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Nasa will send helicopter to Mars to test otherworldly flight

bbc.com

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

#81

Post by jessriedel »

djsumdog wrote: post #70
fvdessen wrote: post #64

Does anybody knows what is the autonomy of this helicopter ?

Considering the lag in communication to earth, it'd have to be fully autonomous. It needs to be able to avoid obstacles, navigate visually (that article states a compass won't work with Mars's magnetic field) and find a place to land, in direct sunlight, whenever it needs to charge its batteries. I'm sure NASA has mapped out some waypoints, but there's no way to really control the actual flight remotely without a hum…

Yea, the daily flight time (3 min) is much less than signal travel time to Earth. So the entire flight needs to be autonomous.

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

#82

Post by jacquesm »

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 GPS signal is already under the noise floor on Earth there is no way with present day tech that you'd be able to get the signals on Mars and besides that the math would not work because the round-off errors regarding the timing would make all satellites appear at the same point in space when looked at from Mars. The distance is hard to appreciate in terrestrial terms without getting into 'golf balls and oranges' kind of explanations.

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

#83

Post by KineticLensman »

dullgiulio wrote: post #62
zitterbewegung wrote: post #42

Earlier quoted context omitted.

The funny thing is that you could almost classify most space missions as drones (or probes).

They are usually called rovers, unless they actually fly. I cannot name any single atmospheric flight on another planet, only controlled plunges.

The Vega-1 and Vega-2 balloons operated for more than 46 hours in the atmosphere of Venus as part of the Soviet Venera programme [0]

[0] https://en.wikipedia.org/wiki/Vega_program

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

#84

Post by jacquesm »

sktrdie wrote: post #20

So if it falls on its side, something that has a probably a 50% chance of happening, can it get back up? I always thought that for exploring another planet, you shouldn't really use something with wheels or wings. Something different like small "jumping robots" would make a lot more sense in a place where you have literally the ability to do 0-hardware maintenance. Instead of a single expensive flying robot, why not…

Neat little robot, reminds me of this animal:

https://en.wikipedia.org/wiki/Springtail

I once spotted some 'jumping dust' around a leaky faucet and it turned out that it was 100's of these little creatures. They can jump 100's of times their own height!

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

#85

Post by TeMPOraL »

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?

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 small fraction of arc second, i.e. basically all coming from the one place. Lastly, there's extra light lag that you have to compensate for, that depends on relative position and orientation of Earth and Mars.

No, GPS is not suited for use in space, especially not far away from Earth. However, I read once that some Earth orbit missions did in fact look / make use of the GPS signals, as in (low) Earth orbit, they're actually easier to receive than on the ground.

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

#86

Post by TeMPOraL »

jacquesm wrote: post #82
maxmcd wrote: post #27

Earlier quoted context omitted.

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

The GPS signal is already under the noise floor on Earth there is no way with present day tech that you'd be able to get the signals on Mars and besides that the math would not work because the round-off errors regarding the timing would make all satellites appear at the same point in space when looked at from Mars. The distance is hard to appreciate in terrestrial terms without getting into 'golf balls and oranges'…

> round-off errors regarding the timing would make all satellites appear at the same point in space when looked at from Mars

Not just timing, also space - Earth is a fraction of an arc second on Martian sky, pretty much a very small dot. All your signals would be coming from that small dot, i.e. practically on top of one another.

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

#87

Post by TeMPOraL »

anoncoward111 wrote: post #65
chiefalchemist wrote: post #22

Earlier quoted context omitted.

"The helicopter uses counter-rotating coaxial rotors about 1.1 m in diameter..." Not to be little it but, in short, a drone. I presume the rocket scientists are jealous ;)

I too found the terminology a bit weird. When I think "helicopter", i think "gigantic rotor blade with a cockpit fit for a human". When i think "quadcopter", I think of something smaller than what NASA has proposed.

Sounds weird, because we're used to media spam. But "drone" wrt. flying machines basically has 3 popular meanings - RC multicopters, any RC aircraft, and those big RC aircrafts with surveillance cameras and Hellfire missiles. Back because multicopter mania caused all RC aircraft to be rebranded as "drones", we used to call them by category - RC plane, RC helicopter, etc. So personally, I'm totally fine with NASA using the word "helicopter" - though I expect the name that's even more cool than "drone" - an UAV.

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

#88

Post by inamberclad »

kersny wrote: post #45
KineticLensman wrote: post #17

Link to the underlying press release [0] which has slightly more info than the BBC article. There is a bit more background about the project at [1], with some key points being: "The helicopter uses counter-rotating coaxial rotors about 1.1 m in diameter. Its payload will be a high resolution downward-looking camera for navigation, landing, and science surveying of the terrain, and a communication system to relay data…

If anyone has AIAA paper access (or a workaround ;), they published a ton of details on their guidance, control, and avionics designs at the beginning of this year: https://arc.aiaa.org/doi/10.2514/6.2018-0023 https://arc.aiaa.org/doi/abs/10.2514/6.2018-1849

check ntrs?

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

#90

Post by jacquesm »

TeMPOraL wrote: post #86
jacquesm wrote: post #82

Earlier quoted context omitted.

The GPS signal is already under the noise floor on Earth there is no way with present day tech that you'd be able to get the signals on Mars and besides that the math would not work because the round-off errors regarding the timing would make all satellites appear at the same point in space when looked at from Mars. The distance is hard to appreciate in terrestrial terms without getting into 'golf balls and oranges'…

> round-off errors regarding the timing would make all satellites appear at the same point in space when looked at from Mars Not just timing, also space - Earth is a fraction of an arc second on Martian sky, pretty much a very small dot. All your signals would be coming from that small dot, i.e. practically on top of one another.

The whole idea of GPS is to turn a very good time reference (an atomic clock) into a space reference, by using multiple such references with known locations at once and then to send out time stamped signals. If you can't distinguish arrival times the signal origins collapse into a point. The travel time of the signal from Earth to Mars is anywhere from 4 to 24 minutes (assuming you have line of sight, which isn't the case when Mars is on the other side of the sun), with flight times that long the difference in arrival time between the signals is meaningless.

The difference in position between the satellites is at best 40,000 km (MEO orbits and satellites in opposite positions around Earth would give you the largest baseline), the difference from Mars to Earth is > 50M kilometers. So when viewed from Mars this would be like trying to triangulate your position in the United States based on signal sources spaced a very short distance apart somewhere in Moscow.

(sorry for the strained analogy)

Another problem with the approach is that of the two possible solutions that are the result from computing your location from GPS satellites one of the solutions is deep inside the Earth, which for both radio related reasons and reasons of practicality can be safely ignored. From a location in space very far away that trick no longer works so you will end up having to pick one of several answers.

Of course you could stick a GPS like transmitter into every Mars orbiter we launch from now on so that at some point there will be enough coverage locally to allow navigation, but that's a pretty expensive trick, besides that you'd also need a bunch of base stations in order to properly compute the orbits of the satellites to the required precision so that you can tell the satellites where they are.

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