Author Topic: How fast is Curiosity moving?  (Read 24218 times)

Offline spectre9

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Re: How fast is Curiosity moving?
« Reply #20 on: 03/26/2013 02:00 am »
No movement for over 50 sols now.

I'm a bit bored of seeing the same images.

Offline Hungry4info3

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Re: How fast is Curiosity moving?
« Reply #21 on: 03/26/2013 02:39 am »
No movement for over 50 sols now.

I'm a bit bored of seeing the same images.
You are aware there has been technical problems recently, right?   :-\

Offline spectre9

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Re: How fast is Curiosity moving?
« Reply #22 on: 03/26/2013 05:45 am »
You are aware there has been technical problems recently, right?   :-\

Of course, and the drilling for samples took a while.

Now Mars will go behind the sun and we'll have to wait even longer to see the landscape change.

I'm keeping up with the mission, I'm just edgy to see some roving.

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #23 on: 03/26/2013 06:21 pm »
According to http://www.jpl.nasa.gov/news/fact_sheets/mars-science-laboratory.pdf Curiousity can go about 200 meters per day. What limits its average speed to such a low value?

Offline Dalhousie

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Re: How fast is Curiosity moving?
« Reply #24 on: 03/26/2013 09:36 pm »
According to http://www.jpl.nasa.gov/news/fact_sheets/mars-science-laboratory.pdf Curiousity can go about 200 meters per day. What limits its average speed to such a low value?

The time to collect samples and then analyse them.  The more interesting the target the more samples will be collected and the more time spent there.

Tthe net result  is the average progress of MSL is much less than the MERs.

We are 227 sols into the mission and distance to date has been 738 m, an average of 3.25 m per sol.

For comparison

Spirit on sol 225 had travelled 3605 m, and average of 16.02 m.

Opportunity on sol 241 (the closest date I could find with odometry) had travelled 1574 m, and average of 6.53 m.

We are a third of the way into the nominal mission and no closer to Mt Sharp.
Apologies in advance for any lack of civility - it's unintended

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #25 on: 03/26/2013 11:39 pm »
Oops my question was misleading. My question is why Curiosity can only go 200 meters per day when it's just going from point A to point B with no science activities? I ask because similar-sized Earth off-road vehicles can go that far in about a minute. I initially thought energy might be the limiting factor but a quite calculation shows its ~100 Watts is enough to go ~3 kilometers straight up each day! Energy rules out it going the 100+ km per day that a Jeep could do in a day, but doesn't explain the 200 meter limit.

Offline QuantumG

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Re: How fast is Curiosity moving?
« Reply #26 on: 03/26/2013 11:41 pm »
I don't know the answer.. but my guess would be that it has something to do with no-one being in the driver's seat. Observe the carnage of the DARPA Grand Challenge.
Human spaceflight is basically just LARPing now.

Offline Hungry4info3

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Re: How fast is Curiosity moving?
« Reply #27 on: 03/27/2013 12:15 am »
The driving is more-or-less automatic since there's no actual driver ( just a set of commands from the ground). The rover proceeds a bit, uses the hazcams to examine the terrain for problems, makes its way a little further, checks for obstacles, etc. There's a lot going on other than spinning the wheel motors.
« Last Edit: 03/27/2013 12:17 am by Hungry4info3 »

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #28 on: 03/27/2013 01:03 am »
Curiosity apparently has a very slow CPU compared to Earthly autonomous cars: http://marsprogram.jpl.nasa.gov/msl/mission/rover/brains/ . Actually I bet some smartphones are faster than that. Maybe the slow CPU has something to do with the rover's slow (physical) speed.

Edit: its CPUs may be slower, but they aren't the thousand times slower required to explain the difference in speeds.
« Last Edit: 03/27/2013 01:11 am by deltaV »

Offline hop

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Re: How fast is Curiosity moving?
« Reply #29 on: 03/27/2013 01:20 am »
I initially thought energy might be the limiting factor but a quite calculation shows its ~100 Watts is enough to go ~3 kilometers straight up each day!
Your calculation is almost certainly wrong. AFAIK energy is the main limit. Note that just rolling the wheels is not the only energy draw!

Offline Dalhousie

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Re: How fast is Curiosity moving?
« Reply #30 on: 03/27/2013 01:29 am »
There are lots of reasons why the rover is slower that terrestrial autonomous vehicles.

