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APRSat Rumors!



Well until 10 minutes ago, there was an APRSat called NATSWEB
scheduled for Launcher integration in 2 days and launch in 3 weeks.
We have been working almost around the clock since XMAS when we were
offered a free Launch if we could build a fully qualified satellite
in 6 weeks.....  We did!

Here is what it had:

A launch to geostationary transfer orbit on the equator at 36,000 km
APogee by 660 km perogee that would give 12 hour a day coverage to anyone
anywhere (except the poles).  The mission was to provide an APRS mobile
position and status reporting link from mobiles anywhere back into the
internet linked worldwide APRS infrastructure.  Our satellite consisted
of:

TWO DIGIPEATERS:
Two completely separate but identical KPC-3+ TNC's and 2 meter radios.
One was on a vertical whip and one on a horizontal whip.  Power out was a
whoping 10 watts each!  Since these were omni antennas and we had no
attitude control, 2 meters was the only option.  (70 cm requires 9
more DB for both up and downlinks).  Each digipeater was backed up with a
failsafe timer circuit that would power-cycle the TNC's if there was no
PTT activity in over a minute.  Kantronics had burned us a pair of ROMS
with our defaults, so we came up ready to go after each power cycle.
We also added a touch tone reset circuit as an added precaution.

POWER SYSTEM and STRUCTURE:
Each system had its own battery and 6 solar panels for nearly 100% sun
illumination.  One of the TNC remote control lines on each TNC was used to
cross connect the power systems in case one system failed; then we
could use its battery for the other one.  Dr Bill Clapp at Weber State in
Ogden UTAH was doing the power systems, and we at the Naval Academy were
doing the COMM package.  We would attach to a 9 foot by 3 foot square open
box truss made out of 3000 lbs of steel built by Boeing as their dummy
mass.  This mass was a vibration mass test unit never intended for launch,
but since there were no other payloads, it became the prime payload.
Unfortunately for us, it was painted all WHITE, so its average
termperature would be a very cold -60 deg C.  We were using a thermal
insulator and then thermal coatings on our boxes to achieve a nice 0 to 30
deg C operating temperature for us.  This thermal design was a non-trivial
exercise!

TELEMETRY:  We used the LEDS ON/OFF switch in the TNC to switch the 5
available analog inputs to two banks of sensors, 4 currents, 4
temperatures, battery voltage and RF power out.  This for each system.
Thus a total of 20 telemetry values from our off-the-shelf KPC-3+'s!
(This satellite has no other command/control system other than the
TNC's).

LINK BUDGET:  ANyone could hit the digipeaters with a 160W mobile amp and
a mobile antenna (optimized for peak power up at an angle of about 40
degrees) (36,000 km is a long way away). Anyone could hear the
downlink with an OSCAR-10 class station.  But the intent was to just have
a half dozen permanent ground stations feed the downlink into the APRServe
network.  THus, eveyone everywhere could see all satellite mobiles via the
existing APRS worldwide infrastructure.

UPLINK:  One uplink was on 144.39 since it was already authorized over the
entire North American continent.  And since target mobiles would be
radiating mostly upward and all other terrestrial users would be radiating
on their horizons, we calculated we could get a 10 to 16 dB SNR so that
the mobiles would be heard above all other users.  (AMSAT also gave us a
possible alternate uplink in the amateur satelltie segment in case APRS
caught on in Europe where 144.39 is a meteor scatter freq.)

DOWNLINK:  We could also downlink on 144.39 just fine, since with 6 ground
stations all listening all the time and feeding their combined signal into
APRServe, the chance that all 6 stations would have local QRM at any
instant is 0.01 %, this gave us a 99.99% probability of success on every
packet.  AND our signal from 36,000 km would be so weak to all other APRS
users, they would not even be able to hear it except with a beam antenna
pointed UP...  THus we could operate fully on 144.39.  BUT 144.39 as a
space downlink is not politically correct in the gentlemens agreement to
keep all such activity in the AMSAT segment, and would cause discontent in
Europe.   This is the primary reason we had completely dual redundant
systems.  One for North America, and one for Europe if APRS caught on over
there.

But alas, the STATE DEPARTMENT just killed us!  Our FREE ride was on the
launch of a totally passive dummy 3,000 lb MASS being launched to test the
SEA LAUNCH system.  SInce the launch will be in international waters,
using a Russian Rocket, on a scandanavian ship with system integration by
Boeing,  BOEING had to get a Technology Export License from the State
Department for the Launch (This takes months if not years!).  Now, since
Boeing was going to add us (an active payload) to their dummy mass, STATE
DEPARTEMNT said NO.  They say, "this is a change to your export license
which will have to be modified and resubmitted."

Boeing was actually getting excited about our system, since it wouild give
them attitude and temperature information which they had no other means
for getting from their totally passive mass.  Integration of our NATSweb
satellite was on their work plan for integration and they have had
engineers working with us in preparation for the clean room evolution for
the last month.
 
Boeing has been fighting for us now for a month trying to convince State
Department that this is a trivial change and that it doesnt need this kind
of bureaucratic process.  But with their BILLION$$$ launch on line and
only weeks away, you can see why they cannot re-do their paperwork (which
has been the subject of lots of State Department oversight of late) just
for our $2000 attachment.  SO here, friday afternoon, we are bumped.
And their 3000 chunk of steel goes to orbit (for hundreds of years)
with no telemetry system at all..

But we DO now have a satellite READY TO GO for the next opportunity!
(anyone know of another free launch...?)

OH YES, it also had a NASA modified GPS unit attached to one of the TNC's
so that we could see how well GPS worked from space!   ARGH!

For details see our web page:

http://web.usna.navy.mil/~bruninga/NATSat.html

The WEB page is a week or so out of date, since we were concentrating more
on building it, than documenting it, but we will clean that up later...

So THANKS to all in Long Beach that had offered to help us when we flew
out for integration next Wednesday, no time now to send you all personal
messages, I have got to go spend some family time, since I have been
working 16 hour days since XMAS and sleeping here overnight in the office
about 30% of the time...

It was fun!

de WB4APR, Bob
Naval Academy Satellite Lab


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