Amsat Oscar AO-51AMSAT-OSCAR 51 was successfully launched on 28.06.2004 on a Dnepr-1 rocket from the Baikonour Cosmodrome in Kazakhstan. The first contact took place at 1452UTC and the first important telemetry data was send. The batteries were fully charged and the solar panels provided enough power. In the next few days, the software was loaded and the telemetry showed good values​​.

The 25-inch cubes is weighing about 10kg. AO-51 has four VHF receivers and two UHF transmitters, one multi-mode receiver and a 2.4 GHz transmitter. It orbits the Earth in a high 850KM, sun synchronic orbit. The inclination is 98.2 °.

With four VHF receivers, two UHF transmitters, six modems, fifty-six channels of telemetry, and various other subsystems AO-51 is quite a complex spacecraft. The two UHF transmitters are connected to two antenna arrays, one in the right-hand circular polarization (RHCP) and one in the left-hand circular polarization (LHCP). Transmitter A (435.150) is connected to the LHCP antennas and is often used for digital modes. Transmitter B (435.300) is often used for analog and is connected to the RHCP antenna.

Orbital parameters

Name                 AO-51
NORAD                28375
COSPAR designation   2004-025-K
Inclination (degree) 98.214
RAAN                 257.170
Eccentricity         0.0084104
ARGP                 147.287
Orbit per day        14.40467899
Period               1h 39m 58s (99.97 Min)
Semi-major axis      7135 km
Perigee x apogee     697 x 817 km
Drag factor          0.000032586 1/ER
Mean anomaly         213.357


435,225 MHz FM analog Voice
435.150 MHz FSK 9600 bps, AX.25 (TX A)
435.300 MHz FSK 9600 bps, AX.25 (TX B)


145.920 MHz FM + 67 Hz PL
145.860 MHz FSK 9600 bps, AX.25

Mode and Antenna Polarization:

T: Linear
V: Linear
U: TX A (usually digital) LHCP
U: TX B (usually analog) RHCP
L: Linear
S: Linear


Broadcast callsign PECHO-11
BBS callsign PECHO-12


AO51 Echo Pre-LaunchAfter much trial and error, we have found a “sweet spot” where AO-51 will stay operational through eclipse for the time being. Cell 3 is a dead short, and cell 2 now goes to zero in eclipse also. It’s amazing the satellite will operate on 2/3rds the designed voltage input! How long AO-51 can be kept operational is anyone’s guess. By the end of this year, eclipses will be headed for 30 minutes long. It is unlikely it will continue to operate as-is at that point. Enjoy while you can.

Uplink is 145.880, no PL
Downlink is 435.150 at about 1 watt

Nov 29, 2011 The satellite no longer respond to commands and it seems that the last battery cell that kept it operational has failed also. So the end of AO-51

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