This is no time for a flat tire.

January 3, 2015 3:08 PM

Wheels on Mars. "There are holes in Curiosity wheels. There have always been holes -- the rover landed with twelve holes deliberately machined in each wheel to aid in rover navigation. But there are new holes now: punctures, fissures, and ghastly tears." A detailed look at the condition of the wheels on the Curiosity rover.
posted by bitmage (40 comments total)

"Each wheel tire was machined from a single block of aluminum."

So, basically, Curiosity is driving around on six MacBook Pro's?
posted by Wordshore at 3:24 PM on January 3, 2015 [9 favorites]

I hope the things that they are doing prevent tire wear work. It would take forever for AAA to get out there to change a tire.
posted by double block and bleed at 3:36 PM on January 3, 2015 [4 favorites]

The original holes in the wheels stamped out "JPL" in Morse code. The backstory that I heard was that JPL wanted to put a little JPL logo on the rover and NASA nixed it because they said it would be tacky, so someone at JPL decided to make the wheels stamp JPL everywhere the rover went on Mars, so there! (No idea if it's precisely true, but it's a good story!)
posted by Blue Jello Elf at 3:36 PM on January 3, 2015 [8 favorites]

An extra 1 mm on the wheels would have added 10 kg to the entire payload. It's a engineering marvel as it is, to be sure.
posted by a lungful of dragon at 3:53 PM on January 3, 2015 [1 favorite]

When they turn the rover around, the rover's middle and front wheels are dragged behind their supporting arms rather than being shoved forward

So, shouldn't the next one have the suspension reversed? The article doesn't bring that up.
posted by ChurchHatesTucker at 3:54 PM on January 3, 2015

I imagine Mars dust is similar to Moon dust, highly abrasive due to lack of weathering? But Mars does have weather, so is it the lack of water?
posted by leotrotsky at 4:07 PM on January 3, 2015 [1 favorite]

So, basically, Curiosity is driving around on six MacBook Pro's?

The big question, then, is did NASA spring for AppleCare?
posted by Thorzdad at 4:12 PM on January 3, 2015 [2 favorites]

So I'm completely wrong. It's apparently hard pointy rocks that are the problem.
posted by leotrotsky at 4:15 PM on January 3, 2015 [1 favorite]

Regardless of the rover's orientation, the wheels will eventually fail (after 10s of kilometers) driving on the terrain with embedded rocks. Driving on other terrain (flagstone or sand) would preserve the wheels more or less indefinitely. So future rovers (i.e. Mars 2020) will likely require tougher wheels, not just a reoriented suspension, assuming similar terrain is expected. But Neither Spirit nor Opportunity have suffered major wheel wear, so landing site selection will matter too.
posted by ddbeck at 4:20 PM on January 3, 2015

This video interview with JPL engineer Amanda Steffy is interesting. She is relentlessly cheerful and I would be too, if I had a job at JPL's Mars Yard doing destructive testing of NASA prototypes.
posted by charlie don't surf at 4:26 PM on January 3, 2015 [9 favorites]

Someone needs to go over there with their giant rubber band ball. Finally they can use them all up.
posted by Oyéah at 4:53 PM on January 3, 2015

I vaguely recall that the JPL code in the wheels were put there to help serve as an odometer of sorts. That way the scientists can look at the treads and get an additional idea of how far they've gone.

So part of the problem is that the rocks that they're encountering are unlike everything they've seen before. That's one of the things I love about science, even the unexpected is an opportunity to learn.
posted by fifteen schnitzengruben is my limit at 5:15 PM on January 3, 2015 [4 favorites]

Great article. So much of the "space news for the layman" out there is short or dumbed down or both, like Universe Today & SEN. I'm must getting interested in their articles when they end. I appreciate both the depth of the writing & the fact that they assumed they were writing for folks who would need the entire issue, from scratch. Bookmarked!

I wonder though, when doing Earth testing what calculations they make for the difference in Gravity?
posted by Devils Rancher at 5:25 PM on January 3, 2015 [2 favorites]

Devils Rancher: I'm not sure about the other systems, but NASA has a testbed called Scarecrow for driving. Scarecrow weighs as much on Earth as Curiosity does on Mars.
posted by ddbeck at 5:40 PM on January 3, 2015 [4 favorites]

This is no time for a flat tire.

That reminds me, years ago Fred Frith imparted to me this bit of wisdom to me: "There is no convenient time to have a flat tire."

A wise man, that Fred.
posted by flapjax at midnite at 5:52 PM on January 3, 2015 [3 favorites]

Interesting, making the wheels as light as possible was mostly for the initial deployment, not overall weight.

Oh well, something new to incorporate for the 20/20 rovet.
posted by Brandon Blatcher at 5:59 PM on January 3, 2015

to me … to me …

sigh

I demand a ten minute edit window
posted by flapjax at midnite at 6:04 PM on January 3, 2015 [3 favorites]

> I appreciate both the depth of the writing & the fact that they assumed they were writing for folks who would need the entire issue, from scratch.

