| Kosmos 638 | |
| Mission Type: | Orbital test flight |
| Operator: | Soviet space program |
| Cospar Id: | 1974-018A |
| Satcat: | 7234 |
| Spacecraft: | Soyuz 7K-TM s/n 71 |
| Manufacturer: | NPO Energia |
| Launch Date: | GMT |
| Launch Rocket: | Soyuz-U |
| Launch Site: | Baikonur 31/6 |
| Disposal Type: | Deorbited |
| Landing Date: | GMT |
| Orbit Reference: | Geocentric |
| Orbit Inclination: | 51.8° |
| Orbit Period: | 89.4 min |
| Apsis: | gee |
| Programme: | Soyuz programme |
| Previous Mission: | Soyuz 13 |
| Next Mission: | Kosmos 656 |
| Programme2: | Kosmos (satellites) |
| Previous Mission2: | Kosmos 637 |
| Next Mission2: | Kosmos 639 |
Kosmos 638 (ru|Космос 638) was an uncrewed test of the 1975 Apollo–Soyuz Test Project Soyuz. It carried an APAS-75 androgynous docking system.
This was followed by another uncrewed test of this spacecraft type, Kosmos 672. It was a Soyuz 7K-TM spacecraft.
When the air was released from the orbital module (which is ejected before re-entry of the capsule) it caused unexpected motions with the spacecraft. This led to the next test also being uncrewed.