Detecting the high def TV for the Google Lunar X Prize.
Robert Clark
"near real time" high definition video transmissions was achievable
for a such a low-cost mission.
It would certainly be doable if the receiving antennas on Earth were
the large radio antennas used for space communications with
interplanetary probes or those radio antennas used for radio
astronomy. This is evidenced by the fact that the Kaguya(Selene) lunar
orbiter mission was able to send high definition video to a large
receiving dish radio antenna. And also by the fact that DirecTV sends
high definition video to only 2 foot size antennas from geosynchronous
orbit; so 10 times larger antennas would be able to receive such
signals from a 10 times larger distance at the Moon.
However, I was wondering if it would be possible to detect this using
amateur sized equipment at such a large distance. Usually for
receiving high data rates you used transmissions at very high
frequencies, as higher frequencies can carry more data. For instance
both Kaguya and DirecTV transmit the high def video at gigahertz
frequencies.
However, for the system I'm imaging I'm thinking of using much lower
frequencies, and necessarily longer wavelengths. What I wanted to do
is transmit at decametric wavelengths. High data transmissions rates
would be achieved by making it be pulsed in an on-off fashion at high
intensity but at a rapid rate.
On that other forum the data rate required for high def TV was given
as 256,000 bits per second. So I wanted to make these transmissions be
pulsed at this rapid rate at wavelengths of a few tens's of meters.
My decametric wavelength requirement was because of the fact that
high schools and universities have programs for detecting radio
emissions from Jupiter at these wavelengths:
NASA's Radio JOVE Project.
http://radiojove.gsfc.nasa.gov/
The Discovery of Jupiter's Radio Emissions.
How a chance discovery opened up the field of Jovian radio studies.
by Dr. Leonard N. Garcia
http://radiojove.gsfc.nasa.gov/library/sci_briefs/discovery.html
These school and university receiving antennas on Earth consist of
dozens to hundreds of vertical dipoles of lengths at the meters scale
to correspond to the radio wavelengths. Some questions I had: how
intense would the pulse have to be on the Moon to be detectable from
the Moon above background noise for a detector on Earth of say a few
dozen dipoles? Could this be done for the transmitter of power of say
a few hundred watts for a low cost, low weight lander mission? Could
the transmitter antenna on the moon be only a few meters size for the
low weight requirement?
A secondary purpose I had in mind was a pet project of mine involving
linking these many school receivers to form a global telescope at
decametric wavelengths:
From: rgcl...@my-deja.com (Robert Clark)
Date: 23 May 2001 11:15:06 -0700
Subject: Will amateur radio astronomers be the first to directly
detect extrasolar planets?
Newsgroups: rec.radio.amateur.space, rec.radio.amateur.antenna,
sci.astro, sci.astro.seti, sci.space.policy
http://groups.google.com/group/sci.astro.seti/browse_frm/thread/c0018b68662c14e9
The long wavelengths should make the requirements for accurate
distance information and timing synchrony between the separate
detectors easy to manage even for amateur systems. Using this method
might make the detection achievable even if the power or transmitting
antenna size requirements are not practical for a low cost, low weight
lander on the Moon for an individual detector on Earth.
The recent achievement of real-time very long baseline interferometry
should make it possible to integrate these separate detector signals
in real-time as well:
Astronomers Demonstrate a Global Internet Telescope.
Date Released: Friday, October 08, 2004
Source: Jodrell Bank Observatory
http://www.spaceref.com/news/viewpr.html?pid=15251
Bob Clark
Jim Lux
> On another forum there was debate about whether the requirement of
> "near real time" high definition video transmissions was achievable
> for a such a low-cost mission.
> It would certainly be doable if the receiving antennas on Earth were
> the large radio antennas used for space communications with
> interplanetary probes or those radio antennas used for radio
> astronomy. This is evidenced by the fact that the Kaguya(Selene) lunar
> orbiter mission was able to send high definition video to a large
> receiving dish radio antenna. And also by the fact that DirecTV sends
> high definition video to only 2 foot size antennas from geosynchronous
> orbit; so 10 times larger antennas would be able to receive such
> signals from a 10 times larger distance at the Moon.
Don't forget that DirecTV radiates a LOT more power than a typical deep
space probe. AND they often have a higher gain antenna. A geosync relay
satellite might have 96 TWTAs, each several hundred watts, on it,
feeding a very clever multiple feed dish which is many meters in
diameter (look at Thuraya, for instance).
> However, I was wondering if it would be possible to detect this using
> amateur sized equipment at such a large distance. Usually for
> receiving high data rates you used transmissions at very high
> frequencies, as higher frequencies can carry more data. For instance
> both Kaguya and DirecTV transmit the high def video at gigahertz
> frequencies.
There's a moderately active Amateur DSN group that listens for things
like Chandrayaan or MRO using relatively small dishes (1-2 meters).
The choice of higher frequencies isn't because it carries more data.
It's because a higher frequency allows you to get more gain with the
same physical antenna size. Double the frequency, and your antenna gain
goes up by a factor of 4, at both ends of the link.. a total of 12 dB
improvement in SNR, for the same transmitter power and receiver noise
figure. And, there's more spectrum available up high.
> However, for the system I'm imaging I'm thinking of using much lower
> frequencies, and necessarily longer wavelengths. What I wanted to do
> is transmit at decametric wavelengths. High data transmissions rates
> would be achieved by making it be pulsed in an on-off fashion at high
> intensity but at a rapid rate.
