gerry@cive.ri.cmu.edu (Gerry Roston) (07/03/90)
All of this talk about small rovers strikes me as being quite silly. Let's get real folks! small rovers can not accomplish meaningful scientific experiments. Let's consider a basic issue, power. One person suggested the use of solar panels. The most efficient solar panels avaiable for commercial use, can deliver approximately 150 W/m^2. If we define a small rover to have an area of 1/4 m^2, we can get ~40W of power HERE ON THE EARTH. If we now move this solar panel to Mars, the amount of power that can be extracted will be approximately 43% of the power on the Earth. Now, let's allow for wiz-bang solar panels which are twice as efficient as current ones, and we arrive at a total energy of about 34W. These same panels have a mass of about 15 kg/m^2. For our rover, this amount to a mass of 3.75 kg for the solar panels ALONE. Since this is to be a simple rover, we will assume minimal computing requirements, say the equivalent of a single MC68020 processor. To get ball park figures, we can look up the power consupmtion for a single board computer. A typical number is about 25 W. Again, let's assume that advanced technologies make this available at 13 W and a weight of 1 kg. To continue the analysis, let's assume that we wish for the computers to remain active during the night. If the vehicle is stationary, then we must simply supply 13 W times 13 hours. However, we must also allow for dust storms which will block the light, so let's up the 13 hours to 25 hours. So, we need a capacity of 325 watt hours of power. Using silver-zinc batteries, which are among the most efficient, we find that we need about 22 Kg of batteries, using about 0.01 m^3 of volume. Now, if the batteries can be slowly charged over the 13 hours of daylight, we must store (assuming 100% efficiency and no leakage) about 13 W/hr. Keeping with the notion of a small rover, let's assume that the rover is 1/2 meter tall, giving a total volume of 0.125 m^3. So, where are we now? We have a rover with solar cells, batteries and a computer. We can supply 34 W/hr of power and we are using 26 W/hr. We also have a mass of 26.75 Kg and have consumed almost 10% of the available space; AND WE STILL HAVE NO LOCOMOTIVE SYSTEM OR EXTERNAL SENSORS! If we assume that half of the available space in our rover if filled such that the average density is that of water, the total vehicle mass would be in excess of 60 kg. If interesting items do indeed occur in areas of rough terrain, the ability of the rover to scale slopes with 30 degree inclines is important. Given the power avaiable for locomotion and assuming to losses during movement, the vehicle could maintain a steady speed of 0.07 m/s going up the incline. I think that this back-of-the-envelope discussion should be sufficient to pursuade folks that the idea of solar powered micro-rovers is a pipe fantasy. This is not to say that they can not be made, but rather that they would be incapable of doing anything meaningful. The size of JPL's Robby and the CMU Ambler reflect this reality. Both vehicles are sized as they are so they can carry out meaningful scientific experiments, overpower the terrain they are in, and carry with them a power supply such as an RTG (radio-isotope, thermo-electric generator). -- gerry roston, field robotics center robotics institute, carnegie mellon university pittsburgh, pennsylvania, 15213 (412) 268-6557 gerry@cive.ri.cmu.edu
mikeb@ee.ubc.ca (Mike Bolotski) (07/03/90)
In article <9792@pt.cs.cmu.edu>, gerry@cive.ri.cmu.edu (Gerry Roston) writes: > All of this talk about small rovers strikes me as being > quite silly. Let's get real folks! small rovers can not > accomplish meaningful scientific experiments. While the current state of knowledge favors large rovers, the referenced does not present a convincing argument against the fundamental implausibility of small rovers. There are simply far too many assumptions in the analysis. > Let's consider a basic issue, power. One person suggested > the use of solar panels. The most efficient solar panels [ calculations omitted ] > have a mass of about 15 kg/m^2. For our rover, this amount > to a mass of 3.75 kg for the solar panels ALONE. The rover does not have to carry its own solar panels. It may well return to a base station to recharge. > Since this is to be a simple rover, we will assume minimal > computing requirements, say the equivalent of a single > MC68020 processor. To get ball park figures, we can look This is another assumption. Far simpler procesors may suffice. > A typical number is about 25 W. Again, let's assume that Are there not low-power computers available with considerably lower power requirements? > of 1 kg. To continue the analysis, let's assume that we > wish for the computers to remain active during the night. If A *major* assumption. Why should the rover be active during the night? Especially if a rudimentary vision system is provided (granted, this wouldn't apply to small rovers, but to midsize ones), wandering about at night is considerably more dangerous than in the day. > a capacity of 325 watt hours of power. Using silver-zinc batteries, > which are among the most efficient, we find that we need about How about molybdenum-lithium batteries? > Keeping with the notion of a small rover, let's assume that the > rover is 1/2 meter tall, giving a total volume of 0.125 m^3. > > So, where are we now? We have a rover with solar cells, batteries > and a computer. We can supply 34 W/hr of power and we are using > 26 W/hr. We also have a mass of 26.75 Kg and have consumed almost > 10% of the available space; AND WE STILL HAVE NO LOCOMOTIVE SYSTEM > OR EXTERNAL SENSORS! The power and weight calculations become quite different given a different set of assumptions. > gerry roston, field robotics center > robotics institute, carnegie mellon university Mike Bolotski, Department of Electrical Engineering, University of British Columbia, Vancouver, Canada mikeb@salmon.ee.ubc.ca | mikeb%salmon.ee.ubc.ca@relay.ubc.ca
fmgst@unix.cis.pitt.edu (Filip M Gieszczykiewicz) (07/03/90)
<All of this talk about small rovers strikes me as being
<quite silly. Let's get real folks! small rovers can not
<accomplish meaningful scientific experiments.
