The manufacturer however admitted that that SCPs on Boeing 601 spacecraft launched prior to August 1997 contain tin-plated relay switches that can experience electrical shorts when several factors are concurrently present. If this applied to all 601-model satellites launched until July 1997, at least 30 of HS 601s in orbit would be equipped with the dreaded tin-plated relays.
The SCP is the on-board computer that controls the satellite. There's also at least one backup SCP aboard every satellite.
The relay serves as an on/off switch within the SCP. Under certain conditions, tiny crystalline structures (known as "tin whiskers") can grow and bridge a relay terminal to its case, causing an electrical short which blows fuses.
|Name||Launched||First SCP failure||Second SCP failure|
|Optus B1 [Optus]||13 August 1992||21 May 2005||-|
|Galaxy VII [PanAmSat]||27 October 1992||13 June 1998||22 November 2000|
|Galaxy IV [PanAmSat]||24 June 1993||(not caused by 'tin whiskers')||19 May 1998|
|Solidaridad 1 [SatMex]||19 November 1993||28 April 1999||27 August 2000|
|DBS-1 [DirecTV]||17 December 1993||4 July 1998||-|
|PAS-4 [PanAmSat]||3 August 1995||3rd quarter 1998||-|
|Galaxy IIIR [PanAmSat]||15 December 1995||21 April 2001||15 January 2006|
|DirecTV 3 [DirecTV]||9 June 1995||4 May 2002||-|