How high a data rate? If you're at 30 MHz (10m lambda), you're not
going to be pulsing at 10 MHz, or you're going to be generating a signal
that extends from 20 to 40 MHz (and then some). You need a low symbol
rate with lots of bits per symbol, which in turn means you'll need lots
of SNR.
> On that other forum the data rate required for high def TV was given
> as 256,000 bits per second.
HDTV, as carried on broadcast TV, is 19.8 Mbps. If you're happy with a
lower frame rate, or can do a lot of frame/frame compression, you can
get it lower.
So I wanted to make these transmissions be
> pulsed at this rapid rate at wavelengths of a few tens's of meters.
> My decametric wavelength requirement was because of the fact that
> high schools and universities have programs for detecting radio
> emissions from Jupiter at these wavelengths:
>
> NASA's Radio JOVE Project.
> http://radiojove.gsfc.nasa.gov/
>
> These school and university receiving antennas on Earth consist of
> dozens to hundreds of vertical dipoles of lengths at the meters scale
> to correspond to the radio wavelengths.
Any one school only has a couple dipoles up.. the gain is quite low.
Some questions I had: how
> intense would the pulse have to be on the Moon to be detectable from
> the Moon above background noise for a detector on Earth of say a few
> dozen dipoles? Could this be done for the transmitter of power of say
> a few hundred watts for a low cost, low weight lander mission? Could
> the transmitter antenna on the moon be only a few meters size for the
> low weight requirement?
How technical do you want to get? There's a book about space
telecommunications system design available for downloading from JPL
(http://descanso.jpl.nasa.gov/ somewhere on that site)
Here's some basic numbers you'll need:
Free space path loss in dB = 32.44 + 20*log10(distance in km) + 20
*log10(frequency in MHz)
That's between isotropic antennas (0dBi)..
Antenna beamwidth is 70 degrees/ (diameter of antenna in wavelengths)
Antenna gain is 27000/(beamwidth^2)
A typical receiver noise figure (after figuring in losses in
coax/waveguide, etc.) is probably 3dB.
kTB noise is -174 dBm/Hertz * 10*log10(bandwidth in Hz)
> A secondary purpose I had in mind was a pet project of mine involving
> linking these many school receivers to form a global telescope at
> decametric wavelengths:
Coherent combining would be a challenge, because of ionospheric
variability at HF, not to mention the other challenges.
Look up LOFAR or the SKA (Square Kilometer Array) for a fairly well
funded scheme.
tom
>
> Don't forget that DirecTV radiates a LOT more power than a typical deep
> space probe. AND they often have a higher gain antenna. A geosync relay
> satellite might have 96 TWTAs, each several hundred watts, on it,
> feeding a very clever multiple feed dish which is many meters in
> diameter (look at Thuraya, for instance).
>
Wow. 96 TWTs with several hundred watts each. From a satellite. And
what's the efficiency?
So these are powered by what? Small nuclear reactors?
Certainly not solar panels.
tom
K0TAR
Sal M. Onella
"Jim Lux" <james...@jpl.nasa.gov> wrote in message
news:h19hoo$i04$1...@news.jpl.nasa.gov...
Snip >
> HDTV, as carried on broadcast TV, is 19.8 Mbps. If you're happy with a
> lower frame rate, or can do a lot of frame/frame compression, you can
> get it lower.
Yes. OP said "near real time," which I take to mean "OK to drop some
frames," like the satellite video phones the reporters use from the
boondocks. Thus, high-def can be confined to a lot lower bandwidth if you
don't mind seeing compression artifacts as each frame is being built on the
screen.
I have a contemporary example: KABC-DT, Channel 7 Los Angeles is high-def
on 7-1 AND high-def on 7-2, with a service called Living Well. See
http://livingwell.tv/Welcome.html.
Living Well is apparently getting a skimpy bitshare, as compression
artifacts are obvious, especially on scene changes and motion, whereas ABC
programming on 7-1 is just beautiful. Living Well is very good, sharp HD,
but you can see details being "painted in" for a quarter-second after a
scene change.
"Sal"
Jim Lux
Not all will necessarily be on at the same time.
Typical narrow band coupled cavity TWTAs can get over 50% efficiency
(DC in to RF out)
Yes Solar Panels..10kW would not be unusual.
See, e.g., http://en.wikipedia.org/wiki/ASTRIUM_E3000 ... 14 kW of
power from 45 m^2 of solar panels and 4500kg of satellite..
This is so far beyond what is used in the scientific space program
it's mind boggling. But, hey, out of the $1-2B cost, the TWTAs are
probably only 5-10% of the total, and there are definitely quantity
discounts.
No Spam
You will never get uncompressed HD video transmitted from the lunar
surface. And really, there is no need for it if the compression is
handled right. Only a few people I know can do that part.
Since the image is mostly repetitive, a low bitrate can be achieved which
should allow for a very good signal level path budget. this would make
for a higher energy per bit and a more reasonable earth station within
the budget of amateurs. (if thats the goal) To achieve a very low
bitrate, such things as Pre/post-distortion to utilize less bits, (black
gamas) using extremely long GOP structures and since the action of the
video is extremely slow and repetitive, a slow frame rate such as 1fps.
These can be counteracted at the receive station with software without
effecting the total image resolution.
The image resolution is where the wow factor is anyway! :-)
My *guess* is that whomever would put a spacecraft on the lunar surface
would only have one high speed datapath back. The HD transport stream
would be muxed in with the other data elements of the spacecraft on a
transmission system without consideration for amateur reception. Perhaps
encrypted if a commercial entity is paying for the broadcast rights.
