AMSAT-OSCAR 51

{{Infobox spaceflight

| name = AMSAT-OSCAR 51 (AO-51)

| image = AO-51-2.jpg

| image_caption =

| mission_type = Amateur radio

| operator = AMSAT-NA

| website = [http://www.amsat.org/amsat-new/echo/ The Echo Project Page]

| COSPAR_ID = 2004-025K

| SATCAT = 28375

| mission_duration =

| spacecraft_bus =

| manufacturer =

| dry_mass =

| launch_mass = {{convert|11.14|kg|lb}}

| launch_date = {{start-date|29 June 2004, 06:30:06|timezone=yes}} UTC{{cite web|url=http://planet4589.org/space/log/launchlog.txt|title=Launch Log|first=Jonathan|last=McDowell|work=Jonathan's Space Page|accessdate=6 December 2013}}

| launch_rocket = Dnepr

| launch_site = Baikonur 109/95

| launch_contractor = ISC Kosmotras

| last_contact =

| decay_date =

| orbit_epoch = 4 December 2013, 10:20:06 UTC{{cite web|url=http://www.heavens-above.com/orbit.aspx?satid=28375|title=AMSAT ECHO - Orbit|first=Chris|last=Peat|work=Heavens Above|date=4 December 2013|accessdate=6 December 2013}}

| orbit_reference = Geocentric

| orbit_regime = Low Earth

| orbit_semimajor = {{convert|7132.45|km|mi}}

| orbit_eccentricity = 0.0082657

| orbit_periapsis = {{convert|702|km|mi}}

| orbit_apoapsis = {{convert|820|km|mi}}

| orbit_inclination = 98.22 degrees

| orbit_period = 99.91 minutes

| apsis = gee

}}

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.{{cite web|title=ANS-126 AMSAT News Service Special Bulletin - AO-51 Batteries Failing|url=http://www.aus-city.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=57786}} 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.{{cite web|last=Drew KO4MA |title=Command Team and Operations Group AO-51 News |url=http://www.amsat.org/amsat-new/echo/CTNews.php |url-status=dead |archiveurl=https://web.archive.org/web/20120125010201/http://www.amsat.org/amsat-new/echo/CTNews.php |archivedate=2012-01-25 }}