Power for the wheels is one.  Limited number of CPUs because of power issues is another.  Curosity has a few hundred watts available, a terrestrial vehicle can have a kilowatt or more of electrical power available.

CPU performance inherent in having a Mars-capable unit.  In particular there is radation resistance to consider.
 
Then there is the navigation question.  Primary route finding for terrestrial autonomous vehicles is GPS, which of course is not available for Mars.  Then there are issues of the terrain roughless and potential hazards, which would slow the rover down.
« Last Edit: 03/27/2013 01:31 am by Dalhousie »
Apologies in advance for any lack of civility - it's unintended

Offline hop

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Re: How fast is Curiosity moving?
« Reply #31 on: 03/27/2013 01:30 am »
The driving is more-or-less automatic since there's no actual driver ( just a set of commands from the ground). The rover proceeds a bit, uses the hazcams to examine the terrain for problems, makes its way a little further, checks for obstacles, etc.
Where the rover drivers have good terrain models, they can just tell the rover "drive from point A to point B".  This is only possible out to a limited distance, after which they have to switch to less efficient autonomous modes.

Quote
Maybe the slow CPU has something to do with the rover's slow (physical) speed.
Autonav and visodom are slower due to processing. However, the top speed for directed drives is only 4 cm/s. IIRC that autonav comes out to about half that, but I may be mistaken (edit: yup, wrong, see below). Curiosity is geared for torque, not speed.
« Last Edit: 03/27/2013 03:46 am by hop »

Offline Dalhousie

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Re: How fast is Curiosity moving?
« Reply #32 on: 03/27/2013 01:42 am »
Autonav and visodom are slower due to processing. However, the top speed for directed drives is only 4 cm/s. IIRC that autonav comes out to about half that, but I may be mistaken. Curiosity is geared for torque, not speed.

That comes to 1728 m per 12 hour day under ideal conditions.  Clearly navigation and surface conditions play a massive role in keeping actual triving distance below what is theroetically possible from the maximum speed.
Apologies in advance for any lack of civility - it's unintended

Offline joek

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Re: How fast is Curiosity moving?
« Reply #33 on: 03/27/2013 02:05 am »
Autonav and visodom are slower due to processing. However, the top speed for directed drives is only 4 cm/s. IIRC that autonav comes out to about half that, but I may be mistaken. Curiosity is geared for torque, not speed.
That comes to 1728 m per 12 hour day under ideal conditions.  Clearly navigation and surface conditions play a massive role in keeping actual triving distance below what is theroetically possible from the maximum speed.

Yes.  There are many things that can stop or slow it or cause it to phone home.  Surface conditions are a significant constraint.  We simply don't know enough about those surface conditions or MSL's behavior on them (at least yet)... a little more wheel slip than expected, then pause; a little more tilt than expected, then pause; an unexpected object, then pause; ...  The team is rightly erring on the side of caution.

Offline mlindner

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Re: How fast is Curiosity moving?
« Reply #34 on: 03/27/2013 02:11 am »
There are lots of reasons why the rover is slower that terrestrial autonomous vehicles.

Power for the wheels is one.  Limited number of CPUs because of power issues is another.  Curosity has a few hundred watts available, a terrestrial vehicle can have a kilowatt or more of electrical power available.

CPU performance inherent in having a Mars-capable unit.  In particular there is radation resistance to consider.
 
Then there is the navigation question.  Primary route finding for terrestrial autonomous vehicles is GPS, which of course is not available for Mars.  Then there are issues of the terrain roughless and potential hazards, which would slow the rover down.

Two cents here. Power is only a problem for calculation because radiation is a problem. They're using decade old (or older) computer electronics because of the radiation protection which makes them lose out a lot on Moore's law. They also redesign the radiation proofed CPUs to use extra computation checking for radiation effects. All in all, if several modern non-radiation hardened CPUs were used in a voting scheme, you'd have much faster performance at lower power, while maintaining the radiation resistance.
« Last Edit: 03/27/2013 02:13 am by mlindner »
LEO is the ocean, not an island (let alone a continent). We create cruise liners to ride the oceans, not artificial islands in the middle of them. We need a physical place, which has physical resources, to make our future out there.