Jim Lux
> Yes. OP said "near real time," which I take to mean "OK to drop some
> frames," like the satellite video phones the reporters use from the
> boondocks. Thus, high-def can be confined to a lot lower bandwidth if you
> don't mind seeing compression artifacts as each frame is being built on the
> screen.
>
> I have a contemporary example: KABC-DT, Channel 7 Los Angeles is high-def
>
> Living Well is apparently getting a skimpy bitshare, as compression
> artifacts are obvious, especially on scene changes and motion, whereas ABC
> programming on 7-1 is just beautiful. Living Well is very good, sharp HD,
> but you can see details being "painted in" for a quarter-second after a
> scene change.
>
There's a fairly complex trade. For a lunar mission, the scene is
going to be pretty static, just shifted. (not like there's a baskeball
team doing a fast break in the field of view), so it should compress
well, given a suitable algorithm.
The challenge is that compression (especially good compression) takes
computational power. So you have a tradeoff: do you spend you joules
on compressing the images and radiate less RF energy, or do you
compress less, and use a bigger power amp. There's also a mass
tradeoff.. big amp or big antenna. The big antenna needs more
accurate pointing, which increases complexity. Or the trade of
frequency selection, higher frequency means more antenna gain, but
usually lower efficiency in the PA and higher NF in the receiver end,
as well as higher probabiliity of weather related fading.
And even there, because Moore's law means that semiconductor
technology is always advancing, the tradespace is shifting towards
more processing (because it gets cheaper in size, weight, power, while
power amps are pretty much at the physics limits)
This is, of course, "rocket science".. or more properly, spacecraft
system engineering. It's straightforward, for the most part, but non-
trivial. Pick your requirements, define the tradespace(s), try
configurations and see what happens.
Robert Clark
> Jim Lux wrote:
> >> Yes. OP said "near real time," which I take to mean "OK to drop some
> >> frames," like the satellite video phones the reporters use from the
> >> boondocks. Thus, high-def can be confined to a lot lower bandwidth if you
> >> don't mind seeing compression artifacts as each frame is being built on the
> >> screen.
>
> Mbps
>
> Let's assume 2GHz for the working frequency (not necessarily a good
> choice, but somewhere to start)
>
> Free Space Path Loss from Moon to earth, between isotropic antennas =
> 32.44 + 20*log10(500E3) + 20*log10(2E3) = 32.44 + 114 + 66 = about 212 dB
>
> Assume an antenna 2m in diameter at one end (moon end)
> lambda for 2GHz is 15cm, so the antenna is 13 wavelengths in diameter
> Beamwidth will be about 70/13 = 5 degrees.. OK, because Earth is 2
> degrees wide from the moon, so you can just point at the middle of the
> visible earth.
>
> Assume an antenna 10m in diameter at the earth end. Beamwidth will be 1
> degree, twice the visible lunar disc size, so you can just point at the
> moon, generally.
>
> Gains of antennas
> 2m @ 2GHz = 30dB
> 10m @ 2GHz = 44dB
>
> Preceived at Earth = Ptransmitted +30 - 212 +44dB = Ptransmit -138dB.
>
> Assume transmitting with 10 Watts or +40dBm..
> Prec = -100dBm
>
> Now, let's look at the receiver:
> Power Spectral density of Noise is kT+NF.. kT is -174dBm/Hz and a decent
> NF might be 2dB (allowing for some plumbing losses, etc.
>
> -172 dBm/Hz
>
> Eb (energy/Bit) = -100dBm -60dB (1Mbps) = -160dBmJ
>
> So, Eb/No is about +12dB... If you allow 2dB for implementation loss,
> that gets you to 10dB, which will get you a BER of 1E-6, which isn't
> terrible. Coding will improve it, etc.
>
> Take home message:
>
> 10W at 2Ghz with reasonably sized antennas at moon and earth can carry 1
> Mbps.
>
> Scales linearly with data rate.. You want 10Mbps, you need 100W. Or
> bigger antennas.
Thanks for the info. This at least should be doable with receiving
antennas operated by universities.
Bob Clark
Robert Clark
>
> The Discovery of Jupiter's Radio Emissions.
> How a chance discovery opened up the field of Jovian radio studies.
In this post I suggested using DirecTV's and other satellite TV
companies receiving dishes for SETI:
Newsgroups: sci.astro.seti, sci.astro, rec.radio.amateur.space,
sci.physics
From: rgregorycl...@yahoo.com (Robert Clark)
Date: 7 Feb 2005 15:07:03 -0800
Subject: Could DirecTV satellite dishes be used for the Square
Kilometer Array - and a more radical proposal[Re: Can DirectTV-type
satellite dishes be used for SETI?]
http://groups.google.com/group/sci.astro.seti/msg/e425e5339227855a
In the discussion in that thread there were mentioned several
problems with that proposal (possibly fixable with some expensive
retrofits) but one big problem is that satellite TV is not designed to
be two-way. Some satellite services are two-way when they are also
used for internet access, but this is a much smaller proportion of the
satellite TV subscribers.
However, instead of using the satellite TV dishes, we could use
individual dipole antennas attached to each house. You would need to
communicate high data rates for the signals detected so you would need
broadband internet access for this.
These dipole antennas as per the Radio JOVE project are just simple
vertical wires so could be attached to the house when the installer is
connecting the wiring for the broadband. Possibly you could use the
same external wiring as for the broadband but that might cause
interference with the internet signals.
As shown on the Radio JOVE page the receivers for these dipole
antennas are quite simple so would contribute minimally to the cost of
installation. You do need accurate positional determination and timing
synchrony for each receiving system to do the very long baseline
interferometry, but at these decametric wavelengths this would be easy
to do with GPS receivers carried by the installers. Over time you
could keep the systems in synchrony by timing stamps accessed over the
internet.
