At 03:56 PM 10/19/2006, [EMAIL PROTECTED] wrote:
G'day Jim and all
Pushing further from the topic (given your day job Jim ;) Also
freely accepting
this is pure speculation...
30% efficiency on the solar cells?! A generous round up I suspect? I thought
Deep Space 1 only got ~23%? And that was the soopa doopa focus layer, no dust
out there to speak of flavour?
You betcha.. by the time you can put 4-5000 kg of container on the
surface of Mars, I suspect that 30% solar cells will be a
reality. Actually, Mars Science Lander (MSL) for launch in 2009 is
probably pretty close to 1000kg (I'd have to go check, but it's
widely described as being roughly the size and mass of a Mini).
I also remember hearing some talk of them developing special cells
for Mars that
were better operating at the slightly different 'coloured' sunlight?
Could be, although the color of the sunlight on Mars isn't all that
much different than earth at least during the middle of the day.
Probably depends on the amount of dust in the air, maybe a bit more
UV (no real atmosphere).
And while lag to Earth in radio is the same for light ('c') what
rates might we
expect if we upgrade to that light carrier technology we've been
hearing about?
Optical comm? It's a ways off for practical use. The robotic space
exploration folks tend to be pretty conservative in choosing
technologies and fairly conventional radio appears to be the ticket
for the immediate future. What is different from, say, 10 years ago,
is the use of relay satellites around Mars. Landed mass costs about
10-100 times what orbiting mass does, so putting a big antenna in
orbit with a relay station, and a small low powered transmitter on
the lander is a good idea.
Big (in terms of wavelength) antennas have to be pointed accurately,
and that's a lot easier in orbit than on a moving rover.
Optical comm shows a lot of promise as a wideband backbone link
(because you could go to an optical receiver in orbit around the
earth, helping solve the "cloudy day" problem), but considering that
we've been flying radios in deep space for almost 50 years, and only
a few small experiments for optical (Galileo carried an optical
experiment), the "maturity" of the technology for RF is a lot more
than for optical.
There's also the political issue (which all cluster builders will be
aware of) that you need to have a *need* for the extra bandwidth (as
in a customer willing to pay for it or willing to accept the
additional risk) before you can fly it. At a billion dollars a crack
for flagship Mars missions, you can't really do the "build it and
they will come" strategy. It's worth noting that the large 64m
antennas at the Deep Space Network were funded back in the early 60s
to be able to get live TV back from the moon. And we're still using
the same antennas today: they got enlarged to 70m a while back, and
the electronics have been steadily improved, but the "dish" and its
mechanical parts are 40 years old.
We're getting megabits per second back from Mars right now (all those
gorgeous high res pictures from the Mars Reconnaissance Orbiter), and
I'm working on next generation radio designs that go up to, say, 100
Mbps or thereabouts. To a certain extent there's a Energy per Bit
issue.. Can't beat Shannon, as they say. Running faster rates is
mostly a matter of either bigger antennas or more power.
The other thing that's going on (and actually Beowulf cluster
related) is that we're getting much better at modeling the antennas,
or more particularly, the interactions of the antennas with the
spacecraft. Vaughn Cable has been developing some automeshing codes
that take descriptions of the spacecraft from mechanical engineers
and 3D drafting packages and turns it into suitable segments, which
can then be run with a variety of Method of Moments codes on one of
the clusters here on lab. (The challenge is that the drafting
packages tend to generate facets and triangles that aren't directly
suitable for EM modeling.. looks just fine in the rendering, but
things like duplicate facets or boxes within boxes cause real troubles)
Unless, of course, you were referring to that patented superluminal
transmitter that also enhances plant growth.
If this post is too far from topic then somebody slap me... it's
just that I'm a
curious animal ;)
Cheers
Stevo
_______________________________________________
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
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