"Sputnik 2 transmitted on 20.005 and 40.002 MHz. After day 4, the telemetry shifted. The heartbeat channel went silent but the carrier wave persisted -- modulating at a frequency that matched no known biological signal. Ground control logged it as instrument error. We are no longer certain."
-- Fragment K-003 // OKB-1 Declassified Telemetry, 2002