Veritasium
10 HN recommenders · recommended in 5 months, 2020–2021
16:01 · 6.2M views · Aug 10, 2019
Veritasium's Derek Muller visits NASA JPL to see the Mars helicopter Ingenuity before it was mounted on the rover. He explains how it can fly in Mars's thin atmosphere with large, fast-spinning contra-rotating rotors and low mass, and covers power and cold.
HN repeatedly recommends it as an excellent explanation of why flying on Mars is hard and how the helicopter was built.
14 comments from Hacker News
Here's a really excellent video that answers all your questions: this video TL;DW: Martian atmosphere is so sparse that it's equivalent to flying at 100,000 feet on Earth. (The altitude record on Earth is 85,000 feet, set by the SR-71.) In order to fly at all the blades have to spin at nearly the (Martian) speed of sound. The drone wouldn't fly on Earth because the atmosphere is so dense that the blades would never make it up to speed.
On top of what others have said, we need advancement it batteries that can withstand low temperatures. Lithium ion batteries generally need to be kept above freezing temps. There have been some advances in capacitors that operate down to -100C, but their energy density makes them a non-ideal option for weight limited applications. This video from Veritasium does a good job of covering the helicopter power system: this video
Saw this Veritasium youtube video a year ago and the technical complexity required to fly on Mars was shocking to me. Since the air density is super low the blades need to spin at a speed which nears the speed of sound at the blade tips. Crossing the speed of sound causes mini sonic booms which could disrupt the flight entirely. Kudos to NASA scientists for this technological breakthrough! Sharing the video: this video
This video this video explains it: they can change the attack angle of rotor blades for different positions, which produces a torque, though you have to compensate for the gyroscopic effect, which lags behind. Humans cannot fly this, but computers can. The video also explains why the chose two contra-rotating rotors instead of a quad-copter design.
Video from Veritasium about the helicopter that talk with the team about this. He mentions that 2/3rds of the daily energy gathered is used for the purpose[1] Other information about the tech; camera & landing, energy use for heating, flight in low pressure atmosphere, the system to actually land the thing, is also really interesting. this video