Author Topic: How fast is Curiosity moving?  (Read 24219 times)

Offline joek

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Re: How fast is Curiosity moving?
« Reply #40 on: 03/27/2013 03:03 am »
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.

All other factors are not equal; Watts/Hz is not necessarily the figure of merit, especially when there is a hard upper bound on Watts (among other things).  As you say, "Moores law" says nothing about Watts/Hz, only transistor density and they are *not* "quite similar" (otherwise Intel's horrid and abandoned NetBust architecture would rule today).

And SpaceX's approach--or any other LEO architecture--is not comparable; "in reality" the conditions are far different and what works in one environment does not necessarily mean it will work in another.  Such "voting logic" is not new, and there are reasons why such a simplistic approach alone is not used for high value deep space missions.

Now can we get off this tangent please?

Offline hop

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Re: How fast is Curiosity moving?
« Reply #41 on: 03/27/2013 03:22 am »
From "Mars Science Laboratory Mission and Science Investigation" http://link.springer.com/article/10.1007%2Fs11214-012-9892-2

Quote
Table 9 A few of the resources that drive science operations and the required minimum capabilities built into the design of MSL

Some resources that drive science operations Required capability

Energy available for science activities250 Wh/sol
Downlink volume (two UHF passes)250 megabits/sol
Rover awake time6 h/sol
Traverse distance50 m/sol

Note: The actual capability on Mars may exceed the requirements for certain environmental conditions or other favorable conditions. The requirements may not be met during anomalous conditions. Science activities include rover traverses. A small fraction of the downlink volume will be used to transmit rover health and housekeeping data
My bold.

Offline mlindner

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Re: How fast is Curiosity moving?
« Reply #42 on: 03/27/2013 03:52 am »
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.

All other factors are not equal; Watts/Hz is not necessarily the figure of merit, especially when there is a hard upper bound on Watts (among other things).  As you say, "Moores law" says nothing about Watts/Hz, only transistor density and they are *not* "quite similar" (otherwise Intel's horrid and abandoned NetBust architecture would rule today).

And SpaceX's approach--or any other LEO architecture--is not comparable; "in reality" the conditions are far different and what works in one environment does not necessarily mean it will work in another.  Such "voting logic" is not new, and there are reasons why such a simplistic approach alone is not used for high value deep space missions.

Now can we get off this tangent please?

Just a correction before we end this conversation. Nearly every CPU has at least one sleep mode, usually several, that drops the power usage greatly. Watts/Hz is a fine figure of merit because computation can be stopped or even duty cycled to reach any power level needed even with very fast power hungry processors.
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 AS-503

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Re: How fast is Curiosity moving?
« Reply #43 on: 03/27/2013 04:29 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.

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.

Yes, voting like the Byzantine General's Problem.

Remember NASA's John Muratore (X-38 among others)?

He gives an insight to the SpaceX voting scheme in this link.

http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog:04ce340e-4b63-4d23-9695-d49ab661f385&plckPostId=Blog:04ce340e-4b63-4d23-9695-d49ab661f385Post:a8b87703-93f9-4cdf-885f-9429605e14df


Wiki's Byzantine Fault tolerance here:

http://en.wikipedia.org/wiki/Byzantine_fault_tolerance

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #44 on: 03/27/2013 09:28 pm »
Radiation-hardening and fault-tolerant control design is interesting but off-topic in this thread.

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #45 on: 03/27/2013 09:36 pm »
From "Mars Science Laboratory Mission and Science Investigation" http://link.springer.com/article/10.1007%2Fs11214-012-9892-2

Quote
Energy available for science activities250 Wh/sol
Traverse distance50 m/sol

Science activities include rover traverses

If only 250 Wh/sol is available for roving then I find energy being limiting quite plausible. That leaves another question however. The total energy available per sol is about (110 W) * (24.6 hours) = ~2700 Whr. Where does the other 2000+ Whr/sol go?

Offline joek

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Re: How fast is Curiosity moving?
« Reply #46 on: 03/28/2013 12:57 am »
If only 250 Wh/sol is available for roving then I find energy being limiting quite plausible. That leaves another question however. The total energy available per sol is about (110 W) * (24.6 hours) = ~2700 Whr. Where does the other 2000+ Whr/sol go?

From An Overview of NASA's Mars Science Laboratory, JPL, 2011
Quote
After descent, the rover only receives the approximately 110W (BOL) ... MMRTG power is used to charge the rover’s two Li-ion batteries, which are the primary source of electrical power for operations. Rover power utilization ranges from 45—70W while sleeping, to approximately 150W minimum when awake, up to greater than 500W peak while “roving” or moving.
The li-ion batteries are 28v ~84Ah total.
« Last Edit: 03/28/2013 01:28 am by joek »

Offline deltaV

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Re: How fast is Curiosity moving?
« Reply #47 on: 03/28/2013 03:37 am »
joek: thanks for your illuminating reply(s). The paper you quoted certainly confirms that the energy available for roving is limited because most of the energy is used for other things.

According to
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38066/1/05-0708.pdf
the heat removal system removes 150 W of heat from the avionics. This heat presumably comes from electricity usage, so this must be where the 150 W minimum waking power usage goes. Why the avionics use 150 W is beyond me however.

