Given the problems that Opportunity is having now, what changes should be made to future rovers to mitigate such problems? Sand isn't exactly rare on Mars, and I very much doubt we've seen the biggest dunes.

Some suggestions:

- Directly detect speed so you know when you're not travelling as fast as the wheels are rotating (using something like an optical mouse sensor, as suggested here by Gary).

- Change of wheel design.

- Some deployable mechanism to help back out of a bad spot (extending spikes in the wheels might do it, but it would be complicated). I am also reminded of the railway sleepers that WW1 tanks used, although I'm obviously not suggesting we send a railway sleeper

- Sensors on the wheel or wheel hubs so you can sense you are digging in. Given the amount of iron around, could this be done magnetically?

- Some mechanism for sensing sand traps. Sound springs to mind, but I guess the atmosphere is too thin.

Chris

Edit: Added link to mouse sensor post

Bigger wheels I think that's probably the way to go - spread out the load a little more. Not sure how feasable the inflateable wheel ideas are in the long-term, but they would offer fantastic grip, and whatever the vehicle equiv of 'wing loading' would be, it would be very low. That has to be the way to go - prevention instead of cure.

But I agree - a direct way to measure wheel slip is a must - and the optical mouse derived idea would surely work very well - seems a no-brainer. Just depends if it's implimentable on a spacecraft easily.

Doug

A robust digging tool on an extendable arm might be useful. Mechanical diggers here on earth can usually use their scoops to pull themselves out when stuck.

simple:
Fly above Mars!

Add more wheels and/or bigger wheels is another option, though the more wheels, the more can get broken.

Maybe add joints in the rocker bogie system (sort of knees) that can be used (after blocking the wheels) to "walk" out: lift two wheels and place them some inches further down while leaving the others in place and intermittendly drag the rover with them. Sort of like a spider (but slower !).

Extracting Opportunity from its current situation is not terribly difficult. Design modifications in a future craft could easily provide a solution. For instance, if the instrument arm were strong enough to support the load without damaging itself the rover could lift itself out of this situation in the same way a construction backhoe can lift itself and shift position without using its wheels. In future expeditions we will encounter more difficult situations as we take on more challenging terrain. How robust is the instrument arm on the MSL? A robotic arm capable of drilling, lifting rocks etc could certainly serve as a backhoe to extract, lift or even turn a tilted rover upright again.

Another thought….We will always be limited in our exploration by our willingness to take any risk with the craft. The rovers are very valuable and easily damaged. One alternative might be to separate the instrumentation from the mobile unit using a rugged faster vehicle to travel and bring samples back to a stationary instrument platform.

Another alternative would be to send two rovers to the same place, a rugged one to be a reconnaissance vehicle to scout ahead and the other to be loaded with equipment and sensors. Each rover could have a tow system that could be used to join the two to get out of tough spots.

On the 'PR' side it would be really cool to have pictures of the rovers 'in situ'

I love those stilty movies of Pathfinder rolling around.

Eric P / MizarKey

I'm sure many of the people at Nasa/JPL fought hard to get bigger wheels on the MER rovers but were faced with the reality of size and weight restrictions. As it was, they had to come up with an ingenious method of folding the wheels in for storage in order to get the rover to fit under the aeroshell.
I like the idea of inflatable wheels. It sounds like the best of both worlds, lightweight, compact and proven technology. (you don't see any ATV's with aluminum wheels) They could be designed to fold up tightly against the rim. (similar to the space-saver spares used in cars) and then inflated after landing. The only drawback I can think of would be the large temperature extremes could pose a problem with a gas filled wheel. Anyone who lives where the climate gets cold in the winter knows you have to add more air to your tires with the onset of winter to compensate for the contraction of the air in the tire.
I suppose one way around this problem would be to fill the tires with a two-part expanding foam compound that is self-curing. This would give you a tire that is permanently inflated and eliminate the risk of going flat. I'm sure this has been kicked around before, I wonder what some of the other drawbacks to an inflatable tire would be?

Gary

Well - metal wheels cant get ripped

There are pics out there, JPL studies of inflateable wheel rovers.

Doug

A larger surface area and bigger wheels will work, 8 or or 12 wheels woulld be another approach. Each wheel could be independently raised. moved to the side and then placed on firmer ground. The remaining wheels still trenched would give the traction for this type of crawling movement.

So roll with the wheels until bogged down, then turn into a slow spider-type crawling means of movement. Design the wheels expecting to get stuck. Design the rovers expecting to fall over onto its back. Design it with a means of catastrophic recovery. (There goes the KISS concept of development.) Future rovers in my opinion do need a little bit more robustness.

Some means of testing the soils firmness before going onto it is needed. I wonder if adding a small air compressor is feasible in the martian atmosphere? It would double as a means to clean the panels. Does anyone have ideas on how to test the firmness of the ground?

Edit: Someone mentioned using the mini-TES for testing ground composition. How fast will that processing be? It needs to be done quickly and with minimum use of power, preferably real time as it moves. Above when I said we need more robustness, I am not taking anything away from these two machines. They have proved themselves to be very tough and astonished us all. (I guess what I want to see is a tank. )

That would probably limit how far the rover would go, though, since you would have travel out then back.

just put the rover near the last rovers and have them follow the tracks.