I suggested before using 10 million dipoles world-wide for detecting
Jovian-sized planets close in to their primaries out to perhaps 10
light-years. According to this page, over 16.6 million new broadband
internet users came online just in one quarter this year alone,
bringing the number of broadband users world-wide to 429 million:
More people worldwide are subscribing to high-speed Internet
connections.
China and other Asian countries among the growth leaders.
http://www.nationmultimedia.com/2009/06/17/technology/technology_30105358.php
New broadband subscribers would automatically get the dipole
antennas. At the rate of increase of broadband subscribers, it would
only take 3 months to reach 10 million separate dipoles. If each
installer when setting up a new system, also retrofitted an another
existing broadband system, then you could reach the full coverage of
all the broadband subscribers dipoles in 6 years.
The number of world-wide broadband subscribers will be 500 million by
2010. At current growth rates it would be 900 million within the 6
years it took to equip each broadband subscriber system with one of
the antenna dipoles. This is nearly two orders of magnitude better
sensitivity than a 10 million dipole system. You could detect out to
100 light-years, opening up many more stars to the possibility of
detection.
Bob Clark
Robert Clark
> On Jun 19, 11:20 am, Robert Clark <rgregorycl...@yahoo.com> wrote:
>
> > On Jun 16, 6:57 pm, Robert Clark <rgregorycl...@yahoo.com> wrote:
>
> > > From: rgcl...@my-deja.com (Robert Clark)
> > > Date: 23 May 2001 11:15:06 -0700
> > > Subject: Will amateur radio astronomers be the first to directly
> > > detect extrasolar planets?
> > > Newsgroups: rec.radio.amateur.space, rec.radio.amateur.antenna,
> > > sci.astro, sci.astro.seti, sci.space.policyhttp://groups.google.com/group/sci.astro.seti/browse_frm/thread/c0018...
>
> > > The long wavelengths should make the requirements for accurate
> > > distance information and timing synchrony between the separate
> > > detectors easy to manage even for amateur systems.
>
> You need not only precise time (straightforward), but also precise
> location (not so straightforward)
>
> You're interested in roughly 20MHz, as I recall. Wavelength of 15
> meters. In time, about 45 nanoseconds.
>
> Let's start with a real relaxed requirement, comparable to the mirror
> flatness for a telescope of lambda/14. That means a time knowledge
> of about 3 ns and a position knowledge of 1 meter, in absolute terms.
>
> Typical GPS receivers that have a 1pps output are good to about 20-30
> nanoseconds. Using that to discipline a quartz oscillator, you can do
> a bit better, but it's non trivial to get to the 1-2 ns range.
> Remember, you're also planning on integrating over time, so you have
> to hold that tolerance for a long time.
>
> It would be difficult to determine your position to an absolute
> accuracy of 1 meter, much less the phase center of the antenna (which
> will change as a function of the angle of incidence, quite
> substantially, unless you're putting those dipoles up 100s of feet in
> the air.
>
> Using this method
>
> > > might make the detection achievable even if the power or transmitting
> > > antenna size requirements are not practical for a low cost, low weight
> > > lander on the Moon for an individual detector on Earth.
> > > The recent achievement of real-time very long baseline interferometry
> > > should make it possible to integrate these separate detector signals
> > > in real-time as well:
>
>
> You need to go beyond looking at press releases from radio
> astronomers.
>
> > However, instead of using the satellite TV dishes, we could use
> > individual dipole antennas attached to each house. You would need to
> > communicate high data rates for the signals detected so you would need
> > broadband internet access for this.
> > These dipole antennas as per the Radio JOVE project are just simple
> > vertical wires so could be attached to the house when the installer is
> > connecting the wiring for the broadband. Possibly you could use the
> > same external wiring as for the broadband but that might cause
> > interference with the internet signals.
>
> create a single narrower lobe pointing up.
>
> > As shown on the Radio JOVE page the receivers for these dipole
> > antennas are quite simple so would contribute minimally to the cost of
> > installation.
>
>
> You do need accurate positional determination and timing
>
> > synchrony for each receiving system to do the very long baseline
> > interferometry, but at these decametric wavelengths this would be easy
> > to do with GPS receivers carried by the installers.
>
> and that isn't achievable by simple handheld devices, like your Garmin
> E-trex, etc. A surveyor using a survey GPS system can get there,
> although absolute position (relative to, say, the center of the earth,
> or some standard datum) to 1 meter would be very challenging.
>
> There's also the not so little problem of tidal bulge. Your position
> changes in absolute (relative to a stellar reference) terms several
> tens of cm. On top of that, tectonic plate movement is on the order of
> several cm/year, which is in the same general ballpark as your
> accuracy requirement.
>
> ...
The NASA Global Differential GPS System.
"The NASA Global Differential GPS (GDGPS) System is a complete, highly
accurate, and extremely robust real-time GPS monitoring and
augmentation system.
"Employing a large ground network of real-time reference receivers,
innovative network architecture, and award-winning real-time data
processing software, the GDGPS System provides decimeter (10 cm)
positioning accuracy and sub-nanosecond time transfer accuracy
anywhere in the world, on the ground, in the air, and in space,
independent of local infrastructure."
http://www.gdgps.net/
This would be enough for the positional accuracy at this wavelength.
This type of highly accurate receiver would probably have to be used
only by the installers as they are likely to be expensive. Perhaps the
positional accuracy could be maintained over time by referring to a
satellite signal.
