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Nasa will send helicopter to Mars to test otherworldly flight

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Re: Nasa will send helicopter to Mars to test otherworldly flight

#51

Post by allannienhuis »

alexozer wrote: post #44
azernik wrote: post #38

Earlier quoted context omitted.

Where do you get 50% from? It's got landing legs, and will be placed right-side-up to start with by the Mars 2020 rover.

All it takes is to land on the side on one rock and it's over. I would say the chance is more like 98% over the span of a few years.

Vision navigation systems are pretty effective these days - 'avoid big rocks' seems like a straightforward use case for that. And clearly the landing systems would need to account for some degree of rough terrain. The wheeled drones go through a tremendous amount of testing of the various conditions they would encounter - a flying drone would go through the same engineering rigour before it was approved for the mission.

Also, I believe most of the activity of these devices is planned out well in advance, so you could even add human review to some of that process. It could take a short flight for a few high-rez pictures, land right near (or exactly) where it took off from, send the pics back to earth for review to pick it's next landing spot.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#52

Post by jessriedel »

mseebach wrote: post #37
maxmcd wrote: post #27

Earlier quoted context omitted.

Wait, could they use earth GPS and it would just be very innacurate?

You mean pick up the signal from earths GPS? Off the top of my head, it would require earth to be in view, and it would be very inaccurate - GPS is already less accurate the further from equator you get, as all the visible satellites are increasingly on one side of you. You'd have this problem in the extreme, as all the satellites would be clustered in a single dot in the sky. Probably also infeasible to meaningfully…

> GPS is already less accurate the further from equator you get, as all the visible satellites are increasingly on one side of you.

Not contradicting you, but just to be clear: GPS satellites are not in geostationary orbits above the equator, or even in geosynchronous orbits. Rather, they are in medium-Earth orbits and their time-averaged density over the Earth is only a little lower over the poles as the equator. At some parts of the month, there are as many visible at the poles as at the equator. See Fig. 4 here:

https://www.researchgate.net/publication/228400966_Analysis_...

The GPS Wikipedia page also has a reasonable illustration of their orbits.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#53

Post by baddox »

YaxelPerez wrote: post #29
dugluak wrote: post #28

Why not a few quadcopters like GoPro or something. I guess those are more stable and cheap.

My guess is a normal quadcopter doesn't have a big enough thrust to weight ratio in Mars' atmosphere.

Can someone check my math/physics? The atmosphere on Mars is about 1.7% as dense as on Earth, meaning that a propeller on Earth will generate 58.8x more thrust than on Mars. An aircraft on Earth will weigh 2.6x of its Mars weight. Drones probably need a thrust to weight ratio of at least 1.5 to be reasonably maneuverable. A drone that has a 1.5 thrust to weight ratio on Mars would have a thrust to weight ratio of 1.5 * 58.8 / 2.6 = 33.9. That is certainly higher than hobbyist Earth drones that I’m aware of, but not terribly hard to imagine. The craziest racing quadcopters I’ve seen have power to weight ratios of around 10.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#54

Post by YaxelPerez »

maxmcd wrote: post #39
YaxelPerez wrote: post #30

Earlier quoted context omitted.

GPS requires a bunch of satellites to be in orbit first, and we haven't sent them to Mars yet.

I meant using the known location of existing earth GPS satellites

Mars is 140 million miles away from earth on average. Even if you could detect signals from GPS satellites on earth they would all be at a single point in the sky.

However, that does bring up an interesting idea. Maybe rovers could navigate using the position of the stars? It doesn't require you to launch 4+ GPS satellites into martian orbit.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#55

Post by ohazi »

maxmcd wrote: post #39
YaxelPerez wrote: post #30

Earlier quoted context omitted.

GPS requires a bunch of satellites to be in orbit first, and we haven't sent them to Mars yet.

I meant using the known location of existing earth GPS satellites

Earth's GPS satellites use earthward facing directional antennas, and even on Earth the signal is several dB below the noise floor, so our receivers have to use process gain to actually get anything useful out of them.

Mars is fifty million kilometers away. A GPS reliever on Mars looking for Earth satellites wouldn't be able to hear anything.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#56

Post by gambiting »

YaxelPerez wrote: post #54
maxmcd wrote: post #39

Earlier quoted context omitted.

I meant using the known location of existing earth GPS satellites

Mars is 140 million miles away from earth on average. Even if you could detect signals from GPS satellites on earth they would all be at a single point in the sky. However, that does bring up an interesting idea. Maybe rovers could navigate using the position of the stars? It doesn't require you to launch 4+ GPS satellites into martian orbit.