Greetings. Let me remind you that that was the
argument used by American carmakers when they
were asked to make compact cars. Nowdays, we
know for a _fact_ that compacts work :-)
You may argue that this has nothing to do with the
topic... Another thing, about using a base and
have the "rover" return at the end of the day
to recharge batteries (while also sending
data "back home" with a larger dish than it would
be possible to carry (even with a larger rover))
can be even applied to a larger rover.
<Let's consider a basic issue, power. One person suggested
<the use of solar panels. The most efficient solar panels
<avaiable for commercial use, can deliver approximately
<150 W/m^2. If we define a small rover to have an area of
<1/4 m^2, we can get ~40W of power HERE ON THE EARTH. If
<we now move this solar panel to Mars, the amount of power
<that can be extracted will be approximately 43% of the
<power on the Earth. Now, let's allow for wiz-bang solar
<panels which are twice as efficient as current ones, and
<we arrive at a total energy of about 34W. These same panels
<have a mass of about 15 kg/m^2. For our rover, this amount
<to a mass of 3.75 kg for the solar panels ALONE.
Again, the base may contain stationary solar panels.
It may also store the energy for the rovers use later,
in the evening... In that case, the small rover may
have small solar cells that just extend its range.
<Since this is to be a simple rover, we will assume minimal
<computing requirements, say the equivalent of a single
<MC68020 processor. To get ball park figures, we can look
Spoken by a true _software_ engineer! I have had
very good success with 4 bit processors. True,
for the image analysis one does require some
*decent* power, but a high speed 68000 might
also do the job. Also, how about fitting the whole
computer system on 2 wafers? Remember, the Fed is
paying (to some extent :-)
<up the power consupmtion for a single board computer.
<A typical number is about 25 W. Again, let's assume that
<advanced technologies make this available at 13 W and a weight
For quite a while I have seen rad-hard CMOS chips
on the market. They don't use THAT much... However,
allowing for some (required) redundancy, this JUST might
be in the ball park...
<of 1 kg. To continue the analysis, let's assume that we
<wish for the computers to remain active during the night. If
<the vehicle is stationary, then we must simply supply 13 W times
<13 hours. However, we must also allow for dust storms which will
<block the light, so let's up the 13 hours to 25 hours. So, we need
<a capacity of 325 watt hours of power. Using silver-zinc batteries,
<which are among the most efficient, we find that we need about
<22 Kg of batteries, using about 0.01 m^3 of volume. Now, if the
<batteries can be slowly charged over the 13 hours of daylight,
<we must store (assuming 100% efficiency and no leakage) about
<13 W/hr.
Is there any possibility of using radar on Mars surface
and have a "compact" rover communicate with the base?
This would allow the movement of the computer power
from the rover to the base. The rover would only
send the collected information. Are there any
adverse fields or magnetic disturbances that would make
high speed radar transfer impossible. (One could use
any frequency, FCC doesn't have jurisdiction (sp?) there ;-)
Then again, looking back at the HST ("Hobbled Spaced-out
Telescope" :-), and the problems it had (has!) with the
communication dishes, that may not be such a good idea :-)
<gerry roston, field robotics center
<robotics institute, carnegie mellon university
<pittsburgh, pennsylvania, 15213 (412) 268-6557
<gerry@cive.ri.cmu.edu
Take care and have fun (in that order :-)
--
_______________________________________________________________________________
"The Force will be with you, always." It _is_ with me and has been for 10 years
Filip Gieszczykiewicz "A man without a dream is like a fish without water."
