| Kosmos 434 | |
| Mission Type: | Spacecraft test |
| Operator: | Soviet space program |
| Cospar Id: | 1971-069A |
| Satcat: | 5407 |
| Mission Duration: | (in orbit) |
| Spacecraft: | T2K No.3 |
| Manufacturer: | OKB-1 |
| Launch Mass: | 7000kg (15,000lb) |
| Launch Date: | UTC |
| Launch Site: | Baikonur 31/6 |
| Decay Date: | 23 August 1981 |
| Orbit Epoch: | 11 September 1971 |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Medium Earth |
| Orbit Periapsis: | 187km (116miles) |
| Orbit Apoapsis: | 11777km (7,318miles) |
| Orbit Inclination: | 51.5 degrees |
| Orbit Eccentricity: | 0.46911647 |
| Orbit Semimajor: | 12353km (7,676miles) |
| Orbit Period: | 227.94 minutes |
| Apsis: | gee |
| Programme: | LK (spacecraft) |
| Previous Mission: | T2K No.2 |
| Programme2: | Kosmos (satellites) |
| Previous Mission2: | Kosmos 433 |
| Next Mission2: | Kosmos 435 |
Kosmos 434 (Russian: Космос 434; meaning Cosmos 434), also known as T2K No.3, 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.
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.