由于没有那么多的推进剂来抵消那么高的速度，所以登陆火星时，减速要依靠火星大气的作用，然而火星大气难以在地面模拟。
Because there is not so much propellant to offset the high speed, the slowdown should rely on the atmosphere of the Mars while landing the Mars. However, it is quite difficult to simulate the atmosphere of the Mars on earth.