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I would like to understand how safe landing of a rover is achieved on mars or any other planet where the pressure is very low. Is it achieved by releasing gas from high pressure to low pressure. I assume the equal and opposite reaction of the escaping gas will be swinging in different directions. Then how do scientists manage to channelize the equal and opposite reaction in one single direction to achieve safe landing?

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To land any lander on the Moon one must fully use some kind of a rocket engine. These engines are characterized on Earth and the thrust is understood, and a careful trajectory is determined.

To land on Mars is quite a bit trickier, but uses less energy. Basically there is a 3 stage landing system for every US lander. The first is to use a heat shield to slow down using the atmosphere of Mars. The second is to use parachutes to get the velocity even lower. The final stage must be accomplished via rockets, similar to landing on the Moon, or airbags to further slow the speed down. These rocket engines are characterized in a similar way. We understand the atmosphere of Mars and have tested the rockets in similar conditions.

The gases do not escape randomly, but are very much in a specific direction. The flow is basically the same of any rocket launching, the tower of flame below them is mostly in a single direction. The atmosphere can affect how the flow happens after, but that flow won't directly affect the rocket.

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  • $\begingroup$ Okk. So the same must be the way the Rocket booster landing of SpaceX works. $\endgroup$ – Mahen Sep 20 at 16:49
  • $\begingroup$ SpaceX's landings don't use parachutes, except for the Dragon capsules. There are videos out there, look for "7 minutes of terror Mars" and you'll find them. $\endgroup$ – PearsonArtPhoto Sep 20 at 19:15
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    $\begingroup$ Note that the airbag landings also used a rocket braking stage. The rocket motors were attached to the payload by a tether, in a more primitive "skycrane" arrangement, and slowed the airbagged payload to a near-halt before it was released. The airbags just made it so high-precision rocket control wasn't needed. $\endgroup$ – Christopher James Huff Sep 20 at 20:42
  • $\begingroup$ Not to mention using thrusters near the ground, which has its own set of issues. $\endgroup$ – PearsonArtPhoto Sep 20 at 21:42
  • $\begingroup$ I had a conflicting thought about Diffusion and what Pearson said "The gases do not escape randomly, but are very much in a specific direction". $\endgroup$ – Mahen Sep 21 at 5:12

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