| Primary satellite | Secondary satellite |
| Name | Cosmos 1821 Rocket | THORAD AGENA D DEB |
| Spacetrack catalog number | 17526 | 42503 |
| Radar cross section | large | small |
| Epoch of two-line elements (UTC) | 2021 Apr 17 07:47 | 2021 Apr 17 10:45 |
| Time of closest approach (UTC) | 2021 Mar 01 20:05:20.899 |
| Minimum distance | 11.975 km |
| Height difference | -1.041 km |
| Relative speed | 14.491 km/s |
| Angle between velocity vectors | 158° |
| Geographic position | 79.0°N, 147.9°E |
| Height | 964 km |
|