Mission typeAmateur radio
COSPAR ID2004-025K
SATCAT no.28375
WebsiteThe Echo Project Page
Spacecraft properties
Launch mass11.14 kilograms (24.6 lb)
Start of mission
Launch date29 June 2004, 06:30:06 (2004-06-29UTC06:30:06Z) UTC[1]
Launch siteBaikonur 109/95
ContractorISC Kosmotras
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Semi-major axis7,132.45 kilometres (4,431.90 mi)
Perigee altitude702 kilometres (436 mi)
Apogee altitude820 kilometres (510 mi)
Inclination98.22 degrees
Period99.91 minutes
Epoch4 December 2013, 10:20:06 UTC[2]

AMSAT-OSCAR 51 or AO-51 is the in-orbit name designation of a now defunct (following battery failure) LEO amateur radio satellite of the OSCAR series; formerly known as ECHO, built by AMSAT. It was launched on June 29, 2004 from Baikonur Cosmodrome, Kazakhstan on a Dnepr launch vehicle. It is in sun synchronous low Earth orbit.

AO-51 contained an FM repeater with both 144 MHz (VHF) and 1.2 GHz (L band) uplinks and 435 MHz (UHF) and 2.4 GHz (S band) downlinks. It also contained a digital subsystem that transmitted telemetry on 70 cm and provided a complete PACSAT BBS that could be configured on both V band and S band uplinks. As well, there was a 10-meter PSK uplink.

AO-51 had four VHF receivers, two UHF transmitters, six modems, and 56 channels of telemetry. The two UHF transmitters were connected to four phased antennas, yielding right-hand circular polarization for the 435.300 downlink and left-hand circular polarization for the 435.150 downlink.

The AO-51 FM satellite was easily workable with an amateur radio VHF dual band hand-held radio, as long as you knew when the satellite's footprint was within reach. Transatlantic contacts had been made without much effort, as long as the satellite was approximately mid-Atlantic so that the edge of the satellites footprint was within reach on either continent.

As of May 2011 the satellite faced problems with the battery.[3] By September, a work around for the battery issue was found, bringing the repeater back in use. On November 29, 2011, the AO-51 Command Team announced that AO-51 has ceased transmission and is not responding to commands.[4]

External links

  • AO-51 Control Team News
  • AMSAT news about AMSAT 2006 Space Symposium
  • ARRL Web Kid's Day Rules
  • How to Work AO-51 with Your HT


  1. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 6 December 2013.
  2. ^ Peat, Chris (4 December 2013). "AMSAT ECHO - Orbit". Heavens Above. Retrieved 6 December 2013.
  3. ^ "ANS-126 AMSAT News Service Special Bulletin - AO-51 Batteries Failing".
  4. ^ Drew KO4MA. "Command Team and Operations Group AO-51 News". Archived from the original on 2012-01-25.