The current software onboard AO-27 breaks the orbit into 6 different states as follows:
TEPR State 1 – Satellite enters Eclipse
TEPR State 2 – Starts a programmed time interval after TEPR State 1 (During Eclipse)
TEPR State 3 – Starts a programmed time interval after TEPR State 1 that's after State 2 (During Eclipse)
TEPR State 4 – Satellite enters Sunlight
TEPR State 5 – Starts a programmed time interval after TEPR 4 (During Sunlight)
TEPR State 6 – Starts a programmed time interval after TEPR 4 that's after State 5 (During Sunlight)
During a daytime pass, AO-27 will enter TEPR State 4 after coming out of eclipse and start charging its batteries. TEPR State 5 time is programmed so the satellite will stay in TEPR State 4 until the footprint reaches latitudes equal to the 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 period that the transmitter can be left on and keep the batteries in a state that will prolong their lifetime. As of June 1999 this is 18 minutes. If the transmitter was left on longer the lifetime of the satellite would be shortened. The TEPR 6 period needs to be long enough to recharge the batteries before AO-27 enters the eclipse again (TEPR State 1).
The time for AO-27 to stay in TEPR 6 places a limit on the southern latitudes that can work the satellite.
AO-27 is set to charge its batteries for "x" number of minutes AFTER entering Sunlight. This is TEPR State 4 expressed in 30-second increments. For example, TEPR 4 value of 42 equals a charging time of 21 minutes (42 * 30 seconds = 1260 seconds or 21 minutes).
TEPR State 5 is then set to the length of time that the transmitter will be on from the start of TEPR 4, but not on until the completion of TEPR 4. For example, TEPR 5 value of 78 means that the transmitter will shut off 39 minutes (78 * 30 seconds = 2340 seconds or 39 minutes) after the start of TEPR 4. Thus the transmitter will turn on at the end of TEPR 4 and turn off at the end of TEPR 5 for a total of 18 minutes. (78 - 42 = 36 -- 36 * 30 seconds = 1080 seconds or 18 minutes).
Acting Control Operator