The "time transfer" accuracy mentioned apparently does mean the many
different sites can be put in time synchrony to within sub-nanosecond
precision by reference to the atomic clocks on several GPS satellites
at the same time:
Global Positioning System.
2.) Basic concept of GPS
* 2.1 Position calculation introduction
* 2.2 Correcting a GPS receiver's clock
http://en.wikipedia.org/wiki/Global_Positioning_System#Basic_concept_of_GPS
Innovation: GPS Time Transfer.
Using Precise Point Positioning for Clock Comparisons.
Nov 1, 2006
By: François Lahaye, Diego Orgiazzi, Patrizia Tavella, Giancarlo
Cerretto.
GPS World
http://www.gpsworld.com/gpsworld/Innovation-GPS-Time-Transfer/ArticleStandard/Article/detail/383189
However, JPL radio astronomer Dr. Dayton Jones responded to my
question about the required timing accuracy at such long wavelengths,
suggesting it might only have to be only at the ten's of nanoseconds
to even microseconds range, depending on the bandwidth being detected:
Newsgroups: rec.radio.amateur.space, rec.radio.amateur.antenna,
sci.astro, sci.astro.seti, sci.space.policy
From: rgcl...@my-deja.com (Robert Clark)
Date: 18 Jun 2001 10:26:50 -0700
Subject: Re: Will amateur radio astronomers be the first to directly
detect extrasolar planets?
http://groups.google.com/group/sci.astro.seti/msg/8a56d6bc52a09590
Note that with the Radio JOVE system the bandwidth being detected is
usually quite small at the tens to hundreds of khz range, as the
emissions consist of short pulses. This would only require timing
accuracy at the microsecond range.
For the cost, note that for cable, DSL, satellite, internet and/or TV
service typically the receivers, modems, routers, etc are only
"rented" where you pay a nominal fee every month. If the cost for the
dipole and receivers were in the range of $100 dollars per
installation then this could be amortized over the life of that
broadband internet system, at say $1 dollar a month or even 50 cents a
month.
Bob Clark
Robert Clark
regards to getting *video* transmissions from Mars orbiter missions. I
was irritated by the spotty coverage of the Mars surface at the best
resolutions so I wanted to send real-time *continuous* imaging back to
Earth receiving stations at the highest imaging resolutions. This
would require very high transmission rates, much higher than what is
currently used.
The idea would be to use light transmissions but only of the on-off
variety. You would use a large surface, many meters across, capable of
being alternatively lit up and darkened. There are computer chips of
course capable of operating at Ghz rates. This would determine if the
large surface was lit up or not electrically, possibly by using a
material whose reflective properties can be changed electrically.
I was worried though about the twinkling seen in point sources, which
this would appear to be, such as with stars due to atmospheric
effects. So this might require the telescope(s) to be in Earth orbit.
The question I had though was whether the atmospheric distortion would
cause an "on" signal to appear "off" and vice versa? My understanding
of atmospheric distortion is that it causes the point source to be
constantly apparently undergoing small shifts in position. But this
wouldn't be a problem if what you want to determine is whether it is
on or off. If that is the case then ground based telescopes would
work.
In the large reflecting surface, I actually wanted to use separate,
say, squares on the reflecting surface that could be put separately in
the on-off position to increase the information transmission rate. But
that would require being able to distinguish the squares from Earth
millions of kilometers away. This is why I wanted to use light rather
than radio for this since the larger wavelengths in radio would make
the reflecting surface impractically large for diffraction limited
resolution.
Even with light you couldn't do this with a single telescope. They
would have to be widely separated. Combining the signals from widely
separated scopes is common in radio astronomy but is not nearly as
successful in optical astronomy. That is because the light wavelengths
are so much smaller and you would have to have nanoscale accuracy in
positioning the widely separate mirrors in relationship to each other.
However, in the case of just detecting an on-off signal this shouldn't
be as big of a problem as you're not trying to form a usable image,
but only trying to see if a particular location is on or off. You
would need though highly accurate timing synchrony between the
separate scopes, within nanoseconds, to be sure they are detecting the
same on-off square. Note also here that the shifting in the image due
to atmospheric distortion very definitely would be bad for using
ground based scopes.
It occurred to me this might be a means of acquiring advertising
support for a Google Lunar X Prize entrant. I had also been trying to
come up with a method of having an illuminated image either on the
Moon or in lunar orbit that would be visible to the naked eye on
Earth. Such an idea was discussed here:
moon advertising.
put a billboard on the moon.
http://www.halfbakery.com/idea/moon_20advertising
I wouldn't be in favor of doing this in a way that would actually
advertise a product. But I was thinking about it as a way of sending a
message in favor of, for example, world peace. In this case you could
still have advertisers who could say in TV commercials for example
they supplied funding to support the mission and the message.
BTW, I would be in favor of advertisers who could pay to have
advertising signs set up at the rover landing site so that if anyone
who wanted to log on to the the rover transmissions or who watched a
TV program on the rover transmissions would see the ads. This to me is
something different than an ad that someone would be forced to see
just by looking up at the Moon.
In any case you would need something large enough so that with naked
eye resolution at the lunar distance it would still be
distinguishable. This page gives the naked eye resolution at the lunar
distance:
Purpose of Building Telescopes.
http://www.astronomy.org/astronomy-survival/telepur.htm
According to this page the resolution of the human eye at the lunar
distance would be about 22 miles. One single object clearly couldn't
do this. However, if you had separate illuminated landers or orbiters
at this large distance apart they could be used to send a message
visible to the naked eye on Earth.
