If a spacecraft is entering the Martian atmosphere (say Curiosity rover in a Sky Crane capsule), is the wind strong enough to actually produce forces on the spacecraft? (like you would see during an Earth re-entry?)
So I’ve read that some Martian wind storms can get up to 60 miles/hr and create dust storms. But I also know that the Martian atmosphere is not really dense. So how can we have such strong winds when the atmosphere is not very dense?
A 60 mph wind on Mars will produce about the same force as a 6 mph wind on Earth, since the density is ~1/100th, and the force goes as velocity squared. So it's still something.
We certainly have taken into account wind for Mars landings, where it is especially significant while the vehicle is descending on the parachute. On Mars Exploration Rover, landing failures could be induced by increased horizontal velocity on impact due to steady winds and swinging of the vehicle due to wind shears, the latter resulting in angle on the terminal descent rockets, themselves increasing the horizontal velocity on impact. Both could contribute to exceeding the horizontal velocity capability of the airbags.
As a result on MER, considerable effort went into modeling the wind at the candidate and final landing sites, affecting the landing site selection, and two systems were developed to mitigate the effect of wind, a transverse rocket system to control the angle of the retro rockets when fired1, and a descent image motion estimation system to measure the horizontal velocity of the vehicle relative to the ground. Both systems turned out to be important for Spirit's successful landing. (The wind was calm, as predicted, for the Opportunity site.)
Mesoscale wind modeling was done for Mars Science Laboratory (Curiosity) as well, where there the requirement to land much more precisely than MER was impacted by wind while on the parachute, and the parachute deployment loads could also be adversely impacted by wind.
- San Martin, A. Miguel, and Erik S. Bailey. "The Mars Exploration Rover Transverse Impulse Rocket System: An Active System to Compensate for Martian High Winds During Landing." Advances in the Astronautical Sciences 121 (2005): 519-539.
