I'm a bit rusty on my physics, but the general idea is that with both methods the total impulse (force over a time interval) is the same. The capsule goes from

I'm a bit rusty on my physics, but the general idea is that with both methods the total impulse (force over a time interval) is the same. The capsule goes from 16mph to 0mph. But, if you let the ground stop you, you end up with all of the energy transfer in a few milliseconds. Because the time is so short, the force spikes to crazy high levels. This breaks equipment and people. The rockets firing spread out that force over a longer period of time. For example (all numbers made up): Time the ground takes to stop you: 25ms Time rockets fire before touchdown: 100ms Landing capsule weight: 2000kg Impulse needed to stop capsule: 7.15264m/s * 2000kg = 14300Ns Assuming in both cases the force is evenly applied over the time period... Force from the ground stopping you: 14300Ns / 25ms = 572,000N Force from the rockets + the ground: 14300Ns / (100ms + 25ms) = 115,000N