OSCAR 51 is an amateur radio satellite AMSAT. Before the start of the satellite as AMSAT- Echo or AMSAT- OSCAR E was known.

AMSAT- Echo has a cubic structure with 25 cm edge length. The sides of the cube are covered with solar cells to ensure the power supply of the satellite. He does not drive as well as a umpolbare magnetic stabilization, but no position sensors and thus no position control. Due to the magnetic stabilization of the satellite to optimize the transmit power over the northern hemisphere was approximately directed towards the Nadir, vice versa in the southern hemisphere. By magnetic reversal, a reversal of the orientation was possible. There are four VHF receiver and two UHF transmitters on board.

The satellite was launched on 29 June 2004 on a Dnepr rocket from Baikonur and exposed in an orbit of 697 × 815 km. The inclination is 98.2 °. In addition to data connections enabled the Satellilt FM radio connections, due to the height of its orbit and intercontinental often. The transponder was in operation until November 2011.

His COSPAR designation 2004 - 025K.