-
A limiting factor in robotic planetary exploration
by
sivodave
on 19 Jul, 2010 23:02
-
Hi all.
I was thinking about the two rovers currently on Mars, Spirit and Opportunity. In five years of exploration of the martian soil, these two small rovers have driven no more then a couple of miles. Why? In my opinion the answer is that the communication delay with Earth (20 minutes for sending a message, other 20 for receiving the answer) doesn’t allow for a real time piloting of these machines. This idea of course applies to any kind of robotic exploration you want to do on the surface of any celestial body in the solar system.
What do you think?
Davide
-
#1
by
Jim
on 19 Jul, 2010 23:18
-
no, with AI they can drive themselves.
-
#2
by
ugordan
on 19 Jul, 2010 23:30
-
Power is the limiting factor, not communications delay.
-
#3
by
KelvinZero
on 20 Jul, 2010 09:17
-
So how fast would NASA drive teleoperated rovers on mars with that lag, if power was not an issue? No particular limitation? Just limit to hops that the camera has given us a fairly good look at?
-
#4
by
racshot65
on 20 Jul, 2010 10:28
-
-
#5
by
ugordan
on 20 Jul, 2010 12:45
-
No particular limitation? Just limit to hops that the camera has given us a fairly good look at?
Best case scenario, meaning freely traversable terrain, yes, you could do large hops at once and depending on your downlink to Earth frequency you could do that a couple times a day.
-
#6
by
Robotbeat
on 20 Jul, 2010 15:42
-
The DARPA Grand Challenge 2005 has shown that, if given enough power, autonomous vehicles can go pretty far rather quickly on "off-road" terrain (i.e. 150 miles in 7 hours), although there are obviously differences in operating on Mars and the constraints of that challenge. For instance, I believe it was known before-hand that the path of the challenge was traversable, and more risks can be taken if you're in a race with a $30,000 vehicle versus on a unique multi-year mission costing billions.
http://en.wikipedia.org/wiki/DARPA_Grand_Challenge#2005_Grand_Challenge
-
#7
by
GClark
on 20 Jul, 2010 16:36
-
Not to mention that this is Science. They frequently stop to do just that. The drives are short mostly because of power, but they also drive to a spot they want to spend some time at.
The Lunokhods may have driven further, but the MERs are stopping more often to do intensive studies.
-
#8
by
sivodave
on 21 Jul, 2010 00:34
-
Well but i think that the communication delay poses some kind of limitation for a robotic exploration mission. maybe is not a big issue but relevant somehow.
Another thing: if we want to explore Mars (or anyother body of the solar system) we can think to explore it inch by inch otherwise it'll take ages. I think that once an area has been explored, the rover should be moved to another area...of course assuming we have enough power.
it's also true that on Mars there are different type of terrain and till now every rover sent to Mars has been sent in a quite easy area to drive. If we want to explore the planet to its full we have also go in more rough areas and then it could be more difficult drive a rover with a time delay.
-
#9
by
hop
on 21 Jul, 2010 03:52
-
Well but i think that the communication delay poses some kind of limitation for a robotic exploration mission. maybe is not a big issue but relevant somehow.
Of course it's a factor. It just isn't a fundamental limiting factor for the kind of missions we can actually build.
I think ugordon actually overstated the case a little bit (even though the basic point is right on.) The MERs are power limited, but the power would be used more efficiently with real time control. A human would have noticed purgatory dune was a problem much sooner, and the following sols (and watt hours) would have been put to driving instead of digging out. Same goes for many other wasted sols.
On the other hand, MERs communication round trip time is
much longer than light time. The rover has to have a scheduled pass with an orbiter (Odyssey is the main relay, has an orbital period of ~2hrs, not every orbit is usable), the orbiter has to relay to earth while fitting into the busy DSN schedule, the team has to analyze the data and so on. If you were willing to invest enough in communications infrastructure, you could operate a rover on Pluto on the same kind of schedule the MERs are on. Wouldn't that be cool
Another thing: if we want to explore Mars (or anyother body of the solar system) we can think to explore it inch by inch otherwise it'll take ages.
It's an entire planet. Exploring it will take ages.
I think that once an area has been explored, the rover should be moved to another area...of course assuming we have enough power.
Which we don't, and won't for the foreseeable future.
it's also true that on Mars there are different type of terrain and till now every rover sent to Mars has been sent in a quite easy area to drive. If we want to explore the planet to its full we have also go in more rough areas and then it could be more difficult drive a rover with a time delay.
