Nasa will send helicopter to Mars to test otherworldly flight • Hacker News Board

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

#121

Post by stephengillie » Sun, May 13, 2018, 5:02 AM UTC

mikec3010 wrote: post #109

reaperducer wrote: post #99

Earlier quoted context omitted.

> drones are just a new name for hobby aircraft With the minor notation that hobby aircraft are permitted in some national parks, while drones are prohibited in all. The Parks Service operates a number of model aircraft airports in some national parks. (I'm not moaning about the perceived inequity with the "drones;" just pointing out a curiosity. I've hated drones ever since they started ruining my ability to peacefu…

To me what makes a drone a drone is the control system algorithm that keeps the aircraft stable. I thought "model aircraft " had to be operated by a sufficiently skilled operator to keep it from crashing. Whereas "drones " automate this skill and present a very simple, dummed down interface such as "go left, turn around, descend" etc

If only self-leveling was more common in drones. None of the drones I own have self-leveling, nor have any owned by other pilots that I know.

There are a multitude of ways to pilot quadcopters, combining the 4 different transmitter modes (Mode 1, Mode 2, Mode 3, Mode 4) with the different control modes (Acro, Rate, Horizon, etc). The lack of standardization can be maddening for beginners - it's like learning Git, Github, and DVCS, while learning to code.

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

#122

Post by nanomonkey » Sun, May 13, 2018, 6:08 AM UTC

skykooler wrote: post #116

ambicapter wrote: post #89

Does this make any sense? Isn't Mars' atmosphere much thinner than Earth's? Wouldn't that count against using rotary wing crafts?

The interesting thing about rotary-wing craft is that they actually work sort of independent of altitude (as long as everything stays subsonic.) As air pressure decreases, lift at a given rotor RPM decreases - but the drag on the rotor also decreases, so the RPM increases and it ends up providing the same amount of thrust. The reason helicopters on Earth haven't flown very high is not because of the rotors, but rathe…

I wonder if a sterling engine would work well for high altitude rotary-wing craft. The higher you go up the cooler the air, causing the sterling engine to be more efficient.

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

#123

Post by rz2k » Sun, May 13, 2018, 3:03 PM UTC

TeMPOraL wrote: post #85

maxmcd wrote: post #27

Earlier quoted context omitted.

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

No. First of all, they would need an absurdly large directional antenna to even receive GPS satellites. GPS signals are already below the noise floor on Earth's surface, and we use mathematical trickery to extract them from the background. Secondly, even that would only be possible when Earth's over the horizon at the location of the probe. Thirdly, the whole span of GPS satellites as viewed from Mars would be a smal…

The third point can be misinterpreted to make it sound like gps involves a steady tone generated from a known location like more traditional navigation aids used in aviation, rather than clocks taking advantage of our understanding relativistic effects.

While Earth is in the Martian sky, and if the signal were strong enough, a viewer could average receiving signals from over half of the constellation rather than only half a dozen. Furthermore the time signals would originate from many of the satellites moving less orthogonally to the viewer and instead moving toward and away from the viewer.

Compared to measuring the sun relative to a changing horizon, it seems plausible that an extremely precise direction and altitude relative to Earth could give even more precise location on Mars.

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

#124

Post by andbberger » Sun, May 13, 2018, 9:45 PM UTC

John_KZ wrote: post #78

andbberger wrote: post #75

Earlier quoted context omitted.

> 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. I'm not buying your blanket statement. Atmosphere is not the only limitation - optics are heavy.

>optics are heavy It depends on the optics. Modern optics for the visual range are incredibly light. Also, since you assume optics are heavy, why do you think putting them on a drone is a good idea? You can haul a metric ton of optics in space for years (if not decades) but that drone can probably carry a handful of kg of equipment, and not that many cameras.

My point is that you can't just conclude a prior that the capabilities could be matched by an orbiter. You need bigger and thus heavier optics to match the performance of a camera on the ground from orbit. The extra mass for the drone might be less than that needed for the larger optics.

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

#125

Post by skykooler » Mon, May 14, 2018, 1:33 PM UTC

nanomonkey wrote: post #122

skykooler wrote: post #116

Earlier quoted context omitted.

The interesting thing about rotary-wing craft is that they actually work sort of independent of altitude (as long as everything stays subsonic.) As air pressure decreases, lift at a given rotor RPM decreases - but the drag on the rotor also decreases, so the RPM increases and it ends up providing the same amount of thrust. The reason helicopters on Earth haven't flown very high is not because of the rotors, but rathe…

I wonder if a sterling engine would work well for high altitude rotary-wing craft. The higher you go up the cooler the air, causing the sterling engine to be more efficient.

The big problem with stirling engines is the power-to-weight ratio; they are much heavier than internal combustion engines for the same power output, too heavy for any practical use in a flying machine.

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

#126

Post by SolarNet » Mon, May 14, 2018, 6:21 PM UTC

maxmcd wrote: post #27

jon-wood wrote: post #23

Earlier quoted context omitted.

It says a lot to how routine using satellite navigation aids has become that my first question was why they’re not using GPS.

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

The distances are literally astronomical. Mars isn't just next door. It isn't like the moon where we can talk almost in real time.

Consider it like running. How far can you run in 1 second. That's the Moon. How far can you run in 21 minutes. That's Mars. It's 1260 times the distance.

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

#127

Post by pvaldes » Tue, May 15, 2018, 8:19 AM UTC

cududa wrote: post #111

pvaldes wrote: post #108

Looks like a more efficient and much faster way to explore the area if they can solve the thinner atmosphere but, if their missions are autonomous and it seems that can't be modified in real time, what happens with the mars storms? I hope that they have a software to take measures if the air pressure or the light levels change suddenly. Couldn't the differences in temperature between shadowed and sunny areas create t…

Yes to all of this but do you assume no one at NASA has thought of any of this? Weird.

Am I assuming that? Where?

This sort of "somebody should have thought about that (and fix it), so don't say it", is probably the safe way for people working in a big company that needs to fit in a hierarchy and please their boss. We aren't in this context and have a bigger margin to freely explore any idea and talk about it. To wonder about the dust storms is a valid question.

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

#128

Post by nanomonkey » Tue, May 15, 2018, 10:57 PM UTC

skykooler wrote: post #125

nanomonkey wrote: post #122

Earlier quoted context omitted.

I wonder if a sterling engine would work well for high altitude rotary-wing craft. The higher you go up the cooler the air, causing the sterling engine to be more efficient.

The big problem with stirling engines is the power-to-weight ratio; they are much heavier than internal combustion engines for the same power output, too heavy for any practical use in a flying machine.

I'm not sure that this is inherent to Stirling engines, or just the past engineering implementations. For one thing, unlike internal combustion engines, there is no need to contain an explosion (otto cycle) or flame front (diesel) so the pistons and cylinder walls can be made of lighter materials and don't need lubricant filters. In fact self lubricating graphite pistons are often used modern Stirling engines. Secondly a higher efficiency implies that more power is extracted from the fuel which indicates that the combined fuel tank and engine can be smaller and that more power will be put to doing work. Lastly, a Stirling engine usually falls short in torque, and that can be compensated for with a hybrid system that utilizes electric motors for instantaneous changes speed, where added torque is required.