Think a Mars mission is difficult Try landing a rock

The sky crane system that delivered the Perseverance rover to Mars last week looks straightforward enough. But drone pilot Nicholas Rehm shows just how difficult it is when he tries to simulate a Martian landing with a drone and a rock.

Because the Martian atmosphere is so thin, a parachute alone isn’t be enough to slow down a heavy payload like Perseverance. So NASA engineers tethered it to a kind of drone they call a sky crane that gently dropped the rover in Jezero Crater.

It sounds simple, but NASA actually rejected the concept in the past because it was believed far too difficult. Clearly, the engineers figured it out since Perseverance landed apparently without scuffing its paint.

How it likely looked at Jezero Crater on February 18

To show what can happen, Nicholas Rehm hooked up a winch and tether to a quadcopter and attempted to land a rock in a backyard. As the winch unwinds, the rock starts to swing. The oscillations cause the drone to move erratically. As Rehm attempts to get the drone under control, things just get worse. It’s a double pendulum and it’s literally chaotic.

Rehm’s attempt at simulation goes wrong in a number of ways, but the hilarity ensues at 4:48

NASA’s sky crane must sense the angle on the tether and quickly and automatically compensate.

Interestingly, this payload on a wire idea is exactly how an Israeli company plans to deliver packages to homeowners. Flytrex is working with Walmart to bring purchases to customers almost as soon as they order them. It anticipates delivering 10,000 packages a month by the end of this year. This video suggests they also have the double pendulum problem figured out. Otherwise consumers would be playing tetherball with their deliveries.

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