FMGST@PITTVMS or fmgst@unix.cis.pitt.edu "My ideas. ALL MINE!!"gerry@cive.ri.cmu.edu (Gerry Roston) (07/03/90)
My previous post was not intended to be a definitive treatment of the small rover. It WAS intended, however, to get some of the day-dreamers on the net to sit down with pencil and paper and start figuring some of these issues out IN DETAIL. The issues of power consumption that I raised are only the tip of the iceberg. The design of a extra-terrestial robot is an extremely complex task which involves multiple conflicting goals. For some one to sit down for the amount of time it takes to write a note for the net and say they have an answer is quite ludicrous. I have been intimately involved with both the JPL Robby and the CMU Ambler and therefore probably have a better understanding of the issues than most people. With this understanding I have come to beleive that the approaches being used are probably the best considering the mission objectives, etc. Now, a challenge to the micro-rover advocates: take some time to carefully plan a mission and a rover to accomplish this mission. You should consider all facets of the mission, robot design, telecommunications, etc. You should refernce manufacturers data for getting accurate values for what ever parameters you need. You need not build a protot-type mockup for study. (Hint: JPL and CMU have spent more than a man decade doing this so far...) gerry -- gerry roston, field robotics center robotics institute, carnegie mellon university pittsburgh, pennsylvania, 15213 (412) 268-6557 gerry@cive.ri.cmu.edu
monty@sagpd1.UUCP (Monty Saine) (07/03/90)
In article <9792@pt.cs.cmu.edu> gerry@cive.ri.cmu.edu (Gerry Roston) writes:
_>Let's consider a basic issue, power. One person suggested
_>the use of solar panels. The most efficient solar panels
_>avaiable for commercial use, can deliver approximately
_>150 W/m^2. If we define a small rover to have an area of
_>1/4 m^2, we can get ~40W of power HERE ON THE EARTH. If
_>we now move this solar panel to Mars, the amount of power
_>that can be extracted will be approximately 43% of the
_>power on the Earth. Now, let's allow for wiz-bang solar
_>panels which are twice as efficient as current ones, and
_>we arrive at a total energy of about 34W. These same panels
_>have a mass of about 15 kg/m^2. For our rover, this amount
^^^^^^^^^^
I think your estimate of weight is over exagerated considering that
thin film solar cells are on the order of .001" thick. If they were designed
in as part of the shell/skin of a rover (assuming the rover has or needs a skin)
I think your mass argument is way off.
_>to a mass of 3.75 kg for the solar panels ALONE.
_>
_>Since this is to be a simple rover, we will assume minimal
_>computing requirements, say the equivalent of a single
_>MC68020 processor. To get ball park figures, we can look
Again you are over designing. Considerable power can be found in
many 4 and 8 bit controllers that do not require the overhead or power you are
imagining. This is using off the shelf componets! If there were to be such a
"micro rover" designed, it could very easily have a extremmly powerfull and low
power processor using only micro-watts of power in an extremly small mass
package. A good deal of the mass in computers we are used to is in the packaging
not in the actual electronics. The disadvantage to this is cost, unless the
volume can be increased. Think about the spin offs of under-sea repair and
exploration that could result.
_>up the power consupmtion for a single board computer.
_>A typical number is about 25 W. Again, let's assume that
_>
_>Keeping with the notion of a small rover, let's assume that the
_>rover is 1/2 meter tall, giving a total volume of 0.125 m^3.
_>
_>So, where are we now? We have a rover with solar cells, batteries
_>and a computer. We can supply 34 W/hr of power and we are using
_>26 W/hr. We also have a mass of 26.75 Kg and have consumed almost
_>10% of the available space; AND WE STILL HAVE NO LOCOMOTIVE SYSTEM
_>OR EXTERNAL SENSORS!
_>
_>If we assume that half of the available space in our rover if filled
_>
_>I think that this back-of-the-envelope discussion should be
_>sufficient to pursuade folks that the idea of solar powered
_>micro-rovers is a pipe fantasy. This is not to say that they
_>can not be made, but rather that they would be incapable of
_>doing anything meaningful. The size of JPL's Robby and the
_>CMU Ambler reflect this reality. Both vehicles are sized as they
_>are so they can carry out meaningful scientific experiments,
_>overpower the terrain they are in, and carry with them a power
_>supply such as an RTG (radio-isotope, thermo-electric generator).
What might be a better solution is a marriage of both small and large
explorers. Have a "Mother explorer" that releases several micro-explorers to
roam around and attempt to indentify things of more interest to be examined in
more depth by the mother. This would allow the micro-explorers to be recharged
on occasion also.
I guess big is not always better and small might not be enough. Let's
hope that the over all planners keep an open mind and consider both methods
on there merits. Knowing government R&D and procurment this is highly unlikely
to happen, but one can hope and dream.
Monty Saineted@nmsu.edu (Ted Dunning) (07/04/90)
truly amazing, at the beginning,
In article <9792@pt.cs.cmu.edu> gerry@cive.ri.cmu.edu (Gerry Roston) writes:
All of this talk about small rovers strikes me as being
quite silly. Let's get real folks! small rovers can not
accomplish meaningful scientific experiments.
