Kosmos 434 (Russian: Космос 434; meaning Cosmos 434) was the final uncrewed test flight of the Soviet LK Lander. It performed the longest burn of the four uncrewed LK Lander tests, validating the backup rocket engine of the LK's Blok E propulsion system. It finished in a 186 km by 11,804 km orbit. This test qualified the lander as flightworthy.

Kosmos 434

LK Lander
Mission type	Spacecraft test
Operator	Soviet Union
COSPAR ID	1971-069A
SATCAT no.	5407
Mission duration	10 years and 10 days
Spacecraft properties
Spacecraft	T2K No.3
Launch mass	7,000 kilograms (15,000 lb)[1]
Start of mission
Launch date	12 August 1971, 09:30 (1971-08-12UTC09:30Z) UTC[2]
Rocket	Soyuz-L
Launch site	Baikonur 31/6
End of mission
Decay date	23 August 1981
Orbital parameters
Reference system	Geocentric
Regime	Medium Earth
Semi-major axis	12,353.00 kilometres (7,675.80 mi)
Eccentricity	0.46911647
Perigee altitude	187 kilometres (116 mi)
Apogee altitude	11,777 kilometres (7,318 mi)
Inclination	51.5 degrees
Period	227.94 minutes
Epoch	11 September 1971[3]

The LK was the only element of the Soviet human lunar programs that reached this status. In 1980-81 there were fears that it might carry nuclear fuel. When it reentered over Australia on August 22, 1981 the Soviet Foreign Ministry in Australia admitted that Kosmos 434 was an “experiment unit of a lunar cabin,” or lunar lander.