Too cool, part 46: Perseverance

This is far from the first place you’re likely to have seen this, but there’s also no way I can let this go past. You have almost certainly heard about the touchdown of the Perseverance rover on Mars a few days back; now we have the videos of that touchdown, even taken from multiple perspectives. This is a distinct first: no surface probe, or even orbiting satellite, has had video capabilities for the landing before (and possibly not even on the surface – I have to check that.)

Why couldn’t we see this when it was happened, back on the 18th? First off, the distance of Mars means that it takes eleven minutes (plus or minus – the distance changes as our two planets orbit) for any transmissions to reach here in the first place. But the factor having more effect is simply having a system ready to transmit it. This takes either a lot of power (because video bandwidth is quite high,) or a bit of time, and NASA of course opted for the latter. There was also the possibility of post-processing to be done before transmission, and certainly post-processing after receiving back on Earth, at least for the clip that I’m going to show below.

But first, we need to know what we’re looking at, so let’s see the pertinent aspects of the landing mission.

As mentioned in the video, they wanted the rover to be in a fairly precise location, and even a small degree of randomness could spell the end (or simply just the uselessness) of a multi-million dollar mission. But they also had to, in order, slow the entry vehicle down in Mars’ very thin atmosphere, then deploy a rocket-directed landing craft equipped with ground-mapping radar that would find a precise location, as well as determining various hazards and avoiding them. Keep in mind this is all autonomously; the 22+ minutes it would take for images (had they been transmitted ‘real-time’) to reach Earth, then for Earth to send back instructions, would have been far too late. So the Perseverance entry vehicle was programmed to suss out all of this on its own.

There’s also the potential issue of colliding with or being obstructed by the various apparatus used for landing, so all of these were intended to separate distinctly – Perseverance would not be covered by its own parachute, for example. But it also had to touch down in a relatively undisturbed area, not affected by hard rocket blasts, so once they got within a few meters of the surface, the rover itself would be lowered by cables to touch down gently, then the rocket shell would lift higher and shear off to a safe distance before crashing down out of the way. And now we get to see what this all looked like.

The video quality is amazing, and the descent speed almost harrowing, but bear in mind, Mars’ atmosphere is less than 1% as dense as Earth’s, while the gravity is only 38%. The parachute had far less to grab, but (the same as the rockets) had less to fight against in the form of gravitational pull. And it all worked quite well. One of the things I had found was that the lander wasn’t intended to stir up too much dust, partially because this might settle again on instruments and solar panels, but it was enough to obscure the lander entirely right before touchdown; hopefully this was within tolerances.

And there’s one more bit: Perseverance has a freaking helicopter on board!

Named Ingenuity, this drone (in the true meaning of the word) spans 1.2 meters across the rotors, and is merely a proof-of-concept demonstrator right now; if all goes well, it could open up the possibility of exploring Mars by helicopter instead of plodding rovers. Remember: 1% of Earth’s atmospheric density and 38% of its gravity. This makes designing a helicopter for those conditions quite challenging, and as an example, the rotors spin at 2,400 RPM; full-size helicopters here operate at roughly 300 RPM, though quadcopters and the like are faster. We should eventually see the lift-off of Ingenuity taken from Perseverance, and a handful of still photos taken by Ingenuity on its brief flight above another planet. Rotorcraft enthusiast that I am, I’m psyched by this one.

There are tons more videos out there (like this fabulous one,) going into greater detail if you have the desire (and you should.) Check them out, but be prepared to go down a rabbit-hole or three. It’ll be well worth the time.

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