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Mars Science Laboratory Website, Now online...
RNeuhaus
post Jan 16 2006, 03:36 PM
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Tire comparision sizes:

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MSL is expected to weigh over 600 kg (1,320 lb) including 65 kg (143 lb) of scientific instruments, compared to the MERs which weigh 185 kg (408 lb) including 5 kg (11 lb) of scientific instruments. At present, MSL's mass is estimated at 775 kg (1,708 lbs).

The MSL tire is about 2.3 times wider than ones of MER and the MSL weigth is between 3.24 (600 kg) and 4.18 (775 kg) bigger than MER.

That leads to me to think that MSL will be less off-road capable than MER since the tire contact surface versus weight has been reduced for MSL in comparision to MER. I don't understand about this design. I see MER has experienced difficulties to overcome some ripples, hill and dunes and the tire design is that the tire width versus weigth must be improved.

Rodolfo
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djellison
post Jan 16 2006, 03:58 PM
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2.3 times wider, and about twice the radius - thus a 'contact patch' 4.6 times larger.

MER 185 / 6 = 30.83kg per 'unit of contact patch'

MSL (600 / 6 ) / 4.6 = 21.7kg per 'unit of contact patch'

When you mean improved - do you mean this number should go up, or down? There's arguments both ways smile.gif Up would give better traction on slopes. Down would give better driving-over-soft-stuff driveability.

DOug
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RNeuhaus
post Jan 16 2006, 04:06 PM
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Doug, Good correction. I didn't take account the tire's radius. The more surface contact is better for rocks (climb and go down) and dunes (surf) and less contact surface is better for wet lands (muds).

Now I see the improvement the off-road capability of MSL with less kg/cm^2.

Rodolfo
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dvandorn
post Jan 17 2006, 03:30 AM
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Also, MSL's wider wheel base will help its off-road driving. The further apart the wheels are, and the greater the distance between the front set and the back set of wheels, the larger a given obstacle has to be to block your path.

-the other Doug


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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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RNeuhaus
post Jan 17 2006, 09:01 PM
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In spite of the fact of good attack, escape and ventral angle, the height from the surface is another important matter for off-road.

The heck that I am surprised of its great weight comparing to MER. In Earth MSL weights like a Formula - 1. But, at Mars, it would weigth around (200-250 kg) along with its low speed, I seems that its off-road versability would be somewhat about the same as to the MER in spite of the fact that its wheel surface contact has improved around 30%. The reason is the greater weight.

According to my experience, the versatility of vehicle does not improve in the same proportion between the weight and wheel surface contact. In the other words, as an example, an vehicle has 100 kg and it has 4 cms^2 of wheel surface contact. The other vehicle has 200 kg and it has 8 cms^2 of wheel surface contact. Which of them is more off-road capable. I, very easy, the lighter ones will win.

I think that the heavier will need to have at least 12 cms^2 of wheel surface contact to compensate of the poor traction due to the physical land properties. It is specially most affected for sandy lands or pending slope. For a firm land, there is no matter.

Rodolfo
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Guest_exobioquest_*
post Jan 18 2006, 12:09 AM
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It would be nice to have some 1-2 meter wide inflatable wheels... don't think fabric science is up to it though, anybody have any info on research on inflatable wheeled rovers, I remember the tumble weed thing, but was the inflatable wheel concept rejected, disregard or forgotten?
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Toma B
post Jan 18 2006, 02:56 PM
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Nice article on Space.com:
Mars Science Laboratory

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The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.
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My "Astrophotos" gallery on flickr...
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RNeuhaus
post Jan 18 2006, 03:42 PM
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Thanks Toma for posting.

The initial targed date:

The primary MSL launch/arrival period is scheduled to extend from September 15 through October 4, 2009. That equates to a rover arrival period at Mars starting on July 10, 2010 and lasting until September 22, 2010.

While the cruise to Mars, as well as descent onto the planet mirrors past missions, the landing part of MSL is new.

Mars Science Laboratory is to use precision landing techniques, steering itself toward the martian surface similar to the way the space shuttle controls its entry through the Earth’s upper atmosphere. In this way, the spacecraft would fly to a desired location above the surface of Mars before deploying its parachute for the final landing.

The above phrase seems that it is referring to Sky Crane System? Or it might be referring to a new MSL Landing module will have some kind of wings alike to Space Shuttle to maneuver the entry throught the Mar's upper atmosphere?

