lit 100% during those previous tests, while they have to be relight during this one. That comes with it's own set of complications of course.
It's also worth noting that the engines were lit 100% during those previous tests, while they have to be relight during this one. That comes with it's own set of complications of course.
see more: http://en.wikipedia.org/wiki/Grasshopper_%28rocket%29 and http://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_d...