It could work with orbiters by the example set of satellite formation
flying by the Cluster mission:
Cluster mission.
http://en.wikipedia.org/wiki/Cluster_mission
I also needed to find how large a brightly illuminated surface needed
to be at the lunar surface to be visible by the naked eye on Earth. I
thought of the example of the "Iridium flares":
Satellite flare.
http://en.wikipedia.org/wiki/Satellite_flare
The Iridium satellites have 3 antennas that happen to be also
reflective in visible light, totaling 4.8 m^2 in area. According to
the Wikipedia page, the flares can be up to -8 in apparent magnitude,
though typically at +6 magnitude, and are produced by an individual
antenna, so by one of area 1.6 m^2.
I'll assume the brightest flares are produced just by the orientation
the antennas happen to be in so we could make our reflective surfaces
be oriented with respect to the Sun to get the greatest brightness.
For the same size surface, the brightness would be lessened by the
greater distance to the Moon. The Iridium satellites are at about 780
km altitude so the Moon is about 500 times further. This would lower
the brightness by a factor of 500^2 = 250,000.
This page gives the apparent brightness commonly visible by the naked
eye in urban areas as +3:
Apparent magnitude.
http://en.wikipedia.org/wiki/Apparent_magnitude
The 250,000 times lesser brightness at the lunar distance for an
Iridium sized reflective surface would give it a +13.5 higher apparent
magnitude so up to +5.5 in apparent magnitude. To make our reflective
surface be at +3 apparent magnitude we could make the area be 10 times
larger, so at 16 m^2 area, or a square 4 meters across.
We would need a method for a flat reflecting surface of unfolding it
to this size. It might be easier instead to have the reflecting
surface be a balloon inflated by stored gas. Since this would be in a
vacuum, you wouldn't need much gas pressure or mass to accomplish
this.
Another consideration is that because of the brightness of the Moon
it could swamp out our illuminated surface. For the orbiter, this
could probably be alleviated by having the orbiter have a highly
elliptical orbit, (this also would be beneficial in minimizing the
required delta-v and fuel load) then it would be visible at the higher
distances from the Moon in its orbit. For the landers it might work
for them to land in the dark lunar maria.
To communicate the message though we would need a method to turn on
and off the reflecting surface. One possibility would be to have the
reflecting surface consist of very many small squares that could be
rotated to reflect toward the Earth or away. Another possibility might
be to have it covered with LCD's. Whichever method it would have to be
both lightweight and low power.
For our first attempts we probably would not want to send so many
orbiter or landers at once to form a naked-eye visible image. We would
first send just a single one to test it out. Note that this method
with a single vehicle could still be used to send high definition
video by having our single reflective surface be turned on and off at
the required rate, about 256,000 times per sec with compression.
Bob Clark
On Jun 16, 6:57 pm, Robert Clark <rgregorycl...@yahoo.com> wrote:
> NASA's Radio JOVE Project.http://radiojove.gsfc.nasa.gov/
>
> The Discovery of Jupiter's Radio Emissions.
> How a chance discovery opened up the field of Jovian radio studies.
> by Dr. Leonard N. Garciahttp://radiojove.gsfc.nasa.gov/library/sci_briefs/discovery.html
Peter Webb
Illuminating an area of Mars or the moon and relying on this secondary
reflection will actually produce less photons returning to earth than aiming
the light source directly at the earth.
Furthermore, the radiation from a reflected area is isotropic - goes in all
directions - and hence very little is directed towards the earth.
If you were using the light source directly, rather than having it
illuminate an area of the ground, you could also use lenses or mirrors to
focus it back on the earth, giving thousands or millions of times the signal
strength on earth, the same technique as is used for radio comms.
"Robert Clark" <rgrego...@yahoo.com> wrote in message
news:d93b5c96-717b-43b1...@h18g2000yqj.googlegroups.com...
Richard Clark
<webbf...@DIESPAMDIEoptusnet.com.au> wrote:
>Furthermore, the radiation from a reflected area is isotropic - goes in all
>directions - and hence very little is directed towards the earth.
Actually, it is lambertian in its distribution, and it would have a
major lobe that was directed in rather typical fashion (at the same,
but negative angle to the norm to the surface). However, as is the
intent of your response, very much less will find its way to the
intended target.
73's
Richard Clark, KB7QHC
Richard Clark
<rgrego...@yahoo.com> wrote:
> I had been thinking about methods of high data rate transmission in
>regards to getting *video* transmissions from Mars orbiter missions. I
>was irritated by the spotty coverage of the Mars surface at the best
>resolutions so I wanted to send real-time *continuous* imaging back to
>Earth receiving stations at the highest imaging resolutions.
A curious distinction in this "continuous." Direct Current
transmission from Mars? I think not. Anything else is rather
conventional.
>This
>would require very high transmission rates, much higher than what is
>currently used.
"Continuous" is not distinctive to rate except at DC. Grab both sides
of conventional 120VAC from any wall socket, and it will seem
distinctly continuous - boosting it 1 THz wouldn't bring any different
sensation.
>The idea would be to use light transmissions but only of the on-off
>variety.
Rates, and on-off have departed the realm of "continuous."
>You would use a large surface, many meters across, capable of
>being alternatively lit up and darkened.
This is entirely unrelated to "continuous" rates or modes of
transmission. In and of itself, in regards to establishing remote
communications at light wavelengths, it is guilding the lily and
painting the rose.
>There are computer chips of
>course capable of operating at Ghz rates.
How that relates to:
>This would determine if the
>large surface was lit up or not electrically, possibly by using a
>material whose reflective properties can be changed electrically.
is bordering on stream-of-consciousness rambling.
