Planetary rovers, SETI and other musings, was Re: update.356 (fwd)

Hi Steve,

Can I forward your questions to another technology list I support as well as
the local high performance rocketry group I'm involved in? I believe
they would be intriqued by your questions.

Forwarded message:

> Date: Tue, 27 Jan 1998 19:56:33 -0800
> From: Steve Schear <schear@lvdi.net>
> Subject: Planetary rovers, SETI and other musings, was Re: update.356 (fwd)
> 
> >ANOTHER VERSION OF QUANTUM TELEPORTATION is

[text deleted]

> I wonder how far off use of this technique for interplanetary rovers might
> be (10 years, 20 years)?  Remote (Earth) rover manipulation is tedious at
> best due to several minutes (or an hour or more to the outer planets) of
> propagation delay.

As I understand the process you don't get around the speed-of-light issue
because the control channel still needs to be sent via radio or laser or
whatever. This was discussed in the in the original teleportation
announcement. However, I don't see anything that would keep you from syncing
two atomic clocks and then using them to make the changes in sync, this
should allow the imposition of the speed of light only on initiation and
occassion syncronization. I'll have to beg ignorance on specifics as I
haven't had the time to really dig into specifics. I haven't even read the
primary references to date.

> Autonomous rovers need enough smarts built-in to handle
> unexpected situations, a non-trivial problem.  An alternative is to
> establish a link using entangled photons. If a simple approach to saving
> these entangled states during signal transit, in both directions, were
> found instantaneous communication and simplified remote control would be a
> reality.

Agreed. It would also solve many terrestrial problems as well.

> Of course one needn't stop there.  If entangled states could be stored for
> several years, instantaneous communication with neighbooring stars is a
> real possibility.  Coupled with advances in mind-machine science it might
> someday be possible to explore, first-hand, our local portion of the galaxy
> without leaving earth, or upload/download one's consciouness to vessels in
> remote locations.

True, but it would be boring compared to being there first person. I do
support robot exploration as a precursor to manned exploration.

> Speaking of which, do the current SETI programs check for signal modulation
> using polarization.

>From what little I have delved into this, most signals coming in from 'out
there' as well as from satellites are circularly polarized. This is the
reason that the antennas have those curly-ques on them (look like a
cork-screw sorta). The last time I even messed with extra-terrestrial
signals was the SL-9 impacts. I worked with several amateur groups using plane
(flat rectangular) loop antennas to measure the increase in the background
noise in various bands (we used a HP spectrum analyzer at my site) during
the impacts. What we saw was a 'jump' across the band of several db's just
at the time-of-flight times we expected. The assumption being this was
caused by the impacts. We monitored 1MHz to 10MHz. I found it pretty
impressive. We got, if memory serves, around 6 of the large impacts.

>  If we've discovered this trick, sure so have other
> intelligent life forms.  Most natural sources of radiation tend to
> unpolarized, so a rapidly flucuating polar modularion might easily appear
> to be noise.

I'll have to disagree, all forms of E-M radiation that I am aware of are
polarized to some frame of reference. The E-M fields after all are
orthogonal. The question is which field you want to pick as a reference
and the relationship of source to sensor. Circularly polarized (ie the
fields rotate around the axis of transmission at some rate) are about the
only sort that would appear essentialy the same irrespective of reference
frame.


    ____________________________________________________________________
   |                                                                    |
   |       The most powerful passion in life is not love or hate,       |
   |       but the desire to edit somebody elses words.                 |
   |                                                                    |
   |                                  Sign in Ed Barsis' office         |
   |                                                                    | 
   |            _____                             The Armadillo Group   |
   |         ,::////;::-.                           Austin, Tx. USA     |
   |        /:'///// ``::>/|/                     http://www.ssz.com/   |
   |      .',  ||||    `/( e\                                           |
   |  -====~~mm-'`-```-mm --'-                         Jim Choate       |
   |                                                 ravage@ssz.com     |
   |                                                  512-451-7087      |
   |____________________________________________________________________|

>>> Speaking of which, do the current SETI programs check for signal
>>> modulation using polarization.
>
>Speaking of SETI, their current intent is to do a distributed
>computation spread across thousands of computers, similar to some of the
>keycracking efforts.  Details at http://www.bigscience.com ;
>the Recent News section says they're currently trying to figure
>out about funding.  Meanwhile, there's www.mersenne.org for
>factoring big prime numbers.

One of the problems I have with SETI is that it assumes that a distant
civilization is sending out a beacon for others to home in on, and that
this beacon is a narrowband signal. What if most such civilizations aren't
looking for anyone and merely going about their own affairs, including
communications for their own needs?

Because of path losses it takes an incredibly strong narrowband signal to
traverse even relatively small cosmological distances and have any hope of
detection with our technology.  For example, Earth's strongest TV signals
could be detected by our present technology out to about 50 light years,
but no image reconstruction would be possible (insufficient S/N).  The
highest power transmitter-directional antenna, at Aricebo, can be heard to
about 300 light years, but its only transmitted a SETI beacon once and only
for a few minutes.

An excellent way to mitigate path loss is trading bandwidth for data rate.
GPS  garners an incredible 63 dB of process gain (or about a 2,000,0000
fold improvement) in this manner. If I was trying to send a electromagnetic
signal vast distances I'd use some form of spread spectrum.  Individually,
narrowband receivers are most insensitive to broadband 'noise' sources.
However, I wonder if it might be possible to configure the SETI@home
software to coordinate the narrowband channels signal analysis so as to
have a better chance of detecting broadband, pseudo-noise, signaling.

--Steve

>> Speaking of which, do the current SETI programs check for signal
>> modulation using polarization.

Speaking of SETI, their current intent is to do a distributed
computation spread across thousands of computers, similar to some of the
keycracking efforts.  Details at http://www.bigscience.com ;
the Recent News section says they're currently trying to figure
out about funding.  Meanwhile, there's www.mersenne.org for
factoring big prime numbers.

Tim wrote:
> Nothing in quantum teleportation has been shown to propagate 
> signals faster than light. (If you don't believe me, look into it.
> Start by reading the FTL discussions about Bell's Theorem.)
But I thought Jim Bell had a solution to .....  :-)

				Thanks! 
					Bill
Bill Stewart, bill.stewart@pobox.com
PGP Fingerprint D454 E202 CBC8 40BF  3C85 B884 0ABE 4639