Good Evening!

In looking images who show Grissom Hill on the horizon, I've asked me a question : "Is it possible for Spirit to roving to Grissom Hill?"
To make me sure, I went on Marsrovers JPL site and searched for an MGS satellite image showing the landing site.


I've calculated approximately the distance : 8 or 9 kms. It's far but this could be a very interesting place ... more than Columbia Hill!
Western from Grissom Hill, I'd seen a very big crater (1 or 2 kms diameter...). This one is certainly interesting for "areologist" who want to study the past of Gusev...

Spirit is in good health. Why not?

Intriguing crater, but could they even get into it?

Two years ago i would have laughed ot loud....now i'm not sure if it's impossible, but it's close to impossible i'd say. That would mean a work load to the non (never) maintained moving parts of roughly two times the odometry allready "under the belt". Not to speak about the dust, that finally will get to her. But when will that be ?

Oops, sorry for not removing the image..

I'd think things that distant ( 4 or 5 times more distance that we've covered so far ) would simply be too far to worth considering, it'd be a waste of time setting off to explore them knowing that the chances of reaching them are so very very small when there might be something less interesting, but a lot more achievable.

To paraphrase Steve, they will die eventually, I'm sure of that.

Doug

Hello Doug,




I started reading this thread with no recollection at all of hills Grisson, Chaffee and White, and with about as much expectation that Spirit could get that far. Then I started thinking about probabilities. Granted that (as you say) they'll both die one day, but taking into account also the much longer than expected lifespan so far, the cleaning events and so on... surely there is a finite (but small) chance that Spirit could live long enough to reach Grissom. Just to pick a random number, let's say there's a 1% probability. Is that enough to warrant torturing ourselves dreaming of the unattainable? Engineering decisions are surely driven by probabilities. To pull another random example... bridges are built to withstand 100, 200, 400 year storms, (assuming that figure's been correctly calculated by the people with the pulsating frontal lobes and access to the the data & tools needed to work it out...) My local suspension bridge* has a design limit of (IIRC) 100mph winds. Well, 120mph winds are not inconceivable here... but very unlikely;once every four hundred years, IIRC. 80mph, OTOH, happens every other year. So, given that faster enough winds will result in it falling into the river that's probably a risk worth addressing, either reducing the probability of it happening, or reducing the consequences of it happening.

Looking at the rovers' lifespans from the inverse point of view... if there's a 1 in 400 chance of Spirit reaching Grissom, and assuming she survives the winter and finishes surveying HP,.. is that a high enough probability to merit spending time thinking about consequences? If OTOH JPL decide to continue puttering around the Columbia Hills, and then we find she's still alive after travelling a distance equivalent to Grissom... there's an opportunity cost.

Anyway... I'm happy that, to me, this is purely idle speculation rather than a decision I have to take

* http://images.google.co.uk/images?hl=en&q=...rch&sa=N&tab=wi

Just to the right off of your image is another crater SSE of the hills (see it in this msss image) we're currently headed toward, its only about half as far as the BIG crater to the left on your image and its only about 2/3ds the size but I'd say thats a much more attractive/reasonable target. It looks like there's virtually nothing else between the hills and that crater interesting looking besids one Bonnevilleish loking crater to the SSW (small and no stratification, or internal structure visible) and we know there was nothing there so.....

Actually, the southern slopes of Columbia Hills may be more interesting than any recent craters in the lowland. I think all lowland was inundated by lava after Gusev was a lake.

That depends. If there is a crater within range that penetrates to what is below the plains, then it is worth it. But that is hard to tell from MGS imagery. Perhaps MRO, with its multispectral capability, would be able to indentify such a crater.

Ha! I say! Go for the gusto! Go for the delta at the mouth of Ma'adim Vallis! Columbia Hills are just crumbs compared to what's down there. :-)

But seriously, I think we've been very lucky with dust etc so far, and I think the next Martian year will be a hard one for both rovers...

I think any big plans for the future -if Spirit keeps up, would be southward in the direction of the channel.
Grissom Hill would sure be interesting for sure, but Castril Crater -the dusty crater would not I think- just too much dust. The northeastern part of Castril's ejecta blanket and the boundaries in this area looks intriguing but fairly rough driving-ground probably.

Nico

One thing that's clear. Spirit wants to stay within the dust-devil activity region. If she's not cleaned sporadically, she'll die.

The way to go is to work southward through and beside the hills after returning to homeplate and it's surroundings in the spring. There's a lot of varied geology along they way.