That's Emily Lakdawalla. She's a god among space writers, and I always look forward to reading any article with her by-line. She's got a Masters in Planetary Geology and sometimes creates her own images for her articles from the original data.

If you really like her writing you can join The Planetary Society, where she works. (I'm not officially affiliated, I'm just a big fan.)
posted by benito.strauss at 6:15 PM on January 3, 2015 [6 favorites]

Holy crap they've already got someone on Mars to do damage assessment!?
posted by herrdoktor at 6:21 PM on January 3, 2015 [2 favorites]

Yeah, that Martian environment gives people out of focus fingers. The condition is fatal, ultimately.
They don't have photoshop on Mars.
posted by Oyéah at 6:39 PM on January 3, 2015 [1 favorite]

Possibly worth noting, there is no possibility of Curiosoity lasting as long as Opportunity has, since it's powered by a RTG with a fixed maximum life expectancy of just a few years. That's another weight trade-off.

And Curiosity isn't just on different terrain, it's a lot heavier than Spirit and Odyssey, which was also the reason for its bizarre landing sequence (Sky Crane! Showoffs!).
posted by localroger at 6:41 PM on January 3, 2015

Scarecrow weighs as much on Earth as Curiosity does on Mars.

Makes sense, thanks. Was wondering if they did it like that or with some sort of equation.
posted by Devils Rancher at 6:47 PM on January 3, 2015

The 4.8 kilograms of Plutonium-238 dioxide RTG in Curiosity began providing 125 Watts, but it falls to 100 Watts after 14 years(wiki). The specified 2-year (687 days) mission duration rating is for the power supply to meet all of the power needs for the rover, but the power supply should last another 12-years. (Whether or not we can get the tires to last another 12 is a different question.)
posted by fragmede at 7:04 PM on January 3, 2015 [1 favorite]

The article I read on it suggested the RTG would become inadequate to support roving within 4 to 6 (Earth) years. Use has no bearing on that as it does not affect the decay rate of the radioactive source material.

The rover might remain functional longer than that if they park it, but it would become a fixed station and no longer be a rover. Which is pretty much what happens if a wheel comes off too.
posted by localroger at 7:39 PM on January 3, 2015

Given that the original Spirit and Opportunity missions were 90 days and Curiosity is at least 2 years, I have no worries about the longevity of the rover hardware. Especially given NASA history of building/extracting performance out of equipment (see also Saturn V thrust, Voyagers 1 and 2, turning Apollo 13's LEM into a lifeboat, the aforementioned rovers, which also overcame a ton of problems like memory issues and heaters that wouldn't turn off).

Steve Squyers wrote Roving Mars, a great book about Spirit and Opportunity and their original missions, I cannot wait to read the book that Emily Lakdawalla is working on.
posted by fifteen schnitzengruben is my limit at 7:53 PM on January 3, 2015 [1 favorite]

The MSL wheels encountered very sharp rocks very solidly embedded in the surface, a particular combination that none of the rovers had ever seen before.

The wheels for Mars 2020 are definitely being redesigned with the MSL wheel problems taken into account. Source: I work on Mars 2020 and have been to some of the meetings where the redesign status is being discussed.
posted by chimaera at 8:06 PM on January 3, 2015 [13 favorites]

Given that the original Spirit and Opportunity missions were 90 days

The original engineers have admitted now in public that they "pulled a Scotty" (from Star Trek TOS) and promised a minimum while really planning for much longer. Curiosity's planners probably felt more confident in predicting a nice long mission, which would help to sell the more expensive deal with its extra risky landing scheme.
posted by localroger at 8:27 PM on January 3, 2015 [1 favorite]

There's a lot of conflicting stuff out there on the MMRTG lifespan, from as little as four years to as many as 55. My guess is that it's just a hard question to answer because the MMRTG supplies heat as well as power.

But there's so many ways for a Mars mission to end, even if it still has power, that I don't think the RTG lifetime will limit the mission duration. Viking 2 had an RTG, but its batteries failed. Viking 1 ended because human error. Soft sand and wheel stalls ended Spirit's mission. For now they've got workarounds for Curiosity's wheels and dying ChemCam focusing laser, but not every problem is going to have a workaround.

And there's Earthly concerns. If the science returns no longer justify the budget—if the money is better spent on another mission—they'll shut down the rover. The MSL team hasn't done an amazing job justifying the mission thus far. In the last NASA Planetary Senior Review (PDF), the panel said that "the Curiosity [Extended Mission] proposal lacked scientific focus and detail" and that "the team felt they were too big to fail and that simply having someone show up would suffice." Mars is not immune from budgets.
posted by ddbeck at 8:37 PM on January 3, 2015 [2 favorites]

Now is a great time to review the Seven Minutes of Terror film they originally produced about the landing sequence. Hard to believe that was two years ago! "When people look at it, it looks crazy. That's a very natural reaction."