At present, MSL project officials don’t see any full-up and costly hover tests of the Sky Crane here on Earth. Pieces of the system, like the parachute and Viking-class retro-rocket engines on the Sky Crane framework can be individually tested. "We think we can do a pretty good job of piecing it together," Cook emphasized.

I seems better that JPL must fully test the functionality of Sky Crane. It says it is not going to take as a full test but as individual test of some pieces....

Rodolfo
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MahFL
post Jan 18 2006, 03:42 PM
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Cook says MSL may last for 10 years smile.gif.
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djellison
post Jan 18 2006, 03:43 PM
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Well - look at the Viking Landers. 2000+ sols.

smile.gif

Doug
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lyford
post Jan 18 2006, 04:18 PM
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Perhaps this has been explained elsewhere, but I am having difficulty understanding the optimistic "scaling up" of the mission timeline comparing MER's 90 days = 2 years to MSL's 2 years = 10 years.

IIRC, the biggest constraint on MER was power, with the reprieve coming from unexpected dust behavior cleaning events - baring any mechanical failure or catastrophic weather, the solar powered rovers could now conceivably run until they hit their battery charge cycle limits.

But MSL is designed with a finite power source with a known rate of discharge - there won't be any free lunch boost of energy during it's mission. Or do the RTGs have some sort of "throttle" of which I am unaware? I didn't think you could power manage the same way as with MER, once it's depleted, there won't be another sunrise tomorrow to power the Mossbauer integration that you put off today.

My point is that power is no longer a wild card and since that seems to have been the factor that has contributed the most to MERs life extension, in order for the MSL engineers to be making optimistic estimates based upon primary mission requirements, there surely must be some realistic estimates on RTG life backing those statements.

Or are they saying that the RTG will last for 10 years, and hoping the mechanics last as long as well?


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RNeuhaus
post Jan 18 2006, 04:28 PM
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The thing that has short live is the material which uses the APXS or Mossbauer that are dependent of some decay material. Will the MSL use alike to them. Will the new instrument scientific last longer?

Rodolfo
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djellison
post Jan 18 2006, 04:50 PM
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QUOTE (lyford @ Jan 18 2006, 04:18 PM)
Or are they saying that the RTG will last for 10 years, and hoping the mechanics last as long as well?
*


Just the first. They will have the power for many years, and it's predictable, unlike solar arrays ( i.e. so much power they had to have afternoon sleeps with Spirit 100 sols ago, and now down to amost half that power makes long term planning hard ) Being 'around' and being 'mobile' are not one and the same smile.gif But - given lessons learnt with MER, I'm sure that they could build MSL to be certain of lasting at least 2 earth years

It's the Mossbauer that has the short halflife material and MSL has an APXS, but no Mossbauer. APXS's sample half life is, ermm, it's in the Steve Q'n'A - can't remember, but it's years and year - 20something

Doug
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Guest_exobioquest_*
post Jan 18 2006, 06:09 PM
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QUOTE (lyford @ Jan 18 2006, 10:18 AM)
Or are they saying that the RTG will last for 10 years, and hoping the mechanics last as long as well?
*

Well considering the history of RTGs I really don't see what there is to worry about, voyager 1&2 may last 40 years on their RTGs!, the rate of decay on a RTG is very easily calculatable. Basically 0.787% power heat watt loss per year when using Pu238 (half-life of ~88 years) also when using thermocouplers the couplers decay to, which is roughly (depending on the type of thermocouple used) double the decay rate or 1.52% electricity production loss per year. Both the MMRTG and the SRG (competing RTGs for MSL) have 14 year warranties, that means they will produce 100 watts of electricity for 14 years, how so? Well the MMRTG will start at ~125 watts of electricity at production, A ~123 by the time it reaches mars, do the calculations with excel it won’t reach 100w until 15-16 years. The SRG won’t have the decay rate of the thermocouples, but will start at a lower wattage of ~110 watts making roughly ~100 by 14 years.

MSL will likely have a battery for peak power use, that could become the major lifetime limiter.
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Chmee
post Jan 18 2006, 06:20 PM
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Add a caption:

MER: "Hey, Get out of my way, your hogging my path!"
MSL: "Don't worry, you'll stop by sunset while I'll keep going..."
biggrin.gif


*

[/quote]
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