Tumbleweed Rover Concepts, Give chance a chance! Options

[lyford]

This thread is for more in depth discussion of the good and bad points of this possible mission to Mars.

[lyford]

Admittedly there is much work to be done before they would be flight ready, but I think the concept lends itself to really "roving" - that is, moving and sampling, moving and sampling, covering quite a range of area with minimum energy.

Instruments are already designed to handle the high g loads of an airbag landing - rolling around on the surface should pose little additional stress, unless it happens upon a "Thelma and Louise Grand Finale" style cliff, a la Valle Marineris. Geronimo!

As for location and communication, that's a tougher nut to crack, but there are ways:
(From the abstract of "Navigation and Localization of the Mars Tumbleweed Surface Exploration Vehicle" Jordan B. Schwarz, North Carolina State University, August 11, 2004)

A recommended configuration was reached,  based on Tumbleweed’s requirements for low power, low mass, and low cost hardware with  the ability to provide frequent, accurate position updates over a long-term mission.  It is  suggested that Tumbleweed carry a Proximity-1 link protocol compatible transceiver, for  communications and radiometric ranging with Mars’ orbiting assets.  Odometry and  gyroscopes will provide real-time position estimates in between less frequent radiometric  updates.  A sun sensor can offer a measure of redundancy and absolute position verification.  By utilizing micro-machined components, the sun sensor and gyroscopes may be  incorporated into Tumbleweed’s electronics payload with a minimal increase in mass and  power consumption.

[DaveM]

Mars Tumbleweeds still give me warm fuzzies. My senior design project as an undegrad at NCSU was to investigate the concept and build a scale demonstrator. It was a lot of fun, but Opportunity's little hole-in-one into a crater pointed out one of the big risks associated with the concept. I think balloons will probably be in use before Tumbleweeds, and I don't think NASA is willing to risk using the concept on an actual mission, even a scout, just yet. Maybe as a piggybacked tech demonstrator first.

[lyford]

Hi Dave, welcome to the board!

From my readings of whats scattered around online, I thought most of the concepts could easily have been able to exit shallow Eagle crater just by being blown out - Endurance or Victoria would have been another matter.

I could see a Tumbleweed "launcher" on the back of a rover - at certain points they could inflate and release a beachball, or even eject one into a treacherous crater on purpose to serve as a disposable probe...

Do you know of any data on what height/speed any of the designs could be released in a piggy back scenario? I could imagine a few scattered over the descent profile landing at different points. With such high surface to mass ratio I understood they could also serve as their own parachutes!

I became fixated on these guys because I became so impatient with covering terrain at 10 mm a second. A Tumbleweed could blow around the planet, sampling whole new terrains almost daily! All you have to do is give up control.

I would love to see a polar mission where it's free to move in any direction with fewer craters or drop it in one end of Valle Marineris which would serve as a "track" or inside Olympus Mons Caldera and let it do laps in the bowl....

In your studies, did anyone uncover a "fatal flaw" that would doom the mission, other than the hole in one problem?

PS - Didn't mean to steal your images on the other thread - the orignal website listed no credits, so I assumed the link would suffice.

PPS - Would love to read your paper - is it available online?

[DaveM]

Hi Dave, welcome to the board!

From my readings of whats scattered around online, I thought most of the concepts could easily have been able to exit shallow Eagle crater just by being blown out - Endurance or Victoria would have been another matter.

I could see a Tumbleweed "launcher" on the back of a rover - at certain points they could inflate and release a beachball, or even eject one into a treacherous crater on purpose to serve as a disposable probe...

Do you know of any data on what height/speed any of the designs could be released in a piggy back scenario?  I could imagine a few scattered over the descent profile landing at different points.  With such high surface to mass ratio I understood they could also serve as their own parachutes!

I became fixated on these guys because I became so impatient with covering terrain at 10 mm a second.  A Tumbleweed could blow around the planet, sampling whole new terrains almost daily!  All you have to do is give up control.

I would love to see a polar mission where it's free to move in any direction with fewer craters or drop it in one end of Valle Marineris which would serve as a "track" or inside Olympus Mons Caldera and let it do laps in the bowl....

In your studies, did anyone uncover a "fatal flaw" that would doom the mission, other than the hole in one problem?

PS - Didn't mean to steal your images on the other thread - the orignal website listed no credits, so I assumed the link would suffice.

PPS - Would love to read your paper - is it available online?

No prob about the images, they're not mine. I was just a lowly summer intern at NASA Langley who started the senior design project. After I graduated it was out of my hands. This link has a copy of a paper that has a lot of our material in it. It's the first document, "Low Cost Mars Surface Exploration: The Mars Tumbleweed." I wrote a lot of the material that's in the intro and I can see in hindsight that I seriously underestimated the capabilities of the MER rovers. One big problem is the lack of dynamic pressure. Even strong gusts will hardly move more than dust around, which is why our vehicle had to be so big and lightweight.

If you really want it, you can download our final projecct report here (warning, it's 26 MB and probably has a lot more detail than you'd ever want). Keep in mind this is a document written by several undergraduate students, each suffering various degrees of senioritis, and therefore I make no claims that our data or results are conclusive. It was a fun project, though.

[helvick]

Nice info in the PDF - clearly much more effort than my back of the envelope calculations :-) .

One thing that's confusing me though is the discrepancy between the wind speed values you used (and correctly given that these are ground truth values from Viking) and the 200-600 kmh speeds that are liberally spread around the web that seem to be from Mariner and now that I think about it those were [a] fairly inaccurate and [b] upper atmospheric. Anyway if <10m/s surface wind speeds are typical then the Tumbleweed design really doesn't have much hope of moving on anything other than a completely flat surface - even the 15cm dunes on the Meridiani plain would probably keep a Tumbleweed permanently trapped.

The (substantially) less comprehensive Pathfinder data seems to indicate that 50kmh speeds might not be unusual even in areas with lots of surface "detail" but even that doesn't seem to be enough to get anything moving with any level of confidence.

Going back to the average wind speeds - the ~10kmh speeds do seem way out of line with the conventional wisdom and somewhat at odds with the conditions that would be needed to generate dust devils in an atmosphere 1% as dense as ours - anyone have any real data on whether the Viking data is representative of the conditions at the two current rover sites?