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AO-27 TEPR State explanation



I have received several email messages regarding the meaning of the TEPR
states that are set on AO-27.  To summarize:  We set the bird to charge its
batteries for "x" number of minutes AFTER it enters the Sun.  This is TEPR
state 4 expressed in 30 second increments, e.g. TEPR 42 means that the
charging time is 21 minutes.  We then set TEPR state 5 to the length of
time, expressed in 30 second increments, that the transmitter would be on
from the start of TEPR 4 but not on until the completion of TEPR 4, e.g.
TEPR 78 means that the transmitter will shut off 39 minutes after the start
of TEPR 4, but the transmitter will be on for 18 minutes. (78-42 =36, or 18
minutes)

AO-27 TEPR States Explained

AO-27 uses a method called Timed Eclipse Power Regulation (TEPR) to
regulate the batteries.  In simple terms, TEPR times how long it has
been in the eclipse or in the sun and decides what subsystems to turn
on or off.

The current software onboard AO-27 breaks an orbit into 6 different
states as follows:

TEPR State 1:  Starts when the satellite enters the Eclipse
TEPR State 2:  Starts a programmed time after TEPR State 1 (Still
during the Eclipse)
TEPR State 3:  Starts a programmed time after TEPR State 1 that's
after State 2 (Still during the Eclipse)

TEPR State 4:  Starts when the satellite enters the Sun
TEPR State 5:  Starts a programmed time after TEPR 4 (Still in the
Sun)
TEPR State 6:  Starts a programmed time after TEPR 4 that's after
State 4 (Still in the Sun)

Current Subsystems by State:
TEPR 1,2,3 - all unneeded Subsystems turned off (This is why there is
no Night time use of the satellite)
TEPR 4     - AO-27 Transmitter is turned to exciter power only. All
other Transmitters are off.
TEPR 5     - AO-27 Transmitter is turned to 0.5 watts (low power)
TEPR 6     - all unneeded Subsystems turned off

Using this Model, During a descending, day-time pass, AO-27 will enter
TEPR 4 after coming out of the eclipse and will start to recharge its
batteries.  We program the TEPR 5 time so the satellite will stay in
TEPR 4 until the foot print reaches latitudes equal to the Northern
United States.  At that time, it changes to TEPR State 5 and the
transmitter turns on.  The duration of TEPR State 5 is set for the
longest we can leave the transmitter on to keep the batteries in a
state that will prolong their life time.  At the current time (June
1999) this is 18 minutes.  If we were to leave it on longer we would
start to limit the life time of the satellite.  The TEPR 6 period
needs to be long enough to recharge the batteries before we enter the
eclipse again (TEPR 1).

The time we need to stay in TEPR 6 is what places a limit on the
southern latitudes we can work in.

73
Chuck, KM4NZ, Acting Control Operator
Michael, N4USI, Control Operator

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