Until the pandemic we were plagued with copter noise here. No evidence of active pandemic on Mars at this time so extra care should be taken during flight operations.
NASA has revealed the wheels it’s just bolted onto the Perseverance Rover, the new Mars assault robot it plans to send to the red planet in July as part of the Mars 2020 mission. Wheels matter because NASA’s Curiosity rover has had trouble keeping a grip on Mars. As we reported in 2017, Curiosity has been popping unintentional …
"... The ‘copter is equipped with cameras, too, so hopefully we’ll get some fabulous footage! ..."
I expect the Space Police will also use it to check that the Martians are social-distancing correctly.
My coat? It's the one with the Illudium Q-36 Explosive Space Modulator in a pocket.
I doubt that there are many tire manufacturers that make tires for surfaces other than roads. There may be some models that are special for all-terrain models, but all tires made on Earth have one thing in common : an atmosphere around them.
Rubber tires in space would be a catastrophe. I saw a documentary on the lunar landing, where it was explained that the tires for the lunar rover were, in fact, a wire mesh that behaved basically like a normal tire.
I wonder why they didn't use that concept ? It's not like NASA didn't know about it, so what reason did they have to reinvent another wheel type ?
@Chris G, I agree with your point on tread design, that should be reasonably reliable once the exact nature of the surface is known. (which we don't know until we go and look)
Within the tyre industry there's no data about tyres working at the temperature & terrain combination found on Mars (our mid arctic winter lowest temp is about the annual average up there) and precious little where tyre/wheel all up weight is a critical issue regardless of the ambient temp.
The big problem with rovers is that NASA want the wheels to work for years with as little performance degredation as possible, I think the moon rover wheels were built for absolute minimum weight and only good for a few dozen miles of life.
When building payloads, mass reduction is really important. You have to get the thing as light as possible. This means you can't over-engineer things - for example the ladder on the side of the lunar lander was only going to be used on the moon, which has less gravity than earth, so they made the ladder too weak to be used in Earth gravity, but strong enough to be used on the moon. Bearing that in mind, there are a lot of differences between the missions:
* The lunar rover had to carry a couple of astronauts in EVA suits; that's a lot of weight. I believe the current mars rovers are lighter, so they can use weaker, lighter wheels.
* The lunar rover only had to last for a week or so of use; the mars rovers have to last years of constant use.
* The lunar rover drove on the moon; the mars rovers drive on Mars which has a different rock composition.
* The lunar rover was built many years ago; more modern materials are available now, and design tools (especially computer simulation) have advanced a lot, so modern designs can have less mass.
* The mars rovers are 6-wheel, and are designed to drive even if one wheel siezes up, to allow the mission to continue even if a motor fails. The lunar rover was 4-wheel.
I don't know if it's important, but as well as all the points mentioned here already, I notice that Mars is much larger than the Moon, and must therefore have considerably more gravity. Add to that the 899kg weight of the rover itself (nuclear-powered craft can't be lightweight) vs the lightweight 209kg moon rover, and we're dealing with quite a different proposition.
There is also the question of the sand composition.
Lunar regolith consists of sharp granules of various sizes. Martian sand is subject to weathering, so it is smaller, rounded granules. Martian sand is therefore more free-flowing so its interaction with wire mesh wheels would be very different than the lunar surface.
Very marginal, the 'copter is tiny. Aero physics are the same but some of the numbers change a lot. As a first attempt I'd expect NASA to be happy if it made one sucessful flight before blowing away in a light breeze.
If anyone knows the design rotor size & RPM please do tell.
Edit: found it. :)
Mars's atmospheric pressure is 1% of Earth's: https://en.wikipedia.org/wiki/Atmosphere_of_Mars
But it's gravity is a bit under 1/2 of Earth's: https://en.wikipedia.org/wiki/Gravity_of_Mars
I'm no rocket scientist by a long way, but I suspect that enough lift can be created if the propellers spin faster. And this can be tested on Earth in a partial vacuum chamber, which is probably the first thing NASA tried before committing to the project.
If the tips go faster than the speed of sound but the roots don't ('cos they do a shorter distance in the same time) then you essentially end up with a shock compression part way down the blade, which is 'a bad thing' structurally and stability speaking.
Even if you could get the entire blade to be supersonic (instantly, no accelerating otherwise see point 1), you then run into issues if you add any velocity to the vehicle as the receding blade may drop below the speed of sound when you combine the velocity of the blade with the velocity of the vehicle, causing the repeated transition shocks from point 1.
"I wonder just how much stress a sonic boom part way down a rotor blade at 1% standard earth atmospheric pressure is?"
You don't have to look far. X15 (sometimes unintentionally) tested this stuff 50+ years ago.
Amongst other things the heating effects are harder to get rid of due to the less dense atmosphere not having many molecules to dump energy into.
I had that same Sand Scorcher, and it was brilliant! Wanted to get another for my own kids, but they are pretty expensive; there was a remake of it in 2010 apparently.
We used to have to build practically the whole thing, and that was a big part of the fun, what I don't like nowadays is that it seems to be almost totally ready built - I'm sure somebody could correct me though?
It's marketing. Only certain people are prepared to actually build their RC models. Many, many more just want to open the box, take it out and play.
Having said that, I know a guy makes model steam engines. He starts with sheets of metal and small billets and lots of tools and heat. Anything else isn't "proper" modelling :-)
Just for clarity.... At this point in time, to the sum of humanity's knowledge about Mars, it is a planet entirely populated by robots.
Dare I add.... As older robots cease to function, newer updated robots continue to be sent from a neighboring planet to replenish the population.
The wheels look very flimsy to me.
OK, the weight of the rover is only a fraction of what it is on Earth, but its mass is just as high. If it strikes a lump in the ground as it drives along, it's the mass, not the weight, that punches against the wheels. I guess they're tougher than they look. Well, I hope so!
I was thinking just that. The Curiosity wheel reminds me of a "Bar Turf" tire - an "R14" in agricultural terms. Looks like they're going back to sand paddles. As far as unequal spacing, Curiosity's wheels have some lines milled into them that spell "JPL" in morse code. The wheel motors have position encoders, but the lines can be seen with the cameras to help calculate wheel slippage. https://www.nasa.gov/mission_pages/msl/news/msl20120829f.html
There's a good article on the Spirit and Opportunity suspension, motor, steering, and wheel design. It's paywalled (IEEE), but if you can get to it look for "Mars exploration rover mobility development" in google scholar. The wheels are milled from a billet of 7075 aluminum.
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