Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!cs.utexas.edu!csc.ti.com!tilde.csc.ti.com!mksol!strohm
From: strohm@mksol.dseg.ti.com (john r strohm)
Subject: Re: Distance to Mars
Message-ID: <1993Jun10.145007.12268@mksol.dseg.ti.com>
Keywords: virtual reality, mars rover, speed of light
Organization: Texas Instruments, Inc
References: <1v5t56INNlkm@flop.ENGR.ORST.EDU>
Date: Thu, 10 Jun 1993 14:50:07 GMT
Lines: 28

In article <1v5t56INNlkm@flop.ENGR.ORST.EDU> brittar@research.CS.ORST.EDU (Robert Wade Brittain) writes:
>
>Hmmm, just one question:  doesn't speed-of-light restrict communication
>speed?  You've probably got delays of a few minutes from here to Mars;
>control like that either implies a really slow robot, or that you can
>anticipate moves so far ahead...
>
>Uh, yes, isn't Mars approximately 26 light-minutes away?  That would translate
>to a 52 minute Minimum Sense-to-Action time.  I've noticed that on several
>occasions while riding my bicycle that turning my head to look at distractive
>scenery for only a few seconds has a tendency to put me in near- catastophic
>predictaments.  I can't imagine going anywhere with a 52-minute reaction time.
>(except very very slowly!!)  Can anyone enlighten me ?

At closest approach to Earth, Mars is roughly 30 million miles away, which
works out to about 160 light-seconds.  At farthest, Mars is some 200 million
miles away, or about 1100 light-seconds, or about 20 light-minutes away.

Obviously, you are not going to do real-time closed-loop manual control,
relying the operator to close the feedback loop with hand/eye coordination.

The EASY answer is to close the loop from Mars orbit, but that requires us
to do something very politically incorrect in certain circles: manned 
spaceflight.

However, there is currently a fair amount of amateur interest in teleoperation
in the presence of time lags, and a fair amount of work being done.  The work
I have been following has been more interested in 2-second time lags.
