If you watched the landing of the Curiosity rover on Mars, you might have noticed that one of the engineers in the JPL's mission control center started celebrating before the formal announcement that the safe landing had been confirmed. Here's a short clip about the guy in question and why he was celebrating a bit early:
Curiosity is so massive that retrorockets would be needed to set the rover down gently, but where to put them? The obvious idea of putting the rockets underneath presented two problems:
- the rocket package would be in the way of letting the rover roll around, and
- blasting the surface directly under the rover (and filling the air with dust) would not be ideal
So (as explained in the video) NASA engineers came up with the idea of putting the rockets in a separate platform on top that would stay a fair distance above the surface while lowering the rover on cables, after which the rocket platform would fly laterally to crash some distance away. So what tipped off the engineer in question that the landing had almost certainly succeeded was an indication that the fly-away operation for the rocket platform had initiated, which he saw before the announcement that the rover itself had reported itself safely down.
Not a big deal, but a nifty look into the human side of the operation.