[amsat-bb] Since there's been a lot of ISS chatter recently, I thought this might be a good time to post

Robert Christ rjc53 at cornell.edu
Wed Jul 14 09:40:53 PDT 2010

Hey everyone.  I'm a researcher at Cornell, and this fall, our
experimental, 1 inch diameter, “chip satellites” are scheduled to be
launched on the final space shuttle flight, STS-134.  They're going to
be mounted on the exterior of the ISS structure, and will be set to
transmit a 902 MHz signal.  Unfortunately, we do not yet have an
antenna for receiving this transmission.  After talking with Bob -
Wb4APR for a while, it was suggested that the fine members of the
AMSAT – BB might be able to help us.

What we’re looking for is a digital capture of this 902MHz frequency
(with a bandwidth of about 200KHz), during at least one ISS pass (only
a few gigs of data, we believe).  No decommutation or other analysis
of the signal will be required, but actually capturing the signal will
require at least a 20 dbB gain receive antenna (more details in a

If any of you can help us in this experiment, or are able to
successfully capture the signal, not only would we be incredibly
grateful, but we would also be prepared to add your names and
contributions to all of the published papers that will result from
this mission.  It goes without saying, though, that we’d also be
entirely open to suggestions if the community, or a member, were aware
of some manner by which Cornell might be able to better avail itself
to the both those who help us on this project and the community as a

So here are the technical details.  There are 3 transmitting antennas,
all tiny, center-fed dipoles: two of them use wires separated by 180
degrees, and one has wires separated by 90 degrees.  Each of these
dipoles is mounted a few mm from large metal panels on the ISS.  The
ChipSats will transmit for approximately 10ms every 1-2 seconds, but
the signal is going to be beneath the noise floor.  Detecting the
signal requires a pseudorandom noise (PRN) code, which Cornell will
handle once the dataset is in hand.  Since we can/will take care of
the post processing, and capture isn’t guaranteed on every ISS pass
(attitude alignment problems still TBD) so anyone who can take a
recording of this frequency at this bandwidth for us, of any ISS pass,
would be incredibly helpful.

The good news is that the chips will be live and transmitting almost
immediately after they are installed from STS-134, and they will
transmit continuously whenever the ISS is in sunlight.  Additionally,
should they survive in their environment, they are set to transmit for
up to two years, which should give us many chances to receive the data
and confirm that the ChipSats are functioning.

Thanks for your time, everyone,
Robert Christ

P.S. a little extra information:  Our website is
http://www.spacecraftresearch.com/projects.html if you're interested.
This mission isn't explicitly mentioned there yet, but is rather a
proof of feasibility study for most of the projects listed on that
site.  Ah and lastly, the ERP of the transmitter is expected to be ~10
dBm, though it will almost certainly be facing in a poor orientation,
giving us only a fraction of that power.  We won't know the exact
amount for a few more days.  Thanks all!

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