So we will need other techniques to explore those areas. *shrug* Wheeled rovers aren't the only option, and autonomous capability is advancing very rapidly. And again, it's an entire freakin' planet, so even if some places are off limits, we aren't about to run out of interesting things to explore.
-
#10
by
docmordrid
on 21 Jul, 2010 05:23
-
A tele-operated Robonaut 2 or 3 on the surface of an otherwise human-inhospitable world, but with humans in orbit for short command relays, would give most of the advantages of a human landing with far reduced risks - remembering that humans won't fell much tactically anyhow due to thick gloves and stereo HD cams give darned good remote 3D vision.
Heck; with today's work in prosthetics, a lot of it at DARPA, sensors can give synthetic remote senses of touch, pressure and texture beyond what an astronaut could feel with gloves on, plus force feedback. The DARPA arm, which has 22 degrees of freedom and an implanted brain-machine interface, goes into FDA human trials very soon.
-
#11
by
simonbp
on 21 Jul, 2010 06:55
-
Power is the limiting factor, not communications delay.
Nope. It's not power. It's the darn scientists.
Even at their best, the rovers only drove at ~20% of their theoretical speed, because the faster they go, the more interesting things they see. And, since most of the instruments took time to measure whatever they saw, any "interesting thing" adds considerable non-moving time.
And thus the difference between space engineers and scientists: the engineers want to go everwhere fast (see "flexible path"), while the scientists want to go to one or two places and actually understand them.
-
#12
by
Archibald
on 21 Jul, 2010 06:56
-
-
#13
by
sivodave
on 21 Jul, 2010 08:39
-
-
#14
by
Garrett
on 21 Jul, 2010 10:37
-
Power is the limiting factor, not communications delay.
Nope. It's not power. It's the darn scientists.
Well, one would presume that there are many factors, but power and the "slow" scientists probably make up the bulk of the "issue". It is of course only an issue to the non-scientist who is more concerned with seeing a lot of lovely Mars terrain imagery. A planetary scientist would probably be just as happy to send a static probe, with the mass of the roving equipment (motor + wheels) replaced with more instruments. The holy grail, so to speak, would be to return Martian soil to Earth and analyse it with higher performance instruments. I would presume that is a much higher priority than making rovers travel faster.
-
#15
by
ugordan
on 21 Jul, 2010 12:20
-
Power is the limiting factor, not communications delay.
Nope. It's not power. It's the darn scientists.
It's power. Case in point: Opportunity trek toward Endeavour crater. Of course I'm assuming there aren't deliberate stops for science as I believe the OP was implying that.
The rovers weren't sent there to max out the odometer, they were sent there to do science.
-
#16
by
Hungry4info3
on 21 Jul, 2010 12:58
-
It's definitely power.
Up until just recently, it's been the same reason they haven't been able to drive every Martian day. They would drive 50 metres, then recharge the next day.
-
#17
by
simonbp
on 21 Jul, 2010 18:53
-
At this point in the mission, yes, it's power due to encrusted panels and over-cycled batteries. But for the first Martian year, when most of the traversing was done by both rovers, it was the scientists spotting things of interest.
And I'm not just making this up, it was told be me personally by Phil Christensen, the PI of Mini-TES, and one the darn scientists himself...
-
#18
by
ugordan
on 21 Jul, 2010 19:26
-
And I'm not just making this up, it was told be me personally by Phil Christensen, the PI of Mini-TES, and one the darn scientists himself...
Look, this isn't about deliberate stops where scientists wanted to check something out every minute, it's about the practical limitation to the maximum drive distance is. That neglects any
deliberate stops. That limitation was and still is (dust or no dust on the solar panels) the available power generated by the solar panels. For MSL it will be the power generated by the RTG over a day and stored in the batteries.
-
#19
by
HIPAR
on 21 Jul, 2010 20:04
-
It's more about size relating to mobility.
The rovers go slowly because they don't have enough ground clearance to avoid becoming stuck in the sand. They also need bigger wheels that don't sink up to the hubs. Of course, they were sized to the delivery constraints.
Spirit is currently mired. Opportunity spent a prolonged session stuck in the sand.
So drivers need to incrementally choose short routes and that's what consumes time. If they were all terrain vehicles they could drive with more impunity.
--- CHAS
