Pedal to the metal…

Oppy is still a long way from Endeavour Crater – a loooooong way. Even driving 70m a day – which is, to use a technical term, “going it some” – it will be perhaps another year until she reaches Cape York (see previous posts), the small rocky “island” she is aiming to make ‘landfall’ on at the end of her epic drive across the vast Meridiani plain –

Or will it?

One of the Mars Exploration Rover drivers, Scott Maxwell, has come up with a plan to shorten the drive by effectively squeezing some more drive-time out of Oppy.

I’ve met Scott a couple of times – once during his visit to the UK a few years ago, and, more recently, when I was lucky enough to be invited to tour JPL. Scott showed me around part of the complex, and spend a lot of time showing me some of the wonderful things there…

There can’t be many people with the same passion and sheer joy for space exploration, and public Outreach, that Scott has, it literally shones out of him like a sci-fi movie special effect, and he clearly adores his job as a “rover driver”. As his Twitter profile says:

On a small red light in the night sky lives four hundred pounds of thinking metal sent from Earth. I tell that metal what to do, and it does it.

How’s that for a job description? 🙂

So, intrigued, I asked Scott for some details of his plan, and he was kind enough to send me the background to his idea which, if it succeeds, will get Oppy, and all of backseat passengers, to Endeavour’s rim sooner than we imagined. Turns out Scott’s plan is a cunning plan worthy of Baldrick himself.

So, what’s the plan, Scott?

Well, bear in mind that this is an experiment, and we’re not sure it’s going to work.  We’d be sequencing a cut-down experimental version of this today (Friday 16th), but ODY is in safe mode.  We’ll do it as soon as  we can.

You probably know already that we used to do ~ 70m blind drives, followed by an autonav segment.  (Autonomous hazard avoidance, that is.)  We had to quit that because of the RF wheel currents: HAZCAMs don’t give good enough range data in Meridiani terrain to support autonav, and the NAVCAMs have to look *forward* for autonav, because behind us the LGA is in the way — but we can’t drive forward any more, because it makes the RF wheel currents rise.  But I thought of a possible way around that limitation.

Roughly, if the experiment works, here’s the eventual procedure.
First, we do a long blind drive (just a little shy of 70m), followed
by a slip check.  Now we’re good to go another 20m, the normal
distance between slip checks.

We slew the NCAMs around so that they’re almost seeing the LGA, but not quite, an azimuth of 162.5 degrees in rover-frame.  Now we turn *Opportunity* the remaining 17.5 degrees (clockwise) so that the NCAMs are looking straight along our intended drive path.  We image the terrain for hazard avoidance and turn back 17.5 degrees anticlockwise.

At this point, we’re aimed (that is, our rear end is aimed) at our
destination and we have imagery in the drive direction.  We do a
straight-backward step of 1m (actually 2 x 50cm steps, for technical reasons) toward our goal, telling Opportunity to take the step only if the hazard-avoidance imagery we took shows it to be safe.  Then we just repeat this turn/image/turn/step loop for 20m worth of driving.

It’s a little more complicated than this, because we first have to
drive about 2.5-3m blind to get onto the nav-map data (the nearest stuff we can see looking over the rear solar panels is about 2m away) and for other reasons, but that’s the basic gist of the idea.  If it works, we can go 90m/sol rather than 70m/sol, a 29% drive-rate improvement.  There will be sols where this doesn’t work — we’re heavily constraining what Opportunity is allowed to do, and if she sees something scary, this procedure doesn’t let her drive around it; also, the turns-in-place might elevate the RF currents, in which case we’ll have to abandon it; and there are other things that can go wrong.  But if this worked perfectly every time, it would cut nearly 40 drives out of our trek to Endeavour — a 2-3-month savings, at least, probably actually more than that.

In a real blue-sky future, we can do a slip check at the 90m point,
followed by *another* 20m of hazard-avoidance driving, and so on.  We can have hazav-only drive sols, similar to what we did over President’s Day weekend in 2005.  When the terrain is a little friendlier, we can do longer blind drives before the hazard-avoidance segment(s).  And there are other possible optimizations.  Right now, I want to perform a basic experiment to see if this even works.

The really great thing is, I seem to have had this idea at just
exactly the right time.  Thanks to that recent cleaning event, we have just now gotten to the point where we have enough energy to drive more than 70m/sol, thus letting us try stuff like this.  Woo-hoo! 

I should also say, incidentally, that several other rover drivers — mainly, Paolo Bellutta, Joe Carsten, and Frank Hartman — helped me hammer my original idea into a workable, sellable version.  I’m proud to have had the original idea, but as usual, this is a real team effort, and I’m *so* lucky to work with those people. 

Now let’s just hope it works.  Fasten your seat belt.  🙂

Thanks Scott! That sounds like a fascinating idea, and well-worth trying; anything that gets Oppy to Endeavour more quickly has to be a good thing.

This adventure just gets better and better, doesn’t it? 🙂

Note: Scott writes a blog, describing his life as a rover driver. It’s an absolutely fascinating read, but PLEASE bear in mind it’s “backdated” by 5 years – the posts are made as if he was writing them 5 years ago, as the events described in the blog were actually happening – so please don’t read it and think that the blog is referring to events happening now! 🙂


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1 Response to Pedal to the metal…

  1. Pingback: Every rover’s doing a brand new dance now… | The Road To Endeavour

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