Since the Martian atmosphere is hard to deal with, the Venus atmosphere should be much easier in comparison! At least it's dense! :)
posted by fifteen schnitzengruben is my limit at 9:02 PM on January 3, 2015 [2 favorites]

Who's idea was it to land on Mount Sharp?!?
posted by fairmettle at 2:41 AM on January 4, 2015 [1 favorite]

Source: I work on Mars 2020 and have been to some of the meetings where the redesign status is being discussed.

i love this site so much sometimes
posted by emptythought at 5:48 AM on January 4, 2015 [3 favorites]

When I was reading my AAA policy for my car in the 80's, I noticed that it had a clause that read "This policy does not extend beyond the earths atmosphere" This struck me as odd but perhaps they were on to something.
posted by boilermonster at 10:06 AM on January 4, 2015 [2 favorites]

The 4.8 kilograms of Plutonium-238 dioxide RTG in Curiosity began providing 125 Watts, but it falls to 100 Watts after 14 years

There are two factors. One is the decay of the ²³⁸Pu, every 87.7 years, half of it decays. The other factor is that the radiation from the decay products gradually damages the thermocouples that actually convert the heat to power. These curves are pretty well known for RTGs in Earth Atmosphere and free space, and those are similar enough that we have a good guess at how they'll behave on Mars. The big power draw is the motors, MSL could run for a couple of decades easy if it's not moving, but I think they expect power to be below motors and the control systems in about 7 years. The RTG is not likely to be the limiting factor.

An extra 1 mm on the wheels would have added 10 kg to the entire payload. It's a engineering marvel.

And that 10kg of payload mass would need a couple of hundred kilograms more fuel to get to Mars, or 10kg would have to come off the rover somehow. In payloads, esp. payloads leaving LEO, grams count.
posted by eriko at 10:08 AM on January 4, 2015 [1 favorite]

Apropos of nothing, the photos in that article were the first I'd see that showed the relative size of the rover. It's as big as a horse! I'd assumed a small dog or something.
posted by peteash10 at 10:19 AM on January 4, 2015

I've heard it described as the size of a mini-cooper. Here's a photo showing the sizes of all the recent Mars rovers, compared to each other and humans. Left to right is Spirit/Opportunity (2004), Sojourner (1997)and Curiosity (2012).

Huh, NASA keeps sending larger and more complex rovers to Mars. I wonder what that means!
posted by Brandon Blatcher at 10:27 AM on January 4, 2015 [2 favorites]

Yeah, I recently started wondering how much the extended ground support affects the budgeting. I mean, I know the lion's share for space projects is the hardware development and launch, is the ground support basically lost in the slush of keeping an operational space program going, or have the extended lifespans of the Spirit and Opportunity missions caused other projects to suffer cutbacks? (or in other words would the MER program have faced additional congressional scrutiny if their costs were originally proposed to contain even 5 years of ground support each instead of the 90 days and done that was originally budgeted for...)

And there's a part of me wondering which is more useful - more rovers or more science? Could we put 4 MER-type rovers on Mars for the same payload budget as Curiosity? Is it more useful to explore more regions with a swarm of less capable rovers than it is to characterize the regions as heavily as Curiosity is capable of?

I love that this is even a topic for discussion. I'm sort of disappointed in the slow pace of manned space work, but jeez if the robots aren't out there kicking ass and taking names.
posted by Kyol at 12:21 PM on January 4, 2015

Is it more useful to explore more regions with a swarm of less capable rovers than it is to characterize the regions as heavily as Curiosity is capable of?

That all depends on what you're looking for, i.e. what the mission is.
posted by Brandon Blatcher at 12:31 PM on January 4, 2015

When I was reading my AAA policy for my car in the 80's, I noticed that it had a clause that read "This policy does not extend beyond the earths atmosphere" This struck me as odd but perhaps they were on to something.

Well duh, you need AAA+ Interplanetary Vehicle. It's the one right above RV+
posted by emptythought at 3:20 PM on January 4, 2015

…or have the extended lifespans of the Spirit and Opportunity missions caused other projects to suffer cutbacks?

It depends on how you look at it, I guess. It's not as if any specific mission suffers because of another mission gets extended. For example, the MER extensions have run at least $100 million, which is about a quarter of a low-cost Discovery Program mission budget. Without MER extensions you might get a new mission a few years sooner than you would otherwise. But nobody's saying that mission X was canned because mission Y was extended.

It's also worth mentioning that there are hidden costs associated with committing to an extended mission. For example, by committing to an extension, there's that much less time available on the Deep Space Network and future missions have to pay for that, in a sense, by designing around the expected time they'll have to return data to Earth or by the DSN's budget having to increase to accommodate the traffic. (Though sometimes you get cooperative extensions, like the Mars orbiters. Rover and orbiter together are probably using less time than both operating independently).
posted by ddbeck at 9:05 PM on January 4, 2015

Who's idea was it to land on Mount Sharp?!?

Should have been a clue.
posted by ChurchHatesTucker at 12:23 PM on January 6, 2015 [1 favorite]