According to the paper linked in the previous paragraph the heat removal circulation pump has pressure drop 25 kPa and flow rate 1.5 liter / minute, which gives it a minimum power consumption of 0.6 W. Unless the coolant pump is crazy inefficient it's not the cause of the high power usage.

Offline JohnFornaro

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Re: How fast is Curiosity moving?
« Reply #48 on: 03/28/2013 11:42 am »
Following the above power conversation:

Watts/Hz is a fine figure of merit because computation can be stopped or even duty cycled to reach any power level needed even with very fast power hungry processors.

How can Watts/Hz be a fine figure of merit?  When the processors are in energy saving mode, their functionality is always reduced.
Sometimes I just flat out don't get it.

Offline mlindner

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Re: How fast is Curiosity moving?
« Reply #49 on: 03/28/2013 11:46 am »
Following the above power conversation:

Watts/Hz is a fine figure of merit because computation can be stopped or even duty cycled to reach any power level needed even with very fast power hungry processors.

How can Watts/Hz be a fine figure of merit?  When the processors are in energy saving mode, their functionality is always reduced.

joek and I took this conversation into PMs as it was off topic for this forum. If this is an interesting enough topic for enough people, we should start a new thread.
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 #50 on: 03/29/2013 12:34 am »
According to
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38066/1/05-0708.pdf
the heat removal system removes 150 W of heat from the avionics. This heat presumably comes from electricity usage, so this must be where the 150 W minimum waking power usage goes. Why the avionics use 150 W is beyond me however.

I read that as it must be capable of removing up to 150W; nominal may be lower (?).  Also, remember that the same rover processor complex used for ground operations on Mars were also used for GNC during Earth-Mars transit and EDL; that may have imposed additional constraints that are not present for Mars ground ops (?).

Offline JohnFornaro

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Re: How fast is Curiosity moving?
« Reply #51 on: 03/29/2013 04:38 pm »
Backing up to the OP for a sec. 

Today's takeaway is that for the moment, there's no "activity", other than testing and validation of systems, until Mars pops out from the other side of the Sun?

Will the rover be stationary all that time?
Sometimes I just flat out don't get it.

Offline hop

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Re: How fast is Curiosity moving?
« Reply #52 on: 03/29/2013 07:47 pm »
Today's takeaway is that for the moment, there's no "activity", other than testing and validation of systems, until Mars pops out from the other side of the Sun?
Not true, Curiosity is back to doing science, see http://www.planetary.org/blogs/emily-lakdawalla/2013/03290840-curiosity-sol227.html

Some science will also be done during conjunction, it just won't be things that are risky or require the ground in the loop.
Quote
Will the rover be stationary all that time?
Curiosity will not move during conjunction. They might be able to sneak in small drive before the April 4 if they really wanted.

Offline JohnFornaro

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Re: How fast is Curiosity moving?
« Reply #53 on: 03/30/2013 11:52 am »
Thanks
Sometimes I just flat out don't get it.

Offline spectre9

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Re: How fast is Curiosity moving?
« Reply #54 on: 05/10/2013 02:13 am »
The rover will move!!!

2.75m  :)

I'm bored, I want to see pictures of the landscape as they trundle along.

Perhaps this rover has too much instrumentation? The scientists have gone mad with glee and want to analyse everything in the immediate vicinity in great detail.

That is their right but it's not very exciting for those of us that want some cool images for our desktop.  :P

Offline kevin-rf

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Re: How fast is Curiosity moving?
« Reply #55 on: 05/10/2013 01:24 pm »
I for one would rather that it returns significant scientific data. We have Pixar and the like for awesome views....
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Offline Dalhousie

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Re: How fast is Curiosity moving?
« Reply #56 on: 05/13/2013 07:30 am »
The rover will move!!!

2.75m  :)

I'm bored, I want to see pictures of the landscape as they trundle along.

Perhaps this rover has too much instrumentation? The scientists have gone mad with glee and want to analyse everything in the immediate vicinity in great detail.

That is their right but it's not very exciting for those of us that want some cool images for our desktop.  :P

There have been relatively few analyses, and the 400 or so scientists on the mission teams are, I suspect, rather frustrated.  At this stage in the MER missions there had been at least a dozen peer reviewed papers.  There have been none yet from Curiosity.
Apologies in advance for any lack of civility - it's unintended

Online catdlr

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Re: How fast is Curiosity moving?
« Reply #57 on: 05/29/2013 06:55 pm »
Curiosity's 9-Month 'Dance' On Mars Time-Lapsed By Tech Geek | Video

Published on May 29, 2013
Professional programmer Karl Sanford wrote a program to compile images from Sol 0 (August 8th, 2012) through Sol 281 (May 21st, 2013) from the Mars Science Laboratory website.

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Offline spectre9

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Re: How fast is Curiosity moving?
« Reply #58 on: 06/06/2013 05:36 am »
Curiosity supposedly moving!!!

I look forward to getting new pictures each time I log in rather than staring at the same rocks  ;D

Who knew taking samples took months? Certainly not me.

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Re: How fast is Curiosity moving?
« Reply #59 on: 06/07/2013 06:34 pm »
Curiosity Rover Report (June 7, 2013): Rover Ready to Switch Gears

Published on Jun 7, 2013
NASA's Curiosity rover switches to long-distance driving mode as she heads to Mount Sharp.


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