Offline joek

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Re: How fast is Curiosity moving?
« Reply #35 on: 03/27/2013 02:28 am »
Two cents here. Power is only a problem for calculation because radiation is a problem. They're using decade old (or older) computer electronics because of the radiation protection which makes them lose out a lot on Moore's law. They also redesign the radiation proofed CPUs to use extra computation checking for radiation effects. All in all, if several modern cpus non-radiation hardened CPUs were used in a voting scheme, you'd have much faster performance at lower power, while maintaining the radiation resistance.

While that additional computational capability may ultimately be of benefit, you still need to characterize and calibrate the vehicle's behavior on unknown (or relatively unknown) surface conditions and terrain.

Given that we're operating on another planet with relatively little experience, what you thought you characterized and calibrated yesterday may not be applicable today.  Doubling or tripling the CPU capacity may help at the margins, but isn't likely to help much when you're faced with the unknown.

Unless you're positing that additional CPU power would be sufficient to provide AI capabilities heretofore unavailable and unknown at any price?

Offline Dalhousie

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Re: How fast is Curiosity moving?
« Reply #36 on: 03/27/2013 02:30 am »
Two cents here. Power is only a problem for calculation because radiation is a problem. They're using decade old (or older) computer electronics because of the radiation protection which makes them lose out a lot on Moore's law. They also redesign the radiation proofed CPUs to use extra computation checking for radiation effects. All in all, if several modern non-radiation hardened CPUs were used in a voting scheme, you'd have much faster performance at lower power, while maintaining the radiation resistance.

How is the power saving achieved with several CPUs rather than one?
Apologies in advance for any lack of civility - it's unintended

Offline mlindner

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Re: How fast is Curiosity moving?
« Reply #37 on: 03/27/2013 02:39 am »
Two cents here. Power is only a problem for calculation because radiation is a problem. They're using decade old (or older) computer electronics because of the radiation protection which makes them lose out a lot on Moore's law. They also redesign the radiation proofed CPUs to use extra computation checking for radiation effects. All in all, if several modern non-radiation hardened CPUs were used in a voting scheme, you'd have much faster performance at lower power, while maintaining the radiation resistance.

How is the power saving achieved with several CPUs rather than one?

Processing power usage is measured in Watts/Hz (or for modern embedded processors MHz/microwatt). Adding a processor performing the same task doubles your power usage. On the other hand Moore's law roughly doubles the processing per Watt every 1.5 years. You either maintain the same power and double the processing (common on desktop systems) or for embedded systems you maintain the same processing and half the power. Curiousity is out roughly 10 years on Moore's law which is 6.7 doublings or a factor of 100 times.

All other factors equal you can add 100 modernly equivalent processors and have the same power usage. In reality you only need something like SpaceX's setup with 3 sets of computers each having 2 processors voting against each other.

(I made a few simplifications, Moore's law more refers to the density of transistors, but the parallels are quite similar.) For reference, the CPU Curiosity is using is in the processing level as the old blue iMac computers of 10 years ago.
« Last Edit: 03/27/2013 02:41 am by mlindner »
LEO is the ocean, not an island (let alone a continent). We create cruise liners to ride the oceans, not artificial islands in the middle of them. We need a physical place, which has physical resources, to make our future out there.

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #38 on: 03/27/2013 02:53 am »
I initially thought energy might be the limiting factor but a quite calculation shows its ~100 Watts is enough to go ~3 kilometers straight up each day!
Your calculation is almost certainly wrong. AFAIK energy is the main limit. Note that just rolling the wheels is not the only energy draw!

Here's the calculation as a Google query: "(110 Watts) * (24.6 hours) / ((3.711 m/s/s) * (900 kg))"; it answers 2.9 km. Unless 90%+ of the power goes to non-wheel activities I don't see how energy could be the problem.

Offline hop

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Re: How fast is Curiosity moving?
« Reply #39 on: 03/27/2013 02:58 am »
From "Selection of the Mars Science Laboratory Landing Site"  http://link.springer.com/content/pdf/10.1007%2Fs11214-012-9916-y

Quote
Table 18 MSL rover drive modes, their usage and estimated drive rates (including slip checks)
Drive ModeUsageRate
BlindNo obstacles, low-slope terrain114 m/hr
AutoNavObstacles, rugged terrain, scarps45 m/hr
VisodomHigh-slope terrain, cohesionless terrain29 m/hr
AutoNav+VisodomRugged, sloped terrain20 m/hr

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