Path: utzoo!attcan!uunet!jarthur!usc!zaphod.mps.ohio-state.edu!swrinde!emory!hubcap!ncrcae!ncr-sd!sagpd1!monty
From: monty@sagpd1.UUCP (Monty Saine)
Newsgroups: comp.robotics
Subject: Re: Micro rovers vs. Stompers
Message-ID: <838@sagpd1.UUCP>
Date: 3 Jul 90 15:08:57 GMT
References: <9792@pt.cs.cmu.edu>
Reply-To: monty@sagpd1.UUCP (Monty Saine)
Organization: Scientific Atlanta, Government Products Div, San Diego, CA
Lines: 71


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 Saine