...
and then he goes on to prove that
a) portable pc's are impractical
b) 10 g of solar cells need nearly 4 kg of support
c) robots _must_ continue at night and during sandstorms
d) detroit was right all along
e) there is only one doxie and she is orthodoxy.
--
Offer void except where prohibited by law.cg108f3@icogsci1.ucsd.edu (Pete Dapkus) (07/04/90)
The stationary motherbase with rechargeable microrovers buys you something else too. It would be much easier to send a new batch of micro-rovers either as replacements or ones with new capabilites (new sensors, tools etc) than it would be to send a new full size rover if it was damaged or didn't have the needed equipment. You wouldn't need to send the mother base again. Just put it somewhere safe. It could even be a start at colonizing mars. And why do the micro-rovers have to be active everyday. Couldn't they recharge with solar arrays while idle for one day and then be active the next Sure it would slow down the mission, but then you could also have more of them and you could keep adding more. Well? pete dapkus cg108f3@icogsci1.ucsd.edu pdapkus@ucsd.edu
cmcmanis@stpeter.Eng.Sun.COM (Chuck McManis) (07/04/90)
I know this is probably beating a dead rover :-) but what is the
requirement for rovers to have a local power source? Suppose for
a moment that it were possible to place into Mars orbit 1 or more
"powersats" that could convert larger quantities of solar power
into reasonably tightly directed microwave beams down to the
rovers. There will certainly be losses due to the atmosphere but
that would not be nearly as severe as say on Earth where such an
idea was considered. Just a posibly ludicrous idea ...
--
--Chuck McManis Sun Microsystems
uucp: {anywhere}!sun!cmcmanis BIX: <none> Internet: cmcmanis@Eng.Sun.COM
These opinions are my own and no one elses, but you knew that didn't you.
"I tell you this parrot is bleeding deceased!"bbc@rice.edu (Benjamin Chase) (07/05/90)
cmcmanis@stpeter.Eng.Sun.COM (Chuck McManis) writes: > [Can the problem of martian rovers be helped by postulating a > orbiting powersat, which could beam (eg.) microwaves down to a rover?] There are lots more useful things such a satellite can do than that. It is more helpful for the satellite to act as a powerful communication link to earth. Put large antennas, good amplifiers and ample power onto a geostationary satellite, and then you can make do with simpler, low-power gear on the land equipment. Heck, you could even have the satellite do store-and-forward for the large amounts of data (eg pictures) returned by the rovers. That is, put a good chunk of data (ie. not program) storage space on the satellite, too, so that you don't need as much (any?) in the rovers. So, can these small cat-like rovers get back on their feet after a fall or stumble? I'm hoping it looks sort of like a cockroach in similar distress, perhaps more capable, but I suppose that's too much to expect. :-) -- Ben Chase <bbc@rice.edu>, Rice University, Houston, Texas
ralph@laas.fr (Ralph P. Sobek) (07/09/90)
In article <11723@sdcc6.ucsd.edu> cg108f3@icogsci1.ucsd.edu (Pete Dapkus) writes: | You wouldn't need to send the mother base again. Just | put it somewhere safe. It could even be a start at colonizing mars. Somewhere safe? Why not just leave it in orbit? Of course, the battery recharging would have to be rethought out. -- Ralph P. Sobek Disclaimer: The above ruminations are my own. ralph@laas.fr Addresses are ordered by importance. ralph@laas.uucp, or ...!uunet!laas!ralph If all else fails, try: sobek@eclair.Berkeley.EDU =============================================================================== Reliable software should kill people reliably! -Andy Mickel, Pascal News #13,78
arh@sage.cc.purdue.edu (Eric B) (07/09/90)
In an article bbc@rice.edu (Benjamin Chase) writes: >cmcmanis@stpeter.Eng.Sun.COM (Chuck McManis) writes: >> [Can the problem of martian rovers be helped by postulating a >> orbiting powersat, which could beam (eg.) microwaves down to a rover?] >It is more helpful for the satellite to act as a powerful >communication link to earth. Put large antennas, good amplifiers and >ample power onto a geostationary satellite... Consider (for an advanced colony) a network of Motorola polar-orbit communications satellites, similar to what they are planning for earth. Then these micros could carry portable phones... 8-) An argument pro-micro: remember that anything one sends to Mars will be outdated by the time it actually arrives. The Hubble was built with that in mind -- modularity. But on Mars, who will replace the modules? >So, can these small cat-like rovers get back on their feet after a >fall or stumble? Comm : Hello, LifeAlert. Synth Voice : HELP! I've fallen... and I can't get up! Comm : Don't worry micro-34, I'm calling your neighbor and police. Eric G. Bolinger 8-) arh@sage.cc.purdue.edu -- [I have the right to state my opinion as well as you have your right to state your opinion about my opinion.]