>I actually wanted to use separate,
>say, squares on the reflecting surface that could be put separately in
>the on-off position to increase the information transmission rate.
There is no causal correlation between many surfaces and rate. This
is merely the substitution of complexity for the appearance of deep
consideration (which it is not).
>This is why I wanted to use light rather
>than radio for this since the larger wavelengths in radio would make
>the reflecting surface impractically large for diffraction limited
>resolution.
You are simply limited in your perception of what RF and Light means.
If one suffers for wavelength, then they both do.
>Even with light you couldn't do this with a single telescope.
Sounds like an artificial objection. Have you tried thinking in terms
of a power budget?
>They would have to be widely separated.
Does not come naturally as a solution from the rather diaphonous
problem put forward to this point, and the following is not a reason:
>Combining the signals from widely
>separated scopes is common in radio astronomy but is not nearly as
>successful in optical astronomy. That is because the light wavelengths
>are so much smaller and you would have to have nanoscale accuracy in
>positioning the widely separate mirrors in relationship to each other.
This is problem of degree, one which you painted yourself into a
corner with. Further, it doesn't necessarily follow one from the
other.
>However, in the case of just detecting an on-off signal this shouldn't
>be as big of a problem as you're not trying to form a usable image,
>but only trying to see if a particular location is on or off. You
>would need though highly accurate timing synchrony between the
>separate scopes, within nanoseconds, to be sure they are detecting the
>same on-off square. Note also here that the shifting in the image due
>to atmospheric distortion very definitely would be bad for using
>ground based scopes.
This is, based on your own objections, rather whipsawed by the
application of the term "nano." Nanoseconds and nanometers are not on
the balance to the solution of your problem. If you had nanometer
issues optically, they are not solved within nanoseconds simply
because they are not forming an image (which is a poor metaphor
because if fails with its own application).
>moon advertising.
>put a billboard on the moon.
>http://www.halfbakery.com/idea/moon_20advertising
Half backed? It is undercooked by half that again.
Let's consider: To obtain a sufficient contrast ratio, the light
would have to exceed the brilliance of the sun.
Did I mention a power budget?
The rest of this hardly borders on novely so much as fantasy. Keep
that to the appropriate groups.
BradGuth
on behalf of interplanetary and interstellar communications, as by far
the most extremely narrow of monochromatic or those of FM photons
accomplishing their one-way or ideally two-way energy and technology
efficient alternative. I kid you not.
The problem is that it’s perhaps too darn good and perhaps even too
energy efficient. Signal pointing and tracking errors from a
satellite platform are seriously narrow, though receiving isn’t all
that insurmountable.
~ BG
On Jun 28, 12:14 am, "Peter Webb"
<webbfam...@DIESPAMDIEoptusnet.com.au> wrote:
> Nice idea, but ...
>
> Illuminating an area of Mars or the moon and relying on this secondary
> reflection will actually produce less photons returning to earth than aiming
> the light source directly at the earth.
>
> Furthermore, the radiation from a reflected area is isotropic - goes in all
> directions - and hence very little is directed towards the earth.
>
> If you were using the light source directly, rather than having it
> illuminate an area of the ground, you could also use lenses or mirrors to
> focus it back on the earth, giving thousands or millions of times the signal
> strength on earth, the same technique as is used for radio comms.
>
> "Robert Clark" <rgregorycl...@yahoo.com> wrote in message
> put a billboard on the moon.http://www.halfbakery.com/idea/moon_20advertising
>
> I wouldn't be in favor of doing this in a way that would actually
> advertise a product. But I was thinking about it as a way of sending a
> message in favor of, for example, world peace. In this case you could
> still have advertisers who could say in TV commercials for example
> they supplied funding to support the mission and the message.
> BTW, I would be in favor of advertisers who could pay to have
> advertising signs set up at the rover landing site so that if anyone
> who wanted to log on to the the rover transmissions or who watched a
> TV program on the rover transmissions would see the ads. This to me is
> something different than an ad that someone would be forced to see
> just by looking up at the Moon.
> In any case you would need something large enough so that with naked
> eye resolution at the lunar distance it would still be
> distinguishable. This page gives the naked eye resolution at the lunar
> distance:
>
> Purpose of Building Telescopes.http://www.astronomy.org/astronomy-survival/telepur.htm
>
> According to this page the resolution of the human eye at the lunar
> distance would be about 22 miles. One single object clearly couldn't
> do this. However, if you had separate illuminated landers or orbiters
> at this large distance apart they could be used to send a message
> visible to the naked eye on Earth.
> It could work with orbiters by the example set of satellite formation
> flying by the Cluster mission:
>
> Cluster mission.http://en.wikipedia.org/wiki/Cluster_mission
>
> I also needed to find how large a brightly illuminated surface needed
> to be at the lunar surface to be visible by the naked eye on Earth. I
> thought of the example of the "Iridium flares":
>
> Satellite flare.http://en.wikipedia.org/wiki/Satellite_flare
>
> The Iridium satellites have 3 antennas that happen to be also
> reflective in visible light, totaling 4.8 m^2 in area. According to
> the Wikipedia page, the flares can be up to -8 in apparent magnitude,
> though typically at +6 magnitude, and are produced by an individual
> antenna, so by one of area 1.6 m^2.
> I'll assume the brightest flares are produced just by the orientation
> the antennas happen to be in so we could make our reflective surfaces
> be oriented with respect to the Sun to get the greatest brightness.
> For the same size surface, the brightness would be lessened by the
> greater distance to the Moon. The Iridium satellites are at about 780
> km altitude so the Moon is about 500 times further. This would lower
> the brightness by a factor of 500^2 = 250,000.