I remember that there was an old hermit who lived out on the other side of the Dune Sea -- old Ben Kenobi, wasn't that his name? Perhaps he could use The Force to help levitate rovers out of stuck positions.

Ben Kenobi would only be of help once a year, on the day which falls between May the third and May the fifth!

Be with you!

What an opportunity for a good joke. Unfortunately, that pun there just crushed my spirit. Ouch.

I like the idea of multiple vehicles. They would make the entourage more adaptable to changing conditions. Specialized vehichles could scout ahead and take greater risk. Slower, safer science packages could follow where it is safe. All could serve as components for rescue. The entourage could accomplish more than a single vehicle and the group would be more adaptable. Sort of a "Wagon Train" to Mars. More "experienced" readers may recognize this reference from way back in the last millenium.

I like to think that my jokes fill a much-needed gap.

Ahem.

Indeed.
You know I was just joking in that post too.

As a gold rule, always travel with more than 3 vehicles when going in off road (Mars) so that the stuck or in trouble ones will be rescated by one of them. Unless, the vehiclue must be specially designateed to travel almost any sort of terrain such as the ones alike to Caterpillar which is very stable and very capable to climb (greater than 30 degrees) , get down (also higher than 30 degree with very little slipping ), and travel over any kind of sands . I think that the next rovers must not carry any wheels but only bands like ones of Caterpillar. This will avoid to send two rovers at the same time. On the other hand, it is better to send a mini MARS GPS which will help rovers to travel easier and faster on Martian land. This will help to free lots of memory and CPU power from the Rover for another purposes .

Rodolfo

Tracked vehicles also have drawbacks (which is the reason most military vehicles are still wheeled)

1. More expensive than wheeled vehicles

2. Tracks wear out quite quickly

3. Require stronger engines because of more friction than wheels

4. Clumsy to steer

5. Less redundancy. If a track fails you are stuck while a multi-wheel (6 or more) vehicle usually can move minus one wheel

tty

Tracked vehicles would also be problematic on much of the chaotic terrain we've seen on Mars. The multi-wheeled independant drive/suspension systems on MER and Pathfinder were developed as a response to the conditions witnessed at the Viking and Pathfinder sites, i.e. the need to egress to rock strewn regions. Tracks are fine for a sandy or fine textured region like Meridiani, but would create a problem with the handful of topography conditions we've observed thus far. Certainly the conditions at Gusev also come to mind.

And, let's face it, we have successfully landed probes at five locations on Mars, and four out of those five locations have very, very similar types of terrain -- rock-strewn with windblown dust/sand drifts building up in various places. Only Meridiani has shown a different type of terrain.

Of course, there are a lot of different terrain types on Mars. But I think a lot of the flatter plains units (the places we're most likely to try landing) are going to be rock-strewn. So the rocker-bogey wheel system is probably going to be the best approach for most future rovers.

-the other Doug

The replies were very interesting. I realice that the tracks has their advantages and disadvantages. However, I think the best lands for tracks are the polar, sandy lands and mountains (lots of climbing and descending) Martian lands.

About the following points:
1) Yes it more expensive but for the project, it is not a matter of the fact that since the project always must look for the best and convenient solution (cheaper solution would be more expensive). The difference is very small when the project is of order of millions versus thousands dollars.

2), I was affraid of this since I saw that the tracks requires more maintenance but the distances that the rovers have advanced is very small (total more than 11 Km!!! and the tracks would still be in good shape.

3), definitely tracks will require engine with more par (force Kg-M) and it is not well suited for solar engine powered but I think, maybe, it would be fine with RTG nuclear isotops.

4) I think it is not a problem. The tracks is also capable to turn - O.

5) I agree it that the multi-wheels has the advantage of redundancy but the tracks band well designated can withstand for many thousands kilometers on soft lands of sands and many hundreds kilometers on harsh land (rockier).

Tha last word is that the tracks are by far needs less help to be rescued for any land, safer to travel (less risk to project of several millions dollars), more capable to reach to any land.

Maybe, the alternative to track is to have a rover with wider wheels and semi-inflated tire or two more wheels if the rover is to ttravel sandy lands and not for polar lands...which would be very slippery. (hard ice).

What I doubt that the rubber tire will not withstand of reactive or corrosive Martian land.

Rodolfo

One other issue to bear in mind with treads - they need to be able to operate at extremely low temperatures. I'm not sure what they've normally made of.
Plus, there are lots of hinges between the individual segments of track - more places for sand to get into, and with no one around to clean it, that might cause problems. But I'm not sure about that; tanks seem fairly robust, though they're also powered by a very strong engine.

One other thing I though of too with treads - space issues. The rover's back 4 wheels were nestled under it during transit, and the front two were folded up at the front. Treads would likely need to be sent into space in their deployed state, which would greatly limit the size of the rover itself.

The another hint would be helpful for Opps to travel is when it is free again and be able to navigate through dunes of sand on the same direction as where the winds blows. That is the rover must travel over crest in perpendicular line since the start of crest is harder (where the wind blows first on the crest) and the other side of crest is softer (where the wind accumulate sand). Going on that way, Opps will climb easier than the other side of crest which is of downslide. That hint is good for Earth sands and I think it will be also good for Mars' sands.