| Primary satellite | Secondary satellite |
| Name | Cosmos 1821 Rocket | Cosmos 991 Rocket |
| Spacetrack catalog number | 17526 | 10693 |
| Radar cross section | large | large |
| Epoch of two-line elements (UTC) | 2021 Jan 23 19:53 | 2021 Jan 23 14:27 |
| Time of closest approach (UTC) | 2020 Nov 29 08:47:16.841 |
| Minimum distance | 54.073 km |
| Height difference | -0.311 km |
| Relative speed | 11.283 km/s |
| Angle between velocity vectors | 100° |
| Geographic position | 79.2°S, 63.5°W |
| Height | 1014 km |
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