> This page gives the apparent brightness commonly visible by the naked
> eye in urban areas as +3:
>
> Apparent magnitude.http://en.wikipedia.org/wiki/Apparent_magnitude
Uncle Al
>
> I had been thinking about methods of high data rate transmission in
> regards to getting *video* transmissions from Mars orbiter missions.
Would modulating a 1 GW continuous laser at Mars be sufficient? The
laser is already in place - and running,
[snip crap]
http://www.mazepath.com/uncleal/race.htm
Hey stooopid - what happened to the Mars surface space face? You
dumped a gigabyte of crap extolling it. Where's the compost?
> Even with light you couldn't do this with a single telescope.
[snip more crap]
What, a gigagatt continuous is not enough? Give an idiot the answer
and obtain NASA ratiocinating on how to get to the moon (and
presumably, back).
> I had also been trying to
> come up with a method of having an illuminated image either on the
> Moon or in lunar orbit that would be visible to the naked eye on
> Earth. Such an idea was discussed here:
[snip rest of crap]
http://www.geocities.com/SouthBeach/1380/crmoon.html
idiot
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2
Robert Clark
> On Sun, 28 Jun 2009 17:14:14 +1000, "Peter Webb"
>
This describes the reflection from the Iridium antennas as specular
where most of the reflected light is concentrated in a single
direction:
SeeSat-L Apr-98: Method for predicting flare.
http://satobs.org/seesat/Apr-1998/0175.html
About specular reflection:
Specular reflection.
http://en.wikipedia.org/wiki/Specular_reflection
We could get even higher concentration of the image by using
parabolic mirror reflectors.
Bob Clark
Sam Wormley
A Mathematical Theory of Communication by Claude E. Shannon
http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html
http://cm.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf
Claude E. Shannon
http://scienceworld.wolfram.com/biography/Shannon.html
Craig Markwardt
> On Jun 28, 1:41 pm, Richard Clark <kb7...@comcast.net> wrote:
>
> > On Sun, 28 Jun 2009 17:14:14 +1000, "Peter Webb"
>
> > <webbfam...@DIESPAMDIEoptusnet.com.au> wrote:
> > >Furthermore, the radiation from a reflected area is isotropic - goes in all
> > >directions - and hence very little is directed towards the earth.
>
> > Actually, it is lambertian in its distribution, and it would have a
> > major lobe that was directed in rather typical fashion (at the same,
> > but negative angle to the norm to the surface). However, as is the
> > intent of your response, very much less will find its way to the
> > intended target.
>
> > 73's
> > Richard Clark, KB7QHC
>
> This describes the reflection from the Iridium antennas as specular
> where most of the reflected light is concentrated in a single
> direction:
>
>
> About specular reflection:
>
> Specular reflection.http://en.wikipedia.org/wiki/Specular_reflection
>
> We could get even higher concentration of the image by using
> parabolic mirror reflectors.
So basically you discovered the parabolic antenna. Congratulations.
CM
BradGuth
> On Jun 28, 1:41 pm, Richard Clark <kb7...@comcast.net> wrote:
>
> > On Sun, 28 Jun 2009 17:14:14 +1000, "Peter Webb"
>
> > <webbfam...@DIESPAMDIEoptusnet.com.au> wrote:
> > >Furthermore, the radiation from a reflected area is isotropic - goes in all
> > >directions - and hence very little is directed towards the earth.
>
> > Actually, it is lambertian in its distribution, and it would have a
> > major lobe that was directed in rather typical fashion (at the same,
> > but negative angle to the norm to the surface). However, as is the
> > intent of your response, very much less will find its way to the
> > intended target.
>
> > 73's
> > Richard Clark, KB7QHC
>
> This describes the reflection from the Iridium antennas as specular
> where most of the reflected light is concentrated in a single
> direction:
>
>
> About specular reflection:
>
> Specular reflection.http://en.wikipedia.org/wiki/Specular_reflection
>
> We could get even higher concentration of the image by using
> parabolic mirror reflectors.
>
> Bob Clark
Yes, and it was all doable as of more than a decade ago. However, at
the rate we're going, perhaps another century is required.
~ BG
Robert Clark
> ...
>
> Look up LOFAR or the SKA (Square Kilometer Array) for a fairly well
> funded scheme.
LOFAR.
http://en.wikipedia.org/wiki/LOFAR
LOFAR like my proposal is to use many separate dipoles to detect long
wavelength radio waves. However, it is to have only 10,000 dipoles
whereas mine at the end will have ca. 1 billion dipoles.
The progenitors of the LOFAR project have argued in papers that it
could be used for the SETI search. However, this article by well known
SETI search scientist Seth Shostak argues LOFAR will be too weak to
detect Earth type radio transmissions at a distance of say 55 light-
years by a factor of 1 million:
Listening for ET’s Television.
November 9, 2006
by Seth Shostak, Senior Astronomer
http://www.seti.org/Page.aspx?pid=917
Then since my proposal will be about 100,000 times more sensitive
than LOFAR, it could detect Earth-like radio transmissions to about
1/3 the distance of 55 lightyears, or to about 18 lightyears way.
There are several star systems in that range. The Shostak article
notes you could get several hundred times better sensitivity by
listening to certain stars over months or years. Then my proposal
could detect such transmissions out to even 55 lightyears and further.
Bob Clark
Richard Clark
<rgrego...@yahoo.com> wrote:
>The Shostak article
>notes you could get several hundred times better sensitivity by
>listening to certain stars over months or years.
And if you lost your keys at night, you might find them faster looking
under street lights.
Yet another troll.