Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!pt.cs.cmu.edu!dsl.pitt.edu!pitt!unix.cis.pitt.edu!fmgst
From: fmgst@unix.cis.pitt.edu (Filip M Gieszczykiewicz)
Newsgroups: comp.robotics
Subject: Re: Micro rovers vs. Stompers
Message-ID: <25610@unix.cis.pitt.edu>
Date: 3 Jul 90 05:09:32 GMT
References: <9792@pt.cs.cmu.edu>
Reply-To: fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz)
Distribution: all
Organization: The Last Jedi
Lines: 95



<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!!"