Remember - it's not the dust devils that actually cleaned Spirit - these cleaning events often happened over night - no dust devils at night

Hills, summits, valleys - that's what we need to keep Spirit clean - places with just strong wind.

Doug

How would one know?

How would one know what? That there's no dust devils at night? They are an afternoon phenom. kicked off by warming slopes by the sun. That the cleaning happened over night? Because solar array output was much higher than it ought to have been just after sunrise compared to the previous day.

Doug

We can't, but the engineering team have very detailed data on the performance of the solar panels and they do. I'm trying (and failing) to find specific links for you but they have repeatedly stated that the cleaning events generally happen overnight and generally are not associated with a DD passing over the rover. The cleaning events happen when there is visible DD activity at Gusev but to the best of my knowledge they haven't spotted any DD's at Meridiani even though Opportunity too has had multiple cleaning events.

Wind gusts can occur any time of day or night. Dust Devils essentially require daytime.

They are locally driven by convective instability, with the near surface boundary layer atmosphere heated by the surface so much more than the atmosphere immediately above it that it is highly instable and vigorously convecting.

At night, the surface rapidly cools below atmosphere temp and the boundary layer thermal gradient is inverted, with the atmosphere warmer than the surface and a chilled-layer at the bottom of the atmosphere in direct contact with the surface. No convection possible. You can have downslope winds, even over very shallow gradients, and complex interactions between such winds and tidally driven atmosphere oscillations as well as more conventional meteorological processes like cold fronts.

'Tidally driven'? Do tell!

Bob Shaw



Have there been any 'dirtying events' observed by either Spirit or Opportunity? You'd think that, from time to time, they'd end up in areas of deposition as well as areas of removal...

Bob Shaw

Given the speed with which Spirit went from shiney and 850WHr+, to "must get to the hills now!" - I think the southern slope of Husband Hill could well be such a place to some extent. I know that the terrain and the season's are not helping, but Spirit has got very dirty very quickly since leaving the summit, and given the El-D feature - it would make sense that in this region, dust is getting dropped.

Doug

Did the power levels suddenly drop off? My understanding was that this is a precautionary move.

Not suddenly - but one need only look at the state of the arrays to see how quickly they go dusty in the 650-750 time frame.

Going to the hill isnt precautionary - it's fundamentally necessary for the survival of the rover.

Doug

Unlike the couple of sudden cleaning events there have been no significant dirtying "events" for Spirit that I'm aware of but we don't have the detailed recent data to be certain of that. Power has dropped off slightly more steeply over the past hundred Sols or so than I expected but I don't have enough data to say if that is because of dust buildup alone. The difference is at most 10% though - most of the drop off in power is simply the seasonal change in Insolation - that curve is at it's steepest right now dropping off at around 0.33% per sol.

As Doug said dust deposition rates are also seasonal and the late summer\autumn period is when that peaks. Sol 0-100 (which should be equivalent to the last 100 or so Sols) averaged around 0.16% loss in efficiency due to dust at the start of the mission, Sol 100-200 averaged around 0.07%, Sols 200-300 0.04%.

"tidally driven"...

The martian atmosphere has thermally driven tides as the planet rotates underneath solar illumination. Dayside atmosphere expands, there are (at a simplest armwaving level) lateral winds toward the terminators at dawn and dusk, and the nightime atmosphere contracts. But it's more complex than that, as the atmosphere has natural periods of oscillation.

The Viking landers got a really good first look at these processes. They had a basic minimal meteorology set: Temperature, Pressure, Wind Speed and Direction. No humidity reading, though. They took 24 hour low data rate meteorology most of the time, and higher data rate sampling at various times for detailed boundry-layer meteorology studies.

Both landers saw pronounced highly repetitive pressure and wind-speed/direction variations on a cyclic daily basis as the atmosphere regularly "sloshed" back and forth under diurnal heating and cooling. There was more complex structure in the pressure and wind cycles due to semi-diurnal tides.. 2 cycles-per-day sloshing. These global tides combined with upslope daytime wind flows and downslope nightime flows at the Viking 1 site. Viking 2, further north (48 deg) saw strong patterns of cyclic cold front passages and/or the pressure/wind patterns of periodic low pressure regions passing by to the north.

During the 1977 double globe-encircling dust storms, the cold front pattern at VL2 changed dramatically, and the diurnal pressure/wind cycles at both landers changed in strength, phase, and relative strength of the diurnal and semi-diurnal components. Much of that reasonably well matched theoretical modeling of the atmosphere's thermal tide responses during varying dust loadings.