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The new Echo satellite is becoming real!




On August 5th, Dick(W4PUJ), Rick(W2GPS) and Tom(W3IWI) met with Mark(N4TPY),
Dino(KC4YMG) and Bob(WA3WDR) at SpaceQuest to review the progress on the
"core" of AMSAT-OSCAR-ECHO.

First off -- the big news: Dino (who is coordinating the launch
arrangements) informed us that the launch date is set for Mar.31, 2004. The
planned orbit will be ~800 km high and sun-synchronous. A total of (up to)
ten satellites will ride to orbit.

During the meeting we were able to view and exercise all the critical
SpaceQuest-provided hardware systems arrayed as an open "flat-sat" on the
bench for testing. Please take a look at
http://www.pbase.com/tomcat/amsat_echo where you will find some selected
photos I took of the hardware. First you will see all the modules (except
for the tray that will house the S-Band transmitter) laid out side-by-side
on the bench. Then you see detailed photos of the innards of all the flight
modules. As a reminder, the trays are about 7"x7" in size and stack one on
top of another to make up the cube-shaped satellite. You can see mounting
bosses on the corners of each of the trays as well as the holes for the long
rods that tie the satellite together. [As a personal note -- Since I was
heavily involved in developing our original Microsats some 14 years ago, it
is a source of considerable personal pride to see how our original design
has evolved and matured thru the intervening years.]

Look thru the pictures as I make a few comments: In the BATTERY tray, the
long rods are the nutation dampers. If you look closely, you will see
temperature sensors on a couple of the battery cells. The red/black wires
tapes on the front connect to one of the solar panels, and the yellow pair
of leads goes to a thermistor on the back of the solar panel.

The large empty space in the RCVR tray is for the DVR (Digital Voice
Recorder). At the front of this tray are the four individual uplink
receivers. The large box is the preamp LNA and receiver input filter.

In the POWER module, note the 6 large surface-mount devices in the center.
These are Power-FETs used instead of lossy diodes to isolate the solar
panels on the 6 sides of the cube.

The XMTR tray has the two 70 cm xmtrs in front and the stripline hybrid
combiner in blue behind the transmitters. Not shown, under the blue hybrid
is the multi-function programmable multi-mode receiver. The bottom of this
tray (a.k.a. the BASEPLATE) is held up by Mark; three antennas have been
replaced by dummy loads and the 4th antenna "spigot" goes off to some
measurement instrumentation. The wires taped to the baseplate are for the
bottom solar cells. The small hole in the center is for the L/S antenna. In
the 4 corners of the baseplate you will see come conical projections. These,
in conjunction with some claps that fit over the corners, are the interface
between ECHO and the launch vehicle.

After viewing the widgets with power off, we fired up ECHO and exercised the
spacecraft "guts" over an RF link from the SpaceQuest command station. You
will see a photo of the spectrum of the spacecraft 70 cm downlink talking
back to the command station at 9600 BPS.

One of the most exciting new innovations in Echo is the "programmable"
attitude control magnet. In the past Microsats, gross attitude control has
been achieved with fixed bar magnets. In Echo, a soft iron rod will be
pulsed to change the direction of the magnetic field. In one photo you see
the MAGNET CONTROLLER board (which will fit into the S-Band transmitter
tray). This pulser works much like a photo flash unit. The large capacitor
is charged, and then discharged as a high current pulse thru the magnet
coil. The both the strength and polarity of the charging pulse can be varied
by uplink command.

One of the "proof of the pudding" tests was to exercise the ACS (Attitude
Control System). After the picture of the controller, you will see a series
of 5 pictures of the MAGNET with a compass. The 5 photos were taken as Bob
sent commands (from the next room by RF link) to program the magnet from
neutral (with the compass pointer perpendicular to the magnetic rod in #1),
then to "red" in #2, then to a "weak white" in #3, and then to a
full-strength "white" in #4, and then finally back to neutral in #5. To
anticipate an obvious question, no decisions have been made on questions of
how often the magnet will be changed operationally; obviously the magnet
will "swap" the up/down faces of the satellite between users in the
northern/southern hemispheres.

Finally you see two of the drawings Dino has received from the Russian
launcher folks. One shows the AMSAT payload along with nine other satellites
that will ride from Baikonar (in Kazakhstan) on an SS-18 rocket on March
31st; the primary satellite is called DEMETER. Finally, you see a photo of
the Russian drawing documenting the details of the launcher interface.

This satellite is really real! Hope you enjoy seeing what it is looking
like.

73 de Tom, W3IWI



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