Can someone explain the phyics of flying a helicopter in such low density atmosphere? It must be less efficient than on earth, but evidently efficiency isn't proportional to density or else it could not fly at all.
How NASA Designed a Helicopter That Could Fly Autonomously on Mars
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Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#42Earlier quoted context omitted.
I would think the atmosphere is too light to support a balloon.
I do remember reading about this - a balloon would work, but it would be absolutely enormous, far larger than anything we can bring into Mars currently. Maybe some day.
Another thing I'm wondering: the drones can probably carry only a small (light) camera, whereas a satellite can carry much more and thus also a much better camera. Wouldn't a satellite+camera be a better option?
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#43One thing that I have been wondering, if the atmosphere is so thin, then how does the RTG cool? I seem to have nerd-sniped myself. It needs a temperature differential to generate electric current and it looks to have fins for convective cooling but the atmospheric pressure is a few % of that of sea level Earth.
You can read a bit about this in quite some detail in this pre-print from the 80s: https://www.osti.gov/servlets/purl/1033420
".. radiation, diurnal and seasonal temperature".
"Convective cooling by the Martian atmopshere, even on a cold windy day makes only a relatively minor contribution to heat rejection"
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#44One thing that I have been wondering, if the atmosphere is so thin, then how does the RTG cool? I seem to have nerd-sniped myself. It needs a temperature differential to generate electric current and it looks to have fins for convective cooling but the atmospheric pressure is a few % of that of sea level Earth.
mars is freezing cold, it's like dust covered ice ball.
Space is cold and yet getting rid of waste heat is a challenge for any spacecraft. The ISS has giant radiators to dissipate heat. It doesn't matter how cold Mars is if it's difficult to transfer the heat away, such as in a very thin atmosphere which has less capability to carry away heat than Earth's atmosphere. There needs to be some kind of medium for the heat to transfer away (aside from radiation), regardless of ambient temperature. It's why a vacuum-walled thermos can keep things warm even in a cold environment. That's what they were asking about.
Heat can be conducted away by contact with another object, probably not what you want if you're using an RTG to power your spacecraft, you don't want your RTG to heat it too much. It can be convected away, which is more difficult in a thin atmosphere like Mars has. Or it can be radiated away by blackbody radiation, which some certainly is, but that is limited and isn't much.
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#45So many interesting details in this article. Snapdragon 801-based hw running Linux, sensor fusion from three sensors whereof some bought COTS from sparkfun (who make breakout boards for sensors, basically the sensor datasheet recommended design). 3 flights planned, but potentially more which will be planned after the three first. 30 day lifetime window, due to dependecy on the rover, which needs to conserve resources…
I went down this rabbithole not long ago with the rovers on-board computer. The writeup from the people who designed the system was really approachable for someone without any aerospace experience. There's a lot of challenges and tradeoffs involved. Some takeaways: > Constrained CPU: 133MHz PowerPC, 128MB RAM, 4GB storage > Software written in C, OS is VxWorks > Only get contact a few times a day, rover must be charg…
> Some tasks require parts preheated for X time, which depends on ambient temp, they use a lookup table for the time of day instead of measuring the temp directly. (Assume this is for reliability purposes)
That's an interesting one. Guessing that there also must not be that much variation of temp and weather conditions?
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#46So many interesting details in this article. Snapdragon 801-based hw running Linux, sensor fusion from three sensors whereof some bought COTS from sparkfun (who make breakout boards for sensors, basically the sensor datasheet recommended design). 3 flights planned, but potentially more which will be planned after the three first. 30 day lifetime window, due to dependecy on the rover, which needs to conserve resources…
Actually the computing power of Ingenuity surpasses one of the Perseverance rover (and probably by a lot). The rover has a radiation hardened RAD 750 CPU (based on PowerPC 750 architecture, which was introduced in 1997 to compete with Intel's Pentium II [1,2]) with 250-150nm technology process operating at 200Mhz[3]. Ingenuity's Snapdragon 801 can reach up to 2.5 GHz and is based on more energy-efficient 28nm modern (released in 2014) ARM architecture [4]. This CPU even has Wi-Fi and GPS, though probably not much of a use on Mars :)
1. https://arstechnica.com/science/2019/11/space-grade-cpus-how...
2. https://en.wikipedia.org/wiki/RAD750
3. https://mars.nasa.gov/mars2020/spacecraft/rover/brains/
4. https://www.qualcomm.com/products/snapdragon-processors-801
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#47Could they use it to try blow dust off the Opportunity rover's solar panels to see if it'll boot again?
I guess the atmosphere would be too tenuous to try to blow dust away with it (max pressure should be a bit more than Ingenuity's mass/rotor surface, so not much).
How long before a commercial autonomous helicopter-based solar panel dusting service on Mars, I wonder?
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#48So many interesting details in this article. Snapdragon 801-based hw running Linux, sensor fusion from three sensors whereof some bought COTS from sparkfun (who make breakout boards for sensors, basically the sensor datasheet recommended design). 3 flights planned, but potentially more which will be planned after the three first. 30 day lifetime window, due to dependecy on the rover, which needs to conserve resources…
Actually the computing power of Ingenuity surpasses one of the Perseverance rover (and probably by a lot). The rover has a radiation hardened RAD 750 CPU (based on PowerPC 750 architecture, which was introduced in 1997 to compete with Intel's Pentium II [1,2]) with 250-150nm technology process operating at 200Mhz[3]. Ingenuity's Snapdragon 801 can reach up to 2.5 GHz and is based on more energy-efficient 28nm modern…
Do you know why radiation hardening is not needed for the Ingenuity? Is there a mechanical shield? Or is it just the shorter runtime that makes the use of an off-the-shelf processor acceptable?
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#49I wish we could have more information on the terrain relative navigation implementation..
Re: How NASA Designed a Helicopter That Could Fly Autonomously on Mars
#50I had the opportunity to speak with one of Ingenuity's engineers in the NASA pavilion at the EAA Fly In in Oshkosh, WI in 2017 (or perhaps 2016). This was before it had been accepted for the Rover2020 mission but just after they had proven the concept flight capable. I asked him about flight conditions on Mars and what they had to do to get their design airborne in such a thin atmosphere. He made a few points.
1. Given the thinness of the atmosphere, the counter rotating blades are balanced among thickness, length, and rotation speed. They're essentially as big as they can spin with the power they have at a speed where the tips are just under the Martian speed of sound.
2. I asked if wind was an issue. He said that it wasn't an issue for the stability of the craft (Martian wind moving much of anything is a movie trope) but the turbulence it caused could be a major issue for the blades, as they're essentially small wings, like a helicopter. The turbulence of a cross breeze could disrupt the flow of air over the blades and cause them to lose lift.
3. The design of the craft was essentially locked once they confirmed it could fly. They would keep most of their original hardware and software, rather than rebuild anything, which I found surprising. Given this was before they were accepted on the mission I'm not sure if anything changed. It does appear to be pretty equivalent to what we saw there.