| Kosmos 1687 | |
| Mission Type: | Early warning |
| Cospar Id: | 1985-088A |
| Satcat: | 16103 |
| Mission Duration: | 4 years |
| Spacecraft Type: | US-K |
| Launch Date: | UTC |
| Launch Rocket: | Molniya-M/2BL |
| Launch Site: | Plesetsk Cosmodrome |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Molniya |
| Orbit Inclination: | 62.9 degrees |
| Orbit Period: | 717.72 minutes |
| Apsis: | gee |
Kosmos 1687 (Russian: Космос 1687 meaning Cosmos 1687) is a Soviet US-K missile early warning satellite which was launched in 1985 as part of the Soviet military's Oko programme. The satellite is designed to identify missile launches using optical telescopes and infrared sensors.
Kosmos 1687 was launched from Site 16/2 at Plesetsk Cosmodrome in the Russian SSR. A Molniya-M carrier rocket with a 2BL upper stage was used to perform the launch, which took place at 19:23 UTC on 30 September 1985. The launch successfully placed the satellite into a molniya orbit. It subsequently received its Kosmos designation, and the international designator 1985-088A. The United States Space Command assigned it the Satellite Catalog Number 16103.