| Kosmos 398 | |
| Mission Type: | Spacecraft test |
| Operator: | Soviet space program |
| Cospar Id: | 1971-016A |
| Satcat: | 4966 |
| Mission Duration: | (in orbit) |
| Spacecraft: | T2K No.2 |
| Manufacturer: | OKB-1 |
| Launch Mass: | 7255kg (15,995lb) |
| Launch Date: | UTC |
| Launch Site: | Baikonur 31/6 |
| Decay Date: | 10 December 1995 |
| Orbit Epoch: | 25 February 1971, 19:00:00 UTC |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Low Earth |
| Orbit Periapsis: | 196km (122miles) |
| Orbit Apoapsis: | 276km (171miles) |
| Orbit Inclination: | 51.63° |
| Orbit Eccentricity: | 0.006043 |
| Orbit Period: | 88.9 minutes |
| Apsis: | gee |
| Programme: | LK (spacecraft) |
| Previous Mission: | T2K No.1 |
| Next Mission: | T2K No.3 |
| Programme2: | Kosmos (satellites) |
| Previous Mission2: | Kosmos 397 |
| Next Mission2: | Kosmos 399 |
Kosmos 398 (Russian: Космос 398; meaning Cosmos 398), also known as T2K No.2, was the second uncrewed test flight of the Soviet LK lander, using the T2K version. It followed the same program as Kosmos 379, launching on February 26, 1971 into a 276 km by 196 km orbit. It main objective was to validate contingency abort-to-lunar orbit manoeuvres.