I don't see why not - automatic celestial nagivation systems are already a thing on earth, you basically have a system that uses a camera to look at the sky and it gives you an accurate position - most military planes use it as backup in case GPS ever goes down.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#57

Post by trothamel »

infogulch wrote: post #47
YaxelPerez wrote: post #30

Earlier quoted context omitted.

GPS requires a bunch of satellites to be in orbit first, and we haven't sent them to Mars yet.

We need a bunch here on Earth so we can get a fix in a reasonable time. But all the robots on Mars move extremely slowly and infrequently. i.e. it would be fine if the bot had to wait 12+ hours for a fix, they'd probably be waiting that long regularly anyways. And it probably doesn't need to be more accurate than 0.1-1 km either. So could we deploy, say, the first three satellites that use a modified version of GPS a…

If you have enough time, a single satellite is enough, provided it's not in a geostationary orbit. My understanding is that this is part of the initial location of landers, but that once they're located there's no point, since it's easier to just optically determine how you moved.

On Earth, similar systems were used for the TRANSIT satellites, and the Cospas-SARSat program. The latter is really cool, as it used weather satellites in low earth orbit to find a person in distress, using a cheap transmitter that's placed on a plane, boat, or very famously, Richard Branson's watch.

The way it works is that the device transmits a very stable frequency. (Perhaps modulated by the identity of the person in trouble part of the time.) As the satellite passes by, it relays the signal to the ground in a way that preserves the doppler shift. When you know the position of the satellite and the doppler shift, you can know the closest point and the distance from it.

After a few passes of your one satellite (or multiple satellites, if you have them), you can get a location that's good enough to start search and rescue.

Of course, time has passed since this was designed in the 70s and early 80s, and now GPS has fallen in price to the point where it's everywhere. So now, the devices send GPS coordinates with the identity info.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#58

Post by fastball »

organicmultiloc wrote: post #31

If this is the sort of experiment that is getting space on a rocket then I kind of wonder if NASA is out of ideas. In other news, Hepatitis C is making a big comeback here in Denver. It's the sort of disease we used to laugh about being a "third world" problem back in the day. We don't use the term "third world" anymore, but we are becoming one nonetheless. I can't stop thinking about what archaeologists will think a…

Are you a markov chain?

Re: Nasa will send helicopter to Mars to test otherworldly flight

#59

Post by John_KZ »

pavel_lishin wrote: post #10
DogestFogey wrote: post #7

It would be interesting to see how the helicopter handles potential dust storms which can have winds of up to 94 km/hr.[1] 1: https://en.wikipedia.org/wiki/Climate_of_Mars#Effect_of_dust...

Aren't they pretty mild despite this, thanks to the very low density of the atmosphere?

They are, but this is a disaster waiting to happen anyway. Extremely high RPM, no redundancy in rotors or engines, flying in an environment full of dust and particles, having to land perfectly every time (or get damaged irreversibly), all these things add up to certain failure. It's definitely very cool, but it's not going to be nearly as reliable or useful as a land-based vehicle. Besides, aerial photos have generally little value for Mars (at least for the surface area such a drone can cover) because the atmosphere is clear and you can get great imagery from space.

So unless they want to reach an otherwise impossible to climb location, I don't see the use for it.

Re: Nasa will send helicopter to Mars to test otherworldly flight

#60

Post by mseebach »

jessriedel wrote: post #52
mseebach wrote: post #37

Earlier quoted context omitted.

You mean pick up the signal from earths GPS? Off the top of my head, it would require earth to be in view, and it would be very inaccurate - GPS is already less accurate the further from equator you get, as all the visible satellites are increasingly on one side of you. You'd have this problem in the extreme, as all the satellites would be clustered in a single dot in the sky. Probably also infeasible to meaningfully…

> GPS is already less accurate the further from equator you get, as all the visible satellites are increasingly on one side of you. Not contradicting you, but just to be clear: GPS satellites are not in geostationary orbits above the equator, or even in geosynchronous orbits. Rather, they are in medium-Earth orbits and their time-averaged density over the Earth is only a little lower over the poles as the equator. At…

Hmm, not sure I understand what you're saying. Figure 5 in that paper is the situation I'm describing: at a certain latitude (52 deg north in this case, incidentally that latitude is my 'hood) there are no satellites visible to the north. Figure 2(b) illustrates why that's bad for precision.
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