Kosmonaut sing Ilang utawa Kosmonaut Memedi (Basa Inggris: Lost Cosmonauts utawa Phantom Cosmonauts) yaiku subyek saka teori konspirasi sing nuduh nek ana kosmonot Soviet sing sampun lunga menyang angkasa luar sadurunge Yuri Gagarin, nanging keberadaan mereka ora tau diberitahuke secara umum dening otoritas ruang angkasa Sovyet utawa Ruslan. Proponen saka teori Kosmonaut sing Ilang nyatakake nek Uni Sovyet berupaya kanggo ngeluncurke loro penerbangan antariksa berawak utawa luwih sadurunge Gagarin, lan paling ora ana loro kosmonaut tiwas ing upaya kasebut. Kosmonaut liyane, Vladimir Ilyushin, diyakini mendarat bebas lan ditahan dening papréntahan Tiongkok. Pamrentah Uni Sovyet diduga nutupi kabar kasebut kanggo ngehindari publisitas elek ing puncak Perang Dingin.

Referensi 
 Encyclopedia Astronautica: Phantom cosmonauts
 James Oberg (1988). Uncovering Soviet Disasters: Exploring the Limits of Glasnost, Random House, 
 Yaroslav Golovanov Cosmonaut #1, Izvestia, 1986.
 Pavel Toufar, 2002/2003, Kruty vesmir, Akcent, , 58–258
 Pavel Toufar, 2001, Vzestup a pad Jurije Gagarina, Regia, 
 Alexander Zheleznyakov, Gagarin was still the first (same in Russian)
 "Komsomolskaya pravda" newspaper (in Russian)
 A.Pervushin "Terrible secret" of soviet space (in Russian)
 Uchitelskaya gazeta (in Russian)
 Ren-TV story (in Russian)

Pranala jaba 
 Encyclopedia Astronautica: Phantom cosmonauts
 Straight Dope on "lost" cosmonauts 
 Oberg chapter on Dead Cosmonauts
 The Lost Cosmonauts web site with the audio recordings

Misteri