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Comment by davedx | Hacker News Reader

1) The original NASA article had a more in-depth explanation - maybe we could change the story URL to use that? [1]

2) Yes, we've known for a while now that Mars has water ice. This is new science because they've built up a comprehensive map with the goal of identifying good landing sites for future missions to Mars, in particular missions focused on in-situ resource utilization of Martian water ice. The data is derived from current Mars probes, the Mars Reconnaisance Orbiter and Mars Odyssey Orbiter.

[1] https://www.nasa.gov/feature/jpl/nasas-treasure-map-for-wate...

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Also, although we know there is water ice at the poles, it's locked under a cap of frozen CO2 between 1 and 8 meters thick. This sub-surface water ice between the polar regions is comparatively much more accessible, only 2.5cm below the surface in some cases.

I can't wait to see the Mars helicopter scout on the 2020 rover mission. It's kind of useless on its own but if the design works it would really open up exploration opportunities to validate large scale maps like this. Add some kind of tool bay that it can fly around and 'do science', returning to the rover to grab a new tool.

It's really cool but I wonder what kind of range it could feasibly achieve. Personally I like the idea of high altitude helium balloons. You can't control the direction but they could stay up for much longer than something that used powered flight.

Could a helium balloon fly in the rarefied Martian atmosphere?

Here's NASA's page on the subject https://mars.nasa.gov/technology/balloons/index.html

Yep. I actually ran the numbers on this (in a spreadsheet) and even ordered a weather balloon to try and built a DIY survey balloon that might also work on Mars. Got bogged down by the hardware side though, and abandoned the project. :D

The demonstrator going to Mars on the 2020 mission can only fly for 90 seconds per day and afaik has no science objectives other than trying to fly. But if it proves viable they could presumably scale it up to something with a longer range (say 5-10km/day).

Correct, it is going to test the technology and take photos with its 2 color cameras.

This is basically a project that was "Let's try this, how much weight does the mission have to spare? Ouch, that's not a lot, let's see what we can do", that's my takeaway from this episode anyway https://www.planetary.org/multimedia/planetary-radio/show/20...

Wow, I would have honestly thought that the Martian atmosphere was too thin for a helicopter to fly!

https://spaceflightnow.com/2018/05/14/helicopter-to-accompan...

> She said the size of the rotors was restricted to 1.2 meters by the space available on the Mars 2020 rover’s belly pan. In turn, the 1.2-meter rotor diameter limits the mass of the helicopter to 4 pounds — 1.8 kilograms — based on the rarefied density of the Martian atmosphere.

> “The biggest thing is the atmospheric density at Mars is very thin,” Aung said in an interview Friday. “It’s 1 percent of that at Earth. It’s equivalent to about 100,000 feet in altitude here on Earth. The other difference is the gravity at Mars is lower. It’s about 40 percent. That plays into how much we can lift.”

> The rotors on the Mars Helicopter will spin between 2,400 and 2,900 rpm, about 10 times faster than a helicopter flying in Earth’s atmosphere.

Yeah rotor tip speed is Mach .7 lol

Here it is running in test chamber at mars equivalent atmospheric density - https://www.youtube.com/watch?v=tMCJGfwj3rY

> Yeah rotor tip speed is Mach .7

The thin atmosphere cuts both ways. It generates less lift. But it inflicts less drag.

It also lowers the speed of sound. This poses some design limitations and since traditionally designed rotors get less efficient near Mach 1- they still work, but not as well. So you have to spin the rotors fast to generate enough lift, but you want to keep them slow so the tips don't go supersonic. Helicopters/drones on Mars are a tough design problem in areas beyond just the atmospheric- you can't use a gas engine because you can't refuel it, recharging a battery with solar energy takes forever because there is less solar radiation. You can't replace the rotors if you crash, so you need to make it robust, but you can't make it too heavy. On and on...

Maybe a balloon to provide most of the lift, then attach a few electric props? And if you have access to ice, maybe we can use solar panel to electrolise it into fuel.

What about solar-powered aircraft?

Would they work in Mars' atmosphere?

I'd like to see it tested in mars equivalent dust. I assume that the higher speed will correspond with more wear from sand blasting.

The Planetary Society had a good interview with MiMi Aung on their podcast earlier this year, I think it is this episode https://www.planetary.org/multimedia/planetary-radio/show/20...

Ok, changed from https://www.engadget.com/2019/12/12/nasa-ice-surface-mars/. Thanks!

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