Hi,

I have read that the people working behind the Mars missions, appear
to have successfully upgraded the Mars Relay to transmit at 256
kilobits/sec, allowing approximately 250 megabits worth of data to be
transmitted in a single relay session. (I'm speaking only of data
rates from Mars Surface to Mars Orbit.)

I have also read several documents on the Net, including some old
1990's specification document on the Mars Global Surveyor relay
antenna. It gave me the idea that the data rate was limited to
around 128 kilobits per second.

This harkens back to a bandwidth-upgrade accomplishment that I
remember well. In the 1990's, I recall the breakthroughs that were
necessary in order to cram data through Galileo's low gain antenna at
Jupiter, after the high gain antenna failed to open after repeated
attempts. If I remember correctly, the 16 bits/sec (max) low-gain
antenna was upgraded well beyond spec via software to perform up to
160 bits/sec (max) uncompressed rate, plus various compression
algorithms (both lossy and lossless) were implemented, to achieve the
equivalent of approximately 1 kilobits/sec rate average. The literal
engineering accomplishment of a very difficult "cramming as many
elephants as possible through a drinking straw as quickly as possible"
problem, so to speak.

I would like to ask -- how was the relay bandwidth upgrade
accomplished, considering the original specifications appears to have
permitted 128 kilobits per second? Was a provision added for 256
kilobits per second relay just in case it was found to be possible, or
was this a software accomplishment that allowed the specs to be
extended while the probes were already in orbit? New
modulation/codec algorithm? Hand-optimized clock-cycle-exact code?
Power supply modulation to antenna? Turning off other instruments to
give enough power for the higher data rate? (Just being wild on
unorthodox ideas that might have been invented to exceed an antenna
system spec -- I am not in the space industry myself but have a basic
understanding of various concepts like these.)

This also leads to another interesting question -- How much room is
there for further improvement? Would an upgrade to 512 kilobits/sec
and 1024 kilobits/sec be theoretically possible using any of the
existing orbiters, especially if a future surface mission had a
theoretical aimable UHF antenna dish that tracked the relay satellite?
Are the satellites theoretically flexible enough to support even
higher data rates for future missions of any existing orbiter
(Surveyor/Climate/Express as of 2003), assuming their missions were
extended to cover such a theoretical future surface mission?

Don't be afraid to be technical; I'm a software engineer here,
although not in the space industry.

Mark Rejhon
www.marky.com (personal webpage)